Isomerization of Diphenyl Polyenes. Part V. The Origin of Fluorescence of l,6-Diphenyl-1,3,5-hexatriene in Poly (vinyl alcohol) Films

Abstract

The effect of temperature on the absorption and fluorescence spectra of l,6-diphenyl-l,3,5-hexatriene (DPH) was investigated in three different polymer films: polyvinyl chloride) (PVCh), polyvinyl formal) (PVF) and polyvinyl alcohol) (PVA) in the temperature range 296-423 K. Anomalous behaviour of the fluorescence intensity was observed only for DPH in non-heated PVA film. The intensity distribution in the fluorescence band of DPH in both non-heated and heated PVCh and PVF films was found to be independent of the excitation light wavelength, A exc . The behaviour of DPH is similar in the PVA film heated to 423 K. For these samples, single exponential fluorescence decay was observed. The behaviour of non-heated DPH samples in PVA is quite different, the intensity distribution and the fluorescence band position depending strongly on ^. exc and the fluorescence decay being double exponential. It can be inferred that the fluorescence of DPH in a non-heated PVA sample consists of two components, the first originating from the all-trans conformer and the second from the ground-state s-eis conformer.

Isomerization of Diphenyl Polyenes. Part VI. Properties of l,8-Diphenyl-l,3,5,7-octatetraene Fluorescence in Poly (vinyl alcohol) and other Polymer Films

“…The heated to 423 K indicate, similar as for DPH [18], the occurrence of all trans conformers only. Unlike PVA, in polymers insoluble in water, no short-wave diffused band responsible for the absorption of the s-eis conformer can be observed at 296 K. In water-methanol mixture (Table 2), upon the 350 nm excitation and observation above 420 nm, a double exponential fluorescence decay occurs, whereas for methanol alone, a single exponential decay is found.…”

“…Similar behaviour was observed for 1,6-diphenyl-1,3,5-hexatriene (DPH) in PVA. In this case, however, the effect was slightly weaker [17,18].…”

“…Heating to 423 K causes that as many as 96% of the molecules undergo transition to the all-trans configuration and only 4% remain as s-eis conformers. This problem was discussed in more detail in [18] for DPH in PVA and other polymers. Nonetheless, the following issues deserve attention.…”

“…1), after heating to 373 K (Fig. 2) and after heating to 423 K ( The preparation of the polymer films (PVCh, PVF, Et A and PVA) was described [18].…”

Self-Aggregation Processes of 1,6-Diphenyl-1,3,5-Hexatriene in Water/Ethanol Mixtures with High Water Percentages

“…The results obtained in the present work show similarities to those observed for transstilbene and derivatives in pure aliphatic hydrocarbon solvent at low temperatures 31,32 and trans-stilbene incorporated in Langmuir-Blodgett surfactant films, [33][34][35][36][37] which indicated aggregation processes. However, in some reports [38][39][40] the spectral changes observed in DPH solutions were equivocally attributed to reactions caused by the light sources of ultraviolet-visible (UV-Vis) and fluorometer apparatuses. In the present work, it is proposed that the variations in the spectrophotometric properties of DPH for high water content in ethanol (above a critical water limit) are caused by DPH selfaggregation phenomena.…”