Ultrafast laser photolysis study on photodissociation dynamics of a hexaarylbiimidazole derivative

Dynamics of the photodissociation process of a hexaarylbiimidazole derivative, 2,2'-di(ortho-chlorophenyl)-4,4',5,5'-tetraphenylbiimidazole (o-Cl-HABI), in benzene solution was investigated by means of the femtosecond-nanosecond laser spectroscopy. The time evolution of the transient absorption of the lophyl radical, the product of the photodissociation, was biphasic with the faster and the slower time constants of 80 fs and 1.9 ps, respectively. The faster time constant was ascribable to the formation of the lophyl radical through the bond fission after the excitation, and the slower time constant may be attributed to the conformational change and/or vibrational cooling of nascent radicals. (C) 2007 Elsevier B.V. All rights reserved.