PHOTOREACTIONS OF PHTHALIC-ACID DIALKYL ESTERS - A FLASH-PHOTOLYSIS STUDY

Phthalic acid di(2-ethylhexyl) ester (DOP), phthalic acid di(2,4,5-trimethylheptyl) ester (DIDP), phthalic acid di(n-decyl) ester (DDP) and phthalic acid dimethyl ester (DMP) were irradiated in dilute solutions of 1,1,2-trichlorotrifluoroethane (TTE), acetonitrile and dichloromethane and in a polyvinyl chloride (PVC) matrix with 20 ns flashes of 266 nm light. Transient absorption spectra formed during the flash ranging from about 250 to 700 nm are attributed to excited triplet states. Emission spectra observed at wavelengths between 300 and 600 nm consist of a short-lived portion, corresponding to delayed fluorescence (mainly P-type in fluid solution and E-type in the rigid PVC matrix) originating from 'unmodified' triplets and a long-lived portion attributed to triplet biradicals. Triplets of phthalic acid esters are quite unreactive towards chlorinated aliphatic hydrocarbons and PVC (k2 less-than-or-equal-to 10(3) l mol-1 s-1). The resulting radicals exhibit optical absorption at lambda < 420 nm. In PVC films, a polymer matrix effect was detected for the decay of triplet excited species. Over the investigated temperature range (229-400 K) the decay can be described according to Kohlrausch's law by 'stretched exponentials': ln([T]t/[T]0) = - alphat(beta). Both the matrix response factor alpha and the dispersion factor beta increase with increasing temperature. The functions alpha = f(T-1) and beta = f(T-1) exhibit a significant discontinuity (kink) at the glass transition temperature T(g) almost-equal-to 353 K.