Self-assembly and ambipolar charge transport in columnar phases of polynuclear gold isocyano–triphenylene complexes

Abstract

An uncommon approach to the synthesis of ambipolar semiconductors based on di- and tri-nuclear gold isocyano–triphenylene complexes of the formula [(AuX)_n(CN–C₆H₄–O–(CH₂)₆)_n–TriPh] (n = 2, 3; X = Cl, CC–Ph) is described. Although mesomorphism has only been obtained with chloro derivatives, the trialkynyl complex has turned out to be a precursor of gold nanoparticles. The chloro complexes self-assemble in lamello-columnar phases, whose supramolecular organizations were confirmed by SAXS/WAXS experiments. Both the tri(chloro-gold) and the di(chloro-gold) complexes display high ambipolar charge transport along the columnar stacking direction, either in the mesophase (trichloro derivative) or in the crystalline solid state (dichloro complex). The analysis of ambipolar charge transport in the chloro-gold compounds has been performed using the time-of-flight (ToF) technique. The dichloro compound exhibits an ambipolar charge carrier mobility of the order of 10⁻⁴ cm² V⁻¹ s⁻¹, whereas the trinuclear compound displays an ambipolar charge carrier mobility of the order of 10⁻³ cm² V⁻¹ s⁻¹, which is attributed to the addition of a supplementary peripheral –NC–Au–Cl complex unit, offering a drift field to the charge carriers and a lower optical bandgap. Quantum chemical calculations show that the introduction of an additional –NC–Au–Cl fragment to the dinuclear complex to give the trinuclear derivative promotes a cofacial stacking of the molecules, which increases the mobility of the charge carriers of the system. Due to their ambipolar charge carrier mobility, the poly-nuclear gold isocyano–triphenylene complexes demonstrate their potential for use in organic electronics and optoelectronic devices.