Reversible cyclisation of a sulfonated arylazo compound containing an o-acetylamino substituent

A sulfonated o-acetylamino arylazo compound unexpectedly cyclised to a cationic benzo-1,2,4-triazinium species under thermal or acid conditions, reversible with base. The same substrate underwent trans to cis-azo photoisomerisation, observable by NMR spectroscopy, under steady state laser irradiation conditions.