Dual intramolecular hydrogen bond as a switch for inducing ground and excited state intramolecular double proton transfer in doxorubicin: an excitation wavelength dependence study.

This paper investigates how solution conditions, especially solvent polarity and hydrogen bonding, influence the fluorescence of an anticancer drug, doxorubicin hydrochloride (DOX). When excited at 480 nm, this molecule shows single fluorescence. However, when excited at 346 nm, it shows dual fluorescence. The ground and excited state intramolecular double proton transfer in DOX has been observed and investigated to shed light on their corresponding spectroscopy and dynamics in different protic and aprotic solvents. An increase in pH results in enhancement of emission from the ionic conformer with parallel dwindling of emission of the neutral species. Based on the experimental and theoretical studies on DOX, a ground and excited state intramolecular double proton transfer mechanism is proposed to explain the unusual excitation-dependent dual fluorescence of DOX.