Chromenes involving a two-photon absorbing moiety: photochromism via intramolecular resonance energy transfer

New derivatives involving the photochromic 2H-benzoNchromene moieties covalently linked to the 2,7-bis(carbazolyl)fluorene-derived two-photon absorbing moiety were designed to enable the possibility of resonance energy transfer from the fluorene donor to the photochromic acceptor. The longest wavelength absorption of the photochromic acceptors overlaps with the fluorescence band of the two-photon absorbing donor and the distance between the both moieties is about 5-7 A. Rapid coloration of colorless solutions was observed upon one- and two-photon absorption.