Alkyl-Parity Controlled Switching of Polar/Antipolar Organic Semiconductors

Abstract

The odd-even effects are renowned as a mysterious phenomenon in broad fields of science but have never been established as an effective approach for materials engineering. We demonstrate that the parity of alkyl carbon number n can cause alternating emergence of polar/antipolar organic semiconductor crystals. This is achieved by the development of a series of polar rod-like molecules, composed of a linkage between extended π-core (head) and alkyl chains (tail), exhibiting both high layered crystallinity and well-balanced end-to-end affinity. The molecules are unidirectionally aligned to form two-dimensional array, and the eventual polar monomolecular layers present two distinct types of interlayer stacking depending on the parity of n: alternating head-to-head and tail-to-tail (antipolar) alignment in odd-n crystals, and uniform head-to-tail (polar) alignment in even-n crystals. The latter allows to obtain polar semiconductor films that considerably improve interfacial carrier transport characteristics. The findings are key for creating polarity-controlled optoelectronic materials and devices.

Flip-flop dynamics in smectic liquid-crystal organic semiconductors revealed by molecular dynamics simulations

“…1a). 9 By contrast, Ph-BTBT-C 10 exhibits an antipolar structure, where the alkyl chains are oriented alternately layer by layer (Fig. 1b).…”

“…These compounds typically undergo three phase transitions from crystal to liquid phases via SmE and SmA phases. Asymmetric SmLC OSCs exhibit unique polar or antipolar layered structures; [6][7][8][9][10][11] pTol-BTBT-C 10 exhibits a polar structure, where all the alkyl chains have the same orientation (Fig. 1a).…”

“…Other SmLC OSCs such as 2-decyl-7-(p-tolyl)- [1]benzothieno [3,2-b][1]benzothiophene (pTol-BTBT-C 10 , 10 cm 2 V À1 s À1 ) also exhibit high mobilities. 8,9 Asymmetric substitution to rigid p-conjugated cores is a key technology to increase thermal stability and induce the highly ordered SmE phase for high mobility. These compounds typically undergo three phase transitions from crystal to liquid phases via SmE and SmA phases.…”

“…1a). 9 All the alkyl chains were oriented in the same direction. The polar structure is different from the antipolar herringbone structure of Ph-BTBT-C 10 , where the alkyl chains are oriented alternately layer by layer (Fig.…”