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Single and two photon time resolved polarised fluorescence studies of probe molecule dynamics in nematic liquid crystals

Monge, EM; Armoogum, DA; Bain, AJ; (2003) Single and two photon time resolved polarised fluorescence studies of probe molecule dynamics in nematic liquid crystals. In: Belfield, KD and Caracci, SJ and Kajzar, F and Lawson, CM and Yeates, AT, (eds.) Multiphoton Absorption and Nonlinear Transmission Processes: Materials, Theory, and Applications. Society of Photo-Optical Instrumentation Engineers (SPIE): Seattle, WA, USA. Green open access

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Abstract

We present the results of combined single and two photon linearly polarised time resolved fluorescence anisotropy measurements of the order and motion of a fluorescent probe (rhodamine 6G) in the nematic phase of 4-n-pentyl4'cyanobiphenyl (5CB). Variation of the excitation polarisation angle (P) with respect to the nernatic director yield a set of initial single and two photon anisotropies R(0,beta). Single photon R(0,beta) measurements yield the [P-2] and [P-4] moments of the ground state orientational distribution function. For rhodamine 6G in 5CB these indicate that the inclusion of higher moments ([P-6] and above) are necessary to describe the probe ordering within the nematic host.. Two photon R(0,beta) measurements however allow the direct measurement Of [P-6], for rhodamine 6G these yield a value close to theoretical predictions. Two and single photon initial anisotropy measurements are wholly consistent with an approximately Gaussian probe distribution at an angle of 38degrees to the nematic director with a full width half maximum of c.a. 26degrees. Variation of beta affords the photoselection of both cylindrically symmetric and asymmetric degrees of probe alignment that are sensitive respectively to theta and theta plus phi diffusion in the laboratory (nematic director) frame. Cylindrically symmetric and asymmetric alignment relaxation are observed to be linear but with distinctly different relaxation rates, indicating highly restricted probe motion within the nernatic environment.

Type: Proceedings paper
Title: Single and two photon time resolved polarised fluorescence studies of probe molecule dynamics in nematic liquid crystals
Event: Multiphoton Absorption and Nonlinear Transmission Processes: Materials, Theory, and Applications
Location: SEATTLE, WA
Dates: 08 July 2002 - 09 July 2002
ISBN: 0819445649
Open access status: An open access version is available from UCL Discovery
DOI: 10.1117/12.453313
Publisher version: http://dx.doi.org/10.1117/12.453313
Language: English
Additional information: Copyright © 2003 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
Keywords: fluorescent probe, liquid crystal, order parameters, two photon, photoselection, fluorescence anisotropy, orientational relaxation, diffusion, rhodamine 6g, anisotropic fluid media, laser techniques, order
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/28942
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