Spectral Properties of a Fluorescent Probe, all-trans-1,6-Diphenyl-1,3,5-hexatriene. Solvent and Temperature Effects

Studying electronic absorption and fluorescence spectra of 1,6-diphenyl-1,3,5-hexatriene (DPH) in twenty-two solvents, several factors were found to affect the spectral parameters. Two groups of DPH spectral behaviour were defined, related to the refractive index and the dispersion interactions parameters of the solvents. DPH molar absorptivity is hardly affected by the nature of the solvent or the increase of temperature (20–50 °C). By contrast, DPH fluorescence intensity increases along with the viscosity and polarizability of solvents and is decreased by elevating the temperature. Investigations on the combined effects of solvent nature and temperature on DPH spectral parameters allowed the solvents to be classed into four groups (referred to as 1 to 4). When the temperature was increased from 20 to 50 °C, DPH fluorescence intensity was only slightly modified in solvents from group 1 (as tetrahydrofuran, I = 100 at 20 °C, I = 80 ± 5 at 50 °C), but was severely decreased in solvents from groups 2 (as ethanol, I = 55 at 50 °C) and 3 (as acetic acid, I = 45 at 50 °C), and still more in solvents from group 4 (tetrachloromethane, I = 10 at 50 °C). Data on the reversibility of the phenomenon in these solvents after returning the temperature from 50 to 20 °C show a concomitant decrease in DPH stability in these solvents. When a water-miscible solvent was used, the decrease in fluorescence intensity was found to be higher after adding water to this solvent. These data may help to assess the spectral behaviour of DPH in the more complex biological media.