trans/cis‐Isomerization of Fluorene‐Bridged Azo Chromophore with Significant Two‐Photon Absorbability at Near‐Infrared Wavelength |
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Authors: | Prof Dr Chih‐Chien Chu Ya‐Chi Chang Bo‐Kai Tsai Prof Dr Tzu‐Chau Lin Prof Dr Ja‐Hon Lin Prof Dr Vincent K S Hsiao |
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Institution: | 1. School of Medical Applied Chemistry, Chung Shan Medical University, South District, Taichung (Taiwan);2. Department of Medical Education, Chung Shan Medical University Hospital, Taichung 40201 (Taiwan);3. Department of Chemistry, National Central University, Jhong‐Li 32001 (Taiwan);4. Department of Electro‐Optical Engineering, National Taipei University of Technology, Taipei 10608 (Taiwan);5. Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Puli 54561 (Taiwan) |
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Abstract: | Azo‐containing materials have been proven to possess second‐order nonlinear optical (NLO) properties, but their third‐order NLO properties, which involves two‐photon absorption (2PA), has rarely been reported. In this study, we demonstrate a significant 2PA behavior of the novel azo chromophore incorporated with bilateral diphenylaminofluorenes (DPAFs) as a π framework. The electron‐donating DPAF moieties cause a redshifted π–π* absorption band centered at 470 nm, thus allowing efficient blue‐light‐induced trans‐to‐cis photoisomerization with a rate constant of 2.04×10?1 min?1 at the photostationary state (PSS). The open‐aperture Z‐scan technique that adopted a femtosecond (fs) pulse laser as excitation source shows an appreciably higher 2PA cross‐section for the fluorene‐derived azo chromophore than that for common azobenzene dyes at near‐infrared wavelength (λex=800 nm). Furthermore, the fs 2PA response is quite uniform regardless of the molecular geometry. On the basis of the computational modeling, the intramolecular charge‐transfer (ICT) process from peripheral diphenylamines to the central azo group through a fluorene π bridge is crucial to this remarkable 2PA behavior. |
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Keywords: | absorption azo compounds charge transfer chromophores isomerization |
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