Narrow emission band ultraviolet/deep-blue thermally activated delayed fluorescence emitters modified with carbazole/carboline as a donor

Abstract

Due to the challenges of a fluorescence spectral red-shift and broadening, the development of ultraviolet (UV) organic light-emitting diodes (OLEDs) remains a significant challenge. Herein, we report four narrowband UV/deep-blue fluorescence thermally activated delayed fluorescence (TADF) molecules based on the boron oxygen polycyclic aromatic hydrocarbon (DOBA) multiple-resonance (MR) structures, namely TDBA-Cz, TDBA-α-Cb, TDBA-β-Cb, and TDBA-γ-Cb. There is a significant twisted structure between the donor (D) of carbazole or carboline and the DOBA acceptor (A), which can weaken the intermolecular interaction of DOBA and improve the luminescence efficiency. OLED devices based on TDBA-Cz, TDBA-α-Cb, and TDBA-γ-Cb exhibit ultraviolet emission (λ_em: 397 nm, 397 nm, and 393 nm). It is worth noting that their full-width at half-maxima (FWHM) are all less than 31 nm, which is one of the narrowest values in the ultraviolet region (λ_em < 400 nm). The maximum external quantum efficiency (EQE) is 3.55%, 3.54%, and 3.81%, respectively. A sky-blue device was further constructed with TDBA-α-Cb as the host material and DSA-Ph as the doped material, with a maximum EQE, current efficiency (CE), and power efficiency (PE) of 5.06%, 10.20 cd A⁻¹, and 7.50 lm W⁻¹, respectively. The above results indicate that DOBA-based carbazole or carboline systems can be used not only as doping materials but also as host materials. This dual-purpose molecule enriches the molecular library for constructing ultraviolet and blue OLEDs.