4-Dimethylaminochalcone as fluorescent probe: effect of the medium polarity on relaxation processes in the excited state
4-Dimethylaminochalcone as fluorescent probe: effect of the medium polarity on relaxation processes in the excited state
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4-二甲氨基查耳酮作为荧光探针：中等极性对激发态弛豫过程的影响
DOI：
10.1007/s11172-005-0015-z
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
S. А. Antipin
中科院分区：
文献类型：
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作者：
S. K. Gularyan;O. Sarkisov;G. Dobretsov;V. Y. Svetlichnyĭ;F. Gostev;S. А. Antipin
研究了4-二甲氨基查尔酮分子在脉宽为70fs的光脉冲激发下的弛豫过程。在激发后的0.4-1ps内，在极性和非极性介质中都形成了最大吸收峰在∼460 nm的激发态S1。随后的弛豫过程取决于介质的极性。在非极性正己烷中，4-二甲氨基查尔酮分子转变为三重态，其最大吸收波长为570 nm(寿命大于600ps)，持续时间为20ps。在极性非质子乙腈中，460 nm处的吸光度缓慢下降(在数百皮秒内)，表明分子返回到基态。在乙腈中还观察到了S1能级在520-550 nm范围内的诱导发射和同一能级的荧光，最大荧光波长在537 nm。因此，找到了从极性介质到非极性介质时荧光产率急剧下降的原因。磷光光谱数据证实了4-二甲氨基查尔酮在非极性介质中的荧光猝灭机理。在非极性溶剂中，4-二甲氨基查尔酮在−的温度为196℃时出现三重激发态的磷光，而在极性溶剂中未观察到磷光。
Relaxation processes in a 4-dimethylaminochalcone molecule after excitation with a light pulse of duration 70 fs were studied. During 0.4–1 ps after excitation, an absorbance of an excited state S1with a maximum at ∼460 nm is formed in both polar and nonpolar media. Subsequent relaxation processes depend on the polarity of the medium. In nonpolar hexane, the 4-dimethylaminochalcone molecule transits to the triplet state having an absorption maximum at 570 nm (lifetime longer than 600 ps) for 20 ps. In polar aprotic acetonitrile, the absorbance at 460 nm decreases slowly (during hundreds of picoseconds), indicating that the molecules return to the ground state. The induced emission from the level S1in a region of 520–550 nm and fluorescence from the same level with a maximum at 537 nm are also observed in acetonitrile. Thus, a reason for a sharp decrease in the fluorescence yield on going from polar to nonpolar media was found. The mechanism of fluorescence quenching of 4-dimethylaminochalcone in nonpolar media is confirmed by the data on phosphorescence. The phosphorescence of 4-dimethylaminochalcone is observed at−196 °C in nonpolar solvents, indicating a triplet excited state, while no phosphorescence is revealed in polar solvents.