Crystal Lattice Design of H2O‑Tolerant n‑Type Semiconducting Dianionic Naphthalenediimide Derivatives

Dianionic bis­(propionate)-naphthalene­diimide (PCNDI2–) formed simple 2:1 cation–anion salts of (M+)2(PCNDI2–)·(H2O)n (M+ = Li+, Na+, K+, Rb+, and Cs+), which exhibited reversible H2O adsorption–desorption behavior because of the presence of their electrostatically binding crystal lattices. The maximum H2O adsorption amounts (n) for M+ = Li+, Na+, K+, Rb+, and Cs+ were 0.25, 6.0, 4.0, 6.0, and 2.0, respectively, whereas the reversible gate-opening (gate-closing) H2O adsorption–desorption isotherms were observed at 273 and 298 K, except for M+ = Li+. High ionic conductivities of around 10–4–10–5 S cm–1 were observed in M+ = Na+ and K+ salts, whereas short-range thermal fluctuations occurred in large cations of M+ = Rb+ and Cs+. The change in the electrostatic lattice energy for M+ = Na+ and K+ salts during the H2O adsorption–desorption cycles was significantly larger than those for M+ = Rb+ and Cs+. Therefore, the Na+ and K+ salts had a considerably flexible electrostatic crystal lattice with a large amplitude of lattice modulation during the H2O sorption cycle. In contrast, the lattice modulation for M+ = Rb+ and Cs+ salts involved a low magnitude of ion displacements, forming a relatively rigid cation–anion electrostatic crystal lattice. The flash-photolysis time-resolved microwave conductivity and transition absorption spectroscopy results revealed the high electron mobility of H2O-adsorbed thin films, wherein the crystallized H2O molecules did not act as electron-trapping sites. The values of electron mobility increased in the order of Cs+ ≈ Rb+ > K+ > Na+ > Li+.双丙酸根-萘二酰亚胺双阴离子（dianionic bis(propionate)-naphthalenediimide，PCNDI²⁻）可形成通式为(M⁺)₂(PCNDI²⁻)·(H₂O)ₙ的简单2:1型阴-阳离子盐，其中M⁺分别为Li⁺、Na⁺、K⁺、Rb⁺与Cs⁺。由于该类盐具备静电结合型晶体晶格，其展现出可逆的水吸附-脱附行为；对于M⁺为Li⁺、Na⁺、K⁺、Rb⁺及Cs⁺的体系，其最大水吸附量（即参数n）依次为0.25、6.0、4.0、6.0与2.0，除Li⁺体系外，其余体系在273 K与298 K下均呈现出可逆的开门（关门）型水吸附-脱附等温线。Na⁺与K⁺盐展现出约10⁻⁴~10⁻⁵ S·cm⁻¹的高离子电导率，而Rb⁺与Cs⁺这类大阳离子体系则存在短程热涨落现象；在水吸附-脱附循环过程中，Na⁺与K⁺盐的静电晶格能变化幅度显著高于Rb⁺与Cs⁺盐，由此可见，Na⁺与K⁺盐具备柔性极强的静电晶体晶格，在水吸附循环过程中晶格调制幅度较大，与之相反，Rb⁺与Cs⁺盐的晶格调制仅伴随小幅度的离子位移，形成了相对刚性的阴-阳离子静电晶体晶格。瞬态光解时间分辨微波电导率与瞬态吸收光谱测试结果表明，吸附水的薄膜具备高电子迁移率，且结晶态水分子并未充当电子俘获位点，电子迁移率的大小依次为Cs⁺≈Rb⁺>K⁺>Na⁺>Li⁺。