Efficient bidirectional photocurrent generation by self-assembled monolayer of penta(aryl)[60]fullerene phosphonic acid.
Efficient bidirectional photocurrent generation by self-assembled monolayer of penta(aryl)[60]fullerene phosphonic acid.
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DOI：
10.1002/asia.200900155
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发表时间：
2009-08
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通讯作者：
Aiko Sakamoto;Y. Matsuo;K. Matsuo;E. Nakamura
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作者：
Aiko Sakamoto;Y. Matsuo;K. Matsuo;E. Nakamura
光电活性分子自组装单层（SAM）电极是实现光电转换的一种原型器件。组件中的每个分子代表一个分子装置，它通过向电极或从电极接收电子来吸收光并产生光电流。在这些分子中，富勒烯衍生物因其对长寿命三重态激发态的高电子亲和力，小重组能和良好的电子传递能力而特别令人感兴趣。然而，富勒烯衍生物的聚集倾向给SAM的形成带来了问题，因为它会导致激发态湮灭和光电流产生效率低。我们最近报道了一种简单的分子设计，有效地解决了这个问题（图1 a）；也就是说，一种类似于阿波罗登月模块的五ACHTUNGTRENNUNG（联苯）[60]富勒烯五羧酸1在400 nm照射下产生阳极（而不是阴极）光电流，量子效率高达18%。在其他已知的双向富勒烯中，单向光电流的产生是独特的，因此值得仔细研究。此外，这5个芳基作为空间和方向控制锚的作用还有待证实。一个实际问题是，ITO上的SAM不是很稳定，不能容忍使用有机培养基。为了研究这些问题，我们研究了含有芳基间隔基但缺乏羧酸基的膦化合物（2a和2b，方案1）。我们发现这些分子在水和有机介质中都能在ITO和SnO2上形成稳定的SAM，并有效地产生阳极和阴极电流。结果表明，五种酸引起了五芳基富勒烯分子的极化
Photocurrent-generating self-assembled monolayer (SAM) of photoactive molecules on an electrode is an archetypal device to achieve photoelectric conversion. Each molecule in the assembly represents a molecular device that absorbs light and generates photocurrent by giving or receiving electrons to or from the electrode. Among such molecules, fullerene derivatives are particularly interesting for their high electron affinity for a long-lived triplet excited state, small reorganization energy, and good electrontransporting ability. However, the propensity of fullerene derivatives to aggregate poses a problem in SAM formation, because it causes excited state annihilation and low efficiency of photocurrent generation. We recently reported a simple molecular design that effectively solves this problem (Figure 1 a); that is, a penta ACHTUNGTRENNUNG(biphenyl)[60]fullerene pentacarboxylic acid 1 resembling an Apollo lunar landing module generated an anodic (and not cathodic) photocurrent with a quantum efficiency of up to 18 % under 400 nm irradiation. The unidirectional photocurrent generation is unique among other fullerenes that are generally known to be bidirectional, and are thus worthy of careful investigations. In addition, the role of the five aryl groups as a spaceand orientation-controlling anchor needs to be confirmed. One practical problem was that the SAM on ITO is not very stable and did not tolerate the use of organic medium. To investigate these issues, we have studied phosphonic compounds (2 a and 2 b, Scheme 1) that bear aryl spacer groups but lack the carboxylic acid groups. We found that these molecules form stable SAM on ITO and SnO2 both in an aqueous and organic medium, and effectively generate both anodic and cathodic currents. The results suggest that polarization of the pentaarylfullerene molecule 1 caused by the five acid