Nonsymmetric Benzo[a]fused and Thiophene/Thieno[3,2-b]thiophene[b]fused BODIPYs: Synthesis and Photophysical Properties

The fusion of sufficient-electron heterocycle rings into the[a]/[b]-position of the BODIPY core would result in a large redshift wavelength, thus achieving red or near infrared emission. In this paper, we described the synthesis of nonsymmetric benzo[a]fused and thiophene/thieno[3,2-b]thiophene[b]fused BODIPY derivatives 2–3 while containing a reactive site, and then, 4–7 were developed by nucleophilic substitution reactions of 3 with various nucleophilic agents in high yields. X-ray crystallographic analysis of 2–7 revealed that the core structure adopted a planar geometry and π–π interactions were observed in the packing structure. BODIPYs 4 and 6–7 displayed a hypochromic shift in the absorption and bathochromic shift in the emission with increasing solvent polarity because of the formation of resonance structures resulting from the change of the C–N distance, which was rationalized by density functional theory (DFT)/time-dependent-DFT calculations.