Abstract
By using organic vapor phase deposition method, nickel phthalocyanines (NiPc) nanowires were successfully prepared, and the effects of heating temperature on the structural and optical properties of NiPc nanowires were investigated. Both the crystal structures of NiPc powders and nanowires are studied by x-ray diffraction patterns (XRD) and Fourier transform infrared spectra (FTIR). The lattice constants of NiPc nanowires from the fitting of XRD patterns are a = 13.04 Å, b = 3.75 Å, c = 24.32 Å, β = 94.10°, belonging to the space group of monoclinic (P21/c). X-ray photo-electron spectroscopy (XPS) suggests main peaks at 284.82 eV and 286.18 eV for C-C and C-N bonds and two peaks at 397.8 eV and 398.8 eV for N-C and the N–Ni bonds, respectively, in NiPc nanowires. FTIR spectra show a structural transition from powder to nanowire. The optical properties of NiPc nanowires have been investigated via a comparison between theoretical and experimental approaches. The most significant absorption peaks of NiPc nanowires in the visible region are located at 626 nm and 672 nm, showing a blue shift comparing with the β-NiPc. We have also theoretically revealed the excitation energies in NiPc single molecule and dimer in the form of α and β phases using time-dependent density-functional theory. These theoretical results are in qualitative agreement with the measurements of optical properties. Moreover, no noticeable change in crystalline form is shown when tuning the heating temperature from 420 °C to 450 °C, suggesting a wide synthesis temperature window. The reduced Ni-Ni distance indicated a clear advantage over powder in terms of potential applications in organic electronics.
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