Structure and nonlinear optical properties of copper phthalocyanine thin films

Abstract

This paper describes a joint study of the structure and nonlinear optical properties of vacuum evaporated thin films of copper phthalocyanine (CuPc for brevity). Film thickness ranges from 50 to 500 nm. The anisotropic paramagnetic resonance of Cu++ ions reveals that the Pc rings lie almost parallel to the substrate plane with however a large angular distribution (30° FWHM). Third harmonic optical generation measurements performed at 1.064 μm and 1.907 μm fundamental wavelengths give respectively an average value of the cubic susceptibility 〈χ(3)(-3ωω,ωω)〉=(4±0.4)·10−12 e.s.u. and (2.1+-0.2) · 10-12 These values, although significantly higher than for a common ionic crystal, are about one order of magnitude lower than in conjugated 1-D systems, which shows that the 2-D π-electron delocalization is less profitable than the 1-D one. Besides third harmonic, we have also observed second harmonic generation. Its polarization dependence is characteristic of a quadratic susceptibility enhanced in one direction, almost perpendicular to the substrate, withdeff comprised between 30 and 60 · 10-9 e.s.u. The possible origins ofdeff are discussed.