Vibrational and Electronic Properties of Functionalized Diamondoids
Final Report Abstract
Diamondoids are well-defined, sp3-hybridized carbon nanostructures with promising properties for electronic, optical, and biological applications. Controlled modifications of diamondoids, e.g., by chemical functionalization, allow to tailor their properties according to the requirements of the applications. For example, the optical transition energy of around 6 eV may be decreased towards the visible range by covalent functionalization or by introduction of so-called sp2 defects, C=C double bonds. The overall aim of this project was to contribute to the understanding of the effects of modifications on the optical and electronic properties of diamondoids. The investigated diamondoids comprised chemically functionalized diamondoids and diamondoid oligomers containing carbon single or double bonds. By resonance Raman spectroscopy into the UV range, we addressed the structural and optical properties of modified diamondoids; density-functional theory computations of the electronic structure and vibrational modes supported the interpretation of the experimental results. In this project, we have shown that based on Raman spectroscopy the type and position of a functional group on small diamondoids can be identified. Furthermore, we have observed the selective enhancement of C=C stretch modes in diamondoid oligomers with carbon double bonds when the excitation energy is in resonance with the π-π* transition located at the double bond. This resonance allowed the observation of the vibrational frequency in the excited state, in agreement with theoretical predictions. More general, we have addressed the potentially different properties of modified diamondoids forming molecular crystals vs. their properties as isolated molecules (e.g. in the gas phase). The high-energy vibrational modes of diamondoids are in general less affected by the vander-Waals interaction in the crystals, whereas the electronic band gap is significantly reduced. In the low-frequency range, however, new crystal-specific modes appear which are attributed to intermolecular vibrations.
Publications
- Experimental and theoretical Raman analysis of functionalized diamondoids, J. Phys. B 46, 025101, 2013
R. Meinke, R. Richter, T. Möller, B.A. Tkachenko, P.R. Schreiner, C. Thomsen, and J. Maultzsch
(See online at https://doi.org/10.1088/0953-4075/46/2/025101) - UV resonance Raman analysis of trishomocubane and diamondoid dimers, J. Chem. Phys. 140, 034309, 2014
R. Meinke, R. Richter, A. Merli, A.A. Fokin, T.V. Koso, V.N. Rodionov, P.R. Schreiner, C. Thomsen, and J. Maultzsch
(See online at https://doi.org/10.1063/1.4861758) - Beyond double-resonant Raman scattering: Ultraviolet Raman spectroscopy on graphene, graphite, and carbon nanotubes, Phys. Rev. B (Rapid Comm.), 92, 041401(R) 2015
C. Tyborski, F. Herziger, R. Gillen, and J. Maultzsch
(See online at https://doi.org/10.1103/PhysRevB.92.041401) - Raman spectroscopy of nondispersive intermediate frequency modes and their overtones in carbon nanotubes, phys. stat. stol. (b) 252, 2551, 2015
C. Tyborski, F. Herziger, and J. Maultzsch
(See online at https://doi.org/10.1002/pssb.201552513) - Electronic and vibrational properties of diamondoid oligomers. J. Phys. Chem. 2017
C. Tyborski, R. Gillen, A.A. Fokin, T.V. Koso, H. Hausmann, N.A. Fokina, V.N. Rodionov, P.R. Schreiner, C. Thomsen, J. Maultzsch
(See online at https://doi.org/10.1021/acs.jpcc.7b07666) - From isolated molecules to a van-der-Waals crystal: A theoretical and experimental analysis of a trishomocubane and a diamantane dimer in the gas and solid phase, J. Chem. Phys. 147, 044303, 2017
C. Tyborski, R. Meinke, R. Gillen, T. Bischoff, A. Knecht, T. Rander, R. Richter, A. Merli, A.A. Fokin, T.V. Koso, V.N. Rodionov, P. R. Schreiner, T. Möller, C. Thomsen, and J. Maultzsch
(See online at https://doi.org/10.1063/1.4994898)
