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

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 <i>y</i> values (CIE_<i>y</i>s) 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-<i>de</i>]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 <i>via</i> 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_<i>y</i> 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.