Long-range exciton transport is a key challenge in achieving efficient solar energy harvesting in both organic solar cells and photosynthetic systems. Self-assembled molecular aggregates provide the potential for attaining long-range exciton transport through strong intermolecular coupling. However, there currently lacks an experimental tool to directly characterize exciton transport in space and in time to elucidate mechanisms. Here we report a direct visualization of exciton diffusion in tubular molecular aggregates by transient absorption microscopy with ∼200 fs time resolution and ∼50 nm spatial precision. These direct measurements provide exciton diffusion constants of 3–6 cm² s^–1 for the tubular molecular aggregates, which are 3–5 times higher than a theoretical lower bound obtained by assuming incoherent hopping. These results suggest that coherent effects play a role, despite the fact that exciton states near the band bottom crucial for transport are only weakly delocalized (over <10 molecules). The methods presented here establish a direct approach for unraveling the mechanisms and main parameters underlying exciton transport in large molecular assemblies.

中文翻译：

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超快速显微镜对管状卟啉聚集体中激子转运的直接成像

远程激子传输是在有机太阳能电池和光合作用系统中实现高效太阳能收集的关键挑战。自组装分子聚集体提供了通过强分子间偶联实现远距离激子传输的潜力。但是，目前缺乏直接表征激子在空间和时间上阐明机制的实验工具。在这里，我们通过瞬态吸收显微镜以〜200 fs的时间分辨率和〜50 nm的空间精度直接报告了激子在管状分子聚集体中的扩散。这些直接测量提供的激子扩散常数为3–6 cm ² s ^–1对于管状分子聚集体，比假设非相干跳跃获得的理论下限高3至5倍。这些结果表明，相干效应起着一定的作用，尽管事实上，对于传输至关重要的能带附近的激子态仅微弱地离域化（超过10个分子）。本文介绍的方法建立了一种直接方法，用于揭示大分子组装体中激子传输的机理和主要参数。