Intermolecular Orbital-Phase Effects on Charge Transport in Dialkyl-Substituted DCNQI Crystals

Abstract

A series of dialkyl-substituted dicyanoquinodiimine derivatives (Cn-DCNQI; n = 1–7, 12) with systematically varied alkyl chain lengths has been synthesized, and the relationships among crystal structure, intermolecular electronic interactions, and organic field-effect transistor properties have been investigated. Electrochemical measurements and molecular orbital calculations show that all derivatives are strong electron acceptors, with LUMOs localized on the DCNQI core and largely independent of the alkyl substituents. Single-crystal X-ray diffraction analyses reveal that the derivatives form either brickwork-type or π-stacked molecular arrangements depending on alkyl chain length, leading to marked changes in intermolecular transfer integrals and carrier-path dimensionality. Owing to the reduction of the overlap integrals ascribed from the destructive interference between molecular orbitals, transfer integrals are not necessarily maximized even in nominally face-to-face π-stacked configurations. Vacuum-deposited Cn-DCNQI (n = 1–4) thin-film transistors exhibit n-channel behavior, and the observed differences in device performance are attributed primarily to packing- and orbital-phase-dependent transport pathways rather than to differences in thin-film crystallinity.