Photophysical Behavior of Terpyridine-Lanthanide Ion Complexes Incorporated in a Poly(N,N-dimethylacrylamide)Hydrogel
Vlasoula Bekiari and Panagiotis Lianos*
Uni V ersity of Patras,Engineering Science Department,26500Patras,Greece
Recei V ed May18,2006.In Final Form:June29,2006
Poly(N,N-dimethylacrylamide)hydrogel forms complexes with terpyridine and various trivalent ions,like Eu3+, Tb3+,Gd3+,and In3+.The hydrogel can be obtained in three different phases:swollen with water,lyophilized(i.e., dried by freeze-drying),where it loses the solvent but preserves the swollen configuration,and dried in the air where it shrinks.The three hydrogel phases affect the type of complex formed between terpyridine and the metal ion.Thus, in the swollen and lyophilized phases,metal-centered emission can be obtained by energy transfer from the excited ligand.In the shrunk phase,an intense green fluorescence is emitted,which is ligand-centered and is independent of the complexed ion.In the absence of any ion,the ligand emits blue luminescence,independently of the hydrogel phase.
In the presence of europium(III)ions,blue,green,or red emission can be thus produced at appropriate compositions and hydrogel phases.Analysis of the photophysical behavior of the polymer-ligand-metal ion complex is related with the photophysical behavior of the ligand and its complexes in various pure solvents.
Introduction
Hydrogels are3D polymer networks that swell but do not
dissolve in water.Shrinking or swelling of these gels can be
activated by several external stimuli,such as solvent,heat,pH,
and electric stimuli,1and this makes them interesting materials
for several useful applications:drug delivery,2-5electrical
applications,6muscle mimetic actuators,2,7hosts of nanoparticles
and semiconductors,1,6,8-12templates,13,14etc.15Even though
studies on hydrogels already cover a broad domain in materials
science,small attention has been paid to hydrogels as hosts of
luminescent species.For example,studies of ligand-lanthanide
luminescent complexes are proliferating in connection with other
host matrixes,but similar studies associated with hydrogels are
rare,if any.To fill the void,the present work introduces a complex
formed between terpyridine(2,2′;6,2′′-terpyridine,abbreviated
Tpy,see Figure1for the chemical structure),Eu3+(or other
ions),and poly(N,N-dimethylacrylamide)(PDMAM)hydrogel and studies the variations of the luminescence behavior of this complex system with respect to the phase transformations of the hydrogel during shrinking or swelling.The diversity of lumi-nescence emissions that this system can offer may be useful for several photophysical applications,both in monitoring phase transformations of the hydrogel itself or of other macromolecules and in sensing or monitoring other environments or stimuli. Ligand-lanthanide ion complexes are well-known efficient luminescent agents.16-18They emit a long-living,narrow band, of practically monochromatic radiation,by ligand-to-metal energy transfer.They are endowed with two major advantages:when excitation is made through the ligand,19they solve the problem of small light absorption cross section by lanthanide ions,and by complexing lanthanide ions,they protect them from lumi-nescence quenching processes.Typical complexes involve a combination of three -diketone molecules20and one molecule of a heterocyclic ligand.16-18Complexes between a heterocyclic ligand alone with a lanthanide ion are also studied with a lot of interest.In this respect,complexes of Tpy with lanthanides as well as with other trivalent metals are a very interesting subject
*To whom correspondence should be addressed.E-mail: lianos@upatras.gr.
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Figure1.Absorption spectra of(1)10-6M and(2)10-3M Tpy in cyclohexane.Inset:chemical structure of Tpy.
8602Langmuir2006,22,8602-8606
10.1021/la061406d CCC:$33.50?2006American Chemical Society
Published on Web08/29/2006
of research both for their rich chemistry and physics and for their numerous applications.Thus,new functional hybrid organic -inorganic polymeric structures have been synthesized by exploit-ing Tpy -metal complexation.21-23Studies on photoinduced charge separation in many cases involve chemical structures also based on Tpy -metal complexation.24,25Lanthanide ions complexed with Tpy impart additional luminescent characteristics,which can be useful in labeling complex structures of biological importance.26The present work exploits complex formation between Tpy and Eu 3+to probe the phase transformations of PDMAM https://www.doczj.com/doc/e018768823.html,plexes between Tpy and Gd 3+,Tb 3+,or In 3+are also studied for comparison and in an effort to clarify the behavior of the Tpy -Eu 3+complex itself.
Experimental Section
All reagents were from Aldrich,unless otherwise indicated,and were used as received.Synthesis of PDMAM is given in a previous publication.12
Tpy -M 3+Complexes (M )Metal).An amount of 6.7mM Tpy and 6.7mM Eu(NO 3)3?5H 2O,Tb(NO 3)3?5H 2O,Gd(NO 3)3?6H 2O,or InCl 3were dissolved in ethanol by preparing two separate solutions.Then,the ligand solution was added to the metal ion solution dropwise under stirring.Stirring continued for about 1h at ambient conditions,and then it was slightly heated to 35°C and was left in the dark to rest for 2days.Precipitates were formed after about 5h.Finally,the mixture was filtered to separate the solid phase.After several times of washing with ethanol,the precipitate was dried,and thus it was ready for characterization.The precipitate was either used in its solid form or redissolved in THF.
PDMAM -Tpy -M 3+Complexes.An amount of 0.1g of dry PDMAM was added in a 0.005M Tpy solution in EtOH and was left to stand in a capped container for 3days.The polymer swelled and thus adsorbed and retained a substantial quantity of Tpy.Then,it was taken out of the solution and was left to dry and shrink in the air.The remaining ethanolic solution retained only traces of Tpy.Almost all ligand was adsorbed by the polymer.Then,the PDMAM -Tpy complex was immersed in an aqueous solution of 0.001M Eu(NO 3)3?5H 2O,Tb(NO 3)3?5H 2O,Gd(NO 3)3?6H 2O,or InCl 3and was left to swell for 3days.Finally,it was taken out and left to dry in air for 1week.In the case of freeze-drying,the sample was frozen to liquid N 2temperature and pumped with a vacuum pump.
