Excited tetraphenylporphine on a silver surface: fluorescence quenching and interference effects
Excited tetraphenylporphine on a silver surface: fluorescence quenching and interference effects
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银表面上激发的四苯基卟吩：荧光猝灭和干扰效应
DOI：
10.1021/j100410a002
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
T. Sakata
中科院分区：
文献类型：
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作者：
S. Oshima;T. Kajiwara;M. Hiramoto;K. Hashimoto;T. Sakata
1.前言对吸附在金属表面上的染料分子激发态的驰豫过程进行了广泛的实验和理论研究。1关于实验，朗缪尔-布洛杰特技术或蒸发法允许制备各种各样的分子-金属体系，在该体系中，染料分子通过间隔物从金属表面分离，例如具有已知固定厚度的脂肪酸或惰性气体的单分子膜。对于这样的体系，染料发光的强度和寿命是作为到表面的距离(D)的函数来测量的，因为对发光的详细测量提供了关于金属对处于激发态的分子的影响的信息。2在较远的距离，观察到发光的量子产额的振荡。这可以用经典的镜像偶极理论来描述，它是激发分子直接发射的光子与金属表面反射的光子相互干扰的结果。3在较小的距离(<；200？)，由于激发态分子向金属的辐射能量转移，量子产额迅速下降到零。库恩修改了镜像偶极理论，以一种近似的方式包括了Forster类型的能量转移。3后来，Chance等人。提出了一个比较完整的金属附近偶极辐射的电磁理论(CPS理论)，成功地解释了许多实验结果。然而，在很小的距离(<；10°)仍然存在有趣的问题，因为被激发的分子和金属之间的电子转移可能开始导致发光猝灭。虽然到目前为止用于实验的染料具有相当长的发光寿命(~100 ns-10 ms)，在本研究中为1·4·5，但选择四苯基膦(H_2TPP)染料是因为它的荧光寿命短于几纳秒，可以与其他驰豫过程的速率竞争。2通过改变十六烷基团的厚度，测量了H_2TPP荧光在银表面的光谱和寿命。在这封信中，我们报告了与普通能量转移理论所期望的结果有很大不同的结果。
1. Introduction The relaxation processes of excited states of dye molecules adsorbed on a metal surface havebeen extensively investigated, both experimentally and theoretically. 1 Regarding the experiments, the Langmuir-Blodgett technique or the evaporation method has permitted the preparation of a wide variety of molecule-metal systems, inwhich dye moleculeshave been separated from a metal surface by a spacer, such as monolayers of a fatty acid or an inert gas, with a known fixed thickness. For such systems, theintensity and lifetimeof the luminescence of the dye have been measured as a function of the distanceto the surface (d) since detailed measurements of the luminescence provide information about theeffects of metals on molecules in an excited state. 2 At large distances, an oscillation in the quantum yield of the luminescence is observed. This can be adequately described by using classical image-dipole theory as an effect of the inter-ferences between directly emittedphotons from an excited mol-ecule and those that are reflected from a metal surface. 3 At small distances (< 200 Á), the quantum yield falls rapidly toward zero due tononradiative energy transfer from the excited molecules to the metal. Kuhn modified the image-dipole theory to include Forster-type energy transfer in an approximate way. 3 Later, Chance et al. presented a more complete electromagnetic theory of dipole radiation near a metal (CPS theory), which has suc-cessfully explained many experimental results. 4 However, there still remain interestingproblems at very small distances (< 10 Á) since electrontransfer between an excited molecule and a metal might begin to contribute to luminescence quenching. While the dyes used so far for the experiments have had rather long luminescence lifetimes (~ 100 ns—10 ms), 1· 4· 5 in the present study, the dye, tetraphenylporphine (H2TPP), was chosen because it has a fluorescence lifetime that is shorter than a few nanoseconds and can compete with the rates of other relaxation processes. 2 The spectrum and lifetimeof H2TPP fluorescence were measured on a silver surface by varying the thickness of a hexatriacontane spacer. In this Letter we report results which are considerably different from those expected from ordinary energy-transfer theory.