Photorearrangement of acyclic nitrones: A luminescent study

Dipolar acyclic nitrones (N1, N2 and N3) exhibit solvatochromism along with some unusual photophysical behavior like excitation wavelength dependent emission, non-mirror symmetric excitation–emission spectra etc. It was observed that at the respective emission maxima, the fluorescence intensity changed with time following a first order kinetics for all the three nitrones in non-polar toluene, intermediate THF as well as in polar acetonitrile, indicating a time dependent deactivation of excited state. The experimentally measured rate constants also depend on the nature of solvent used. No such corresponding behavior was observed in steady state absorption study. Possibly it is the first luminescence study in this aspect. This could be intelligible considering the photorearrangement of these acyclic nitrones. The ground state energy barriers and free energy of activation of the rearrangement have been calculated using density functional theory (DFT) for the three nitrones in gas phase and in dielectric medium as well. Theoretically calculated barrier energies and free energy can satisfactorily explain the experimental trend of 1st order rate constant.