Abstract

Two dimensional delocalised electronic systems such as the macrocylclic dyes Tetrabenzporphyrins and Phthalocyanines exhibit nonlinear absorption. Their nonlinear absorption and refraction at the molecular level are due mainly to a mechanism that involves the actual formation of large populations of excited states induced by the small conformational changes that the macrocycle undergoes upon excitation. This takes place in reasonably broad regions of their linear absorption spectrum where there is little or no linear absorption. In this region of the optical spectrum they exhibit both excited singlet as well as excited triplet absorption albeit in different time frames which are determined by the dipole dephasing times in the case of the singlet states (of order picosecond) and the formation time in the case of the triplet states (of order microseconds).

© 1996 Optical Society of America