Solid-state photoreactivity of 9-substituted acridizinium bromide salts

Abstract

A series of 9-X-acridizinium bromides (where X = F, Cl, Br, I, CH3, C(CH3)3) was synthesised, and their solid-state [4+4] photoreactivity was investigated using crystallographic and spectroscopic methods, while their thermal stability was studied using thermal gravimetry and differential-scanning calorimetry. The study aimed to identify how the nature and size of the substituent on the acridizinium cation affects the regioselectivity of the [4+4] cycloaddition reactions, the reaction’s yields and relative reaction rates. Computational methods were utilised to rationalize the unexpectedly high regioselectivity of the solid-state photodimerisation of 9-Cl-acridizinium bromide salt.