A Photophysical Study Of Substituted Arylethynylenes

摘要

A study of a group of compounds based on the 1,4-bis(phenylethynyl)benzene (1) architecture was undertaken to improve our understanding of their photophysics and the factors which control their geometry and hence the n-conjugation pathway in the ground and excited state of these compounds. 1 exists as a range of molecular rotamers in the ground state, resulting from the low barrier to rotation around their C(sp)-C(sp2) bonds. These compounds are highly conjugated systems with good electron conducting properties, due to delocalisation of the HOMO and LUMO over the molecule. In the electronic excited state they are capable changing their molecular conformation and will adopt a planar, or near planar, low energy conformation prior to fluorescence emission in solution. In a glassy matrix at 77 K with sterically hindering substituents on the benzene rings of 1, emission form high and low energy conformations are observed. 1 is highly emissive owing to the high oscillator strength of the S_1→S_0 transition. All the compounds studied maintained their C=C character in the excited singlet and triplet states. The substitution of the central benzene ring in 1 with a thiophene moiety increases the singlet oxygen generation quantum yield, which is consistent with greater intersystem crossing to the triplet excited state.