Absorption and solvatochromic properties of 2-methylisoindolin-1-one and related compounds: interplay between theory and experiments

The excited states of 2-methylisoindolin-1-one ( INS) have been investigated by absorbance spectroscopy and theoretical calculations performed at the TDDFT level and compared with those of three related compounds involved in DNA photosensitization: indanone (IND), indoprofen (INP), a nonsteroidal anti-inflammatory drug and one of the INP photoproducts, the 2-(4-acetylphenyl)isoindolin-1-one (KINP), in order to understand the influence of the nitrogen atom and of substitutions on the lowest singlet excited states of the isoindolinone chromophore. TDDFT calculations combined with a polarizable continuum model (PCM) reproduced fairly well the experimental spectra and the solvatochromism. The study of the molecular orbitals allows us to assign the nature of their lowest excited singlet states: while for INP and KINP, it corresponds mainly to a pi-pi* transition with charge transfer character, the other compounds exhibit a lowest excited state with n pi* character, although the assignment is ambiguous for INS. The interactions of the molecules with the solvent are also discussed in the framework of a simple model based on dipole-dipole interactions.