The controllable of BODIPY dimers without installing blocking groups as both fluorescence and singlet oxygen generators.

We compared a range of BODIPY dimer derivatives without installing blocking groups by optimizing geometry structures and analyzing energies, frontier molecular orbitals, Chole&Cele map, electron density difference, spin-orbit coupling (SOC) matrix and decay rate constants from excited states. The dihedral angles of the β-β-linked BODIPY dimer and the α-α-linked BODIPY dimer tend to flatten in the T1 state, which is detrimental to the occurrence of the intersystem crossing (ISC). Conversely, the dihedral angle of the meso-β-linked BODIPY dimer, the meso-meso-linked BODIPY dimer and α-γ-linked BODIPY dimer is within the range of 125°-143° in the T1 state, facilitating ISC and the generation of singlet oxygen. Notably, the transition from S1 to S0 involving lowest unoccupied molecular orbital to highest occupied molecular orbital with long-wavelength emission and moderate oscillator strength underpins the remarkable long emission peaks observed experimentally for α-γ-linked BODIPY dimer. Moreover, the apparent SOC matrix enhances the ISC process, resulting in a respectable efficiency in generating singlet oxygen for this dimer. In meso-β-linked BODIPY, meso-meso-linked BODIPY, and α-γ-linked BODIPY, the S1→T1 process is characterized by a significant charge transfer, specifically transitioning from the 1CT state to the 3LE state, indicative of a spin-orbit charge transfer ISC (SOCT-ISC) mechanism. The ability to regulate the photosensitivity of BODIPY dimers by adjusting the dihedral angle between the two units in the T1 state unveils new avenues for designing high-performance photosensitizers for both therapeutic and imaging applications.