Synthesis, Characterization, and Photophysical Study of Fluorescent N-substituted Benzo[ghi]perylene Swallow Tail Monoimides

A set of N-substituted benzoperylene monoimide (BPI) fluorophores was synthesized and characterized structurally and photophysically. Condensation of benzo[ghi]perylene-1,2-dicarboxylic anhydride in the presence of swallow tail alkyl amines produced fluorophores that are soluble in a range of organic solvents, highly absorbing in the near-UV (epsilon(334) = 79 000 M(-1)cm(-1)), and fluorescent in the visible range. Photophysical behavior of the compounds was studied with steadystate and time-correlated single photon counting. The synthesized BPIs exhibit positive solvachromatic emission (lambda(em), (hexane) = 469 nm; lambda(em) (ethanol) = 550 nm) as a function of solvent polarity with little change in their excited-state lifetime (9.6-6.5 ns) and fluorescence quantum yield (0.27-0.44) over the polarity range studied. Solvachromatic shifts were analyzed using the Lippert- Mataga approach. In nonpolar hydrocarbon solvents evidence of dual emission from closely spaced (562 cm(-1)) S-1 and S-2 excited states is observed. Preliminary peak assignments for the anomalous S-2 emission are made.