Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Motooka, Nishu-ku, Fukuoka 819-0395, Japan.
Phys Chem Chem Phys. 2010 Sep 28;12(36):10923-7. doi: 10.1039/c003023f. Epub 2010 Jul 26.
We investigated the fluorescence properties of dye aggregates formed in a poly(vinylalcohol) (PVA) matrix by phase separation. Trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (PyAm) was used as a fluorescent dye molecule. The size of PyAm aggregates in the PVA thin films were increased with increasing dye concentration, which was confirmed by atomic force microscope (AFM) measurements. The fluorescence spectra of PyAm in the PVA film at a lower concentration of 0.001 mol% only showed the monomer emission. The fluorescence peak shifted to the red with increasing dye concentration, which was assigned to a dimer or excimer-like emission. Changes in the fluorescence spectra relate to the formation of aggregates in the films. The fluorescence anisotropy decay time constant increases with increasing PyAm concentration up to the order of 100 ps. It is suggested that the exciton efficiently diffuses within the aggregates, and then was trapped at the dimer sites. We also demonstrated the application for gas sensing of nitroaromatics: 2,4-dinitrotoulene (DNT) based on the fluorescence quenching by the photoinduced electron transfer. The quenching efficiency of PyAm fluorescence reached about 43% under concentration of 2.0 mol%. The fluorescence intensity efficiently quenched at the dimer or excimer-like band. These results indicated that the efficient fluorescence quenching increases the reaction probability between PyAm and DNT by the exciton diffusion in the aggregates, called "amplified quenching". The nano-sized aggregates of PyAm formed in the PVA films are responsible for high sensitivity as an artificial fluorescent chemosensor for vapors of the nitroaromatics.
我们研究了通过相分离在聚乙烯醇（PVA）基质中形成的染料聚集体的荧光性质。三甲基-（2-氧代-2-吡喃-1-基-乙基）-溴化铵（PyAm）用作荧光染料分子。通过原子力显微镜（AFM）测量证实，PVA 薄膜中 PyAm 聚集体的尺寸随染料浓度的增加而增大。在较低浓度 0.001 mol%的 PVA 膜中，PyAm 的荧光光谱仅显示单体发射。随着染料浓度的增加，荧光峰向红移，这归因于二聚体或激基缔合物样发射。荧光光谱的变化与薄膜中聚集体的形成有关。荧光各向异性衰减时间常数随 PyAm 浓度的增加而增加，直至 100 ps 左右。这表明激子在聚集体内有效扩散，然后被捕获在二聚体位置。我们还展示了基于光诱导电子转移的荧光猝灭对硝基芳烃（如 2,4-二硝基甲苯（DNT））的气敏应用。在 2.0 mol%的浓度下，PyAm 荧光的猝灭效率达到约 43%。荧光强度在二聚体或激基缔合物带处有效猝灭。这些结果表明，通过聚集体中的激子扩散，PyAm 和 DNT 之间的有效荧光猝灭增加了反应概率，称为“放大猝灭”。PyAm 在 PVA 薄膜中形成的纳米级聚集体是作为硝基芳烃蒸气的人工荧光化学传感器具有高灵敏度的原因。
