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Open AccessArticle

Efficient Molecular Aggregation of Rhodamine 6G and Pseudoisocyanine by Light-Induced Force

1
Department of Physics, Faculty of science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
2
Advanced Ultrafast Laser Research Centerand Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
3
Department of Electrophysics, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300, Taiwan
*
Author to whom correspondence should be addressed.
Appl. Sci. 2020, 10(10), 3563; https://doi.org/10.3390/app10103563
Received: 26 April 2020 / Revised: 15 May 2020 / Accepted: 18 May 2020 / Published: 21 May 2020
A highly efficient light-induced aggregation of porphyrin molecules in solution was recently reported for 4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid (TPPS). Here, we demonstrate that rhodamine 6G (R6G) and pseudoisocyanine (PIC) also show efficient light-induced aggregation in unsaturated aqueous solution, being detected with a multichannel lock-in amplifier as the absorbance decrease/increase in the monomers/aggregates, induced by a laser at 633 nm, which is non-resonant off their main monomer absorption wavelengths. The light-induced aggregation states are H-aggregates that are hardly formed in the thermal equilibrium. The similar absorbance changes are absent in the monomer molecules fixed in polyvinyl alcohol (PVA) films. The aggregation efficiency defined as ( Δ A / A ) / ( U t r a p / k B T ) , where A is the absorbance of the monomers, Δ A is the absorbance increase in the aggregates, U t r a p is the optical gradient force potential, and k B T is the thermal energy at room temperature, is approximately 100 for R6G and 500 for PIC, which are much smaller than that of TPPS. View Full-Text
Keywords: light-induced force; gradient force; J-aggregate; H-aggregate; pseudoisocyanine; rhodamine 6G; aqueous solution; polyvinyl alcohol film; Frenkel exciton; pump-probe spectroscopy light-induced force; gradient force; J-aggregate; H-aggregate; pseudoisocyanine; rhodamine 6G; aqueous solution; polyvinyl alcohol film; Frenkel exciton; pump-probe spectroscopy
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Shirakawa, M.; Kobayashi, T.; Tokunaga, E. Efficient Molecular Aggregation of Rhodamine 6G and Pseudoisocyanine by Light-Induced Force. Appl. Sci. 2020, 10, 3563.

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