Measurements.Absorption measurements were made with a Cary 1E spectrophotometer and luminescence measurements with a Cary Eclipse spectrofluorometer.Europium and terbium luminescence decay times were also measured with the Cary Eclipse spectro-fluorometer.Nanosecond decay profiles were recorded by the photon-counting technique using a homemade apparatus employing an IBH hydrogen flash and Ortec electronics.
Results and Discussion
To better understand the photophysical behavior of Tpy complexes in connection with the PDMAM hydrogel,the photophysical behavior of pure Tpy and of Tpy -M 3+complexes in neat solvents has been first studied and discussed in the following three paragraphs.
Photophysical Behavior of Pure Tpy in Neat Solvents.Tpy was dissolved in several solvents,both polar and nonpolar,both at low and relatively high concentrations.The obtained absorption and emission spectra are shown in Figures 1and 2.Figure 1
shows the absorption spectrum of 10-6M and 10-3M Tpy dissolved in cyclohexane.At low concentration,Tpy has an absorption band stretching below 320nm.The corresponding fluorescence spectrum (Figure 2)stretches between 300and 400nm with a maximum at 334nm,while the corresponding excitation spectrum (Figure 2)lies in the same spectral region as the absorption spectrum.The assignment of Tpy electronic transitions has been made in an early work by Fink and Ohnesorge.27These low-wavelength absorption and emission bands are due to π-πtransitions.Tpy is most probably in a cis -cis conformation during these transitions.27Both the absorption and fluorescence behavior of low-concentration Tpy remained practically the same in ethanol and other tested solvents.At high Tpy concentration,an additional absorption band was detected between 320and 400nm (Figure 1),while fluorescence was then registered above 400nm (Figure 2).The low-wavelength emission was no longer detectable,apparently due to self-absorption by the concentrated solution.In this respect,the excitation spectrum of 10-3M Tpy overlapped the fluorescence spectrum of 10-6M Tpy (Figure 2).The fluorescence spectrum was substantially structured in cyclohexane but lost all its structure in polar solvents.This blue emission is not detected at low-concentration solutions because it is due to a weak n -πtransition.27The fluorescence decay time for the n -πtransition was a single-exponential decay with a lifetime τ)9.3ns in cyclohexane and 9.6ns in ethanol solutions.Tpy is soluble in water only at low concentration.At neutral or basic pH,the spectral behavior of aqueous Tpy solutions is similar to that in all other tested solvents.However,Tpy becomes highly protonated in low-pH aqueous solutions.27In that case,fluo-rescence is emitted in a drastically different spectral region,as seen by curve 5of Figure 2.This emission is also a π-πtransition,27but it is most probably due to a cis -trans or trans -trans conformation.27This conclusion is drawn by the fact that in low-temperature rigid solutions the green emission is no longer detected,apparently because no conformation transition is then allowed.
Photophysical Behavior of Tpy -M 3+Complexes in Neat Solvents.Figure 3shows the fluorescence and excitation spectra of the Tpy -Eu 3+complex precipitated from ethanol and redissolved in THF.Luminescence is now characteristic of europium emission,both in terms of structure and of decay time (single-exponential decay:τ)0.58ms).The corresponding excitation spectrum shows that light is absorbed by the ligand
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72.
Figure 2.Excitation spectra of cyclohexane solutions of (1)10-6M Tpy (emission wavelength,334nm)and (3)10-3M Tpy (emission wavelength,437nm);fluorescence spectra of cyclohexane solutions of (2)10-6M Tpy (excitation wavelength,280nm)and (4)10-3M Tpy (excitation wavelength,361nm);(5)fluorescence spectrum of 10-6M Tpy in water at pH )1(excitation wavelength,290nm).
Hydrogel -Terpyridine -Lanthanide Complexes Langmuir,Vol.22,No.20,20068603
and energy is transferred from the excited ligand to Eu 3+emissive states.The two most intense luminescence peaks at 592and 616nm correspond to transitions from the 5D 0state (17250cm -1)to the 7F 1and 7F 2Eu 3+states,28respectively.In fact,the former overlaps the 5D 0f 7F 0transition 28at 583nm.The weak transition at 650nm is identified with the 5D 0f 7F 3transition.28Two weak transitions at 538and 557nm are identified with the 5D 1f 7F 1and 5D 1f 7F 2transitions.28The intensities and the positions of these peaks are all listed in Table 1.The 5D 1state lies 28at 19000cm -1.For ligand-to-metal energy transfer to occur to both the 5D 1(19000cm -1)and,more successfully,to the 5D 0
(17250cm -1)states,it is necessary that the triplet state of Tpy,from where transfer is made,lies close and above 19000cm -1.The triplet state of Tpy was determined by a standard procedure,29,30i.e.,by studying the complex of the ligand with Gd 3+.The presence of the heavy metal in the complex,i.e.,in the close vicinity of the ligand,facilitates intersystem crossing and population of the ligand triplet state.However,the Gd 3+emitting level lies too high (>30000cm -1)31to allow energy transfer from Tpy.Therefore,no other emission is expected but by transition from the ligand triplet state to its singlet ground state.This transition is,of course,forbidden,and for this reason it is very weak and is observed only at low temperature.Figure 4shows the emission
of the Tpy -Gd 3+complex precipitated from ethanol and redissolved in THF.The spectrum was recorded with the help of a cryostat at liquid nitrogen temperature.This spectrum contains several peaks,but obviously the triplet emission is identified with the peak at 503nm that corresponds to 19880cm -1.This level is convenient for energy transfer to both the 5D 0and 5D 1emissive states of Eu 3+,as already discussed.
