title: trans/cis-Isomerization of fluorene-bridged azo chromophore with significant two-photon absorbability at near-infrared wavelength.
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.
authors.affiliation: School of Medical Applied Chemistry, Chung Shan Medical University, South District, Taichung (Taiwan); Department of Medical Education, Chung Shan Medical University Hospital, Taichung 40201 (Taiwan). jrchu@csmu.edu.tw.
authors.forename: Chih-Chien
authors.initials: CC
authors.lastname: Chu
authors.forename: Ya-Chi
authors.initials: YC
authors.lastname: Chang
authors.forename: Bo-Kai
authors.initials: BK
authors.lastname: Tsai
authors.forename: Tzu-Chau
authors.initials: TC
authors.lastname: Lin
authors.forename: Ja-Hon
authors.initials: JH
authors.lastname: Lin
authors.forename: Vincent K S
authors.initials: VK
authors.lastname: Hsiao
mesh_terms: D001391:Azo Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005461:Fluorine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D017785:Photons; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D019265:Spectroscopy, Near-Infrared; D013059:Spectrum Analysis, Raman; D013237:Stereoisomerism
chemical_list: D001391:Azo Compounds; D005461:Fluorine
keywords: absorption; azo compounds; charge transfer; chromophores; isomerization