Geometry Governs Intervalence Charge Transfer and Symmetry Breaking Charge Separation in Far-Red Absorbing BODIPY Dimers

Intervalence charge transfer (IVCT) was observed in the directly connected BODIPY dimer D1, as evidenced by splitting of the reduction waves and the appearance of a characteristic near-infrared electronic transition, whereas no IVCT was detected in the weakly coupled dimers D2–D5. Second, distance-dependent symmetry-breaking charge separation (SBCS) has also been explored in solvents of varying polarity using pump–probe spectroscopy combined with quantum calculations. The initial indication of SB–CS in these dimers was obtained from emission studies, which showed significant quenching relative to the control monomer with increasing solvent polarity. The redox gap from electrochemical studies was smaller than that of the singlet excited state (S1), indicating the thermodynamic feasibility of SB–CS in these dimers. Next, DFT calculations optimized the structure, and their electrostatic potential maps revealed a quadrupole state that transitions to a dipolar state upon photoexcitation. Finally, transient absorption experiments confirmed the formation of the charge-separated state. The lifetime of the CS state ranged from a few picoseconds to nanoseconds, depending on the dimer and the solvent used. These discoveries highlight that structure–property relationships in multichromophoric systems revealing fascinating mechanisms in IVCT and SB–CS.