Laser flash photolysis of chlorobenzene in polar solvents

• Published in: Journal of photochemistry 1985-01, Vol.30 (3), p.259-267
• Main Authors: Previtali, C.M., Ebbesen, T.W.
• 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: 0047-2670
• DOI: 10.1016/0047-2670(85)85047-4

The laser flash photolysis of chlorobenzene at 266 nm was studied in methanol (MeOH) and other polar solvents. The triplet state properties in MeOH were determined: φ T = 0.7 ± 0.2; λ max = 305 nm; ϵ 305 = 6500 ± 800 M −1 cm −1; τ = 715 ± 20 ns. In the presence of LiCl a long-lived transient absorption with λ max = 350 nm was observed and it was assigned to Cl -rad 2. Part of the absorption was formed immediately after the laser pulse and a slow growth was also observed in the following microsecond. This was interpreted as being partly due to a singlet state very fast CCl bond homolysis and partly due to a triplet-mediated generation of Cl·. Also the characteristic absorption of solvated electrons was found in MeOH. A photo-ionization quantum yield of 0.03 ± 0.01 was estimated. The triplet lifetime was determined in various solvents and it was found to decrease with increasing dielectric constant. The photolysis mechanism of chlorobenzene is discussed in terms of a singlet state photosubstitution reaction with the radical cation as an intermediate, and a singlet and triplet homolytic CCl bond breakage.