Realization of H-Type Aggregation in Rubrene-Doped OLEDs and Its Induced Enhancement of Delayed Fluorescence

Abstract

The molecular aggregation effect on the photophysical properties of many organic semiconductors has been well studied, but this behavior of rubrene molecules is still vague in rubrene-doped organic light-emitting diodes. Surprisingly, via recording temperature-dependent electroluminescence and photoluminescence spectra, an intriguing H-type aggregation of rubrene molecules is realized from rubrene-doped devices and films only when 4,4′,4″-tris­(N-3-methyl­phenyl-N-phenyl-amino)­triphenyl­amine (m-MTDATA) or 4,4′,4″-tris­(N-(2-naphthyl)-N-phenyl-amino)­triphenyl­amine (2TNATA) is selected as the host; otherwise, the J-type aggregation of rubrene molecules is solely observed. We propose that this H-type aggregation is caused by the increased steric hindrance between adjacent rubrene molecules because the unique molecular structures of 12 freely rotating chemical bonds in m-MTDATA or 2TNATA are suppressed in rubrene-doped solid-state films. More importantly, we find that the H-type aggregation of rubrene molecules induces a nearly 3-fold increase in the fluorescence of rubrene-doped devices at 20 K. The increased fluorescence can be mainly attributed to the intensified triplet–triplet annihilation (TTA) process because the parallel alignment of transition dipole moments in H-aggregation can facilitate the TTA process via enlarging the TTA reaction cross-section. Thus, our findings deepen the understanding of molecular interactions in aggregation systems and pave the way for achieving highly efficient devices operated especially in a low-temperature environment such as outer space.

Photodynamic-Assisted Electrochemiluminescence Enhancement toward Advanced BODIPY for Precision Diagnosis of Parkinson

“…A series of UV–vis absorption spectra were acquired in the detection system to characterize the optical properties of the BET-[BMIm] complex. As seen in Figure A there emerges a classical conjugated absorption peak at 504 nm for the BET coupled with a shoulder peak at 470 nm (curve b), which corresponds to the H-type aggregation of organic molecules . The absorption peak is red-shifted to 514 nm without any shoulder peak upon attachment of the BET with [BMIm] + (curve a).…”

“…As seen in Figure 2A there emerges a classical conjugated absorption peak at 504 nm for the BET coupled with a shoulder peak at 470 nm (curve b), which corresponds to the H-type aggregation of organic molecules. 34 The absorption peak is red-shifted to 514 nm without any shoulder peak upon attachment of the BET with [BMIm] + (curve a). By contrast, pure [BMIm][BF 4 ] hardly shows any peak in the same wavelength region (curve c).…”

Hybridization of short-range and long-range charge transfer boosts room-temperature phosphorescence performance

“…Due to the planar characteristics of the ICz core, both VTCzNL-Cl and VTCzNL-Br exhibited significant H-aggregation caused by the strong p-p interactions. [36][37][38] The weak intermolecular forces also contributed to the aggregation of adjacent molecules. For VTCzNL-Cl, a C-H/p distance of 2.841 Å was observed, which is benecial for restricting molecular motion.…”

Cation-Stacking Approach Enabling Interconversion between Bis(xanthylium) and Its Reduced Species

“…First, by introducing functional groups and/or side chains into -conjugated molecules with a wide -plane, attractive interaction between molecules can induce aggregation, where the formation of aggregates is more enthalpically favorable in the crystalline state or under conditions of high concentration and low temperature. [24][25][26] Second, by the inclusion of two or more -conjugated molecules in a cage-shaped molecule, molecules are forced to be stacked and interact with each other. [27] Third, by using cyclophanetype structures with two or more linkers, the -planes are forced to be closely arranged and form a faceto-face stacked structure.…”