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

Abstract

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 D_I and D_II. In practise D_I exhibits negligible fluorescence emission, but a strong absorption band {ε(477 nm) = 102 000 mol⁻¹ dm³ cm⁻¹}, while D_II 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 D_I, as well as to D_II. Donor–donor energy migration is also shown to occur between excited and ground state D_II. Both D_I and D_II are of potential interest in examining structure-function of proteins and lipid membrane systems.