Peri-Substituted Acyl Pyrrolyl Naphthalenes: Synthesis, Reactions and Photophysical Properties.

The preparation of two 1-acyl-8-pyrrolylnaphthalenes ( and ) and one pyrrolone () are reported along with the issues complicating the preparations of other compounds. The photophysical behavior of the fused, planar derivative is explored in detail. The fluorescence of shows solvato-chromism due to intramolecular charge transfer in the excited state and enhanced emission in protic solvents. The emission intensity increases very linearly with the H-bond-donating strength of the solvent. Preferential solvation studies, multilinear regression analysis and computational modeling suggest that the fluorescence enhancement results from inhibition of the spin-orbit coupling-promoted intersystem crossing from the π→π* singlet state to an n→π* triplet state. Some of the inhibitions are due to the dielectric stabilization of the excited singlet state. A stronger effect is obtained from H-bonding, which not only further stabilizes the singlet state but also negatively impacts the vibronic coupling between the states.