Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
J Phys Chem B. 2011 Sep 15;115(36):10592-603. doi: 10.1021/jp2053019. Epub 2011 Aug 18.
The extreme sensitivity of circularly polarized luminescence (CPL) to long-range excitonic interactions inside a helical aggregate is investigated. It is found to persist even in the presence of strong energetic disorder and coupling of the exciton to molecular vibrations, when the emitting exciton is localized to only a few chromophores. The CPL dissymmetry, g(lum), is found to depend on a modulated sum over the excitonic couplings, ∑(n,s)J(n,n+s)s sin(φs), where J(n,n+s) is the coupling between molecules separated by s lattice spacings and φ is the pitch angle between adjacent chromophores. The validity of this relation is confirmed through full-scale numerical simulations of helical MPOV4 aggregates using the disordered Holstein Hamiltonian. In addition, an analytical expression for g(lum) is obtained for a helical chain containing a single, energetically detuned chromophore to represent strong disorder. Subsequently, the resulting expression is generalized to include full distributed disorder. Our results demonstrate that the spatial dependence of extended interactions can be extracted from experimental spectra, without having details on disorder or exciton-vibrational coupling.
研究了螺旋聚集体内部长程激子相互作用对圆偏振发光（CPL）的极端敏感性。发现在存在强烈的能量无序和激子与分子振动的耦合的情况下，当发射激子仅局限于少数发色团时，CPL 各向异性比 g(lum) 仍然存在。发现 CPL 各向异性比 g(lum) 取决于激子耦合的调制和，∑(n,s)J(n,n+s)s sin(φs)，其中 J(n,n+s) 是由 s 个晶格间距分隔的分子之间的耦合，φ 是相邻发色团之间的螺旋角。通过使用无序 Holstein 哈密顿量对螺旋 MPOV4 聚集体进行全规模数值模拟，验证了该关系的有效性。此外，还获得了一个含有单个能量失谐发色团的螺旋链的 g(lum) 的解析表达式，以表示强无序。随后，将得到的表达式推广到包含完整分布无序的情况。我们的结果表明，可以从实验光谱中提取扩展相互作用的空间依赖性，而无需了解无序或激子-振动耦合的细节。
