Homoleptic copper(I) arylthiolates as a new class of p-type charge carriers: Structures and charge mobility studies

Polymeric homoleptic copper(I) arylthiolates [Cu(p-SC6H4-X)](infinity) (X=CH3 (1), H (2), CH3O (3), tBu (4), CF, (5), NO2 (6), and COOH (7)) have been prepared as insoluble crystalline solids in good yields (75-95 %). Structure determinations by powder X-ray diffraction analysis have revealed that 1-3 and 6 form polymers of infinite chain length, with the copper atoms bridged by arylthiolate ligands. Weak intra-chain pi center dot center dot center dot pi stacking interactions are present in 1-3, as evidenced by the distances (3.210 angstrom in 1, 3.016 angstrom in 2, 3.401 angstrom in 3) between the mean planes of neighboring phenyl rings. In the structure of 6, the intra-chain pi center dot center dot center dot pi interactions (d=3.711 angstrom) are insignificant and the chain polymers are associated through weak, non-covalent C-H center dot center dot center dot O hydrogen-bonding interactions (d = 2.586 angstrom). Samples of 1-7 in their polycrystalline forms proved to be thermally stable at 200-300 degrees C; their respective decomposition temperatures are around 100 degrees C higher than that of the aliphatic analogue [Cu(SCH3)](infinity). Data from in situ variable-temperature X-ray diffractometry measurements indicated that the structures of both 1 and 7 are thermally more robust than that of [Cu(SCH3)](infinity). TEM analysis revealed that the solid samples of 1-5 and [Cu(SCH3)](infinity) contained homogeneously dispersed crystalline nanorods with widths of 20-250 nm, whereas smaller plate-like nanocrystals were found for 6 and 7. SAED data showed that the chain polymers of 1-3 and [Cu(SCH3)](infinity) similarly extend along the long axes of their nanorods. The nanorods of 1-5 and [Cu(SCH3)](infinity) have been found to exhibit p-type field-effect transistor behavior, with charge mobility (mu) values of 10(-2)-10(-5) cm(2) V-1 s(-1). Polycrystalline solid samples of 6 and 7 each showed a low charge mobility (< 10(-6) cm(2) V-1 s(-1)). The charge mobility values of field-effect transistors made from crystalline nanorods of 1-3 and [Cu(SCH3)](infinity) could be correlated with their unique chain-like copper-sulfur networks, with the para-substituent of the arylthiolate ligand influencing the charge -transport properties.