Work function engineering of two-dimensional (2D) materials by application of polymer coatings represents a research thrust that promises to enhance the performance of electronic devices. While polymer zwitterions have been demonstrated to significantly modify the work function of both metal electrodes and 2D materials due to their dipole-rich structure, the impact of zwitterion chemical structure on work function modulation is not well understood. To address this knowledge gap, we synthesized a series of sulfobetaine-based zwitterionic random copolymers with variable substituents and used them in lithographic patterning for the preparation of negative-tone resists (i.e., "zwitterists") on monolayer graphene. Ultraviolet photoelectron spectroscopy indicated a significant work function reduction, as high as 1.5 eV, induced by all polymer zwitterions when applied as ultrathin films (<10 nm) on monolayer graphene. Of the polymers studied, the piperidinyl-substituted version, produced the largest dipole normal to the graphene sheet, thereby inducing the maximum work function reduction. Density functional theory calculations probed the influence of zwitterion composition on dipole orientation, while lithographic patterning allowed for evaluation of surface potential contrast via Kelvin probe force microscopy. Overall, this polymer "zwitterist" design holds promise for fine-tuning 2D materials electronics with spatial control based on the chemistry of the polymer coating and the dimensions of the lithographic patterning.

The photophysics of 5,6-dihydroxyindole (DHI) following excitation to its lowest two optically bright states was investigated using the complete active space self-consistent field method with second-order perturbative energy corrections. There is a barrierless pathway for the molecule to relax from the second-lowest bright state (2ππ*) to the lowest bright state (1ππ*). The 1ππ* state has a conical intersection with the optically dark 1πσ* state, which further intersects with the ground state along the NH and OH stretching coordinates. Moreover, the 1ππ* has out-of-plane conical intersections with the ground state. For accessing the conical intersections with the ground state, there are energy barriers, which are higher than the available energy following vertical excitation to the lowest bright state. The nature of the calculated deactivation pathways helps interpret the experimentally estimated lifetimes of the lowest two bright states of DHI. The relatively long lifetime of the lowest excited state suggests that isolated DHI in monomeric form cannot rationalize the ultrafast deactivation property of eumelanin.

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Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS 2 ), are of significant current interest as inexpensive, earth-abundant catalysts for reactions such as electrochemical hydrogen evolution and CO 2 reduction. While several high-throughput studies have focused on understanding the relative activities of various TMDs, including their multiple phases, the role of support effects on modulating adsorbate−TMD interactions is less well studied. Here, focusing on MoS 2 as a model TMD, we employ density functional theory calculations to understand the interactions of monolayers of 2H, 1T, and 1T′ phases of MoS 2 with three transition-metal (TM) supports: Au, Ag, and Cu. In particular, we study the interfacial energetics and charge-transfer interactions at monolayer MoS 2 /TM interfaces, and we correlate these with the energetic stabilization of the metastable 1T and T′ phases. We also examine the role of Cu supports in modulating the interaction of the supported monolayers with adsorbates such as H and CO, whose adsorption free energies can be considered as descriptors for hydrogen evolution and CO 2 reduction reactions. While pristine basal planes of MoS 2 are relatively unaffected by supports, vacancy defects, well-known active sites in the MoS 2 basal plane, can be profoundly affected to the extent that catalyst poisoning becomes a distinct possibility. Our studies demonstrate that support effects ought to be taken into consideration when screening 2D TMD catalysts, especially in the presence of strong charge-transfer interactions as might be expected at interfaces between electrodes and TMD catalysts.

The design, synthesis and fluoride sensing ability of a 7-nitro-2,1,3-benzoxadiazole (NBD) based chemodosimeter is reported. Theoretical calculations were used to design a more applicable off-on response, by choosing NBD as the accurate fluorophore. Reaction of the NBD-probe with 300 equivalents of tetrabutyl ammonium fluoride (TBAF) exhibited a response time of 80 minutes and the reaction was selective to F(-) and sensing of the ion was marked by a 110-fold enhancement of green fluorescence. The off-on fluorescence characteristics of the probe enabled its application in live-cell imaging of intracellular F(-) ions.