An experimental and TD-DFT theoretical study on the photophysical properties of Methylene Violet Bernthsen

Abstract

We revisited the photophysics the Methylene Violet (MV) Bernthsen dye in aprotic solvents to rationalize both its peculiar solvatochromism, which cannot be explained by the standard solvatochromic empirical models, and the large dependence of its excited states decay kinetics upon changes on the polarity of the medium. To this end, MV singlet and triplet excited states were characterized by stationary and time-resolved absorption and emission techniques. The experimental information was combined with a detailed theoretical study using TD-DFT to characterize not only the emitting states but also all dark states which would play a role in determining the fate and properties of the experimentally populated excited states. It is concluded that owning to both the high permanent dipole and polarizability of MV, singlet and triplet excited states are stabilized by the medium to a very different extent, leading to an unusual solvatochromism and decay kinetics.