Achieving Highly Efficient Pure Organic Single-Molecule White-Light Emitter: The Coenhanced Fluorescence and Phosphorescence Dual Emission by Tailoring Alkoxy Substituents

Developing the single-molecule white-light emitters (SMWLEs) at room temperature is very challenging for pure organic metal-free system, and it is even more challenging to achieve the high efficiency of pure organic SMWLE. Here, alkoxy substituents are tailored at 2-positioned thioxanthone (TX) to finely tune the molecular packing mode and the intermolecular interaction between TX units, and the photoluminescence (PL) efficiency (phi(PL)) of SMWLE is improved successfully from 1.5% (TX) to 45.0% (TX-OCH(CH3)(2)). This simultaneous enhancement of dual emission between fluorescence and phosphorescence can be ascribed to i) a moderate intersystem crossing (ISC) rate for the equilibrium distribution between singlet and triplet excitons, ii) simultaneously accelerated radiative rates of singlet and triplet excitons due to J-aggregation of TX units, and iii) effective suppression of nonradiation through strong hydrogen bond interactions by alkoxy chains. As a result, this work provides a novel molecular design strategy to harvest high-efficiency pure organic SMWLE using a precise manipulation of pi-pi stacking mode and intermolecular interaction by tailoring alkoxy substituents.