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

Abstract

commonly used multicomponent strategy for white-light emitter, SMWLEs possess many attractive and distinctive advantages, such as absent phase separation, minimal color-aging, easy fabrication, good stability, etc. [2] However, the high-efficiency SMWLE has been always a serious scarcity, as a result of the extremely challenging single-molecule mechanism for whitelight emission according to the Kasha's rule. [3] Typically, the simultaneous dual emission or ternary emission is required to make up white-light emission in singlecomponent material, corresponding to two-color (blue and yellow/orange) or three-color (blue, green and red) emissive sources. [4] In terms of the simplest dual-emission strategy, it can be assigned to two emissive excited states: one excited state is responsible for blue emission and the other one contributes to yellow/orange emission. Usually, the former is locally excited (LE) singlet state, while the latter can be the one among charge-transfer (CT) state, [5] excimer state, [6] proton-transfer state, [7] self-assembly state, [8] the lowest triplet (T 1 ) excited state for room-temperature phosphorescence (RTP), [9] and so on. [10] What is more, this dual emission can also be assigned to dual RTP emission, corresponding to the coemission from both T 1 and T 2 states, respectively. [11] With the recent progress of pure organic RTP materials, [12] more and more dual emission of fluorescence and phosphorescence were observed with SMWLE property. However, the efficiency improvement of pure organic SMWLEs from the dual emission of fluorescence and phosphorescence is one of the most challenging issues. This is because that spin-orbit coupling (SOC) in pure organic systems is weak, which can afford neither the effective intersystem crossing (ISC) for triplet exciton generation nor the efficient triplet exciton radiation to surpass all possible nonradiations (e.g., vibrational quenching, oxygen quenching). [13] More importantly, in comparison with multicomponent white-light emitter, the difficulty will be dramatically increased to achieve the simultaneous enhancement of dual emission of fluorescence and phosphorescence. As for the reasons, there are many internal and external factors affecting these two emissive excited states (fluorescence and phosphorescence) and the balance between them due to the 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 (Φ PL ) of SMWLE is improved successfully from 1.5% (TX) to 45.0% (TX-OCH(CH 3 ) 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 b...

Modulating Room Temperature Phosphorescence by Oxidation of Thianthrene to Achieve Pure Organic Single-Molecule White-Light Emission

“…As shown in Figure 4d, the original pattern of a "sun" was made of two kinds of SMWLE materials: one is 1OTA with the characteristic of long-lived RTP, and the other is TX-OCH 3 without persistent afterglow. 63 Once the pattern was excited under a 365 nm UV lamp, it initially presented a white "sun." Switching off the UV light suddenly, the yellow-green "moon" with the long-lived RTP could be readily observed.…”

Dual emission in purely organic materials for optoelectronic applications

“…Thus, by the introduction of a simple substituent the PL efficiency of powders increased from 1.5% for the parent thioxanthone to 21.4% for 38 with pure white light emission (CIE (0.33, 0.33)). 94 While the above-mentioned examples of dual PF/RTP were observed in highly-ordered crystalline states, intense dual blue PF/yellow RTP was achieved by Fraser et al in a polymer ratiometric sensor, 39 (Fig. 12).…”

Different molecular conformation and packing determining mechanochromism and room-temperature phosphorescence

“…S17). The strong π-π interactions in solid state could promote the persistent RTP [59,60]. In addition, there are four types of C-H…O and ten types of C-H…π intramolecular interactions in the dimer of Crystal Y.…”