Electronic and Vibrational Properties of Diamondoid Oligomers

Abstract

We analyzed the vibrational and electronic properties of diamondoid oligomers via resonance Raman spectroscopy. The compounds consist of lower diamondoids such as adamantane or diamantane that are interconnected with double bonds. Therefore, all oligomers have ethylene-like centers strongly influencing the character of the optical transitions. The double bond localizes the HOMO (highest occupied moluecular orbital) in between the diamondoids accompanied by a significant decrease of optical transition energies. Comparing Raman spectra of the compounds to pristine diamondoids, we find several characteristic modes originating from the ethylene moieties. Supported by DFT (density functional theory) computations, we attribute these modes to highly localized vibrations that can partially be derived from the vibrational modes of parent ethylene. We further observe two new Raman modes in the compounds: a dimer breathing mode and a rotational mode of the entire ethylene moieties.

Phonon dispersion of MoS$_2$

“…Long-range non-covalent interactions in both groundstate and phonon calculations were included through the semi-empirical DFT-D3 correction with Becke-Johnson damping [36] that we added on top of the PBE exchange-correlation. We used a set of parameters for the D3 corrections that was fitted to successfully reproduce the experimental lattice constants of a wide variety of layered and bulk materials [21,45,46]. A more detailed description of the experimental and theoretical methods can be found in the supplementary material.…”

Vibrational signatures of diamondoid dimers with large intramolecular London dispersion interactions

“…4) does not show any modes both in the computations and experiments, clearly indicating that the discussed modes are structure induced. The ring-like compounds 11 and 12 do not exhibit a clear DBM or other dimer modes but rather show ring-like breathing modes 24 .…”

“…4. 24 Rotational modes are vibrations in which the whole monomers rotate with respect to each other around the interconnecting carbon-carbon bond. In the computations we find one rotational mode for each direct dimer, i.e., for compounds 5-9.…”

“…Dimer modes with the largest frequencies are the dimer breathing modes (DBM). In double-bond interconnected diamondoid dimers, the DBM has an inverse dependence on the sizes of the compounds 24 . We can follow the same trend for the single-bond dimers both in the experiments and computations, as shown in Fig.…”

Nanotechnology of diamondoids for the fabrication of nanostructured systems

“…By investigating the C-C-C bending or C-C stretching mode in the low-frequency region of the spectra, differentiation of the geometric properties of diamondoids has become possible and more assessable. The distinctive vibration modes also provide the necessary knowledge for further exploring the vibrational properties of different diamondoid derivatives [57,[72][73][74] and dimers [75,76].…”