Ultrafast excitation dynamics in organic multicromophoric systems after two-photon excitation

摘要

In this contribution we report two-photon excited time-resolved fluorescence and fluorescence anisotropy for several macromolecular systems of different symmetry such as cyclic (single ring) thiophene-based annulenes, triphenylamine-centered branched trimers with pyridine acceptor groups, and linear chromophores possessing high TPA-cross-section. We have compared the ultrafast fluorescence anisotropy dynamics for one- and two-photon excitation routes using time-resolved fluorescence up-conversion setup with femtosecond time resolution. For linear systems the initial anisotropy was found to be about factor 1.4 higher than that for one-photon excitation as predicted by theory. For macromolecular strongly coupled planar systems under two-photon excitations we observed a relatively low initial fluorescence anisotropy (～0.1) and specific femtosecond anisotropy dynamics. Two-photon excited fluorescence anisotropy is strongly correlated to the orientation and value of the transition moment from the excited state to the second and higher lying states and can be used as a direct indicator of strong coupling regime.