UV-light-induced polymerization in the amorphous solid-state of a spontaneously non-polymerizing 3-phenylbenzofulvene monomer

Benzofulvene derivative 2-Pyr-BF3a was designed and synthesized to evaluate the effects of a pyridine ring in position 2 of the 3-phenylbenzofulvene moiety on the spontaneous solid-state polymerization. The monomer was found to organize into an ordered crystalline solid-state without significant spontaneous polymerization, but the irradiation of amorphous film samples with UV-light produced photopolymerization. Resulting poly-2-Pyr-BF3a was characterized by NMR spectroscopy, MALDI-TOF mass spectrometry, and photophysical studies in comparison with the corresponding monomer. Interestingly, monomer 2-Pyr-BF3a was weakly emissive in diluted solutions, but increased its PLQY in the crystalline solid. Conversely, after photopolymerization the monomeric unit in the polymer enhanced its emission intensity in solution while in the solid state results weakly emissive. Even more interestingly, this benzofulvene monomer and its synthetic precursors 2 and 3 showed long-lived emission suggesting a phosphorescence nature of the emission process. Finally, DFT and TDDFT calculations were performed in order to rationalize the experimental data.