Optical absorption studies of copper phthalocyanine thin films

The optical absorption of thermally evaporated copper phthalocyanine (CuPc) was studied in the UV-VIS-NIR region. The absorption spectra recorded in the UV-VIS region show two well-defined absorption bands of the phthalocyanine molecules, namely, the Soret (B) and the Q-band. The Q-band shows its characteristic splitting (Davydov splitting) of the main absorption peak in the metal phthalocyanine correlates with the relative tendencies of the metal to out-of-plane bonding. Some of the important spectral characteristics such as the molar extinction coefficient (epsilon(molar)) the oscillator strength (f), the electric dipole strength (q(2)) and absorption half-bandwidth (Delta lambda) of the principle optical transitions were evaluated. The analysis of the spectral behavior of the absorption coefficient a in the absorption region revealed two indirect allowed transitions with corresponding energies 2.95 +/- 0.03 and 1.55 +/- 0.02 eV. The spectra of the infrared absorption allow characterization of vibration modes for the powder, as-deposited material and thin films of CuPc annealed at 423 K for two hours. Discussion of the obtained results and their comparison with the previous published data are also given. (c) 2006 Elsevier Ltd. All rights reserved.