CALCULATION OF THE EXCITATION TRANSFER-MATRIX ELEMENTS BETWEEN THE S(2) OR S(1) STATE OF CAROTENOID AND THE S(2) OR S(1) STATE OF BACTERIOCHLOROPHYLL

Formalism of the excitation transfer matrix element applicable for any multiconfigurational wave functions is made. On the basis of the resu ltant formulas, the excitation transfer matrix elements between the S2 or S1 state of a carotenoid, neurosporene, and the S2 or S1 state of bacteriochlorophyll a are calculated at various stacked configurations of the two molecules. The results show that the excitation transfer f rom the carotenoid S1 state to the bacteriochlorophyll S1 state via th e Coulomb mechanism including multipole-multipole interactions takes p lace very efficiently in a speed more rapid than that via the electron -exchange mechanism. The results also show that the excitation transfe r from carotenoid to bacteriochlorophyll occurs directly from the caro tenoid S2 state, as well as from the carotenoid S1 state. Furthermore, it is shown that the excitation transfer matrix element due to the el ectron-exchange interaction has an oscillatory dependence on the displ acement of one molecule from the other when the distance between the p lanes of the tau systems is kept constant. Based on these results, a p ossible mechanism of the excitation transfer from carotenoid to bacter iochlorophyll in vivo is discussed.