FLUORESCENCE AND PHOSPHORESCENCE EMISSION AND NONRADIATIVE RELAXATION OF ACRIDINE IN A CRYSTALLINE MATRIX OF 2,3-DIMETHYLNAPHTHALENE

The results of experimental studies of fluorescence and phosphorescence of acridine, selectively excited within its absorption band, in a crystalline host lattice of 2,3-dimethylnaphthalene, are reported. The energies of the first excited singlet and triplet states of acridine in this crystalline matrix were determined. The spectra of both emissions display a broadening caused by the orientational disorder of the host lattice. The intensity and the decay time of the fluorescence and phosphorescence show moderate temperature dependence (in the 4.2-300 K temperature range). It is concluded that over the whole temperature range the most important mode of the nonradiative relaxation of the excited acridine molecule is that of the (nearly) temperature-independent intersystem crossing from the S-1(pi,pi*) singlet to the T-3(pi,pi*) and/or T-2(n,pi*) triplet states.