Study of the coherent states in two-dimensional dye aggregates

本研究的目的是获得染料聚集体中二维激子态的分子图像。为此，我们进行了以下实验：（1）建立了J-和H-聚集体的制备技术。对于前者，从溶液中吸附产生最理想的结果，而对于后者，Langmuir-Blodgett技术工作得最好。(2)我们制作了一个低温恒温器，配备了显微镜，使我们能够在单层中从0.02 mm直径区域进行光谱分析。(3)我们进行了从液态氦温度到室温的吸收和发射光谱。(4)我们研究了H-聚集体的谐波产生。(5)用条纹照相机测量荧光寿命。(6)利用泵浦-探测方法进行了初步的研究，发现：（1）光谱数据可以用Frenkel激子图像进行很好的描述，并考虑了静态无序和声子的影响。(2)在光学性质中，维数没有定性地出现。(3)荧光寿命极快，这似乎是大量相干激发分子的表现，是二维的定性特征。(4)局域场近似很好地描述了H聚集体中二次谐波的产生过程，即相干性不影响谐波的产生。

The purpose of this study was to gain the molecular picture of the two-dimensional excitonic states in dye aggregates. For this purpose, we have performed the following experiments :(1) We established the preparation techniques for J- and H-aggregates. For the former, adsorption from solution produced most desirable results whereas, for the latter, Langmuir-Blodgett technique worked best. (2) We made a cryostat equipped with a microscope which enabled us to do spectroscopy from 0.02 mm diameter area in a monolayr. (3) We performed absorption and emission spectroscopy from liquid He temperature to room temperature. (4) We studied harmonic generation from H-aggregate. (5) The fluorescence lifetime was measured with a streak camera. (6) A preliminary study was done using a pump-and-probe method.Our findings are as follows :(1) The spectroscopic data can be perfectly described by the Frenkel exciton picture modified with the static disorder and phonons. (2) The dimensionality does not appear qualitatively in the optical properties. (3) The fluorescence lifetime is extremely fast, which seems to be the manifestation of the large number of coherently excited molecules, a qualitative signature of two-dimensionality. (4) The local-field approximation well describes the second-harmonic generation process in H-aggregate, i.e.the coherency does not affect the harmonic generation.