Ultrathin films of 2-ferrocenyl-1,3-dithiolane and 2-ferrocenyl-1,3-dithiane (Fcs), which are chemically inert at ambient conditions, are studied on the basal plane of highly oriented pyrolytic graphite (HOPG) using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Films are prepared by drop-casting using Fcs dissolved in different solvents. Films prepared from methanol and dichloromethane show structural polymorphs on HOPG, while those prepared from ethanol, acetone, and dimethylformamide show an exclusive selection of one of the polymorphs. The selection of growth patterns of Fcs shows interesting correlation to the bulk solubility of molecules in the corresponding solvents and the solvent boiling point. The growth of Fcs at the submonolayer coverage is templated by the surface symmetry, and the molecular level packing on the surface is understood using high-resolution AFM, STM, and the bulk crystal packing of the molecules.
Cesium lead halide (CsPbX3) perovskites, having stood out for solar cell applications, are now garnering attention in the field of photocatalysis as well. With a fundamental challenge in photocatalysis of...
The ultrathin films of 2-ferrocenyl-1,3-dithiolane (FcS 2 C 3 ) and 2-ferrocenyl-1,3-dithiane (FcS 2 C 4 ) dropcasted from toluene on highly oriented pyrolytic graphite (HOPG) surface are investigated using atomic force microscopy (AFM). Two types of growth polymorphs have been observed, which are distinctly different based on their nature of growth and the molecular level packing. We have developed a new type of temperature-dependent desorption experiment named "microscopic thermal desorption analysis" (MTDA) for understanding the adsorption energetics related to the observed growth polymorphs on the surface. Using MTDA, we have calculated the adsorption energies of growth polymorphs of both molecules and further revealed that their formation requires an activation energy. The subtle relation between the adsorption energies and activation energies of growth polymorphs account for their average abundance on the surface. The experimental observations are further supported by density functional theory (DFT) calculations.
Efficient charge extraction in lead halide perovskite
nanocrystals
is frequently sought-after and probed using various probe molecules.
Often ignored, the chemical bonding of the molecules to the perovskite’s
surface, as dictated by the terminal anchoring functional group, can
have implications on the excited-state interactions between perovskite
nanocrystals and the charge-shuttling molecules. Considering the remarkability
of the recent work on ferrocene-based molecules in allowing charge
transfer in perovskite nanocrystals, we have employed ferrocene molecule
functionalized with various functional groups to understand the binding
and charge-transfer process at the interface of the perovskite nanocrystal
and the redox relay molecule. We evidenced that the charge transfer
enhanced with enhancement in binding, as validated by the association
constant evaluated as high as 1.71 × 107 M–1. In particular, the −COOH and −NMe2 functional
groups led to the efficient quenching of photoluminescence (PL) emission
and a decrease in photoluminescence lifetime than the other functional
group analogues, showing their feasibility in charge transfer studies.
More importantly, the −NMe2 functional group indicated
passivation of the defects on the perovskite surface, attributed to
the interaction between the lone pair of nitrogen and the undercoordinated
surface Pb2+ cations. This was also evident in the transient
absorption spectra, where the excited-state interaction could be analyzed
better. This work opens avenues for exploring anchoring moieties in
facilitating charge transfer across the perovskite interface, thus
impacting its photocatalytic applications.
Funding information Visveswaraya PhD SchemeA new class of ferrocenyl surfactants based on covalent linkage between amino acids or peptides and ferrocene was designed. Accordingly, five ferrocenyl amphiphiles, FcS1-5, were synthesized, and their aggregation behaviors in aqueous solutions were studied. Compared to the other surfactants containing ferrocenyl units, FcS have a relatively smaller size and low molecular weight and are easy to synthesize. The influences of the number of carboxylic acid head groups and the number of Fc group in the hydrophobic tail, on the stability and aggregation behavior of these amphiphiles in aqueous medium, were explored to deduce the structure property relationships. A combination of fluorescence and dynamic light scattering techniques was used to elucidate the behavior of these molecules. A good agreement between the results obtained using different techniques was observed.
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