Femtosecond spectroscopic study of relaxation processes of three amino-substituted coumarin dyes in methanol and dimethyl sulfoxide
Femtosecond spectroscopic study of relaxation processes of three amino-substituted coumarin dyes in methanol and dimethyl sulfoxide
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DOI：
10.1021/jp980282d
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发表时间：
1998-06-04
影响因子：
2.9
通讯作者：
van der Meulen, P
中科院分区：
文献类型：
--
作者：
Gustavsson, T;Cassara, L;van der Meulen, P
利用荧光上转换技术记录了三种氨基取代香豆素染料在甲醇和二甲亚砜中的时间分辨荧光光谱，仪器响应函数接近200 fs fwhm。这三种氟化香豆素是7-氨基-4-三氟甲基香豆素（C151）、7-二乙基氨基-4-三氟甲基香豆素（C35）和具有julolidine结构的固化氨基香豆素（C153）。发现动态斯托克斯位移由一个特征时间短于目前时间分辨率约为50秒的超快分量主导。将动态Stokes位移与基于20种溶剂中稳态数据的“Kamlet和Taft”分析的估计进行了比较。研究发现，超快成分主要是分子内弛豫。讨论了光致溶质-溶剂氢键变化对光谱位移的影响。在这两种溶剂中，氨基氢键的断裂都非常快，并嵌入在超快溶剂惯性弛豫中，而羰基氢键的重组被认为在10-20 ps的时间尺度上发生在给氢键溶剂甲醇中。然而，不可能明确地将一个特定的实验时间常数与氢键的断裂或形成联系起来。
Time-resolved fluorescence spectra of three amino-substituted coumarin dyes have been recorded in methanol and dimethyl sulfoxide using the fluorescence upconversion technique with an apparatus response function of approximate to 200 fs fwhm. The three fluorinated coumarins are the 7-amino-4-trifluoromethylcoumarin (C151), the 7-diethylamino-4-trifluoromethylcoumarin (C35), and the rigidified aminocoumarin with a julolidine structure (C153). The dynamic Stokes shifts are found to be dominated by an ultrafast component with a characteristic time shorter than the present time resolution of approximate to 50 fs. The dynamic Stokes shifts are compared to estimations based on a "Kamlet and Taft" analysis of steady-state data in 20 solvents. It is found that the ultrafast component can be assigned mainly to intramolecular relaxation. The influences of photoinduced changes of solute-solvent hydrogen bonds on the observed spectral shifts are discussed. The breaking of hydrogen bonds at the amino group is very fast in both solvents and embedded in the ultrafast solvent inertial relaxation, while the reformation of hydrogen bonds at the carbonyl group is believed to occur on the 10-20 ps time scale in the hydrogen bond donating (HBD) solvent methanol. However, it is impossible to unambiguously correlate a particular experimental time constant with the breaking or the formation of a hydrogen bond.