3,5-Dianilino Substituted Difluoroboron Dipyrromethene: Synthesis, Spectroscopy, Photophysics, Crystal Structure, Electrochemistry, and Quantum-Chemical Calculations†

4,4-Difluoro-3,5-bis(phenylamino)-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene (1), a symmetric fluorescent difluoroboron dipyrromethene dye, has been synthesized by nucleophilic substitution of 3,5-dichloro-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene with aniline. The solvent-dependent spectroscopic and photophysical properties have been investigated by means of UV−vis spectrophotometry and steady-state and time-resolved fluorometry and are compared to those of the nonsymmetrically substituted 5-chloro-4,4-difluoro-3-phenylamino-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene (2). A new, generalized treatment of the solvent effect, proposed by Catalan (J. Phys. Chem. B 2009, 113, 5951−5960) and based on a set of four mutually independent, empirical scales (dipolarity, polarizability, acidity, and basicity of the medium) is the most appropriate for describing the solvatochromic shifts of the UV−vis absorption and fluorescence emission of 1 and 2. In contrast to the nonsymmetric compound 2, the symmetric...