Singlet energy transfer in bis(phenylethynyl)phenylene-bridged zinc–free base hybrid diporphyrins

Abstract

A set of bis(phenylethynyl)phenylene-bridged diporphyrins 1–3 has been prepared by the acid-catalysed double condensation reaction of bis(4-formylphenylethynyl)benzene 8 and 9, and 3,5-di-tert-butylbenzaldehyde 11 with bis(3-hexyl-4-methylpyrrol-2-yl)methane 12 or the Pd⁰-catalysed coupling reaction of acetylene-substituted porphyrin 14 with 1,4-diiodobenzene. Intramolecular singlet excitation energy transfer in Zn–free base hybrid diporphyrins 1–3(ZH) has been studied by picosecond time-resolved fluorescence spectroscopy. The determined k_EN values are in the order of 1(ZH) > 2(ZH) ≈ 3(ZH). The energy transfer mechanism is discussed in terms of varying contribution of through-space and through-bond interactions.