Electronic excitation of [2,2′-bipyridyl]-3,3′-diol (BP(OH)2) generates the diketo-tautomeric form of the system. The long-lived transient absorption (TA) of BP(OH)2 was assigned as the T-T absorption of the diketo-tautomer. The effect of the stimulated emission pumping on TA excludes the essential contribution of the absorption from the ground-state diketo form. The rate constants of T-T annihilation and of oxygen quenching are kTTA = 2.4 × 1010 M−1 s−1 and kqO2 = (2–3) × 109 M−1 s−1. The contribution of the second-order process to the overall decay of the triplet BP (OH)2, and the origin of the delayed fluorescence of the diketo form, are discussed.
Sepiol, J., Grabowska, A., Bulska, H., Mordzinksi, A., Perez Salgado, F., & Rettschnick, R. P. H. (1989). The role of the triplet state in depopulation of the electronically excited proton-transferring system [2,2′-bipyridyl]-3,3′-diol. Chemical Physics Letters, 163(4-5), 443-448. https://doi.org/10.1016/0009-2614(89)85165-6