Studies on unimolecular and bimolecular photoprocesses of a newly synthesized selenium compound, 7-chloro-2-phenyl-9H-[1]-benzopyrano[3,2-b]-selenophene-9-one (SeP)

Using steady state/time resolved spectroscopic and electrochemical techniqu es the spectroscopic and photophysical studies were made on a novel synthes ized selenophene compound SeP in nonpolar methylcyclohexane (MCH), polar ap rotic acetonitrile (ACN) and polar protic ethanol (EtOH) solvents at the am bient temperature as well as at 77 K. Both from the studies on unimolecular and bimolecular photoprocesses this selenophene compound was found to poss ess several electronic levels, B-1(b), L-1(a), L-1(b), (all are of pi pi* n ature and L-1(b) is hidden within L-1(b) band envelop like the characterist ics of most of the acenes) and (1)(n(O)pi*) state arising due to carbonyl o xygen atom. In polar ACN environment this n(O)pi* state disappears because it moves within the envelop of intense L-1(b) band due to large destabiliza tion. Large overlapping of different band systems within the L-1(b) band of Sep was confirmed from the observed depolarization effect. The lack of pho sphorescence of SeP both in R ICH and EtOH rigid glassy matrix at 77 K has been inferred due to large vibronic interactions between closely lying trip lets of the corresponding (1)n(O)pi* and L-1(b) states. From the bimolecula r investigations, it reveals that SeP acts as a good electron donor in pres ence of the well known electron acceptor 9 cyanoanthracene (9CNA). Transien t absorption spectra measured by laser flash photolysis technique demonstra te the formation of ion-pair when the acceptor is excited. From the analysi s of the fluorescence quenching data it seemingly indicates that the major contribution in the diminution of the fluorescence intensity of the accepto r 9CNA in presence of SeP is not only due to the photoinduced electron tran sfer (ET) but also originates from static type (instantaneous) quenching pr ocesses along with external heavy atom effect. The possibility of occurrenc e of photoinduced ET reaction in Marcus inverted region is hinted. (C) 2001 Elsevier Science B.V. All rights reserved.