Langmuir–Blodgett Films of Charge-Transfer Complexes: Ethylenedithio-Substituted Amphiphilic Bis-TTF Macrocycle and F<sub>4</sub>TCNQ or Br<sub>2</sub>TCNQ
作者:Toru Endo、Tomoyuki Akutagawa、Teppei Kajiwara、Keiko Kakiuchi、Yoko Tatewaki、Shin-ichiro Noro、Takayoshi Nakamura
DOI:10.1246/bcsj.82.968
日期:2009.8.15
Charge-transfer (CT) complexes between ethylenedithio-substituted bis-TTF macrocycle 1a, as an amphiphilic electron donor, and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) derivatives, as electron acceptors, were fabricated as Langmuir–Blodgett (LB) films. For the 1a–F4TCNQ LB film deposited at a surface pressure of 5 mN m−1 onto a substrate surface, the stoichiometry between the donor and acceptor was determined as 1:2 using XPS measurements. In contrast, a donor/acceptor ratio of 1:0.3 was observed for the 1a–Br2TCNQ LB film, indicating that a fraction of Br2TCNQ was lost during the LB film formation process. Similarity of the round-shaped domains that cover the surfaces of the 1a–Br2TCNQ and neutral 1a LB films indicates the presence of neutral 1a within the 1a–Br2TCNQ LB film. For the (1a2+)(F4TCNQ−)2 LB film, the presence of a CN-stretching frequency signifies the formation of a fully ionic electronic ground state. The LB film of 1a–Br2TCNQ exhibited a broad absorption at ca. 3 × 103 cm−1, which is characteristic of an intermolecular CT transition for a partial CT state. 1a–Br2TCNQ LB film consisted of neutral 1a and CT complex of 1a–Br2TCNQ. The room temperature conductivity of the 1a–Br2TCNQ LB film (1.2 × 10−2 S cm−1) was two orders of magnitude higher than that of 1a–F4TCNQ (3.9 × 10−4 S cm−1).
作为两亲性电子给体的亚乙二硫代双 TTF 大环 1a 与作为电子受体的 7,7,8,8- 四氰基对醌二甲烷 (TCNQ) 衍生物之间的电荷转移 (CT) 复合物被制成了朗缪尔-布洛杰特 (LB) 薄膜。对于在 5 mN m-1 的表面压力下沉积到基底表面的 1a-F4TCNQ LB 薄膜,通过 XPS 测量确定了供体和受体之间的配比为 1:2。相比之下,1a-Br2TCNQ枸杞薄膜的供体/受体比为 1:0.3,表明在枸杞薄膜形成过程中损失了一部分 Br2TCNQ。覆盖在 1a-Br2TCNQ 和中性 1a LB 薄膜表面的圆形畴具有相似性,这表明在 1a-Br2TCNQ LB 薄膜中存在中性 1a。对于 (1a2+)(F4TCNQ-)2 LB 薄膜来说,CN 拉伸频率的出现标志着完全离子电子基态的形成。1a-Br2TCNQ 的枸杞薄膜在约 3 × 103 cm-1 处显示出宽吸收,这是由于枸杞薄膜中的枸杞离子在枸杞基态上的吸收率较低。3 × 103 cm-1 处的宽吸收,这是部分 CT 态分子间 CT 转变的特征。1a-Br2TCNQ LB 薄膜由中性 1a 和 1a-Br2TCNQ 的 CT 复合物组成。1a-Br2TCNQ LB 薄膜的室温电导率(1.2 × 10-2 S cm-1)比 1a-F4TCNQ 的室温电导率(3.9 × 10-4 S cm-1)高出两个数量级。