Time-resolved EPR and ODMR studies on the lowest excited triplet states ofalpha-silyl and alpha-germyl ketones

Sublevel properties of the lowest excited triplet (T-1) n pi* states of alp ha -silyl and alpha -germyl ketones were examined by means of ODMR, time-re solved EPR and optical spectroscopy. The EPR parameters, D, E and g, popula tion ratios, and triplet lifetimes were obtained. The D value and the tripl et lifetime varied among the molecules. In contrast the E value and populat ion ratio remains nearly the same. These properties together with their sol vent dependence and emission properties are interpreted in terms of spin-or bit couplings between T-1 (n pi*) and higher S-1 (n pi*), T-2 (pi pi*) and S-2 (pi pi*) states. An origin of the remarkable red-shifts of (1,3)(n pi*) are discussed based on a model of delocalized n, pi and pi* electrons over the Si and Ge atoms. This model is also consistent with all the triplet pr operties obtained.