Theoretical Investigation Of Photoinduced Electron Transfer For Several Typical Indene Derivatives

In the present paper,the quantum chemical methods and electron transfer theories are employed to study the absorption and emission spectra of several typical indene derivatives,including the 2-(2'-hydroxyphenyl)benzoxazole,the 2-(2'-hydroxyphenyl) benzothiazole,the oxazole[4,5-b]pyridine,and the boron 2-picolinoylpyrrole complex (BOPPY).The mechanism of intramolecular photoinduced electron transfer(PET),the electronic structures,and the solvent effect on the absorption and emission spectra are investigated in detail.1.Theoretical studies on electronic structures and spectral properties of amino 2-(2'-hydroxyphenyl)benzoxazole derivativesIn this section,the meta amino derivatives(4-AHBO) and the para amino derivatives(5-AHBO) of 2-(2'-hydroxyphenyl)benzoxazole are chosen as the studied system.The geometries of these compounds in the ground and the first excited states are optimized using quantum chemical methods,and the relative stabilities of their isomers in different solvents are analyzed in detail.The absorption and emission spectra of the isomers of 4-AHBO and 5-AHBO are calculated by means of the time-dependent density functional theory(TDDFT).In addition,the electronic structures and spectral feature are investigated.The calculated results show that the dual fluorescence of 4-AHBO(5-AHBO) is produced by its different tautomers,but not by the same isomer: the long wavelength emission is from the keto tautomer,and the short wavelength band is produced by four kinds of enol isomers.Moreover,the abnormal emission spectrum of 5-AHBO in proton solvent is explained reasonably.The geometries,spectral properties and electronic structures of 4-AHBO and 5-AHBO are related to the substituted position of the amino group in the phenolic ring,which are investigated in detail.The solvent effect is considered in the spectral calculations.All of the theoretical results are in good agreement with the experimental observations.2.Investigation of electronic structures and mechanism of charge transfer in oxazolo[4,5-b]pyridine derivatives by the time-dependent density functional theoryIn this section,the excited state intramolecular charge transfer(ICT) of oxazolo[4,5-b]pyridine four derivatives with different electron withdrawing and electron donating groups are investigated by means of the time-dependent density functional theory(TDDFT) in the different solvents.The calculated results from TD-B3LYP and TD-MPW1PW91 are consistent with the experimental observations. Our theoretical investigations indicate that the most intense absorption and emission of the derivative P₁ are of the characteristics ofπ→π^* and LE transitions.However,the most intense absorption and emission of P₂,P₃,and P₄ are CT state withπ→π^* transitions from donor to acceptor.The effect of protonation on the electronic spectra is investigated in detail.Our calculated results show that the great change of the absorption spectrum is due to the protonation of the pyridine nitrogen and the diethylamino nitrogen atoms.3.Quantun chemical studies of the geometry,spectral property and electronic coupling matrix element of boron 2-picolinoylpyrrole complex(BOPPY)In this section,the photoinduced electron transfer of BOPPY is investigated using the time-dependent density functional theory(TDDFT) in different solvents.It is found that the results from the PCM-TD-B3LYP and the PCM-TD-MPW1PW91 methods are consistent with the experimental observations.Our theoretical investigations indicate that the most intense absorption and emission of BOPPY are CT state withπ→π^* transition from donor pyrrole moiety to acceptor pyridine moiety.It seems that the solvent polarity have a little effect on the positions of spectral peaks.The calculated results show that the fluorescence has large Stokes shifts with the intramolecular charge transfer.In addition,the calculations of electronic coupling matrix element for the electron transfer have been carried out in the framework of the generalized Mulliken-Hush(GMH) formalism.Our calculations confirm that the strong electron transfer is assigned to theÏ€-Ï€^* transition.All of the calculated absorption and emission spectra are in good agreement with the experimental observations.