Photophysics of 6,11-dihydroxynaphthacene-5,12-dione in different organic solvents

Abstract

The absorption and steady-state and time-resolved emission characteristics of 6,11-dihydroxynaphthacenedione (6,11-DHNpQ) have been investigated in different organic solvents. A red-shifted absorption band has been observed at 555 nm in protic solvents which are either hydrogen-bond donating or accepting in nature, e.g. alcohols and aprotic solvents such as DMSO and DMF. This band is absent in all other solvents. This observation is explained on the basis of intermolecular hydrogen-bonding complexes between the solute and the solvent molecules. An unusual emission characteristic has been observed in methanol, attributed to the same hydrogen-bonding complexes. In benzene, DMSO, DMF and acetone the fluorescence quantum yield of the quinone is quite low owing to exciplex formation and/or subsequent charge separation depending on the solvent polarity.