Optical spectroscopy of PPV-based block copolymers of nanostructured supramolecular organic semiconductor

The third-order nonlinearity of a PPV-based nanostructured supramolecular organic semiconductor (DBAB), with an electron donor (D) connected to an electron acceptor (A) via nonconjugated and flexible bridge (B) units, was investigated in this work at both near-resonant (532 nm) and nonresonant (1064 nm) wavelength by using degenerate four-wave mixing. The second hyperpolarizabilities of D, A, and DBAB at 532 nm were found to be approximately 2.42 x 10(-43) m2/V2, 7.75 x 10(-44) m2/V2, and 1.80 x 10(-43) m2/V2 in copolarization geometry, and approximately 1.59 x 10(-43) m2/V2, 2.59 x 10(-44) m2/V2, and 1.18 x 10(-43) m2/V2 in orthogonal polarization geometry, respectively. The second hyperpolarizabilities of DBAB at 1064 nm were approximately 1.66 x 10(-46) m2/V2 and approximately 8.77 x 10(-47) m2/V2 for parallel and orthogonal polarization cases.