Synthesis, Spectroscopy, Crystal Structure, Electrochemistry, and Quantum Chemical and Molecular Dynamics Calculations of a 3-Anilino Difluoroboron Dipyrromethene Dye

An asymmetrically substituted fluorescent difluoroboron dipyrromethene (BODIPY) dye, with a phenylamino group at the 3-position of the BODIPY chromophore, has been synthesized by nucleophilic substitution of 3,5-dichloro-8-(4-tolyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. The solvent-dependent spectroscopic and photophysical properties have been investigated by means of UV-vis spectrophotometry and steady-state and time-resolved fluorometry and reflect the large effect of the anilino substituent on the fluorescence characteristics. The compound has a low fluorescence quantum yield in all but the apolar solvents cyclohexane, toluene, and chloroform. Its emission maxima in a series of solvents from cyclohexane to methanol are red-shifted by approximately 50 nm in comparison to classic BODIPY derivatives. Its oxidation potential in dichloromethane is at ca. 1.14 V versus Ag/AgCl. The absorption bandwidths and Stokes shifts are much larger than those of typical, symmetric difluoroboron dipyrromethene dyes. The values of the fluorescence rate constant are in the (1.4-1.7) x 10(8) s(-1) range and do not vary much between the solvents studied. X-ray diffraction analysis shows that the BODIPY core is planar. Molecular dynamics simulations show that there is no clear indication for aggregates in solution.