meso-Carbazole decorated BODIPYs – an electron donor–acceptor system with excellent fluorosolvato/vapochromic behavior, aggregation-induced emission, and antileishmanial activity

Abstract

We report the synthesis and photophysical properties of meso-carbazole BODIPY C1 and its β-monobromo (C2) and β,β′-dibromo (C3) substituted derivatives. Since carbazole is electron-rich as compared to BODIPY, the compounds C1 and C2 act as electron donor–acceptor systems and show red-shifted fluorosolvato/vapochromism with a Stokes shift of 170–180 nm as the dielectric constant of the solvent increases. This fluorosolvato/vapochromism is attributed to twisted intramolecular charge transfer (TICT), as confirmed by viscosity-dependent studies. The fluorescence emission and solvent polarity-dependent fluorochromism are hardly observed in the dibromo derivative C3 due to the enhanced intersystem crossing (ISC), which is evident from DPBF titrations and the molecular orbital analysis. All three luminogens show excellent aggregation-induced emission (AIE) behavior and act as red-light-emitting aggregates. Thus, the low-intensity TICT-induced red emission can be enhanced by aggregate formation. Moreover, here we report for the first time the anti-leishmanial activity of carbazole BODIPYs against Leishmania donovani promastigotes, which can be taken forward as potential anti-leishmanial compounds.