Reactivity of aromatic amines with triplet 1,8-dihydroxyanthraquinone: A laser flash photolysis study

The property of the lowest excited triplet states of 1,8-dihydroxyanthraquinone (DHAQ) was investigated by using time-resolved laser flash photolysis at 355 run in organic solvents, i.e. acetonitrite and cyclohexane. The transient absorption spectra of the excited triplet DHAQ were obtained in acetonitrile, which have an absorption maximum at 480 nm and two broad absorption bands around 350 and 650 mn. (3)DHAQ* is efficiently quenched by triphenylamine (TPA) via photoinduced electron transfer pathway, which was testified by the finding of TPA radical cation. In addition, aniline derivatives such as N,N-dimethylaniline (DMA), 3,5,N,N-tetramethylaniline (TMA), 4-dimethylaminobenzoic acid (DMABA) and dimethyl-p-toluidine (DMT) could also quench (3)DHAQ* rapidly. Evidence for electron transfer interaction with anilines in acetonitrile was obtained from transient spectral characterization of formed radicals. Experimental k(q) values approach the diffusion-controlled rate limit, and decrease significantly from DMT (1.85 x 10(10) M-1 s(-1)) to DMABA (1.95 x 10(9) M-1 s(-1)). These kq values depend on the charge density on the N atom of anilines, which could be quantified by Hammett sigma constant. (c) 2006 Elsevier B.V. All rights reserved.