PROPERTIES OF EXCITED MOLECULES IN PHOTOLYSIS OF 2,6-DIPHENYL-1,4-BENZOQUINONE WITH AMINES

Abstract

To date, it is considered established that quinones with lower energy state, under the action of light tear away a hydrogen atom from a hydrocarbon or an electron donor from inorganic anion-radicals, which have a high reduction potential. However, even for the simplest quinones (1,4-benzoquinone, 1,4-naphthoquinones, 9,10-anthraquinone and their derivatives) there is no consensus in the science literature about the nature of the initial event in photoreaction with compounds which are potential donors of hydrogen atom and electron. The first step in many photochemical reactions is the formation of complexes between donors and acceptors of electrons in the excited state (exiplexes). Photoreactive quinones as elementary acts include the transfer of electron (or) hydrogen atom. The mechanism depends on the presence and strength of donor-acceptor complexes (DAC) of the quinones with the reagents. Studies of triplet exiplexes allow you to set the details of the elementary reaction acts. Only short-lived intermediate product was registered upon photoexcitation of the studied quinone Q in low-polarity solvents. The kinetic of decay of the first order with rate constant of about 2∙106 s-1 in toluene and dibutylphthalate and the introduction of oxygen leads to a decrease in the lifetime of the product in the triplet state. With the introduction of solutions of amines quenching of triplet state (QT) with rate constant close to diffusion was observed. Rate constants of quenching by dissolving in benzene and by dissolving in dibutyl phthalate were determined. It is established that formation of intermediate products is carried out from triplet state (QT). Excited complexes with charge transfer in acetonitrile were not observed. It is concluded that with decrease in electron affinity of the acceptors, when the connection of the molecules in the complex becomes weaker, the lifetime of TE increases significantly.