INVESTIGATION OF DIAMONDOID AND FUNCTIONALIZED DIAMONDOID MOLECULES UNDER EXTREME CONDITIONS
We have compressed pure diamondoids: the  tetramantane up to 20 GPa and observed a phase transition at high pressure from powder x-ray diffraction (XRD). Meanwhile, we observed only continuous changes in the CCC bending and CC stretching regions from Raman spectroscopy, suggesting that the carbon framework of the diamondoid molecules remains intact with pressure. The phase transition observed in XRD is probably due to the molecular packing rearrangement.
We also discovered interesting pressure-induced electronic properties changes in newly synthesized functionalized diamondoids, particularly the Ag-adamantane-thiol, from Raman spectroscopy. First, there is an abrupt emergence of photoluminescence when the crystals are compressed to 2-3 GPa, suggesting an indirect to direct band gap transition. Second, the phonon modes begin to diminish, when the crystal is further compressed to 4-5 GPa. Pressure-induced disappearance of the Raman modes has been observed in inorganic strongly-correlated materials, and is associated with insulator-to-metal transitions. In our case this phenomenon happens at much lower pressures, presumably due to the higher compressibility of the organic-inorganic hybrid structure.
This project will be advanced by combining single crystal XRD to unambiguously determine the high pressure structure of  tetramantane and functionalized diamondoid molecules. We will also collaborate with theoreticians to develop a further understanding of this novel material for future energy application.