Observation of Dual Room Temperature Fluorescence–Phosphorescence in Air, in the Crystal Form of a Thianthrene Derivative

Abstract

Thianthrenes have been nearly forgotten as phosphors in recent years, but are now coming back, showing their strong potential in luminescent applications. Here, we present a comprehensive photophysical study of a carbazolyl derivative of thianthrene in different matrices and environments. The diffusion of oxygen is slowed down in the rigid environment of thianthrene organic crystals suppressing their phosphorescence quenching, as well as triplet-triplet annihilation. This facilitates the observation of simultaneous fluorescence and phosphorescence emissions at room temperature, in air, giving origin to strong white luminescence. Moreover, the color coordinates of the dual fluorescence-phosphorescence white emission, which is observed only in rigid amorphous media and in crystals, can be tuned.

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

“…On the other hand, there have been some examples of fully organic RTP emitters that didn't possess steric hindrance in the structure, or the side groups were big enough to slow the motion sufficiently to observe RTP phosphorescenceemission at higher temperatures. Several examples of RTP compounds that contain thianthrene and phenothiazine were reported by Pander et al (e.g., 1, CbTT, and 2), [65][66][67] whilst Zhang andc o-workers reported aD -A-type xanthone-coredR TP compound (CX;F igure 6). [68] As imilar approach for the design of new RTP molecules with the typical orange-red RTP emission has recently been developed.…”

Dual emission in purely organic materials for optoelectronic applications

“…The rigid environment within organic crystals is known to slow down the rate of diffusion of oxygen and molecular vibrations. 40 Both these factors facilitate the observation of simultaneous fluorescence and phosphorescence in air, giving rise to strong white luminescence. Triplet-triplet annihilation (TTA) can also be active in crystalline systems due to triplet exciton diffusion through adjacent chromophores.…”

“…39 Furthermore, the diffusion of oxygen is slowed down in ordered media such as an organic crystal, therefore suppressing DF/phosphorescence quenching. 40 As a result, the ratio between fluorescence and delayed emission can be manipulated by the degree of crystallinity of a sample. 41 The diversity of fortuitously discovered DE materials has prompted us to assess and review the different reported cases of this phenomenon.…”

Modulation of charge transfer by N-alkylation to control photoluminescence energy and quantum yield

“…In recent years, uorescence spectroscopy has been used to characterize a wide range of different compounds and uncover new functional phenomena such as thermally activated delayed uorescence (TADF), [2][3][4][5][6][7] aggregation induced emission [8][9][10] and room temperature phosphorescence. [11][12][13] TADF is of particular interest as it increases the efficiency of organic light-emitting diodes (OLEDs) used in displays and devices. The TADF process is contingent on the formation of charge-transfer (CT) states, i.e., the spatial redistribution of electron density in the excited state.…”