Photophysics of 3,5-diphenoxy substituted BODIPY dyes in solution

We have prepared two fluorescent dyes derived from 8-(4-tolyl)-4,4- difluoro-4-bora-3a,4a-diaza-s-indacene with phenoxy and (o-bromo)phenoxy substituents at the 3,5-positions by a novel nucleophilic substitution reaction of the corresponding 3,5-dichloroBODIPY analogue. UV-vis absorption, steady-state and time-resolved fluorimetry have been used to investigate their solvent-dependent photophysical properties. The two BODIPY derivatives show narrow absorption and emission bands and display small Stokes shifts. The substituents at the 3,5-positions (phenoxy in 1 and o-bromophenoxy in 2) have a minor effect on the fluorescence quantum yields (0.16-0.40 for 1, 0.17-0.44 for 2) and lifetimes (1.09-2.51 ns for 1, 1.11-2.78 ns for 2). For both compounds, the fluorescence rate constant equals (1.5 ± 0.1) × 10⁸ s^-1.