Department of Chemistry, University of California, Riverside, Riverside, California 92521, USA.
J Phys Chem A. 2010 Mar 18;114(10):3471-82. doi: 10.1021/jp910277j.
Electronic energy transfer plays an important role in many types of organic electronic devices. Forster-type theories of exciton diffusion provide a way to calculate diffusion constants and lengths, but their applicability to amorphous polymer systems must be evaluated. In this paper, the perylenediimide dye Lumogen Red in a poly(methyl methacrylate) host matrix is used to test theories of exciton motion over Lumogen Red concentrations (C(LR)'s) ranging from 1 x 10(-4) to 5 x 10(-2) M. Two experimental quantities are measured. First, time-resolved anisotropy decays in films containing only Lumogen Red provide an estimate of the initial energy transfer rate from the photoexcited molecule. Second, the Lumogen Red lifetime decays in mixed systems where the dyes Malachite Green and Rhodamine 700 act as energy acceptors are measured to estimate the diffusive quenching of the exciton. From the anisotropy measurements, it is found that theory accurately predicts both the C(LR)(-2) concentration dependence of the polarization decay time tau(pol), as well as its magnitude to within 30%. The theory also predicts that the diffusive quenching rate is proportional to C(LR)(alpha), where alpha ranges between 1.00 and 1.33. Experimentally, it is found that alpha = 1.1 +/- 0.2 when Malachite Green is used as an acceptor, and alpha = 1.2 +/- 0.2 when Rhodamine 700 is the acceptor. On the basis of the theory that correctly describes the anisotropy data, the exciton diffusion constant is projected to be 4-9 nm(2)/ns. By use of several different analysis methods for the quenching data, the experimental diffusion constant is found to be in the range of 0.32-1.20 nm(2)/ns. Thus the theory successfully describes the early time anisotropy data but fails to quantitatively describe the quenching experiments which are sensitive to motion on longer time scales. The data are consistent with the idea that orientational and energetic disorder leads to a time-dependent exciton migration rate, suggesting that simple diffusion models cannot accurately describe exciton motion within this system.
电子能量转移在许多类型的有机电子设备中起着重要作用。Förster 型激子扩散理论为扩散常数和扩散长度的计算提供了一种方法，但必须评估其在非晶聚合物体系中的适用性。本文以聚甲基丙烯酸甲酯基质中的苝二酰亚胺染料 Lumogen Red 为模型，研究了浓度范围为 1 x 10(-4) 至 5 x 10(-2) M 的 Lumogen Red 染料的激子运动理论。实验测量了两个物理量。首先，仅含有 Lumogen Red 的薄膜中的时间分辨各向异性衰减提供了光激发分子初始能量转移速率的估计值。其次，通过测量混合体系中 Malachite Green 和 Rhodamine 700 染料作为能量受体的 Lumogen Red 寿命衰减，来估计激子的扩散猝灭。从各向异性测量中发现，理论准确地预测了偏振衰减时间 tau(pol)与浓度的 C(LR)(-2)依赖关系，以及其在 30%以内的量级。该理论还预测扩散猝灭速率与 C(LR)(alpha)成正比，其中 alpha 范围在 1.00 到 1.33 之间。实验上，当 Malachite Green 作为受体时，发现 alpha = 1.1 +/- 0.2，当 Rhodamine 700 作为受体时，发现 alpha = 1.2 +/- 0.2。基于正确描述各向异性数据的理论，预测激子扩散常数为 4-9 nm(2)/ns。通过使用几种不同的猝灭数据分析方法，实验发现扩散常数在 0.32-1.20 nm(2)/ns 范围内。因此，该理论成功地描述了早期的各向异性数据，但未能定量描述对更长时间尺度上运动敏感的猝灭实验。这些数据与取向和能量无序导致激子迁移率随时间变化的观点一致，这表明简单的扩散模型不能准确描述该体系中的激子运动。
