Open-Shell Effects on Optoelectronic Properties: Antiambipolar Charge Transport and Anti-Kasha Doublet Emission from a N-Substituted Bisphenalenyl

By stabilizing unpaired spin in the ground state, open-shell pi-conjugated molecules can achieve optoelectronic properties that are inaccessible to closed-shell compounds. Here, we report the synthesis and characterization of a N-substituted, bisphenalenyl pi-radical cation [3(OTf)] that shows antiambipolar charge transport and fluorescence via anti-Kasha doublet emission. 3(OTf) produces a red emission (634-659 nm) by radiative decay from beta-LUMO to beta-SOMO, based on density functional theory and configuration interaction singles calculations, and records one of the highest photostabilities (t(1/2) = 9.5 x 10(4) s) among fluorescent radicals. Characterization of 3(OTf)-based field-effect transistors reveals that the observed electrical conductivity (sigma(RT) <= 1.3 x 10(-2) S/cm) is enabled by hole and electron transport (mu(e)/mu(h) <= 5.70 x 10(-5) cm(2) V-1 s(-1)) that is most efficient in the absence of gating, which represents the first example of antiambipolarity in a molecular material.