Intramolecular charge transfer promoted fluorescence transfer: a demonstration of re-absorption of the donor fluorescence by the acceptor

Abstract

Intramolecular charge transfer (ICT) promoted fluorescence transfer has been investigated in two polar solvents, acetonitrile and water. The ICT species of 4-N,N-dimethylaminobenzonitrile (DMABN) produced exclusively in the photoexcited state serves as the donor while phenosafranin (PSF), a cationic phenazinium dye, acts as the acceptor. A transfer of the fluorescence occurs from the ICT state of DMABN to PSF in both the media. Time-resolved fluorescence decay analysis in combination with the steady state fluorometric observations conclusively rule out the involvement of the fluorescence resonance energy transfer (FRET) process and establish the fluorescence transfer as a consequence of re-absorption of the fluorescence of the donor by the acceptor. Thus, apart from citing an example of a coupled interaction of ICT and fluorescence transfer, importance of the present work lies in providing a demonstration in differentiating between the Förster resonance energy transfer and the trivial energy transfer through re-absorption.