Electronic ground and excited state properties of dipyrrometheneboron difluoride (BODIPY): Dimers with application to biosciences

Numerous derivatives of BODIPY (4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene) are frequently used as fluorescent probes in modern protein and lipid research. Present studies of purpose-synthesised molecules show that the BODIPY chromophore can form two different ground state dimers, denoted DI and DII. In practise DI exhibits negligible fluorescence emission, but a strong absorption band {ε(477 nm) = 102 000 mol−1 dm3 cm−1}, while DII is fluorescent with the radiative lifetime 20 ns, and red-shifted absorption {ε (577 nm)} = 26 000 mol−1 dm3 cm−1} relative to that of the monomer. Energy transfer is demonstrated from monomeric BODIPY to DI, as well as to DII. Donor–donor energy migration is also shown to occur between excited and ground state DII. Both DI and DII are of potential interest in examining structure-function of proteins and lipid membrane systems.