Polarized absorption and anomalous temperature dependence of fluorescence depolarization in cylindrical J-aggregates |
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| Affiliation: | 1. Federal Institute for Materials Research and Testing, Richard-Willstaetter-Strasse 11, D-12489 Berlin, Germany;2. Institute for Theoretical Physics and Materials Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands;3. Institute of Chemistry, Humboldt University, Hessische Strasse 1-2, D-10115 Berlin, Germany;4. Institute of Physics, University of Potsdam, Am Neuen Palais 10, D-14415 Potsdam, Germany;1. Department of Electrical Engineering, IIT Madras, Tamilnadu 641003, India;2. Santa Fe Partners, Santa Fe, New Mexico, U.S.;1. School of Materials Science and Engineering/Institute of Polymers, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China;2. Jiangxi Provincial Key Laboratory of New Energy Chemistry, College of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China;1. Thin Film Laboratory, Semiconductor & Nano-ScienceLabs., Department of Physics, Faculty of Education, Ain Shams University, Roxy, 11757 Cairo, Egypt;2. Department of Physics, Faculty of Science and Arts, Aljouf University, Aljouf, Saudi Arabia;3. Faculty of Science, King Khalid University, P.O. Box 9004, Abha, Saudi Arabia;4. Centre of Nanotechnology, King Abdul Aziz University, Jeddah, Saudi Arabia;1. Institute of Applied Chemistry, Riga Technical University, 3/7 Paul Walden Str., LV, 1048, Riga, Latvia;2. Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV, 1063, Riga, Latvia |
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| Abstract: | We study chiral J-aggregates of the amphiphilic dye 1A that are spontaneously and asymmetrically generated from achiral dye monomers. These aggregates occur in two types. One type possesses a threefold split J-absorption band and forms micrometer-sized superhelices. The other type has a twofold split J-absorption band and forms smaller nanoparticles. We show that the analysis of optical experiments with polarized light in terms of an exciton model yields strong indications that the smaller aggregates have a cylindrical structure as well; the lower exciton band is polarized along the cylinder axis, while the higher band is polarized perpendicular to it. Our analysis allows for an estimate of the number of molecules around the circumference of the cylinder. Fluorescence–polarization excitation spectra at room temperature confirm the cylinder model. At low temperature, these spectra reveal a surprising loss of fluorescence polarization upon excitation in the higher exciton band. Possible explanations for this observation are discussed. |
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