Charge transfer properties of bis(phthalocyaninato) rare earth (III) complexes: Intrinsic ambipolar semiconductor for field effect transistors

Density functional theory calculations were carried out to study the charge transfer properties of bis(phthalocyaninato) yttrium and lanthanum double-decker complexes M(Pc)₂ (M = Y, La) for organic field effect transistors. The results indicate that the intrinsic delocalized hole in M(Pc)₂ (M = Y, La) induces the high energy level of highest occupied molecular orbital and low energy level of lowest unoccupied molecular orbital in the sandwich double-decker molecules as well as the small ionization potential and large electronic affinity. These factors lead to very small injection barrier relative to Au source-drain electrode of these two double-deckers for both hole and electron and render them as good potential ambipolar semiconductor. Associated with the very small reorganization energy for hole and electron and large transfer integral in crystal, these two complexes M(Pc) ₂ (M = Y, La) display intrinsic charge transfer mobility of 0.034 and 0.17 cm² V^-1 s^_1 for hole and 0.031 and 0.088 cm² V^-1 s^_1 for electron in crystal according to the calculation results. The high intrinsic mobility for both hole and electron in mese double-deckers was rationalized by examining the changes of geometric and electronic structures upon reduction and oxidation and charge transfer integral of different transfer modes in crystal. Charge transfer integrals in all the possible dimers composed of two Y(Pc)₂ molecules were systematically studied to simulate the molecular arrangement of bis(phthalocyaninato) rare earth complexes in thin solid films.