A new and versatile fluorescence standard for quantum yield determination

It is demonstrated that a new bichromophoric compound, N-2,N-3-[bis(1-hexylheptyl)-benzo[ghi]perylene-2,3,8,9,11,12-hexacarboxylic-2,3:8,9:11,12-tris(dicarboximide)]-N-1,N-1'-(1,2-ethyl)-[N-2'-(1-octylnonyl)-perylene-3,4:9,10-bis(dicarboximide)] (denoted by 1-2), provides a versatile reference molecule for measurements of fluorescence quantum yields. The compound consists of a donor (1) and an acceptor (2) part for the electronic energy. Absorption spectra of 1-2 form a nearly perfect superposition of the corresponding spectra for 1 and 2. In addition to a fluorescence quantum yield of one, 1-2 allows for choosing excitation wavelengths between 300 and 530 nm. The fluorescence lifetime of 1-2 is 4.0 +/- 0.1 ns and is independent of the excitation wavelength. The fluorescence excitation anisotropy reveals that the S-0 --> S-1 and S-0 --> S-2 transition dipoles of 1 are preferentially polarised parallel and perpendicular, respectively, to the C-2-symmetry axis of 1. The rapid transfer of electronic energy is compatible with energy transfer of the Forster type.