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

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 k_rec¹ = (7.0 ± 0.2) × 10⁵ s^-1, and the separated photoproducts recombine by a diffusional back-electron-transfer rate constant of k_rec² = (1.5 ± 0.2) × 10⁹ M^-1̇s^-1. Photoejection of the electron from BPD^̇- yields the neutral π-system, and the ejected electron reduces an unreached 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_rec = (1.0 ± 0.2) × 10¹⁰ M^-1̇s^-1 (at room temperature).