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

Abstract

By stabilizing unpaired spin in the ground state, open-shell π-conjugated molecules can achieve optoelectronic properties that are inaccessible to closed-shell compounds. Here, we report the synthesis and characterization of a <i>N</i>-substituted, bisphenalenyl π-radical cation [<b>3</b>(OTf)] that shows antiambipolar charge transport and fluorescence via anti-Kasha doublet emission. <b>3</b>(OTf) produces a red emission (634-659 nm) by radiative decay from β-LUMO to β-SOMO, based on density functional theory and configuration interaction singles calculations, and records one of the highest photostabilities (<i>t</i>_1/2 = 9.5 × 10⁴ s) among fluorescent radicals. Characterization of <b>3</b>(OTf)-based field-effect transistors reveals that the observed electrical conductivity (σ_RT ≤ 1.3 × 10^-2 S/cm) is enabled by hole and electron transport (μ_e/μ_h ≤ 5.70 × 10^-5 cm² V^-1 s^-1) that is most efficient in the absence of gating, which represents the first example of antiambipolarity in a molecular material.