Photophysical Behavior of the Tpy -Eu 3+Complex in a Nonconventional Solvent.Tpy -Eu 3+complex can be dispersed in polyether solvents such as poly(ethylene glycol)(PEG).PEG of an approximate molecular weight equal to 200has been repeatedly used in our laboratory to disperse ligand -lanthanide ion complexes.32-36Figure 5shows the excitation and emission spectrum of Tpy -Eu 3+dissolved in PEG-200together with the excitation spectrum of Figure 3,which corresponds to that of the precipitated from ethanol complex,for comparison.No metal-centered emission was observed in that case,and this is in accordance with previous findings.33,34The broad green emission at 509nm is a ligand-centered emission.This is concluded by the following findings:the decay time was only τ)2.8ns;complexes formed with a multitude of other metals,like In 3+,Tb 3+,Gd 3+,and several others,gave exactly the same green emission,independent of the metal used.Even though it lies close to the Tpy triplet emission at 503nm (cf.,Figure 4),it is not a triplet emission.This is concluded by the fact that its decay
(28)Dejneka,M.;Snitzer,E.;Riman,R.E.J.Lumin.1995,65,227.
(29)Sager,W.F.;Filipescu,N.;Serafin,F.A.J.Phys.Chem.1965,69,1092.(30)Weibel,N.;Charbonniere,L.J.;Guardigli,M.;Roda,A.;Ziessel,R.J.Am.Chem.Soc.2004,126,4888.
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3189.
Figure 3.(1)Excitation spectrum (emission wavelength,616nm)and (2)luminescence spectrum (excitation wavelength,336nm)of the Tpy -Eu 3+complex dissolved in THF.
Table 1.List of Eu 3+and Tb 3+Transitions,Peak Wavelengths,
Peak Wavenumbers,and Relative Intensities,in Various
Environments
lanthanide ion transition
wavelength (nm)wavenumber (cm -1)relative intensity a
Tpy -Eu 3+complex 5D 1f 7F 153********dissolved in THF
5D 1f 7F 255717953125D 0f 7F 0,1592168921215D 0f 7F 2617162073505D 0f 7F 3650153858Tpy -Eu 3+-PDMAM 5D 0f 7F 158********system 5D 0f 7F 2614162871205D 0f 7F 3647154563Tpy -Tb 3+-PDMAM 5D 4f 7F 64872053418system
5D 4f 7F 554218450305D 4f 7F 45821718265D 4
f 7F 3
619
16155
3
a
The peak intensities in this table do not fit the values in Figures 7and 8because intensities are normalized for comparison reasons in the second case.In addition,no direct comparison of intensities can be made between solid samples and
solutions.
Figure 4.Luminescence spectrum of the Tpy -Gd 3+complex
dissolved in THF and recorded at liquid nitrogen
temperature.
Figure 5.(1)Excitation spectrum of the Tpy -Eu 3+-PEG-200complex (emission wavelength,509nm);(2)luminescence spectrum of the Tpy -Eu 3+-PEG-200complex (excitation wavelength,370nm);(3)excitation spectrum (emission wavelength,616nm)of the Tpy -Eu 3+complex dissolved in THF.
8604Langmuir,Vol.22,No.20,2006Bekiari and Lianos
time is too short and that it is very intense,even though it is recorded at room temperature.Indeed,the green emission recorded with the Tpy -M 3+/PEG-200system has a fluorescence quantum yield that rises up to 0.63,while the fluorescence quantum yield of pure Tpy in PEG-200was found to be only 0.13.34Apparently,the green emission could be associated with the emission produced by a different Tpy conformer,as in the case of the highly protonated Tpy of Figure 2.We believe that,when the dispersion medium allows it,a different kind of Tpy -metal complex can be formed from that precipitated from standard solvents,like ethanol.The complexing power of the polyether groups in PEG-200apparently facilitates (or forces)the formation of such a modified complex between Tpy and the metal ion,and in that case a different ligand conformer takes part in the Tpy -M 3+complex.Tpy can form tridentate complexes with,for example,Eu 3+(cis -cis isomerization),bidentate complexes (cis -trans isomerization),or monodentate complexes (trans -trans isomer-ization),37depending on the type of the metal ion and the dispersion environment.It is not surprising then that a different type of complex,based on a different conformer,can be obtained in the particular environment provided by PEG-200or other complex environments,as in the present case of hydrogels,as will be seen in the next paragraph.A strong indication that a different Tpy conformer emits the luminescence of Figure 5from that which emits the luminescence of Figure 3is the fact that the excitation spectra are very distinct in the two cases.Indeed,as seen in Figure 5,the two spectra peak at different wavelengths,i.e.,at 370and 336nm,respectively.
