Low-Energy Excitation Leading to Symmetry-Breaking Charge Separation in Near-Infrared-Absorbing Bisstyryltriphenylamine–BODIPY Dimers

BODIPY chromophores have attracted significant attention due to their various applications in optoelectronics. Notably, symmetry-breaking charge separation (SB-CS) in BODIPYs has been studied to imitate natural photosynthesis, enabling the efficient production of radical ion pairs upon light absorption. However, most of the chromophores, including the BODIPY derivatives investigated for SB-CS, primarily absorb visible light, unlike natural chlorophylls, which absorb in the far-red and near-infrared (NIR) regions. This results in partial utilization of solar energy, leaving the useful far-red and near-infrared light energy untapped. To overcome the visible-light constraint of conventional artificial chromophores, we introduce NIR-absorbing bisstyryltriphenylamine-BODIPY dimers that bridge the long-standing gap with natural photosynthetic absorbers. Steady-state spectroscopy combined with femtosecond transient absorption studies revealed the ultrafast formation of the charge-separated (CS) state upon photoexcitation. Electrochemical measurements confirm that this process is thermodynamically feasible, as the redox gap is lower than the excited-state energy. The presence of a low-lying charge-transfer state and strong communication between the two monomer units─especially in dimer 2─is further supported by quantum-computational calculations, given their coplanarity. These findings demonstrate that these dimers provide a useful platform for SB-CS and NIR light harvesting, offering guidelines for designing next-generation molecular systems with efficient photoinduced energy capture and conversion.