Insight into Spectral Properties and Solvatochromic Behavior of [b]‐Fused BODIPYs: Experimental and Computational Study

Two π‐extended derivatives of boron‐dipyrromethene (BODIPY) – unsymmetrical benzo[b]‐fused BODIPY 1 and symmetrical naptho[b]‐fused BODIPY 2 – were synthesized. Spectroscopic and photophysical properties of the synthesized fluorescent dyes were investigated in various organic media. Both BODIPY 1 and BODIPY 2 distinguished by bathochromically shifted absorption and emission bands compared to their non‐fused derivatives, while possessing green (526 – 543 nm) and red (664 – 708 nm) absorbance and fluorescence, respectively. Spectral characteristics of the investigated fluorescent dyes were found to be weakly depended on solvent polarizability in case of BODIPY 1 and greatly influenced by both solvent polarizability and dipolarity in case of BODIPY 2. Quantum chemical calculations were used to clarify the relationships between geometry/electronic structure and spectral properties/solvatochromic behavior of BODIPY 1 and BODIPY 2.