Photophysical Behavior of the Tpy -Eu 3+Complex in PDMAM Hydrogels.PDMAM gives hydrogels,which swell in the presence of water or alcohol and shrink when they are dried.However,if freeze-drying is performed,12that is,if the material is frozen at liquid nitrogen temperature and dried under vacuum,i.e.,lyophilized,then the swollen polymer preserves its volume and its conformation even after all (or almost all)solvent is evaporated.The swelling hydrogel can adsorb a large percentage of substances dissolved in the solvent and retains them when it is dried.Thus,the polymer can be enriched with a great variety of chemical species both neutral and charged and both hydrophilic or hydrophobic.12In the present work,a series of ligands have been dissolved in PDMAM and their luminescence has been recorded at all three polymer phases:swollen,lyophilized,and shrunk (ambient dried).No important variations of the emission properties of these ligands have been observed by going from one phase to the other.This holds true also for the blue-emitting Tpy,the fluorescence spectrum of which is shown in Figure 6(curve 1).This fluorescence,together with the accompanying absorption profile,is identified with the high-concentration Tpy n -πfluorescence of Figure 2.However,when a metallic ionic species is codissolved with Tpy,then the emission spectrum changes in going from one polymer phase to the other.This phenomenon has been observed with a large variety of different metal ions.Figure 7shows luminescence spectra by ligand-centered excitation (cf.,absorption spectrum in Figure 6,curve 2)for the Tpy -Eu 3+-PDMAM system.Water-swollen PDMAM emits metal-centered emission,characteristic of Eu 3+ions (cf.,Figure 3and Table 1).Exactly the same spectrum was recorded with a lyophilized sample.However,a shrunk sample (ambient dried)gave a completely different spectrum:a structureless green luminescence similar to that of Figure 5.This green emission of the Tpy -Eu 3+-PDMAM system is very intense,stronger than the blue emission of the Tpy -PDMAM system (i.e.,that of
Figure 6,curve 1).Some contribution of blue luminescence adding to the form of curve 2of Figure 7obviously comes from isolated (noncomplexed)Tpy molecules.Also some weak Eu 3+lumi-nescence at the long-wavelength tail of curve 2of Figure 7means that the green emission is produced at the broad expense of the metal-centered luminescence.When a nonemitting metal was used in the place of Eu 3+,for example,Gd 3+or In 3+,emission by energy transfer could not be produced.The swollen or the lyophilized phase did not offer any emission at all,while the shrunk phase again produced the intense green emission,as can be seen in Figure 7,curve 2.When another emitting ion was used in the place of Eu 3+,i.e.,Tb 3+,the behavior was similar to that of the Tpy -Eu 3+-PDMAM system.As seen in Figure 8,water-swollen PDMAM produced metal-centered emission character-istic of terbium ions (curve 1),while shrunk PDMAM produced the ligand-centered green emission observed with the other ions (curve 2).Metal-centered emission was obtained by ligand-centered excitation (excitation wavelength,336nm)and sub-sequent ligand-to-metal energy transfer.The characteristic Tb 3+peaks of Figure 8(curve 1)correspond to transitions from the 5D 4(approximately 20500cm -1)38state of Tb 3+to its 7F 6
(487nm),7F 5(542nm),7F 4(581nm),and 7F 3(619nm)states,respectively 38(cf.,Table 1).The emission of Tb 3+by energy transfer from Tpy is a surprise since the 5D 4energy level lies higher than the value of 19880cm -1measured for the Tpy triplet state.Apparently,it is justified only as a result of perturbations since the two states lie close to each other.This
(37)Chapman,R.D.;Loda,R.T.;Riehl,J.P.;Schwarzt,R.W.Inorg.Chem.1984,23,1652.
(38)Joshi,B.C.J.Non-Cryst.Solids 1995,180,
217.
Figure 6.(1)Fluorescence spectrum of PDMAM swollen in water retaining Tpy alone;(2)absorption spectrum of PDMAM swollen in water retaining Tpy alone;(3)absorption spectrum of shrunk PDMAM retaining both Tpy and Eu 3+
.
Figure 7.Luminescence spectra of the Tpy -Eu 3+-PDMAM system:(1)water-swollen or lyophilized (excitation wavelength,336nm)and (2)shrunk (excitation wavelength,370nm).
Hydrogel -Terpyridine -Lanthanide Complexes Langmuir,Vol.22,No.20,20068605
is in accordance with the fact that the metal-centered luminescence of the Tpy -Tb 3+-PDMAM system was much weaker than the corresponding luminescence of the Tpy -Eu 3+-PDMAM system (Table 1).
The above results show that two different types of complexes can be formed between Tpy and trivalent metal ions:(1)simple complexes of Tpy with Eu 3+or Tb 3+,i.e.,with emitting lanthanide ions,precipitated from common solvents such as alcohol,facilitate strong room-temperature metal-centered emission by ligand-centered excitation,population of the ligand excited triplet state,and subsequent energy transfer to the metal emitting https://www.doczj.com/doc/e018768823.html,plexes of the same type but with nonemitting trivalent cations,like Gd 3+or In 3+,do not lead to any luminescence at room temperature.However,some weak ligand triplet luminescence can be registered at low temperature.(2)Complexes coordinated in the presence of a third agent bearing polar chemical groups capable of binding metal ions,like polyether groups or acrylamide groups,produce ligand-centered intense green fluorescence.This fluorescence is independent of the nature of the metal ion,which seems to play only an intermediary role.The behavior of luminescence with respect to PDMAM hydrogel phase trans-formations is in line with the above two different types of complexes.In the case of water-swollen PDMAM,complexes of the first type apparently precipitate and are subsequently stabilized and retained by the polymer.Thus,metal-centered emission is observed in that case,red in the case of Eu 3+and green in the case of Tb 3+.When the water-swollen hydrogel is lyophilized,i.e.,freeze-dried,the polymer preserves its swollen conformation and retains the type 1complexes without variation.When,on the contrary,the polymer is ambient dried and shrinks,the nature of the complex changes and becomes of the second type.Type 2complexes are apparently coordination complexes between Tpy,metal ions,and the polymer polar groups themselves.Subsequently,no metal-centered emission but an intense ligand-centered green fluorescence independent of the nature of the complexed ion is in that case observed.
