Experimental and quantum chemical studies of cooperative enhancement of three-photon absorption, optical limiting, and stabilization behaviors in multibranched and dendritic structures.

This paper reports on cooperative enhancement of three-photon absorption (3PA) cross section, studied by nonlinear transmission method, in going from a one-branched to a three-branched and then to a dendritic structure. Experimentally, we observe a 72% enhanced 3PA cross-section value in going from the one-branched chromophore to the dendritic chromophore, and a 49% enhanced 3PA cross-section value in going from the one-branched chromophore to the three-branched chromophore, when the 3PA cross-section values are normalized per structure unit. Quantum chemical calculation for the one- and three-branched structures, using the cubic response (CR) theory applied to a single determinant self-consistent field (SCF) reference state, also predicts such an enhancement. Two-dimensional pi-delocalization, resulting in extended charge-transfer network in the case of the multibranched structures, is the main cause of the cooperative enhancement. Owing to the increased 3PA cross-section value for the dendritic chromophore, improved optical limiting performance at an optical communication wavelength of 1310 nm was observed, compared with the one-branched (or three-branched) chromophore, using comparable structure-unit-based concentrations. Optical stabilization capability of the dendritic chromophore was also observed at this wavelength.