Anisotropic second-harmonic generation of electric quadrupolar origin in copper phthalocyanine films epitaxially grown by molecular-beam epitaxy

In order to investigate relatively strong second-harmonic generation (SHG) in centrosymmetric molecular films of copper phthalocyanine (CuPc), we have epitaxially grown CuPc films with ${\mathit{D}}_{4\mathit{h}}$ symmetry by the molecular-beam epitaxy technique. SHG exhibits a periodic change while rotating the film about its ${\mathit{C}}_4$ axis. This fact indicates that electric quadrupole and/or electric quadrupole coupling mechanisms significantly contribute to SHG. © 1996 The American Physical Society.