Diffuse reflectance laser photolysis studies of triplet-state absorption spectra of anthracene in Shpol'skii matrixes

Abstract

The triplet-triplet absorption spectra of anthracene and perdeuteriated anthracene in a frozen n-heptane Shpol'skii matrix at 12 K were obtained by diffuse reflectance laser flash photolysis. Incorporation of the anthracene into a Shpol'skii matrix resulted in significant sharpening of the vibronic bands in the weak, low-energy transitions. Four new vibronic bands in the low-energy /sup 3/A/sub 1g//l arrow/ /sup 3/B/sub 2u/ and /sup 3/B/sub 3u/ /l arrow/ /sup 3/B/sub 2u/ transitions are observed in the Shpol'skii matrix which are not resolved in the transient optical density spectra in a 3-methylpentane glass at 12 K. The widths of the vibronic bands in these transitions are about half as broad in the Shpol'slii matrix compared to the glass. No sharpening and no new bands are observed in the higher energy /sup 3/B/sub 1g/ /l arrow/ /sup 3/B/sub 2u/ transition. Here, solvent-dependent Franck-Condon envelopes of the /sup 3/B/sub 1g/ /l arrow/ /sup 3/B/sub 2u/ transition of anthracene in a series of n-alkane Shpol'skii matrices at 12 K were observed. In odd n-alkanes the 400-nm band was less intense than the 426-nm band while in even n-alkanes the peak intensity pattern was reversed. At room temperature the transient spectra are the same for allmore » the n-alkanes except for slight wavelength shifts. The changing intensity at low temperature is shown to be caused by photolysis of anthracene whose efficiency is matrix dependent.« less