Eumelanin Adsorption on Silicon: Optical Properties of Si(001)-Adsorbed Eumelanin Tetrameric Protomolecules

Abstract

We predict the optical properties -in particular optical absorbance and Reflectance Anisotropy Spectra (RAS) -of the silicon(001) surface organically functionalized by the adsorption of chosen tetrameric eumelanin protomolecules. These Si(001):tetramer systems can be considered as models of hybrid (porous) silicon-eumelanin interfaces, a system with potential applications in photovoltaics. In spite of a weak effect of tetramer adsorption on Si(001) overall absorption spectra, first-principles results based on plane wave density functional theory allowed us to identify specific regions, in the interesting IR and visible range, where the adsorbed molecules yield large enhancements in surface absorbance, and the appearance of new RAS features.

First-Principles Investigation of the Optical Properties of Eumelanin Protomolecules

“…We checked the basis set convergence by adopting the Aug-cc-pVTZ (augmented, polarized triple-ζ) basis set, but it turned out that the Aug-cc-pVDZ basis already provides a very good agreement with experiments. We would like to point out that, in previous calculations on other molecular systems carried by some of us, ,− it had been found that using the B3LYP XC functional , and the 6–31+G*basis set was sufficient to obtain relaxed structures in good agreement with the corresponding experimental data, in particular for the eumelanin related precursors (DHI) and protomolecules. ,, In contrast, we find here that for systems like the tetrameric molecules of eumelanin such a level of theory (in terms of XC functional and basis set) leads to rather unsatisfactory results.…”

Silver Nanocatalysts Supported by Multiple Melanin Carriers with a Photothermal Effect for Reduction of Methylene Blue and 4-Nitrophenol

“…Even though the precise molecular makeup of SE is still being investigated, 42 the literature reports that it is abundant in functional groups such as −NH and −OH. 43 As shown in Figure 2A, natural SE and synthetic Ag/SE present a similar absorption spectrum with characteristic absorption peaks: the broad peak of 600−800 cm −1 contributes to the aromatic ring and has been replaced to form a conjugated system; the absorbing band at 1350−1690 cm −1 is mainly formed by the superposition of symmetric stretching modes of C�O, asymmetric stretching modes of C�O, C−OH stretching modes, 44 and peaks of organic groups such as C� C and C�N (the narrow peak at 1400 cm −1 is caused by a symmetric stretching of C�O in COOH, the large peak at 1617 cm −1 is caused by the C�C in-plane vibration in pyrrole and C�O stretching in quinone and partly asymmetric stretching modes in COOH); 44 the broad absorption band of 3100−3400 cm −1 is composed of −OH vibration (3169 cm −1 ) and −NH (3376 cm −1 ) in indole or pyrrole. 45 In general, since the loading of Ag NPs on the SE surface leads to some masking effect and connection of the active groups on the SE interface, the absorption peak intensity of Ag/SE is weaker than that of SE.…”

Ab Initio Spectroscopic Investigation of Pharmacologically Relevant Chiral Molecules: The Cases of Avibactam, Cephems, and Idelalisib as Benchmarks for Antibiotics and Anticancer Drugs

“…At a difference with classical MD, ab initio techniques allow the explicit treatment of the system's electronic properties and their effect on spectroscopic features. Within this framework, the optical properties of several both biologically and technologically important molecules, and their dependence on conformational details, chemical substitutions, solvation, and adsorption on surfaces were investigated by some of us in recent years [13,[18][19][20][21][22][23][24][25][26].…”