Dual fluorescent photochromic colorants bearing pyrano[3,2-c]chromen-5-one Moiety

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Title:	Dual fluorescent photochromic colorants bearing pyrano[3,2-c]chromen-5-one Moiety
Authors:	Lin, C.-C.,?Hsieh, C.-C.,?Yu, Y.-C.,?Lai, C.-H.,?Huang, C.-N.,?Kuo, P.-Y.,?Lin, C.-H.,?Yang, D.-Y.?,?Chou, P.-T.
Contributors:	Department of Chemistry, Tunghai University
Keywords:	Closed form;Fluorescence detection;Fluorescence quantum yield;Fluorescence switch;Frequency factors;Intersystem crossing;Isosbestic point;Photo-induced;Photochromic reactions;Ratiometric fluorescence;Ring opening reaction;Temperature dependent;Thermal bleaching;Time-resolved absorption
Date:	2009
Issue Date:	2013-05-14T09:02:42Z (UTC)
Abstract:	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 CH 2Cl 2). 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 x 10 -2 and 5.8 x 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 x 10 5 and 3.6 x 10 5 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/cm 2) photolysis, manifesting the fact that other relaxation processes, such as enhanced intersystem crossing, may govern the deactivation of 3 (3-CF) upon excitation. ? 2009 American Chemical Society.
Relation:	Journal of Physical Chemistry A 113 (33) , pp. 9321-9328
Appears in Collections:	[Department of Chemistry ] Periodical Articles

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