Molecular defect-containing bilayer graphene exhibiting brightened luminescence.

The electronic structure of bilayer graphene can be altered by creating defects in its carbon skeleton. However, the natural defects are generally heterogeneous. On the other hand, rational bottom-up synthesis offers the possibility of building well-defined molecular cutout of defect-containing bilayer graphene, which allows defect-induced modulation with atomic precision. Here, we report the construction of a molecular defect-containing bilayer graphene (MDBG) with an inner cavity by organic synthesis. Single-crystal x-ray diffraction, mass spectrometry, and nuclear magnetic resonance spectroscopy unambiguously characterize the structure of MDBG. Compared with its same-sized, defect-free counterpart, the MDBG exhibits a notable blue shift of optical absorption and emission, as well as a 9.6-fold brightening of its photoluminescence, which demonstrates that a single defect can markedly alter the optical properties of bilayer graphene.

Bowl Inversion in an Exo-type Supramolecule in the Solid State.

Bowl inversion is a unique property of buckybowls. The polarity and assembly configuration of buckybowls are reversed after bowl inversion. So far, this unique phenomenon has been studied in solution and on surface, but not in solid state due to spatial constraint. Now a series of exo-type supramolecular assemblies of trithiasumanene and nanographene are investigated. Tuning the electron density of the nanogaphene component was found to directly affect the binding constant of the complex. Reversible bowl inversion in the solid state was then successfully achieved by subjecting the trithiasumanene-nanographene assembly with the weakest binding strength to repeated heating-cooling cycles, which was unambiguously observed by single crystal X-ray diffraction.

Molecular bilayer graphene.

Bilayer graphene consists of two stacked graphene layers bound together by van der Waals interaction. As the molecular analog of bilayer graphene, molecular bilayer graphene (MBLG) can offer useful insights into the structural and functional properties of bilayer graphene. However, synthesis of MBLG, which requires discrete assembly of two graphene fragments, has proved to be challenging. Here, we show the synthesis and characterization of two structurally well-defined MBLGs, both consisting of two π-π stacked nanographene sheets. We find they have excellent stability against variation of concentration, temperature and solvents. The MBLGs show sharp absorption and emission peaks, and further time-resolved spectroscopic studies reveal drastically different lifetimes for the bright and dark Davydov states in these MBLGs.