Tuning Optical Properties by Controlled Aggregation: Electroluminescence Assisted by Thermally‐Activated Delayed Fluorescence from Thin Films of Crystalline Chromophores

Abstract

Several photophysical properties of chromophores depend crucially on intermolecular interactions. Thermally‐activated delayed fluorescence (TADF) is often influenced by close packing of the chromophore assembly. In this context, the metal‐organic framework (MOF) approach has several advantages: it can be used to steer aggregation such that the orientation within aggregated structures can be predicted using rational approaches. We demonstrate this design concept for a DPA‐TPE (diphenylamine‐tetraphenylethylene) chromophore, which is non‐emissive in its solvated state due to vibrational quenching. Turning this DPA‐TPE into a ditopic linker makes it possible to grow oriented MOF thin films exhibiting pronounced green electroluminescence with low onset voltages. Measurements at different temperatures clearly demonstrate the presence of TADF. Finally, this work reports that the layer‐by‐layer process used for MOF thin film deposition allows the integration of the TADF‐DPA‐TPE in a functioning LED device.

Interplay of structural dynamics and electronic effects in an engineered assembly of pentacene in a metal–organic framework

“…19,20 In the recent years, it has been possible to preconceive OSC arrangements for a large variety of applications, including optoelectronics. [21][22][23][24][25][26] Originally developed for applications in gas storage and separation, MOF-based materials have found interest also with regard to other application elds, based on properties like large electrical conductivities 27 of the order of 10 3 S m À1 , room temperature charge carrier mobility 28 as large as 220 cm 2 V À1 s À1 , and other interesting properties like thermal activated delayed uorescence, 29 emphasizing the emergent nature of MOF-based optoelectronic materials. [30][31][32][33] In the present work, we demonstrate the potential of the MOF-based approach to create structurally-controlled 1D OSCs based on Pn.…”

Crystalline Metal‐Organic Materials with Thermally Activated Delayed Fluorescence

“…[42] For metal-organic polymers, the reported cases mainly concentrate on organic ligand-based TADF emitters. [43] Besides the small ΔE(S 1 -T 1 ), the long-lived and stable triplet states are also crucial for the RISC of excitons for any type of TADF emitters. [18,19] TADF is based on a thermally activated photophysical process that is certainly sensitive to temperature.…”

“…In 2020, Wöll and co-workers reported a TADF-active MOF, Zn-DPA-TPE (Figure 44e), [43] prepared by using a diphenylamine-tetraphenylethylene (DPA-TPE) chromophore featuring aggregation-induced emission (AIE) property and Zn atoms. In consideration of the AIE behavior of DPA-TPE, MOF was selected as an appropriate host structure to support DPA-TPE chromophore for building the TADF emitter.…”

Programmed Molecular Assembly of Abrupt Crystalline Organic/Organic Heterointerfaces Yielding Metal‐Organic Framework Diodes with Large On‐Off Ratios

“…[ 23 ] By a diffuse doping gradient of TCNQ in the film, a diode‐like current rectification was demonstrated. [ 24 ] With respect to electronic applications, field‐effect transistors, [ 25 ] solar cells [ 26 ] and light‐emitting diodes [ 27,28 ] with MOFs as active layer were realized. The efficiency of the presented devices is far from ideal, also due to the poorly‐defined interface between the layers.…”