B-embedded disulfide-bridged π-conjugated compounds: structures and optical tuning

Two novel B-embedded disulfide-bridged π-conjugated compounds (BS-CZ and BS-N) bearing different electron donor groups (phenyl carbazole and triphenylamine) have been prepared and show different optical mechanisms. The compound BS-CZ exhibits significant multiple resonance thermal activation delayed fluorescence (MR-TADF) properties with a small singlet-triplet energy gap (ΔE_ST = 0.16 eV) and a narrow half-peak full width (FWHM = 33 nm), while the compound BS-N shows traditional fluorescence luminescence (FL) characteristics with a larger ΔE_ST (0.28 eV) and FWHM (57 nm). Time-dependent density functional theory (TD-DFT) calculations show that the lowest excited singlet state (S₁) of the compound BS-CZ exhibits local excited (LE) state characteristics, while the charge transfer (CT) state characteristics can be found in S₁ of the compound BS-N. Considering good optical performance, the compound BS-CZ is used as an emitting layer of the organic light-emitting diode device and achieved saturated blue emission (473 nm) with a narrow FWHM (39 nm), and CIE color coordinates of (0.12, 0.21). This work provides an important strategy for the optical mechanism regulation and photoelectric applications of B-embedded disulfide-bridged π-conjugated molecules.