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

Abstract We compared a range of BODIPY dimer derivatives without installing blocking groups by optimizing geometry structures and analyzing energies, frontier molecular orbitals, C hole& C ele 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 T 1 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 T 1 state, facilitating ISC and the generation of singlet oxygen. Notably, the transition from S 1 to S 0 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 S 1 →T 1 process is characterized by a significant charge transfer, specifically transitioning from the 1 CT state to the 3 LE 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 T 1 state unveils new avenues for designing high‐performance photosensitizers for both therapeutic and imaging applications.