The nature of the green fluorescence is not completely clear.As already discussed,most probably this fluorescence is generated by a different conformer than the normal cis -cis Tpy conformer,which makes tridentate complexes.In the presence of a third complexing agent,it is possible that isomerization is induced on Tpy so that bidentate (cis -trans conformers)or monodentate (trans -trans conformers)37are formed and produce fluorescence similar to that of the highly protonated Tpy 27(cf.,Figure 2)or of the Tpy -Eu 3+-PEG-200system (Figure 5).Most of the previous works studying Tpy -metal complexes deal with metal-
to-ligand charge-transfer (MLCT)luminescence,39-41which,in most of the cases,is very weak and is observed at low temperature.The presently observed green luminescence is not of the MLCT type.This is concluded by the following data:MLCT lumi-nescence has a rather long decay time,while τwas only 2.8ns in the present case;MLCT luminescence is rather weak,while the fluorescence quantum yield rose as high as 0.63in the present case.34MLCT luminescence is usually observed by excitation in the visible,while excitation in the present case is obviously a ligand-centered n -πtransition (cf.,Figure 1and the related discussion).Indeed the absorption spectrum of the complex (see curve 3of Figure 6)largely extends into the visible.However,excitation in the visible did not produce any room-temperature luminescence at all.As already said,we also rule out the possibility that the green emission is phosphorescence.Phosphorescence is the ruling emission in the case of the Tpy -Ir complex.24,42However,phosphorescence cannot be justified in the present case,neither in terms of intensity nor in terms of decay time.We then adopt the original explanation that the green emission is due to a different conformer obtained in the presence of a third complexing agent.
If we take into account the fact that pure Tpy emits blue luminescence,we note that by combining PDMAM,Tpy,and Eu 3+at different proportions and physical states one can obtain all three basic colors,i.e.,blue,green,and red.
Conclusion
We have found that PDMAM hydrogels can solubilize and retain complexes of Tpy with various metal ions.The variation of the physicochemical state of the macromolecule affects the photoluminescence emission properties of the complex.Thus,the Tpy -Eu 3+complex solubilized in PDMAM emits red metal-centered emission when the polymer is in the solvent-swollen state or lyophilized swollen state but emits green ligand-centered luminescence when PDMAM is in its dried shrunk phase.Similar is the behavior of the Tpy -Tb 3+complex.If a nonemitting metal ion is used,then swollen PDMAM does not emit any luminescence under ambient conditions,but shrunk PDMAM emits green ligand-centered https://www.doczj.com/doc/e018768823.html,parison of these data with the behavior of pure Tpy or Tpy -metal complexes in various solvents leads to the conclusion that precipitated complexes give metal-centered luminescence but complexes formed in the presence of a third complexing agent emit green ligand-centered luminescence associated with a cis -trans or a trans -trans Tpy conformer.The behavior of the Tpy -M 3+complex in PDMAM can be used as a model for studying similar phenomena in other macromolecular phases,e.g.,molecules of biological importance.
Acknowledgment.We are thankful to Professor G.Bokias of the Chemistry Department of the University of Patras for providing PDMAM and for many helpful discussions concerning this work.We thank the European Social Fund (ESF),Operational Program for Educational and Vocational Training II (EPEAEK II),and particularly the Program PYTHAGORAS II,for funding the present work.
LA061406D
(39)McMillin,D.R.;Moore,J.J.Coord.Chem.Re V .2002,229,113.(40)Maestri,M.;Armaroli,N.;Balzani,V.;Constable,E.C.;Thomson,A.M.W.C.Inorg.Chem.1995,34,2759.
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3837.
Figure 8.Luminescence spectra of the Tpy -Tb 3+-PDMAM system:(1)water-swollen or lyophilized (excitation wavelength,336nm)and (2)shrunk (excitation wavelength,370nm).
8606Langmuir,Vol.22,No.20,2006Bekiari and Lianos
Uncivilized behavior of Chinese tourists “You see, it’s common, most people didn’t care”said by one female tourist who is just throwing trash on the San Ya beach which has already been reduced to a dumping ground. When the beautiful island meets holiday crowd, under the hustling and bustling scene, we absolutely startled by the carving “Dao ci yi you”, dumbling beer bottles, spilling peels and half-burned branches. These facts are still far from enough.Uncivilized behavior makes headlines in the National Day holidays. At the memorable flag-raising ceremony at Tiananmen Square on October 1, over 120,000 participants left five tons of trash behind after showing their respect to the country. Sometimes, you could not find a place to sit –men take up all the benches in the park, lying full-length and blissfully snoring the afternoon away.Spitting, talking loudly and random littering are frequent scenes in tourist attractions. Countless visitors allow their children to use the city streets as a toilet, even though there is a toilet nearby. Newsstand and bookshop proprietors also suffer from bad-mannered people who tear the wrappers off magazines and read the contents without buying them. Bookstore visitors ignore the signs of asking them to rest only in designated areas instead of sitting on the stairwell. Similar stories are testing the tolerance of public opinion almost every day. We could be denied those undesirable manner. Nevertheless, it will be more persuasive to point out that China's tourism industry is not developing in a gradual way, but in a blowout manner. Growing wealth enables more Chinese people to seek leisure and fulfillment from traveling. Considering China's large population, some problems and challenges must emerge at the same time.We might be disappointed but not be desperate. Objectively speaking, before the national holiday, civilized traveling aroused surges of attention such as Wechat hot debate, media focus, screen exposure, which is beyond the past several years.Under the supervision of public opinion, the index of civilized golden week presents positive improvement. However,it’s still a serious short board that reflects on Chinese social moral deficiency. Not only should we take it seriously, but also wake up the consciousness of citizen responsibility and turn it in to action to make up. Forming harmonious social morality as if human’s maturation. We need time. I do believe the enlightened public moral education combined with perfected facilities will take several generations to nurture civilized behavior and display a positive image of Chinese tourists.
