Solid-state photoreactivity of 9-substituted acridizinium bromide salts

Abstract

A series of substituted acridizinium bromides was studied to determine how substituents affect the regioselectivity of the solid-state [4 + 4] photodimerisation. A series of 9-X-acridizinium bromide salts (where X = F, Cl, Br, I, CH 3 , C(CH 3 ) 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 affected the regioselectivity of the [4 + 4] cycloaddition reactions, the reaction yields and relative reaction rates. Computational methods were utilised to rationalize the unexpectedly high regioselectivity of the solid-state photodimerisation of the 9-Cl-acridizinium bromide salt.