Affiliations 

  • 1 Centre for Fundamental and Frontier Sciences in Nanostructure Self-Assembly, Department of Chemistry, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia; Low Dimensional Materials Research Center, Department of Physics, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address: t_selvi@um.edu.my
  • 2 Centre for Fundamental and Frontier Sciences in Nanostructure Self-Assembly, Department of Chemistry, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
  • 3 Low Dimensional Materials Research Center, Department of Physics, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
  • 4 Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36, Postal Code 123, Muscat, Sultanate of Oman
  • 5 Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36, Postal Code 123, Muscat, Sultanate of Oman. Electronic address: abouzied@squ.edu.om
PMID: 39644819 DOI: 10.1016/j.saa.2024.125549

Abstract

This study investigates the photophysical and electrical properties of 4-heptamethyl-trisiloxanyl-n-undecyloxy-4'-nitrostilbene (SNS), a low molar mass organosiloxane liquid crystal containing a nitrostilbene chromophore. Real-time monitoring of the absorption and fluorescence spectra of the nitrostilbene moiety was conducted in dichloromethane solution and thin films (in both crystalline and Smectic C (SmC) phases). A charge transfer excited state is formed following vibrational cooling and solvent interaction within 0.4 to 1.6 ps, which then relaxes to the ground state in 1.6 ns. Five distinct lifetime components were identified in thin films, attributed to the heterogeneous local environment and aggregate formation. Notable differences in excited-state lifetimes were observed between the crystalline and SmC phases, with slower dynamics in the former due to the rigidity of the crystalline phase. Photoconductivity under UV irradiation was examined in SmC, Smectic A (SmA), and isotropic phases, showing a significant increase in current response, particularly in the SmC phase. Polarizing optical microscopy revealed morphological changes post-UV exposure, such as reduced SmC domain size and decreased birefringence. Dielectric measurements indicated distinct relaxation peaks in SmC and SmA phases, reflecting more disordered molecular arrangements. The study reveals that UV exposure significantly enhances SNS conductivity, particularly within the SmC phase. This enhancement is likely attributed to UV excitation promoting the formation of an intramolecular charge transfer state within the trans-stilbene moiety. These findings provide valuable insights into the potential applications of nitrostilbene-functionalized organosiloxane liquid crystals in optoelectronic devices, such as light switches and photodetectors.

* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.