Photodimerization of Ferroelectric N,N'-Ditetradecyl-stilbenediamide Derivative

A solid state [2 + 2] photodimerization reaction of ─C═C─ bonds in solids has been designed by controlling the molecular arrangement using supramolecular chemistry. Stilbene derivative (C14SDA) with alkyl amide chains (─CONHC₁₄H₂₉) forms intermolecular amide hydrogen-bonding chains and exhibits reversible successive phase transitions (S1 → S2 → S3 → L) corresponding to the dynamics of the alkyl chains. In the high-temperature solid phase S3, the alkyl chains partially melt, resulting in a one-dimensional (1D) dynamic intermolecular amide hydrogen bond and ferroelectric behavior with hysteresis in the electric field-polarization curve due to polarization reversal of the dipole moment by an external electric field. The S1 phase of C14SDA did not exhibit a photodimerization reaction, while the dynamic S2 and S3 phases exhibited a [2 + 2] photodimerization reaction to form reaction products with cyclobutane rings. In the dynamic ferroelectric S3 phase, trans-cis isomerization of stilbene was observed simultaneously with the formation of the photodimerization product. When the photodimerization reaction was attempted with an electric field applied to the S3 phase, thermal molecular fluctuations were suppressed by the electric field, increasing the distance between ─C═C─ double bonds and reducing the photoreaction yield.