Photoejection of Electrons from Cycloocta[1,2,3,4-def;5,6,7,8-d‘e‘f‘]bisbiphenylene Radical-Anion and Dianion Derivatives: Identification of a Light-Induced Disproportionation

Abstract

Photoejection of electrons from 2,5,8,11-tetra-tert-butylcycloocta[1,2,3,4-def;5,6,7,8-d'e'f']bisbiphenylene radical anion, BPD - , and the respective dianion, BPD 2 - , are described. Photoejection of an electron from BPD 2 - yields a [BPD - e - ] cage complex and separated BPD - and e - /Li + species. Recombination of the cage photoproducts proceeds at room temperature with a rate constant of k1 r e c = (7.0 ′ 0.2) x 10 5 s - 1 , and the separated photoproducts recombine by a diffusional back-electron-transfer rate constant of k 2 r e c (1.5 ′ 0.2) x 10 9 M - 1 s - 1 . Photoejection of the electron from BPD - yields the neutral π-system, BPD, and the ejected electron reduces an unreacted BPD - to form BPD 2 - . The photoejection of the electron from BPD - thus yields the disproportionation products, BPD and BPD 2 - . The disproportionation products recombine by a diffusional process, k r e c = (1.0 ′ 0.2) x 10 1 0 M - 1 s - 1 (at room temperature).