One‐Step Access to Ultra‐Bright Macrocyclic Oligo‐BODIPYs Featuring Long‐Lived Cyclic Excitons

ABSTRACT The controlled organization of chromophores into defined assemblies with collective photophysical properties is a key concept for natural and artificial photonic systems. A template‐free, one‐step synthesis affords a series of methylene‐bridged macrocyclic oligo‐BODIPYs from readily available BODIPY precursors. Brønsted acid catalysis with paraformaldehyde as a C 1 synthon links multiple BODIPY cores into β ‐connected linear oligomers and macrocycles comprising up to twelve non‐conjugated chromophores. Optical spectroscopy and quantum chemical calculations provide initial insights into the photophysical mechanisms: steady‐state and time‐resolved spectroscopy reveal pronounced excitonic coupling across the chromophore arrays, which is confirmed by quantum chemical investigations at the simplified time‐dependent density functional theory level. The linear oligomers display typical J‐type characteristics, while the macrocyclic systems exhibit distinct multiband emission and unusual size‐dependent photophysical properties. Distinct excitonic regimes seem to coexist in the macrocyclic oligomers. Intense absorption bands are consistent with localized J‐coupled chromophore segments within the ring, while fluorescence can occur from J‐coupled segments and a lower‐lying cyclic exciton state with strongly reduced oscillator strength. In summary, our work establishes cyclic oligo‐BODIPYs as a versatile platform for investigating topology‐dependent excitonic phenomena, and also for developing functional superchromophores with tunable photophysical properties.