Listen to part of a lecture in a biology class. The class is discussing animal behavior. Okay Ok , the next kind of animal behavior I want to talk about might be familiar to you. You may have seen, for example, a bird that's in a the middle of a mating ritual. and suddenly it stops and prines preens . You know, takes a few moments to straight straighten its feathers. and then returns to the mating ritual. This kind of behavior, this doing something that seems completely out of place. It's is what we call a displacement activity. Displacement activities are activities that animals engaged animal's engaging in when they have conflicting drives. If we take our example for from a minute ago if the bird is afraid of its mate, it's conflicted. It wants to mate, but it's also afraid and wants to run away. So instead, it starts grooming itself. So the displacement activity the grooming, the straightening of its feathers seems to be an irrelevant behavior. So what do you think another example of the a displacement activity might be? How about an animal that , um, instead of fighting its enemy or running away, it attacks a plant or a bush. That's a really good suggestion, Carol Karl . But that's called redirecting. The animal is redirecting its behavior to another object. In this case, the plant or the bush. But that's not an irrelevant or inappropriate behavior. The behavior makes sense. it's appropriate under the circumstances, but what doesn't make sense is the object behaviors direct the behavior's directed towards. Okay Ok , who else? Carol? I think I've read in another class about an experiment were where an object that the animal was afraid of was put next to its food. next to the animal's food. And the animal, it was conflicted between confronting the object and eating the food, so instead
Public Behavior Thanks to years of huge effort, China is getting stronger and stronger. However, when the bright side is showing, something bad arises too ——terrible public behavior. When we are watching TV, it is normal to hear some bad behavior that happened. But the most common one in our daily life should be breaking traffic rules, or more accurately, running the red light. Large numbers of passengers, motorists, or even car drivers, ignoring the red light which means stop, continued on their way, abandoning their morality as well as lives. Tragedies that had happened seem to be unable to arouse their vigilance. As a result, more and more tragedies are going on. Others may value their lives indeed, but do not pay the same attention to the environment as they should, which makes spitting and littering a common but terrible phenomenon. When asked about the behavior, most of the public will surely admit that it is not right. And yet what force one to do the things he thinks is wrong? Just because of the need of convenience, or more deeply, the superficial understanding of environmental consciousness. And furthermore, the third bad behavior, as the least intolerable one, is the problem of queuing. Though there is an old saying: first come, first served, public seems not willing to obey it. Jumping the queue is widely seen everywhere. Worse still, sometimes there is even no queue but a noisy crowd, pushing and jostling as if they were enemies. It is sad that bad public behavior is far more than these. But I am strongly assured it will get better. All we need is time and education. Root the correct idea into public’s mind is particularly important. The Audience is not only the present generation, but the generation to come. 工信1409 叶欣
Organizational Behavior Part1: Introduction to Organizational Behavior Chapter1:organizational behavior overview Organizational behavior (OB) is a field of study devoted to understanding, explaining, and ultimately improving the attitudes and behaviors of individuals and groups in organizations. OB source: 1.Industrial and organizational psychology 2. Social psychology 3. Sociology 4. Anthropology 5. Economics Integrative model of organizational behavior 1.Individual outcomes: Job performance;Organizational commitment 2.Individual mechanisms: Job satisfaction; stress; motivation; trust,justice and ethics; Learning and decision making Individual characteristics: Personality; cultural values; ability Group mechanisms: Teams; leaderships
behavior的用法和辨析 今天和大家一起学习一下behavior的用法，快来一起学习吧，下面就和大家分享，来欣赏一下吧。 词汇精选：behavior的用法和辨析 一、详细释义： n. 行为;举止;态度[U] 例句： Their behavior towards me shows that they do not like me. 他们对我的举止说明他们不喜欢我。 例句： His strange behavior made the police suspicious. 他不寻常的举止引起了警察的怀疑。 (机器等的)运转状态，性能[U]
例句： The aircrafts behavior was satisfactory on its first test flight. 那架飞机在第一次试飞时运转情况令人满意。 (事物的)反应，变化;作用[U] 二、词义辨析： behavior,conduct,manner 这些名词均含有“行为，举止”之意。behavior普通用词，侧重指某人在特定场合对他人或在他人面前的行为、举止。conduct较正式用词，泛指某人的行动。侧重根据社会道德标准和责任感。manner主要用来指人的习惯行为。 三、相关短语： behavior therapy 行为疗法 behavior modification 行为修正 四、参考例句： Her behavior enraged him.
她的行为激怒了他。 Your behavior frenzied me. 你的行为使我愤怒。 Her odd behavior defies understanding. 她的古怪行为无法理解。 Her behavior alienated her friends. 她的行为使自己跟朋友们疏远了。His behavior borders upon madness. 他的行为几乎算得上疯狂。 My behavior is above reproach. 我的做法无可厚非。 Her behavior was beyond reproach. 她的行为无可指责。 She has a spontaneous behavior . 她的举止很自然。 His behavior was beyond bearing.
