Structural distinction of zigzag-edge coronoids analyzed by spectroscopies

Unlike armchair-edge coronoids, the band gap of zigzag-edge coronoids (ZCs) can be adjusted via the molecular and cavity sizes. Herein, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy are used to identify 12 structures of ZCs with different molecular and cavity sizes. Evidently, the C1s peak positions of the ZCs depend on the number of carbons (NC) between the inner and outer edges: they shift to a lower and higher binding energy if the ZCs have an even and odd value of NC, respectively, compared with that of structures without a cavity because of the change in band gap. The C1s peak positions of ZCs with NC = 2 and NC = 3–6 differ by more than 0.4 eV. Raman spectroscopic analysis reveals that the detected characteristic modes depend on NC. For structures with NC = 2, C−H vibration and C−C stretching vibration mode bands are observed, whereas for structures with NC = 3–6, C−H vibration and breathing mode bands are observed. In particular, the band originating from the C−H vibration on the inner edge appear in structures with NC = 3–6 and a pore size larger than 8.26 Å. As the molecular size increases, the intensities of the characteristic bands change and the breathing mode band shift to a higher wavenumber. These results indicate that the molecular and cavity sizes of the ZCs can be distinguished using XPS and Raman spectroscopy.