Early-Stage Functionalization of AzaDioxaTrianguleniums: Access to 5-Substituted Dyes with Tunable Photophysical and Electrochemical Properties

We present a synthetic strategy for electronic modulation of ADOTA+ dyes via early-stage functionalization of an acridinium precursor. This approach enables regioselective installation of electron-withdrawing groups (EWGs) at positions inaccessible through electrophilic aromatic substitution on the ADOTA+ core, unlocking a versatile platform for late-stage diversification. Six 5-substituted ADOTA+ derivatives were prepared and their photophysical and electrochemical properties evaluated. EWGs result in moderate redshifts while preserving high fluorescence quantum yields and long fluorescence lifetimes. Electrochemical studies reveal stabilization of both HOMO and LUMO levels, leading to increased excited-state oxidizing power, demonstrated by reactivity differences in the photoredox-catalyzed aerobic bromination of aromatic and heterocyclic substrates. This work establishes a general and flexible platform for tuning ADOTA+ dyes while retaining their favorable photophysical properties.