High-efficiency nondoped near-ultraviolet organic light-emitting diodes based on spiro luminogens with high-lying reverse intersystem crossing

Abstract

Near-ultraviolet (NUV) organic light-emitting diodes (OLEDs) have drawn abundant attention due to their practical applications in diverse frontier fields. However, high-efficiency NUV luminogens with Commission Internationale de L’Eclairage (CIE) coordinate y values (CIE_ys) of <0.06 and electroluminescence (EL) peaks of ≈400 nm are rarely reported. In this work, three robust NUV luminogens based on spiro[fluorene-9,8′-indolo[3,2,1-de]acridine] donor and benzonitrile acceptor (SFIAC-PCN-1, SFIAC-PCN-2 and SFIAC-PCN-3) are designed and synthesized. These spiro luminogens in neat films emit strong NUV light with photoluminescence (PL) peaks in the range of 412–421 nm and high PL quantum yields of 68–90%. As evidenced by excitation-dependent transient PL decay spectra and theoretical calculations, these luminogens are able to utilize triplet excitons via high-lying reverse intersystem crossing processes, and the nondoped OLEDs using them as emitters radiate strong NUV light with EL peaks at 402–414 nm, narrow full widths at half maximum of 43–49 nm, and low CIE_y values of 0.029–0.039, and furnish impressive EL performances with maximum luminance and peak external quantum efficiencies of up to 7176 cd m⁻² and 7.90%, respectively. These EL performances are among the state-of-the-art nondoped NUV OLEDs.