Intramolecular-Locked High Efficiency Ultrapure Violet-Blue (CIE-y <0.046) Thermally Activated Delayed Fluorescence Emitters Exhibiting Amplified Spontaneous Emission

Rational manipulation of frontier orbital distribution and singlet-triplet splitting is crucial to exploit the luminescent properties of organic molecules. To realize ultra-blue luminescence, both blue-shifted wavelength peak (lambda(peak)) and narrow full-width at half-maximum (FWHM) are required. Herein, a new thermally activated delayed fluorescence (TADF) skeleton by inserting the diphenyl methylene intramolecular-lock to adjust the torsion angles and restrict the intramolecular relaxation is developed. Two rigid emitters, incorporating phenoxazine (PXZN-B) and acridine (DMACN-B) as donors and mesitylboron as an acceptor, exhibit narrow FWHMs (<50 nm) with deep-blue (0.133, 0.147) and violet-blue emission (0.151, 0.045), respectively. In particular, the Commission Internationale de l'Eclairage (CIE) coordinates of a DMACN-B-based device closely approach the Rec.2020 standard (0.131, 0.046). Moreover, both of the organic light-emitting diodes (OLEDs) based on PXZN-B and DMACN-B show TADF character, with high external quantum efficiencies (EQEs) exceeding 10%. Furthermore, owing to the large orbital overlap, these TADF emitters own a fast S-1-S-0 transition rate exceeding 10(8) s(-1), thereby exhibiting marked amplified spontaneous emission (ASE) with low thresholds. Therefore, the intramolecular-lock strategy provides not only innovation for realizing high-efficiency deep-blue TADF emission with high color purity but also an avenue for a TADF-based ASE and lasing application.

Automated summary

The rational manipulation of molecular frontier orbital distribution and singlet-triplet splitting is crucial for exploiting the luminescent properties of organic molecules. In this study, a new TADF skeleton is developed by inserting a diphenyl methylene intramolecular lock to adjust torsion angles and restrict intramolecular relaxation. Two rigid emitters show narrow FWHMs and emit in deep blue and violet-blue, with fast S-1-S-0 transition rates and low ASE thresholds.