Various optical nonlinear processes in J-aggregates

Molecular J-aggregates have attracted much attention because of ultrafast and large optical nonlinearity caused by excitonic resonance. Especially, porphyrin J-aggregates are materials of great interest since they are model substances for the light-harvesting mechanism in a system of antenna chlorophyll. In the present paper, we performed femtosecond pump-probe measurement of porphyrin J-aggregates and observed two new transitions from one-exciton to homo- and hetero-2-exciton states. Blue-shifted induced absorption was found around Q/sub x/-band due to the transition to homo-2-exciton states. J-aggregate size was estimated as N/spl ges/15 by using the energy shift from the monomer to the J-aggregates.