Nanographene‐Based Metal‐Organic Framework Thin Films: Optimized Packing and Efficient Electron‐Hole Separation Yielding Efficient Photodetector

Abstract

Organic semiconductors, specifically polycyclic aromatic chromophores like pentacene, coronene, and nanographenes (hexa‐peri‐hexabenzocoronene, HBC), are often utilized in optoelectronic applications due to their intriguing single‐molecule properties. However, the integration of these aromatic compounds into optoelectronic devices frequently encounters significant obstacles, primarily due to the unpredictable and challenging control over the structure and morphology of their condensed phase. Rather than resorting to chemical modifications or advanced thin‐film manufacturing methods such as chemical vapor deposition, the so‐called metal‐organic framework (MOF) approach is employed to create a highly photoresponsive, nanographene‐based thin film employing a layer‐by‐layer, liquid‐phase epitaxy method. It is demonstrated that the novel Cu‐HBC MOF thin film exhibits excellent photoresponsive behavior under ultraviolet illumination, including a fast response time (˂ 0.02 s) and high current switching ratio (≈104), which significantly outperforms an isostructural MOF Zn‐HBC. Furthermore, it is demonstrated that the metal nodes inside the MOF can be used to enhance the photoresponse by efficient exciton splitting.

Unveiling Energy Transfer Mechanisms in Nanographene-Incorporated Metal–Organic Frameworks

“…In stark contrast, in another nanographene-based MOF with the HBC linker and Cu paddle-wheel, we observed a LMCT process leading to luminescence quenching. 36 Surprisingly, it showed completely different photophysical properties from UMOF-2, which also includes HBC and Cu paddle-wheel. Therefore, we speculate that the spatial configuration of the linker and metal node plays a crucial role in determining photophysical properties and impacts the energy transfer mechanism within MOFs.…”

“…29,30 Metal−organic frameworks (MOFs), a highly designable material platform, could be an ideal candidate for isolating nanographene molecules by preventing the π−π interactions when nanographenes are used as linkers. 31,32 For example, MOFs based on one of the nanographene molecules, hexabenzocoronene (HBC), have been reported with fascinating properties such as electrical conductivity, 33,34 photocatalysis, 35 photodetection, 36 and structural transition. 37 However, research on nanographene-based MOFs is still in its infancy.…”

“…In stark contrast, in another nanographene-based MOF with the HBC linker and Cu paddle-wheel, we observed a LMCT process leading to luminescence quenching . Surprisingly, it showed completely different photophysical properties from UMOF-2, which also includes HBC and Cu paddle-wheel.…”

“…This behavior promotes the nonradiative decay of the excited state, thereby hampering the emission process . Although numerous MOFs containing paramagnetic metal ions have been reported for photocatalysis, − optoelectronics, − and photodetector , applications, investigations into their photophysical properties are extremely rare and limited. , For the development of new MOF systems with enhanced performance, it is essential to understand the fundamental photophysical processes and the correlation between photophysical properties and the underlying topological network. , …”