Two-photon photochromism of a diarylethene enhanced by Forster resonance energy transfer from two-photon absorbing fluorenes

Resonance energy transfer from two-photon absorbing fluorene derivatives to the photochromic compound 3,4-bis-(2,4,5-trimethyl-thiophen-3-yl)furan-2,5-dione (PC 1) is investigated in hexane under one- and two-photon excitation. The quenching of the steady-state fluorescence of donor molecules in the presence of the diarylethene acceptor is used to study the nature of resonance energy transfer. The Forster distances and critical acceptor concentrations are determined for non-bound donar-acceptor pairs in homogeneous molecular ensembles. Quite significantly, up to a two-fold enhancement in the velocity of a photochromic transformation of 1, in the presence of two-photon absorbing fluorene derivatives, is demonstrated.