Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

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• 作者：Taihong Liu ; Mykhailo V. Bondar ; Kevin D. Belfield ; Dane Anderson ; Artëm E. Masunov ; David J. Hagan ; Eric W. Van Stryland
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：May 26, 2016
• 年：2016
• 卷：120
• 期：20
• 页码：11099-11110
• 全文大小：718K
• 年卷期：0
• ISSN：1932-7455

文摘

The synthesis, comprehensive linear photophysical and photochemical study, two-photon absorption (2PA) spectrum, ultrafast relaxation kinetics in the excited states, and efficient superluminescence properties of a new symmetrical three-armed star-shaped squaraine derivative (1) are presented. The steady-state spectral parameters of 1 in a number of organic solvents, including fluorescence excitation anisotropy spectra, revealed a weak interaction between the squaraine branches and the effect of symmetry breaking in the ground electronic state. The degenerate 2PA spectrum of 1 was obtained over a broad spectral range with a maximum cross section of ∼8000 GM using the open aperture Z-scan technique. The nature of the fast dynamic processes in the excited electronic states of 1 was investigated by the femtosecond transient absorption pump–probe method, revealing characteristic relaxation times of ∼3–4 ps. The efficient superluminescence emission of 1 was observed in relatively low concentration solution (≈ 2.3·10^–4 M) under femtosecond transverse pumping. A quantum-chemical study of 1 was performed using ZINDO/S//DFTB theory levels. Simulated 1PA and 2PA absorption spectra were found to be in a good agreement with experimental data. The figure of merit for 1 is ∼10¹¹ GM,1 one of the highest values ever reported for two-photon fluorescence molecular probes, suggesting strong potential for its application in two-photon fluorescence microscopy and bioimaging.