Photodimerization and Photosalient Effects of 4-Styrylpyridine Cocrystals Using Aromatic Poly(carboxylic acid)s as Hydrogen Bonding Templates

In molecular crystals, observing the modulation in photoactuation properties provides insight into the dimerization of olefins, resulting from the [2 + 2] photocycloaddition reaction. Photodimerization and photosalient effects were examined in the cocrystals of 4-styrylpyridine (4-spy) employing aromatic dicarboxylic acids as hydrogen bonding templates, namely, the crystals with phthalic acid (1), isophthalic acid (2), and terephthalic acid (3). The observed effects were most notable in 3 for the former and in 1 and 3 for the latter. The efficiency of dimerization varied depending on the distance between adjacent C═C in 4-spy molecules and the parallel-to-cross arrangement ratio as well as the protonation/deprotonation ratio of the pyridine moieties, as determined by single crystal structural analyses.