5,6,7,9-Tetrahydro-[1,3]dioxolo[4,5-h]carbazol-8-one: A solvatochromic PET-acceptor fluorescent probe

Abstract

In the present work, 5,6,7,9-tetrahydro-[1,3]dioxolo[4,5-h]carbazol-8-one (TDCO) has been established as a solvatochromic probe and an acceptor of photoinduced electron transfer through electronic absorption spectroscopy, steady-state and time-resolved fluorescence measurements and also by using the laser flash photolysis technique. Fluorescence spectra of the compound are more sensitive than its absorption spectra towards the nature of solvent and the composition of solvent mixture. In solvents with higher dielectric constant and better H-bond formation ability, fluorescence maximum of the compound shifts toward red. The reasons behind such solvent sensitivity of TDCO in electronic excited state are its higher dipole moment in excited state and formation of hydrogen bond with solvents. TDCO interacts with aromatic amine bases N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) in excited state and as a consequence its fluorescence intensity and lifetime are quenched. The quenching order is the same as the order of ionization potential of the amines. Transient absorption studies indicate the involvement of photoinduced electron transfer from the amines to TDCO as a result of which the corresponding radical cations and anions have been formed. Simulation studies show that TDCO has the tendency to remain in stacked conformation with DMA and DEA, which facilitates photoinduced electron transfer.