International customer behavior Abstract: Consumer buying behavior refers to the people to meet the needs and desires and looking for, select, purchase, use, evaluation and disposal of products, services, the process of intervention activities, including consumer's subjective psychological activities and objective material activity two aspects. Consumers' purchasing behavior is composed of a series of links, element complete process. In this process, the purchase decision in the central position; Decisions correctly or not directly decided to purchase behavior, pointing to the way and the size of the utility. Keywords: behavior, consumer, purchase, process Consumer buying behavior refers to the people in order to meet the person, family life need or enterprise in order to meet the needs of production, when buying a hobby products or services of all kinds of behavior, and the purchase decision process. Consumer buying behavior, diversity, dynamic and interactive volatility, impulsivity, trading, etc. Strictly speaking, the customer purchasing behavior is composed of a series of links, namely customer purchasing behavior is derived from the purchase decision-making process in the system, and under the influence of internal and external factors. Customer purchase behavior of complex, puts forward more on sales staff, a higher challenge. For excellent sales staff, to master the customer buying decision process and understand the factors that affect the customer to make a buying decision and so on all aspects, such as critical. Procurement is the buyer in accordance with the requirements, in a reasonable time, with the most reasonable price to buy the best goods; We can learn that in the process of buyers to purchase, there are a few points are requires consideration of sales people; Is first buyers demand, that is to say, you should be very good to know the requirement of the buyer; Secondly, time, time is a limited resource, you need to ensure a good delivery date; Third: the prices or costs. In flooded with goods, can you guarantee to the buyer to provide a competitive price, if you can't, so if you can provide other high additional value? Buyers in the purchase process, which can be roughly divided into two kinds: one kind is looking for a particular product; Is a kind of choice to cooperation supplier; Your cooperation buyers is to belong to that kind of situation? A type of buyer you are looking for that? How to make the targeted sales, these are worth each export friends thinking about;
组织行为学 题型剖析： 选择题（15*1=15）、多选题（5*2=10）名词解释（5*3=15）、简答题（5*6=30）、论述题（10*1=10）、案例分析（20*1=20） 知识点： 1、如何利用工作团队来增强团队的互动？ 【解析】工作团队：是由一些知识技能互补、彼此承诺完成一项共同目标或是一系列绩效目标的成员组成的特殊群体，每个成员都负有共同的责任。 高效团队：是指成熟的团队，发展目标明确，完成任务前后对比效果明显增加，团队成员在有效的领导下相互信任、沟通良好、积极协同工作的团队。 高效团队的特征：①共同目标②相关技能③相互信任④一直承诺⑤良好的沟通⑥高效的领导高效团队的建设途径和技巧：①制定共同的团队目标②确定不同能力的成员③创建互信的环境（坚持的原则：公开、公正、公平；有效的沟通；不能任人为亲。）④改进领导方式和团队结构 ⑤正确的绩效评估和薪酬体系。 2、如何运用决策提高领导的有效性？ 【解析】领导决策是领导者的基本职能和首要任务，是指领导者为实现领导活动目标，组织制定多种决策方案，从中选择并执行最佳方案的全部活动过程。 领导决策具有预测性、目的性、选择性、关键性、风险性等特点。 决策领导的基本原则：①信息准确性原则②可行性原则③系统分析原则④对比分析原则 ⑤集体决策原则 领导决策的基本程序：①发现问题②确定目标③拟定方案④评估方案⑤方案优选⑥组织实施 ⑦追踪反馈 群体决策的方法：①头脑风暴法②德尔菲法③案例提前分析法④提喻法 决策的民主化的条件和途径：领导者要具备民主作风和素质、建立起决策参与民主机制、实现决策制定程序和执行程序民主化、建立决策监督机制接受群众监督决策。 3、组织设计应遵循的原则？ 【解析】原则：①专业化分工原则②统一指挥原则③控制幅度原则④权责对等原则⑤柔性经济原则 4、内聚力的定义，作用，影响因素？ 【解析】定义：群体凝聚力又称群体内聚力，它是群体成员施加各种影响，使之在群体内积极活动和拒绝离开群体的全部力量的总和，是群体对个体的吸引力 作用：①内聚力和工作绩效的关系②内聚力与员工满意度的关系③内聚力与员工个人的成长1、如果群体目标与组织大目标一致，且群体成员对组织大目标持支持态度时，凝聚力高的群体比凝聚力低的群体更为有效。 2、如果群体目标与组织大目标不相一致，且群体成员们又不支持组织大目标时，则群体的凝聚力越高，完成组织大目标的工作效率就会越低。 影响：①成员一致性②群体规模地位③与外部的关系④成员对群体的依赖⑤奖酬体制 ⑥群体的绩效⑦信息沟通⑧领导方式 5、期望理论有什么作用？ 【解析】期望理论：（人的固定要求决定了他的行为以及行为方式）只有当人们认为存在实现预期目标的可能性，并且实现这种目标又是非常重要的时候，他们的激励程度或动机水平才会最大。也就是说决定行为动机的因素有两个，即期望与效价。用公式表示为：激励强度=期望值×效价。 作用：总的来讲：具有一定的导向作用。期望值越高，表明人们对努力与绩效之间关系的相信程度越大，人越容易做出努力的决断，反之同理。有利于提高员工的工作绩效。
《Consumer Behavior》课程教学大纲 一、课程基本信息 课程代码：050873 课程名称：消费者行为学（全英） 英文名称：Consumer Behavior 课程类别：专业课 学时：48 学分：3 适用对象:金融学（“2+2”实验班）本科生 考核方式：考试 先修课程：宏观经济学 二、课程简介 消费者行为学是研究个人或组织选择、购买、使用或淘汰产品、服务、思想或经验以满足其需求的整个过程的学科。具体而言，本课程介绍消费者行为学的有关基本理论，包括消费者个人的认知、学习和记忆、动机、情境、价值观、自我等。同时对消费者决策过程、影响消费者决策和行为的各种因素包括态度、组织、社会媒体、社会阶层和生活方式等进行了分析和探讨。 Consumer behavior is the study of the processes involved when individuals or groups select,purchase,use,or dispose of products,services,ideas,or experiences to satisfy needs and desires.Specifically,this course introduces the basic theories of perception,learning and memory,motivation,global values and the self of consumers as individuals.It also deals with the process of decision making,how different factors including attitudes,groups,social media,social class and lifestyls affect decision making and consumer behavior. 三、课程性质与教学目的 消费者行为学是金融学（“2+2”实验班）本科生的专业必修课。通过课程学习，让学生能够掌握消费者行为学的基本理论，包括消费者个体的自我、知觉、学习和记忆、动机和价值观，消费者的决策过程、购买与处置行为，消费者决策如何受到自身态度、外部群体、社会化媒体、生活方式及文化等因素的影响等，并能够将理论与中国的实际相结合。 四、教学内容及要求 Chapter1Buying,Having,and Being:An Introduction to Consumer Behavior （一）目的与要求
