Optical Second Harmonic Generation Spectra in Vacuum-deposited Thin Films of Various Phthalocyanines

Abstract

We have observed fairly strong second-harmonic generation (SHG) in vacuum-deposited thin films of phthalocyanines (Pc) having central metal atoms; Co , Cu , Zn , VO , TiO , Pb , Sn and a metal-free Pc. Based on the remarkable spectral dependences, the SHG was concluded to be due to higher-order mechanisms: in all the films, a resonance peak due to an electric quadrupole transition was observed at the SH wavelength corresponding to the higher-energy side of the Q band. The spectral structures in the molecules with a similar shape are similar to each other, indicating that the electronic states responsible for the spectra are ascribed to Pc macrocycles. The χ(2) values corresponding to [Formula: see text] in C ∞v symmetry and the conventional electric dipole mechanism are in the range of 1.4 ∼ 10 × 10−9 esu for these Pc films.