Politecnico di Milano, Dipartimento di Chimica, Materiali e Ing. Chimica G. Natta, and INSTM, UdR Milano, p.za Leonardo da Vinci 32, 20133 Milano, Italy.
Phys Chem Chem Phys. 2010 Feb 21;12(7):1600-9. doi: 10.1039/b920792a. Epub 2010 Jan 14.
We present a computational study on the electrical bistability behavior of four xanthene derivatives based on sodium fluorescein. Intra- and intermolecular charge transfer parameters are computed and employed to rationalize the efficiencies experimentally determined for resistive memory devices based on these organic materials. Charge injection at the electrode/organic interface in the presence of pristine and reduced molecular species is estimated by comparing the electron affinities of xanthene derivatives with the work function of commonly employed electrodes, and bulk charge transport is modeled assuming a charge hopping regime. It is shown that the OFF state is injection limited and that the efficiency of the bistability phenomenon is governed by sizeable intramolecular reorganization energies associated with electron transfer. The computed results reveal that the combined role of electron attractor groups and conformational degrees of freedom contributes to a more favorable level alignment at the interface and to the desired increase of the intramolecular reorganization energies. These optimal conditions are fulfilled for Rose Bengal. It is expected that the interrelated role of molecular parameters, conformational degrees of freedom and electron attractor character of substituents disclosed by this study might be used to formulate general structure-property relationships for the design of new, more efficient restive memory devices based on molecular semiconductors.
我们提出了一个基于钠荧光素的四种呫吨衍生物的电双稳行为的计算研究。计算了分子内和分子间的电荷转移参数，并用于合理化基于这些有机材料的电阻式存储器件的实验确定的效率。通过比较呫吨衍生物的电子亲和力与常用电极的功函数，估计了在原始和还原分子物种存在下在电极/有机界面处的电荷注入，并且假设在电荷跳跃机制下对体电荷输运进行建模。结果表明，OFF 状态是注入限制的，双稳现象的效率受与电子转移相关的较大分子内重组能控制。计算结果表明，电子吸引基团和构象自由度的组合作用有助于在界面处实现更有利的能级对准，并期望增加分子内重组能。对于玫瑰红而言，这些最佳条件得到了满足。预计，本研究揭示的分子参数、构象自由度和取代基的电子吸引特征的相互关系作用，可以用于制定基于分子半导体的新型、更有效的电阻式存储器件的一般结构-性能关系。
