Excited state proton transfer assisted fluorescence resonance energy transfer in an inclusion complex of a β-CD derivative

Abstract

Abstract The inclusion complex of Rhodamin B (Rh B) with (N-6-deoxy- β -cyclodextrin-6-yl-1-aminocarbonyl)-3-(4-fluorobenzoyl)-7-pyridin-4-yl indolizine [designated as compound ( 1 )] is shown to be a potential pH sensor based on fluorescence resonance energy transfer (FRET). By steady state and time-resolved fluorimetry it has been established that (i) an excited state proton transfer (ESPT) occurs between the two prototropic forms, ( 1 ·H + ) and ( 1 ·H 2 +2 ) of ( 1 ), (ii) a FRET occurs in the inclusion complex whereby energy is transferred to Rh B and (iii) ( 1 ·H 2 +2 ) * is much more efficient than ( 1 ·H + ) * in the FRET. Hence this FRET is ESPT-assisted. Donor–acceptor distance from the FRET result shows that the (4-fluorobenzoyl)-7-pyridin-4-yl indolizine cap of ( 1 ) opens up in the ( 1 ·H 2 +2 ) form.