Triplet states of symmetrically disubstituted biphenyl derivatives. Triplet exciplex formation between benzophenone triplet and benzidine

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 1994-03, Vol.78 (3), p.221-227
• Main Authors: Naik, D.B., Dey, G.R., Kishore, K., Moorthy, P.N.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics)
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/1010-6030(93)03725-V

The absorption spectra of the triplet states of 4,4′-diaminobipheyl (benzidine, BZD) and 4,4′-dibromobiphenyl (DBRBP) in benzene and of 4,4′-dihydroxybiphenyl (DHXBP) in a mixture of 90% benzene and 10% ethanol were recorded in the 300–600 nm region using the pulse radiolysis technique. The extinction coefficients at λ max were estimated to be 30 600,21 630 and 45 060 dm 3 mol −1 cm −1for BZD, DBRBP and DHXBP respectively and the corresponding triplet energies were 61±1.5, 63±0.5 and 63±0.5 kcal mol −. The rate constants for energy transfer from benzene and biphenyl triplets to these compounds and from the compound triplets to acceptor molecules such as naphthalene and coumarin-1 were determined. The triplets of the compounds BZD, DBRBP and DHXBP were found to react with the corresponding ground state molecules with rate constants of 5.4×10 6, 4.1×10 6 and 2.1×10 7 dm 3 mol −1 s −1 respectively. In the case of the benzidine triplet reaction with the ground state gave transient species with a λ max at 390 and 620 nm, which has been suggested to be a mixture of semi-reduced and semi-oxidized species. The benzophenone triplet reacts with benzidine to give an exciplex species with an absorption maximum at 380 nm.