The Photochemistry of Some Main Chain Liquid Crystalline 4,4 '-stilbene Dicarboxylate Polyesters

Authors

Alline P. Somlai, University of Southern Mississippi
Richard A. Cozad, University of Southern MississippiFollow
Kirt A. Page, University of Southern Mississippi
Holly R. Williams, University of Southern Mississippi
David Creed, University of Southern MississippiFollow
Charles E. Hoyle, University of Southern MississippiFollow

Document Type

Article

Publication Date

2008

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

Several aspects of the photochemistry and photophysics of four main chain liquid crystalline polyesters with a rigid trans-stilbene 4,4′-dicarboxylate mesogen as chromophore and flexible spacer groups are reported. The three polymers with the longest ‘spacer’ groups are liquid crystalline at room temperature, two have smectic phases. Chromophore aggregation has a dramatic effect on the photophysics and photochemistry of these polymers. Each of the polymers in poor solvents or as films has greatly perturbed UV-Vis absorption and fluorescence spectra due to aggregation of the stilbene chromophore. These effects are more pronounced upon annealing above the glass transition temperature, T_g, and in the mesophase. Film fluorescence is excitation wavelength dependent and is suppressed at elevated temperatures. The stilbene ‘environment’ in both films and solution is clearly heterogeneous and energy transfer processes relatively slow. The dominant photochemical reaction upon direct excitation above 300 nm is 2 + 2 photocycloaddition rendering polymer films insoluble. No significant trans-to-cis photoisomerization can be detected upon initial irradiation of the polymer films. There is evidence for the formation of aldehyde and carboxylate functionality upon irradiation in the presence of air. Loss of the aggregate UV-Vis absorption and fluorescence occurs during irradiation. Difference UV-Vis spectra of irradiated films suggest preferential initial consumption of dimeric aggregates. Loss of stilbene UV-Vis absorption upon irradiation above 300 nm can be partly photoreversed upon subsequent 254 nm irradiation. The rate of stilbene chromophore loss from films increased significantly above Tg and in the smectic phase above room temperature.

Publication Title

Photochemical & Photobiological Sciences

Volume

7

Issue

5

First Page

578

Last Page

587

Recommended Citation

Somlai, A. P., Cozad, R. A., Page, K. A., Williams, H. R., Creed, D., Hoyle, C. E. (2008). The Photochemistry of Some Main Chain Liquid Crystalline 4,4 '-stilbene Dicarboxylate Polyesters. Photochemical & Photobiological Sciences, 7(5), 578-587.
Available at: https://aquila.usm.edu/fac_pubs/1461