Spectral dependence of nonlinear absorption and refraction in terthiophene-based organic semiconductors

Abstract We present results related to the determination of third-order nonlinear optical (NLO) properties of three organic semiconductors (OSCs) with a π -conjugated terthiophene (3Th) core and symmetrically or asymmetrically end-capped with specific terminals. The spectral dependences of the real and imaginary part of the cubic hyperpolarizability γ were obtained from Z-scan studies in the 600–1200 nm range. The 3Th-based OSCs show only moderate nonlinear absorption at twice the wavelength of the main one-photon absorption peaks (∼750 nm) but appreciable two-photon absorption cross sections ( σ 2 ≈ 120 GM) close to 600 nm.