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trans / cis ‐Isomerization of Fluorene‐Bridged Azo Chromophore with Significant Two‐Photon Absorbability at Near‐Infrared Wavelength
Author(s) -
Chu ChihChien,
Chang YaChi,
Tsai BoKai,
Lin TzuChau,
Lin JaHon,
Hsiao Vincent K. S.
Publication year - 2014
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201402896
Subject(s) - isomerization , chromophore , fluorene , wavelength , photochemistry , infrared , photon , two photon excitation microscopy , materials science , near infrared spectroscopy , chemistry , optoelectronics , optics , physics , fluorescence , organic chemistry , polymer , catalysis
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 ( λ ex =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.