Synthesis And Photophysical Behavior Of 2-(2-Hydroxyphenyl) Benzozoles And Its Dyads With Tetraphenylporphyrin

In this paper,the effect of solvents on the spectral properties of 2-（2-hydroxyphenyl）be-nzoxazole（HBO）,2-（2-hydroxy-5-aminophenyl）benzimidazole（NH₂-HBI）and excited intra-molecular proton transfer（ESIPT）were studied by theoretical and experimental methods.The interaction between NH₂-HBI and NH₂-TPP,as well as NH₂-HBO and NH₂-TPP were discussed.Five dyads were synthesized by amidation reaction,and their molecular structures were characterized by ¹H NMR and MS.The spectral properties and intramolecular photoinduced energy transfer were studied.1.The proton transfer type compounds HBO and NH₂-HBI were synthesized.The UV spectra of NH₂-HBI and the fluorescence spectra of both NH₂-HBI and HBO were measured in different solvents.The results showed that the maximum absorption peak of NH₂-HBI are red shifted with the increase of solvent polarity.There are enol and keto fluorescence peaks in NH₂-HBI and HBO.With the decrease of solvent polarity,the intensity of enol fluorescence peak of NH₂-HBI and HBO decreased and the keto fluorescence peak increased,which indicated that the decrease of solvent polarity was beneficial to the ESIPT reaction.Furturmore,the simulated fluorescence spectra at TD B3LYP/6-311++G（d）theoretical level well correspond to the experiments.2.The interaction between NH₂-HBI and NH₂-TPP,as well as NH₂-HBO and NH₂-TPP were studied by theoretical and experimental methods.The results showed that NH₂-HBI or NH₂-HBO as energy donor and NH₂-TPP as energy acceptor can form fluorescence resonance energy transfer（FRET）systems.It was found that the fluorescences of NH₂-HBI and NH₂-HBO is partially quenched,but the fluorescence of NH₂-TPP is significantly enhanced in the FRET.Meanwhile,the ESIPT process of NH₂-HBI coupled with FRET.The result also showed that binding ratio of NH₂-HBI with NH₂-TPP is 1:1.The quantum chemical calculation indicated that the hydrogen bond complex of NH₂-TPP with enol or keto form of NH₂-HBI could be formed in ground and excited state,which mole ratio is 1:1.The calculated and experimental emission wavelength were relatively close for the compounds.3.Five dyads HBI-TPP、HBO-TPP、HBI=TPP、HBT=TPP、HBO=TPP were synthesized.The UV and fluorescence spectra of HBI-TPP,HBO-TPP,HBT=TPP and HBO=TPP were measured in different solvents.The effects of metal cations on the fluorescence spectra of HBI-TPP and HBO-TPP,as well as p H values of solution on the HBI-TPP,HBO-TPP and HBT=TPP,were investiged.It was found that the UV spectra is less affected by solvents.The characteristic emission perk of benzazoles group are all quenched owe to the intramolecular energy transfer at photoexcitation.It was also found that there is only characteristic emission perk of porphyrin ring in fluorescence spectra and the intensity are all enhanced with the increase of solvent polarity.The results showed that the fluorescence are quenched obviously by Cu²⁺ion for HBI-TPP and HBO-TPP.The results showed that when p H=1,the fluorescence quenching is serious,but when p H=12,13 and 14,the characteristic fluorescence peaks of proton transfer molecules and porphyrin derivatives appear.The the ground state frontier molecular orbitals of HBI-TPP and HBO-TPP were calculated by Quantum chemical calculation.It is also proved that the stable configuration of HBI-TPP in the ground state and excited state is enol form.