Self-assembly and polymerization of a molecular switch based on the benzofulvene structure

In the search of new molecular switches structurally related to Green Fluorescent Protein (GFP) chromophore and based on a 3-phenylbenzofulvene scaffold, we found that some of them were stable in the ordered crystalline state, but in the disordered amorphous state, PEGylated derivative ethyl (E)-6-[2-[4-(2,5,8,11,14,17,20,23,26,29-decaoxatriacontyl)-1H-1,2,3-triazol-1-yl]ethoxy]-1-(2-oxopyrrolidin-3-ylidene)-3-phenyl-1H-indene-2-carboxylate [(E)-VC1801] underwent spontaneous polymerization leading to random co-polymer materials with molecular oxygen, but containing homo-polymer sequences. Thus, NMR spectroscopy and dynamic light scattering techniques were employed to gain information about the self-assembly process of (E)-VC1801 in the relatively disordered state in which polymerization occurs, and the results highlighted the importance of the aromatic specific interaction in the aggregation process. Very interestingly, the study of the interaction of benzofulvene derivative (E)-VC1801 with light revealed that UV excitation could induce photochemical reactions in the solid state with the formation of new species showing increased emission features. The analysis of the irradiated films showed that along with the photoisomerization reaction of (E)-VC1801 into the corresponding (Z)-VC1801, also a polymerization process occurred. Intriguingly, the polymerization reaction was more efficient in the presence of atmospheric oxygen than in the sample irradiated under reduced oxygen content, and the photophysical features of the corresponding polymeric materials were significantly different. These differences in the emission features supported the existence of differences in the composition of the samples such as their content in homo-polymer sequences.