Photoreactive salt cocrystal: N+-H⋯N hydrogen bond and cation-π interactions support a cascade-like photodimerization of a 4-stilbazole

Abstract

We describe hydrogen bonds (i.e., N+-H⋯N) in combination with cation⋯π interactions to enable a cascade-like [2 + 2] photodimerization of 4-stilbazole in a salt cocrystal. A four-component crystal assembly is composed of photoactive pyridinium ion pair4-stilbzH+(4-stilbz=trans-1-(4-pyridyl)-2-(phenyl)ethylene) and photostable molecule pair4-stilbz. UV irradiation givesrctt-1,2-bis(4-pyridyl)-3,4-bis(phenyl)cyclobutane (4-pyr-ph-cb) in quantitative yield. An intermediate structure2(4-stilbz)·(4-pyr-ph-cb)2H+is isolated that undergoes a partial single-crystal-to-single-crystal transformation. The single-crystal X-ray data provides a snapshot of movements in the salt cocrystal in the course of the photodimerization.