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Tuning of 2D materials properties through controlled functionalization with opto-electroactive complexes

Periodic Reporting for period 1 - Terpy2DMat (Tuning of 2D materials properties through controlled functionalization with opto-electroactive complexes)

Reporting period: 2017-11-01 to 2019-10-31

Two dimensional (2D) materials are a hot topic in chemistry, physics, materials science or even biology. However, proper functionalization of these ultrathin layers to tune their electronic charge and spin properties beyond current systems is still under development. In this scenario, Terpy2DMat pursued the tailoring of the electronic and optical properties of 2D transition metal dichalcogenides (TMDCs) through the anchoring of electroactive metal complexes. The specific goals of the project were:
1. Developing new protocols for functionalizing the exfoliated TMDCs surfaces with electroactive conjugated molecules
2. Full characterization of the hybrid structures by complementary techniques
3. Integration of the functionalized 2D materials into simple devices to prove their photo-electronic properties and potential technological applications
To reach these goals we focused on the electrostatic functionalization of MoS2 layers (the most representative TMDC) with metallo-terpyridyl complexes.
During the development of the project, electroactive metallic complexes based on terpyridyl ligand (4’-aminophenyl terpyridyl, TPY) have been synthetized. These complexes can be protonated at optimum pH values. Thanks to this property it is possible to functionalize the negatively charged MoS2 ultrathin layers with the TPY complexes. Thus, the formation of the new hybrid material is driven by soft electrostatic forces and the integrity of the components is not compromised. Interestingly, it has been observed that there is a nearly vertical alignment of metallo-terpyridyl complexes on the MoS2 layers. Finally, thanks to the preparation of simple devices, it has been possible to measure optoelectronic properties in solid state and it has been observed that photo-current measurements depend on the nature of the coordinated cation in the metallo-terpyridyl complexes.
The work done in this project can have a significant impact on the domain of two-dimensional transition metal dichalcogenides (2D-TMDCs). We have optimized a process by which one can easily functionalize and modulate opto-electronic properties of chemically exfoliated MoS2 without affecting the MoS2 nor the molecular unit structures. The hybrid structures consisting of MoS2 and redox-active, photo-responsive molecules offer many advantages in designing opto-electronic devices.