Dual Fluorescent Photochromic Colorants Bearing Pyrano[3,2-c]chromen-5-one Moiety

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• 作者：Chao-Chen Lin ; Cheng-Chih Hsieh ; Ya-Chien Yu ; Chin-Hung Lai ; Chin-Neng Huang ; Pei-Yu Kuo ; Chi-Hui Lin ; Ding-Yah Yang ; Pi-Tai Chou
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：August 20, 2009
• 年：2009
• 卷：113
• 期：33
• 页码：9321-9328
• 全文大小：363K
• 年卷期：v.113,no.33(August 20, 2009)
• ISSN：1520-5215

文摘

In this study, the photochromic processes of 8-N,N-dimethylamino-2,2-dimethyl-2H-pyrano[3,2-c]chromen-5-one (1) and its derivatives (2, 3) are investigated with steady-state, temperature-dependent and time-resolved absorption and emission spectroscopy. The differences among compounds 1−3 lie in their various substituents anchored at the pyran moiety that is subject to the photoinduced ring-opening reaction. Compounds 1 and 2 exhibit salient photochromism with a very unique phenomenon, in which fluorescence is observed in 1 for both the ring-closed form (1-CF, λ_max ≈ 445 nm) and the ring-open form (1-OF, λ_max ≈ 650 nm in CH₂Cl₂). The yields of forward and reverse photochromism processes were determined to be 0.40 and 1.0% for 1. Along with fluorescence quantum yields of 9.5 × 10⁻² and 5.8 × 10⁻³ for 1-CF and 1-OF, respectively, 1 enables fluorescence detection while it exhibits photochromism in both directions, that is, a photoinduced on/off fluorescence switch. An increase in on/off ratiometric fluorescence between 1-OF and 1-CF can reach a factor of 4.0 upon excitation at the absorption isosbestic point. The activation energies for the ground-state OF_trans → CF thermal bleaching processes were determined to be 58.2 and 54.8 kJ/mol, with frequency factors of 1.7 × 10⁵ and 3.6 × 10⁵ s⁻¹ for 1 and 2, respectively. Conversely, bromo-substituted 3 did not undergo photochromic reaction, as evidenced by the lack of changes in the absorption spectrum after a prolonged (2 h) 354 nm (0.2 W/cm²) photolysis, manifesting the fact that other relaxation processes, such as enhanced intersystem crossing, may govern the deactivation of 3 (3-CF) upon excitation.