Two photon absorption properties of bis(n-carbazolyl)-poly-phenylenes

We studied the two photon absorption (TPA) properties of conjugated, symmetric bis(N-carbazolyl)-di-phenylpolyenes and bis(N-carbazolyl)-tri-phenylpolyenes. These novel molecules relate to the family of bis-donor-di-phenylpolynene recently shown [1] to possess very high two-photon absorption and fluorescence coefficients. The symmetric substitution of carbazole end-groups enhances the photostability of the molecules and at the same time maintains high TP coefficients (δmax>1000 GM) as determined from two-photon fluorescence measurements with picosecond pulse excitation. A blue shift of the linear absorption and a red shift of the TP peak reflect a larger proximity of the one and two photon states in carbazole substituted chromophores. High fluorescence quantum yield (0.6–0.8) was found in most of the molecules studied. These results suggest that efficient and photo-stable TP chromophores with carbazole donors are promising materials for applications in two-photon imaging and sensitization.