Laser Flash Photolysis Studies On Photo-induced Electron Transfer Mechanisms Of Some Polycyclic Organic Molecules

Time-resolved laser flash photolysis is a new technique used to investigate the transient species of photochemistry systems at room temperature and has been applied in different research fields. The properties and dynamic characteristics of transients in photochemical processes could be obtained via transient absorption spectra and the change of transients' concentration accompanied with the change of time. In this work, we mainly used home-made laser flash photolysis combined with steady Uv-vis absorption spectrum, fluorescence (phosphorescence) spectrum and quantum calculation to investigate some photo-induced electron transfer reactions. Detailed works are divided into four parts:1. Transient absorption spectra and corresponding dynamic parameters of triplets NQ and NQS in acetonitrile (benzene) were studied. Rate constants of ~3NQ~* (~3NQS~*) quenched by some aliphatic alcohols, phenols, aliphatic amines and aromatic amines were obtained. Photo-induced proton/electron transfer mechanisms were deduced. In addition, photo-induced electron transfer mechanism was testified by thermodynamic results. Standard redox potentials, gas phase ionization/affinity potentials and charge density distributions of some reagents were calculated by DFT method.As sensitizers, NQS is more active than NQ. It was approved by quantum calculation results. All the quenching rate constants measured in benzene are higher than those measured in acetonitrile. The increased reactivities of sensitizers in benzene can be explained by a conversion of excited state configuration of NQ (NQS) from ~3(Ï€,Ï€)~* to ~3(n,Ï€)~3 . Furthermore, the relations between k_q and Hammett constants, redox potentials and charge density distributions calculated by DFT method were also discussed.2. Transient absorption spectra, dynamic constants, excited states energies and standard oxidation potentials of 2,3-dimethylquinoxaline (DMQ) and 2,3,6,7-tetramethylquinoxaline (TMQ) were obtained for the first time.The quenching reactions between DMQ, TMQ, 2,3-dimethylnaphthene (DMN),...