Enhancements Of PET And ICT Of Polypyridyl Derivatives

Polypyridines belong to polydentate ligands, which can chelated with transition metalcations to form metal coordination complexes. Metal polypyridyl complexes have beenwidely applied in the solar energy transformation and chemosensors due to their versatilephotophysical and photochemical characteristics. In the solar energy transformation aspect,these complexes act as photosensitizers to realize the photoinduced charge separation uponexcitation by light. In the chemosensor aspect, the ligands or the complexes have the similarformation of interaction between the enzyme and the substrate, and act as host receptors torecognize metal cations.A series of substituted groups were introduced to bipyridines or terpyridines, whichconsist of electron donating groups and extendedÏ€-conjugated entities. The effect of all thesesubstituted groups on the photophysical characteristics of these ligands or their metalcomplexes were studies. The results indicated that different substituted groups on differentposition would like to change the coordination affinity of these pyridines. Polypyridines haveICT character when extendingÏ€-conjugated groups were introduced. Their fluorescent spectrawere studied and it was found that the metal coordination with polypyridines would stabilizedthe ICT state of these ligands. T1 is the A-D-A molecule and its different fluorescent spectralchange were observed upon addition of different cations. It was found that Zn²⁺ acts aselectron acceptor to stabilized the ICT state by calculating the ICT driving force of T1. Twodifferent pyrazoline ruthenium complexes were obtained when pyrazoline ligands interactedwith different valence ruthenium complexes, which is indicative of existence of redoxreaction.Two and four tyrosine ethyl ester chains were introduced to the bipyridyl rings of theruthenium bipyridyl complexes to mimic the tyrosine D and Tyrosine Z in photosystemâ…¡.The UV-Vis absorption, emission spectra and lifetime of these photosensitizers remainedunchanged when tyrosine ethyl ester chains were introduced. The electron transfer from thetyrosine or deprotonated tyrosine to the oxidated Ru(â…¢) were measured by flash photolysismethod. It was found the intramolecular electron transfer from tyrosine to Ru(â…¢) take placewith a rate constant of k_f＞1×10⁸ s^-1 (Ï„_f＜10 ns) and introducing two tyrosine ethyl esterchains to ruthenium bipyridyl complexes is ideal approach to improve the intramolecularelectron transfer efficiency. Intramolecular electron transfer was observed whentriphenylamine group as electron donor was introduced to polypyridyl ruthenium complexesand methyl viologen as electron acceptor was added to realize the long distance stable chargeseparation.The pyrene or anthracene-substituted terpyridine ligands was synthesized. The self-assembly of terpyridine 1 with Zn²⁺ resulted a fluorescent and ratiometric sensor forpyrophosphate in aqueous HEPES buffer. 2-Zn and 3-Zn also showed ratiometricfluorescence change to selectively recognize phosphates in aqueous solution. Compared with2-Zn, the fluorescence maxima of 3-Zn undergoes 32 nm red-shift. The three chemosensorsbelong to ICT sensor. Chemosensor 4-Zn is weakly fluorescent, which is ascribed to theoxidative PET. The fluorescence of 4-Zn was selectively turned on when phosphates anionswere added and 4-Zn belong to PET sensor. The affinity of tpy-Zn²⁺ places between that ofDPA-Zn²⁺ and bpy-Zn²⁺, which guarantee tpy-Zn²⁺ derivatives use in the aqueous phase, andit is proved the metal zinc detached from terpyridine in presence of phosphate anions.PTZ-Ru was synthesized, where phenothiazine as electron donor was covalently linkedto a ruthenium bipyridyl type photosensitizer with diethylamine flexible chains. Theinteraction between various anions and diethylamine flexible chains in CH₃CN was studiedthrough their UV-Vis absorption, emission, UV and time-resolved absorbance spectra. Uponexcitation by light, intramolecular electron transfer from PTZ to Ru(â…¢) takes place with arate constant of k_f=1.43×10⁶ s^-1 in presence of methyl viologen.