Composites复合任务 Sequence顺序任务/序列任务 The Sequence task is similar to an "and" operation. It will return Failure as soon as one of its child tasks return Failure. If a child task returns Success then it will sequentially run the next task. If all child tasks return Success then it will return Success. Sequence任务类似于“and”操作。一旦其子任务之一返回Failure，它将返回Failure。如果子任务返回Success，那么它将按顺序执行下一个任务。如果所有子任务返回Success，那么它将返回Success。 Selector选择任务 The Selector task is similar to an "or" operation. It will return Success as soon as one of its child tasks return Success. If a child task returns Failure then it will sequentially run the next task. If no child task returns Success then it will return Failure. Selector任务类似于“or”操作。一旦其子任务之一返回Success，它将返回Success。如果子任务返回Failure，则它将按顺序执行下一个任务。如果没有子任务返回Success，则它将返回Failure。 Parallel并行任务 Similar to the Sequence task, the Parallel task will run each child task until a child task returns Failure. The difference is that the Parallel task will run all of its children tasks simultaneously versus running each task one at a time. Like the Sequence class, the Parallel task will return Success once all of its children tasks have return Success. If one tasks returns Failure the Parallel task will end all of the child tasks and return Failure. 与Sequence任务类似，Parallel任务将运行每个子任务，直到子任务返回Failure。不同的是，并行任务将同时运行其所有子任务，而不是每次运行一个任务。像Sequence任务一样，当所有的子任务都返回Success时，Parallel任务将返回Success。如果一个任务返回Failure，Parallel任务将结束所有子任务并返回Failure。 Parallel Selector 并行选择任务 Similar to the Selector task, the Parallel Selector task will return Success as soon as a child task returns Success. The difference is that the Parallel Selector task will run all of its children tasks
大学生英语演讲 Civilized behavior 大学生英语演讲范文：Civilized behavior A man will not render good services to his country if he can do nothing civilized ,for in proportion as he respect himself while he respects his country. The civilized behavior is the birthplace of true patriotism. It is the secret of social welfare and national greatness .It’s the basis and origin of civilization. Civilized behavior is not a matter of boast or the quality of imagination; it’s the matter of down –to- earth principle. It’s the freshness of the deep springs of life. Civilized behavior means a temperamental predominance of responsibility over superficiality, of the appetite for initiation over the love of conformity. We do not choose to be born. We do not choose our parents. We do not choose our historical epoch, the country of our birth or the immediate circumstances of our upbringing. We do not, most of us, choose to die; nor do we choose the time or conditions of our death. But within all
Part 1 Introduction Chapter 1 Introduction 1. Which of the following decision should be considered legitimate topics of concern in the study of consumer behavior: (a). selecting a college (b). purchasing a life insurance policy (c). Smoking a cigarette (d).selecting a church to join (e).selecting a dentist (f).visiting an auto showroom to see new models (g).purchasing a college textbook 2. Consumption behavior begins with the step of: (a). purchasing process (b). Information search and evaluation (c). Problem recognition (d). Postpurchasing behavior 3. ____occurs when an individual perceives a difference between an ideal state of affairs and the actual state at any given moment. (a). Problem recognition (b).search (c).alternative evaluation (d).choice (e).outcome 4. The research scope of consumer behavior includes: (a). Psychological characteristics of consumer such as needs, motives, personality, attitudes and general effect of such psychological process as perception and learning on consumer behavior (b).Application of psychology research accomplishments on marketing strategies such as influences of such factors as brand, package, price, advertisement on consumer behavior (c). Family, social group, social class, culture, subculture influences on consumer purchasing 5. From which of the following we can see the research of consumer behavior is being widened? (a). From the past research of “customer” to present “consumer” (b). From the simple describe of the relationship of variables to the study of the cause and effect relationship, and performing laboratory research of many problems (c).The work abstract level improved Many consumer theory models are put forward. (d).From static concept to dynamic concept 6. What are the two parts psychology includes: (a). Psychology process (b). Psychology characteristic (c).recognition and perception (d).personality consciousness
Immoral Behavior in Public Write a composition entitled Immoral Behavior in Public. You should write at least 120 words according to the outline given below in Chiness. 1.我们经常在公共场合见到各种不文明的行为； 2.这些不文明的行为会有哪些影响； 3.我们应该怎样改善这种现象。 英语四级作文写作步骤构思： 步骤1： 审题：这是一篇以公共文明为主题的说明文。 步骤2： 引入话题：指出不文明现象在社会的广泛存在； 展开话题：阐述不文明现象两方面的主要影响； 话题结论：如何改变这种情况，并提出自己的观点。 Immoral Behavior in Public Immoral behaviors in public are everywhere. One can find people spitting on overpasses, picking flowers in parks and jumping e queue while waiting in banks. 公众场合的不文明行为比比皆是。你会发现，人们在天桥上随地吐痰，在公园里摘花，在银行排队等候时插队。引入话题:指出不文明现象在社会的广泛存在； Immoral behaviors in public bring about a series of problems. First of all, one of the most serious ones is that it may exert a negative impact on our sense of social responsibility. ln addition, if we keep turning a blind eye to the other people's feelings, we, in turn, will be disrespected someday. 公众场合的不文明行为会造成一连串的问题。首先，最严重的问题就是会降低我们的社会责任感。此外，如果我们继续忽视他人的感受，终有一天我们自己也会失去他人的尊重。 To get rid of this phenomenon is certainly not easy. I propose that we should punish those people who fail to respect the common good. What's more, stricter policies for this should be made to correct this phenomenon as soon as possible. (121words) 消除这种现象绝非一件容易的事。我的建议是，我们应该严惩那些不尊重大众利益的人。此外，需采取更严格的政策，尽快消除这种不良的风气。