Orientation of adsorbed dyes in the interlayer space of clays.: 2 -: Fluorescence polarization of rhodamine 6G in laponite films
Orientation of adsorbed dyes in the interlayer space of clays.: 2 -: Fluorescence polarization of rhodamine 6G in laponite films
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DOI：
10.1021/cm051518a
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发表时间：
2006-03-21
影响因子：
8.6
通讯作者：
Martínez, VM
中科院分区：
文献类型：
--
作者：
Arbeloa, FL;Martínez, VM
采用荧光偏振法研究了罗丹明6 G（R6 G）在锂皂石（Lap）粘土矿物上的吸附择优取向。为此目的，对于常见的水平偏振激发光，记录发射偏振器的水平和垂直方向的荧光光谱，作为膜相对于激发（和发射）光束的扭转角δ的函数。吸附在粘土膜中的荧光物种的取向可以从最近建立的荧光二色性比和扭转角θ之间的线性关系来评估。(1.2)对于低染料负载R6 G，分子被吸附到拉普表面作为单体单元与倾斜psi角为28度相对于粘土层，与通过可见光吸收与偏振光得到的结果一致。荧光共面J型二聚体的R6 G也观察到在拉普膜中的中等染料负载与类似的取向角约30度。共面R6 G H型二聚体和高阶聚集体的存在下，在中等和高负载R6 G/Lap膜的荧光各向异性的J二聚体，归因于一个激发能量转移过程，并减少这种荧光方法的适用性，导致去偏振。然而，目前的实验结果证实了这些H聚集体相对于Lap层的更垂直的配置。新的荧光偏振方法可以外推，以确定在刚性和有序的2D主体材料中的任何吸附的荧光团的取向。
A new fluorescence polarization method is applied to evaluate the preferential orientation of rhodamine 6G (R6G) adsorbed into laponite (Lap) clay mineral in supported films. For this purpose, the fluorescence spectra for the horizontal and vertical directions of the emission polarizer were recorded for a common horizontally polarized excitation light as a function of the twist angle delta of the film with respect to the excitation (and emission) beam. The orientation of the fluorescent species adsorbed in the clay films can be evaluated from the linear relationship between the fluorescence dichroic ratio and the twist angle 6 recently established.(1.2) For low dye-loading R6G, molecules are adsorbed into the Lap surface as monomeric units with a tilt psi angle of 28 degrees with respect to the clay layer, in agreement with results obtained by visible absorption with polarized light. Fluorescent coplanar J type dimers of R6G are also observed in Lap films for moderate dye loadings with a similar orientation angle around 30 degrees. The presence of coplanar R6G H type dimers and high-order aggregates in moderate- and high-loading R6G/Lap films causes a depolarization for the fluorescence anisotropy of the J dimer, ascribed to an excitation energy-transfer process and reducing the applicability of this fluorescence method. However, present experimental results confirm a more-perpendicular disposition of these H aggregates with respect to the Lap layer. The new fluorescence polarization method can be extrapolated to determine the orientation of any adsorbed fluorophore in rigid and ordered 2D host materials.