Charge Polarity Control in Organic Transistors of Mixed and Segregated Complexes Based on Diaminonaphthalene and Pyrene

Organic cocrystals
of diaminonaphthalene (DAN) and diaminopyrene
(DAP) with bromanil (BA) and tetracyanoquinodimethane (TCNQ) are an
exemplar system for understanding the charge-transport process, where
from the viewpoint of partition theory, orbital symmetry plays a crucial
role in controlling the carrier charge polarity of transistors. In
the mixed-stack complexes of BA and other p-quinone
acceptors, a comparatively weak donor, 1,5-DAN, shows p-channel characteristics
owing to the counteractive contribution of the next highest occupied
molecular orbital for electron transport. This characteristic behavior
occurs because the BA molecule, situated on top of the amino group,
overlaps with half of the DAN molecule. By contrast, the BA and TCNQ
complexes of a stronger donor, 1,6-DAP, exhibit n-channel transport
due to the cooperative path and orthogonal orbitals. Similarly, TCNQ
complexes of variously substituted DAN show n-channel transport, where
the TCNQ molecules are located on top of the DAN molecules. However,
when the carbon electrodes of (1,5-DAN)(BA) are replaced by silver,
electron transport appears due to the competitive effect of the Schottky
barriers. In a highly conducting segregated complex of (1,6-DAP)(TCNQ),
ambipolar transistor characteristics are observed without subtracting
the bulk current by using carefully prepared thin-film transistors.