On the temperature-dependent isomerization of all-trans1,6-diphenyl-1,3,5-hexatriene in solution: a reappraisal

Abstract

In this work, we present absorption, emission, and excitation of emission spectra of all-trans-DPH obtained in solution between 77 and 363 K. The analysis of these spectra allows to evaluate that this molecular probe, widely used in biophysics, does not isomerizes in solution to s-cis-DPH at the temperatures explored. These results are in contradiction to those reported by previous studies that emphasize that (a) all-trans-DPH isomerizes to s-cis-DPH when dissolved and the temperature ranges from 283 to 373 K and (b) the molar fraction of s-cis-conformer equals, or even exceeds, the molar fraction of the all-trans-conformer at the highest temperature studied. In this work, we show how we can infer the changes taking place in the molecular structure of DPH looking at the wavenumber (ν) shift of the peaks on the absorption and emission spectra as a function of temperature. The analysis of these band shifts allows us to corroborate the change, determined by Ogawa et al. by X-ray diffraction, that occurs in the structure of DPH in the crystalline phase through a bicycle pedal process with temperature