Identification of two-photon states in phthalocyanines by third harmonic generation spectroscopy

The dispersive behaviour of the magnitude and phase of χ3(−3ω; ω, ω, ω) of sublimated metal-free (PcH2) and copper phthalocyanine (PcCu) thin films has been investigated via third harmonic generation (THG) spectroscopy in the range of 950 to 2000 nm. A two-photon state placed at around 500 nm, between the two one-photon allowed levels, has been identified and correlated with transitions from the au to the b1u∗ levels. In PcCu an additional two-photon state located at the lower energy side of the Q band, likely associated with a d-d transition, has also been inferred from the spectrum.