Synthesis and Photophysical Properties of New Highly Substituted Symmetrical and Nonsymmetrical Fluorescent Triazaborinine Derivatives

The synthesis and photophysical properties of highly substituted symmetrical difluoro-boron-triaza-anthracene (BTAA) 5a–g and nonsymmetrical difluoro-boron-triaza-cyclopentanaphthalene 8a–h (BTCPN) derivatives are reported. Herein, the 2-pyridone was used as a platform to render these highly substituted structures. The BTAA and BTCPN derivatives were efficiently obtained in five steps and characterized by different spectroscopy methods and X-ray data. An experimental analysis of the substituent effect on the photophysical properties of 5a–g and 8a–h was performed. The leading absorption bands of 5a–g and 8a–h are observed at ca. 348 nm, and the emission bands at ca. 536 nm. From series 5a–g and 8a–h, the compounds 5c and 8c showed the highest fluorescence quantum yield obtained in CH₂Cl₂ (φ = 58 and 76%, respectively). The large quantum yield of 5c and 8c is related to a small HOMO-LUMO gap, analyzed by cam-B3LYP/6-311++g**/6-311+g*. A bifurcation of the excitation pattern improves the quantum yield 8a compared to 5a. The large quantum yield of 8a is explained by two probable transitions involving the HOMO-LUMO and HOMO-LUMO + 1 excitation processes.