From Isolated Diamondoids To A Van-Der-Waals Crystal: A Theoretical And Experimental Analysis Of A Trishomocubane And A Diamantane Dimer In The Gas And Solid Phase

The electronic properties of sp(2)/sp(3) diamondoids in the crystalline state and in the gas phase are presented. Apparent differences in electronic properties experimentally observed by resonance Raman spectroscopy in the crystalline/gas phase and absorption measurements in the gas phase were investigated by density functional theory computations. Due to a reorganization of the molecular orbitals in the crystalline phase, the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy gaps are lowered significantly by 0.5 eV-1 eV. The pi -> pi(*) transition is responsible for large absorption in both gas and crystalline phases. It further causes a large increase in the Raman intensity of the C=C stretch vibration when excited resonantly. By resonance Raman spectroscopy we were able to determine the C=C bond length of the trishomocubane dimer to exhibit 1.33 angstrom in the ground and 1.41 angstrom in the excited state.