Mähringer Andre, Jakowetz Andreas C, Rotter Julian M, Bohn Bernhard J, Stolarczyk Jacek K, Feldmann Jochen, Bein Thomas, Medina Dana D
Department of Chemistry , Ludwig-Maximilians-Universität (LMU) , Butenandtstr. 11 (E) , 81377 Munich , Germany.
Nanosystems Initiative Munich (NIM) and Center for NanoScience (CeNS) , Schellingstr. 4 , 80799 Munich , Germany.
ACS Nano. 2019 Jun 25;13(6):6711-6719. doi: 10.1021/acsnano.9b01137. Epub 2019 Jun 4.
Two-dimensional triphenylene-based metal-organic frameworks (TP-MOFs) attract significant scientific interest due to their long-range order combined with significant electrical conductivity. The deposition of these structures as oriented films is expected to promote their incorporation into diverse optoelectronic devices. However, to date, a controlled deposition strategy applicable for the different members of this MOF family has not been reported yet. Herein, we present the synthesis of highly oriented thin films of TP-MOFs by vapor-assisted conversion (VAC). We targeted the M-CAT-1 series comprising hexahydroxytriphenylene organic ligands and metal-ions such as Ni, Co, and Cu. These planar organic building blocks are connected in-plane to the metal-ions through a square planar node forming extended sheets which undergo self-organization into defined stacks. Highly oriented thin Ni- and Co-CAT-1 films grown on gold substrates feature a high surface coverage with a uniform film topography and thickness ranging from 180 to 200 nm. The inclusion of acid modulators in the synthesis enabled the growth of films with a preferred orientation on quartz and on conductive substrates such as indium-doped tin oxide (ITO). The van der Pauw measurements performed across the M-CAT-1 films revealed high electrical conductivity values of up to 10 S cm for both the Ni- and Co-CAT-1 films. Films grown on quartz allowed for a detailed photophysical characterization by means of UV-vis, photoluminescence, and transient absorption spectroscopy. The latter revealed the existence of excited states on a nanosecond time scale, sufficiently long to demonstrate a photoinduced charge generation and extraction in Ni-CAT-1 films. This was achieved by fabricating a basic photovoltaic device with an ITO/Ni-CAT-1/Al architecture, thus establishing this MOF as a photoactive material. Our results point to the intriguing capabilities of these conductive M-CAT-1 materials and an additional scope of applications as photoabsorbers enabled through VAC thin-film synthesis.
二维三亚苯基金属有机框架（TP-MOFs）因其长程有序性与显著的导电性相结合而引起了科学界的极大兴趣。将这些结构沉积为取向膜有望促进其融入各种光电器件中。然而，迄今为止，尚未报道适用于该MOF家族不同成员的可控沉积策略。在此，我们展示了通过气相辅助转化（VAC）合成高度取向的TP-MOF薄膜。我们以包含六羟基三亚苯有机配体和金属离子（如Ni、Co和Cu）的M-CAT-1系列为目标。这些平面有机结构单元通过方形平面节点在平面内与金属离子相连，形成延伸的片层，这些片层会自组装成确定的堆叠结构。在金基底上生长的高度取向的薄Ni-CAT-1和Co-CAT-1膜具有高表面覆盖率，膜形貌均匀，厚度在180至200nm之间。在合成过程中加入酸调节剂能够在石英和诸如铟掺杂氧化锡（ITO）等导电基底上生长出具有择优取向的膜。对M-CAT-1膜进行的范德堡测量显示，Ni-CAT-1膜和Co-CAT-1膜的电导率值高达10 S/cm。在石英上生长的膜可以通过紫外可见光谱、光致发光光谱和瞬态吸收光谱进行详细的光物理表征。后者揭示了在纳秒时间尺度上存在激发态，其持续时间足够长，足以证明在Ni-CAT-1膜中发生了光生电荷的产生和提取。这是通过制造具有ITO/Ni-CAT-1/Al结构的基本光伏器件实现的，从而将这种MOF确立为一种光活性材料。我们的结果表明这些导电M-CAT-1材料具有引人入胜的性能，并且通过VAC薄膜合成作为光吸收剂还有额外的应用范围。
