A new and versatile fluorescence standard for quantum yield determination

Abstract

It is demonstrated that a new bichromophoric compound, N²,N³-[bis(1-hexylheptyl)-benzo[ghi]perylene-2,3,8,9,11,12-hexacarboxylic-2,3:8,9:11,12-tris(dicarboximide)]-N¹,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 S₀ → S₁ and S₀ → S₂ transition dipoles of 1 are preferentially polarised parallel and perpendicular, respectively, to the C₂-symmetry axis of 1. The rapid transfer of electronic energy is compatible with energy transfer of the Förster type.