Invited feature articleVariable-temperature absorption and emission properties of 1,2-diphenylacetylene and 1,4-diphenylbuta-1,3-diyne derivatives

- Energy activation of internal conversion of acetylene and buta-1,3-diyne are measured.
- The conformational change of 1,2-diphenylacetylene and its derivatives in the excited state shows an activation energy.
- Conformational changes of 1,4-diphenylbuta-1,3-diyne and its derivatives in the excited state are barrierless .

Variable-temperature absorption and emission data over the range 80-300 K have been collected for 1,2-diphenylacetylene (DPA) and its derivatives, as well as 1,4-diphenylbuta-1,3-diyne (DPB) derivatives in 2-methyltetrahydrofuran (2-MeTHF). Moreover, the influence of temperature on fluorescence lifetime and quantum yield has also been investigated. A strong coupling between solvation dynamics and solute structure is observed in the low-temperature regime as well as at intermediate temperature where the structure of the compound is evolving in the course of excited-state relaxation. Moreover, the dependency of fluorescence quantum yield on temperature indicates that the energy of activation of radiationless transition for 1,2-diphenylacetylene and its derivatives is larger than the activation energy of viscous flow of 2-MeTHF, while for 1,4-diphenylbuta-1,3-diyne derivatives the opposite is observed. This finding implies that the conformational change of DPA and its derivatives in the excited state in 2-MeTHF shows an activation energy, contrary to DPB and its derivatives for which conformational changes are barrierless.

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