Experimental evidence derived from a comprehensive study of a self-assembled organosilane multilayer film system undergoing a process of postassembly chemical modification that affects interlayer-located polar groups of the constituent molecules while preserving its overall molecular architecture allows a quantitative evaluation of both the degree of intralayer polymerization and that of interlayer covalent bonding of the silane headgroups in a highly ordered layer assembly of this type. The investigated system consists of a layer-by-layer assembled multilayer of a bifunctional n-alkyl silane with terminal alcohol group that is in situ converted, via a wet chemical oxidation process conducted on the entire multilayer, to the corresponding carboxylic acid function. A combined chemical-structural analysis of data furnished by four different techniques, Fourier transform infrared spectroscopy (FTIR), synchrotron X-ray scattering, X-ray photoelectron spectroscopy (XPS), and contact angle measurements, demonstrates that the highly ordered 3D molecular arrangement of the initial alcohol-silane multilayer stack is well preserved upon virtually quantitative conversion of the alcohol to carboxylic acid and the concomitant irreversible cleavage of interlayer covalent bonds. Thus, the correlation of quantitative chemical and structural data obtained from such unreacted and fully reacted film samples offers an unprecedented experimental framework within which it becomes possible to differentiate between intralayer and interlayer covalent bonding. In addition, the use of a sufficiently thick multilayer effectively eliminates the interfering contributions of the underlying silicon oxide substrate to both the X-ray scattering and XPS data. The present findings contribute a firm experimental basis to the elucidation of the self-assembly mechanism, the molecular organization, and the modes and dynamics of intra- and interlayer bonding prevailing in highly ordered organosilane films; with further implications for the rational exploitation of some of the unique options such supramolecular surface entities can offer in the advancement of a chemical nanofabrication methodology.

2D covalent organic frameworks (COFs) could have well-defined arrangements of photo-and electro-active units that serve as electron or hole transport channelsf or solar energy harvesting and conversion, but their insufficient charge transfer and rapid charge recombination impede the sunlightdriven photocatalytic performance.W er eport an ew donoracceptor (D-A) system, PyTz-COF that was constructed from the electron-rich pyrene (Py) and electron-deficient thiazolo-[5,4-d]thiazole (Tz). With its bicontinuous heterojunction, PyTz-COF demonstrated exceptional optoelectronic properties,p hotocatalytic ability in superoxide anion radical-mediated coupling of (arylmethyl)amines and photoelectrochemical activity in sunlight-driven hydrogen evolution. Remarkably, PyTz-COF exhibited ap hotocurrent up to 100 mAcm À2 at 0.2 Vv s. RHE and could reach ah ydrogen evolution rate of 2072.4 mmol g À1 h À1 .T his work is paving the wayf or reticular design of highly efficient and highly active D-A systems for solar energy harvesting and conversion.

The structure of a series of alcohol-terminated bifunctional long-tail organosilane films with varying numbers of superimposed monolayers (between 1 and 11), prepared on smooth, hydrophilic silicon substrates by the layer-by-layer self-assembly approach, has been investigated with the purpose of elucidating details of the molecular organization and the intra-and interlayer modes of binding in such films. To this end, experimental results obtained by synchrotron X-ray scattering, micro-Raman, and Fourier transform infrared (FTIR) spectroscopic techniques have been combined and compared. A comprehensive analysis of all data demonstrates that the studied multilayer films consist of stacks of uncorrelated discrete monolayers, the inner molecular order of which is preserved with the growing total number of superimposed layers. Similar to self-assembled films of long-tail silanes with terminal -COOH groups, 1 the intermolecular binding in the present films is characterized by partial intra-and interlayer covalent bond formation. The molecular hydrocarbon tails are perpendicularly oriented on the layer planes, forming a densely packed rotator phase like hexagonal lattice with a molecular surface area of ∼20 Å 2 and a lateral correlation length of the order of 16 molecular diameters.