Dianionic bis(benzenesulfonate)-naphthalenediimide (BSNDI2-) formed simple 2:1 cation-anion salts (Cn-BSNDIs) by the combination of two molar alkylammonium (CnH2n+1NH3+) in which the alkyl-chain length (n) was systematically changed from 1 to 16 to study then-dependent phase transition behavior, molecular assembly structure, dielectric response, and transient conductivity of a series ofCn-BSNDIsalts. The electrostatic cation-anion and van der Waals interactions in the molecular assembly compensated for each other, where the elongation of the −CnH2n+1chain increased the energy contribution from van der Waals interactions. The crystal lattices of short-chainCn-BSNDIs(n= 1-4) were rigid and static without temperature- and frequency-dependent dielectric responses. By contrast, large dielectric responses were observed inCn-BSNDIsalts with intermediaten= 5-8 because of the motional freedom of the cation-anion arrangement and thermal fluctuation of the flexible alkyl chains. In the case ofCn-BSNDIswithn= 9-16, the thermal fluctuation of long alkyl chains primarily contributed to the dielectric responses. The one-dimensional intermolecular interactions ofCn-BSNDIsalts (n= 1 and 2) showed a dimensional crossover to the two-dimensionalC3-BSNDI, and the transient conductivity (ϕΣμ) ofC3-BSNDIandC4-BSNDIthin films was much larger than those of the other salts. The rigid crystal lattice ofCn-BSNDIs(n= 3 and 4) became dynamic whenn≥ 5, with a successive phase transition and an even-odd effect in the dielectric constants and ϕΣμ values. The observed interplay of van der Waals and electrostatic interaction allows the dynamic tuning of electronic properties with identical molecular cores as represented by their dielectric response and transient conductivity.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films