Crystallization induced green-yellow-orange emitters based on benzoylpyrenes

We report the synthesis, X-ray structures and photophysical properties of a few benzoylpyrene (BP) derivatives. Steric hindrance due to incremental benzoyl groups causes a systematic reduction in the orbital overlap (pi-pi) between vicinal pyrene units affording green-yellow-orange solid-state emitters. Crystallization induced emission could arise from: i) electronic (dipolar/excitonic) interactions, ii) arrested bond rotations, and/or iii) lack of solvation in crystalline 1-4BP (Phi(Fl) similar to 2-26%) when compared to that in solution (Phi(Fl) <= 1%). Our earlier effort [Chem. Commun. 2014, 50, 8644] on progressive acylation, in contrast to benzoylation, results in a gradual increase in the pi-pi overlap between vicinal pyrenes.