Nonlinear optical anisotropy and molecular orientational distribution in poly(p-phenylene benzobisthiazole) Langmuir–Blodgett films

Abstract

Xray reflectivity study of behenic acid Langmuir-Blodgett mono and multilayers on SiO2 surfaces asdeposited and after thermal treatment: Influence of substrate/film interactions on molecular ordering and film topology Poling dynamics and investigation into the behavior of trapped charge in poled polymer films for nonlinear optical applicationsThe orientational distribution and packing of polymer chains were investigated in poly͑p-phenylene benzobisthiazole͒ ͑PBT͒ Langmuir-Blodgett ͑LB͒ films by nonresonant third-harmonic generation measurement at a wavelength of 1907 nm. The tensor components of the third-harmonic susceptibility on the PBT LB film with a surface pressure of 50 mN/m were determined to be XXXXThe large nonlinear optical anisotropy can be explained as a result of highly oriented packing of the polymer chains induced by a flow orientation. A Gaussian distribution function with a standard deviation of ϭ0.40 gives a practical description of the orientational distribution of PBT polymer chains. A maximum ͑3͒ value of ͑26.8Ϯ4.4͒ϫ10 Ϫ12 esu is predicted assuming a perfect alignment of polymer chains. The XXXX (3) value increased by factor of 2 with the surface pressure from 30 to 50 mN/m mainly due to the packing density of the polymer chains, while the orientational degree did not change.

Rigid‐Rod Polymers

“…For PBZT, χ (3) xxxx is (6.0-83) × 10 − 12 e.s.u. The anisotropy of χ (3) is observed in biaxially oriented PBZT films, yielding values of χ (3) yyyy from 1.5 × 10 − 12 to 2 × 10 − 12 e.s.u., and χ (3) xxyy , 0.9 ×1 0 − 12 e. s.u (319,327,(329)(330)(331)(332). For PBO, the nonresonant χ (3) is (8.1-70) × 10 − 12 e.s.u.…”

A further exploitation of the attenuated-total-reflection technique to measure the complex second hyperpolarizability for the quadratic electro-optic effect of a linear conjugated polymer

“…zzzz,r(im) is the real (imaginary) part of the complex third-order nonlinear susceptibility zzzz ; E is the applied electric field; f = (n 2 + 2)/3 and f 0 = ε(0)(n 2 + 2)/[n 2 + 2ε(0)] are the local-field factors at optical frequency and in the presence of static or low-frequency electric field, respectively, where ε(0) = 2.702 is the static dielectric constant of PDAO-PPF; a zz is the transformation matrix element between molecular and laboratory coordinates; the angle brackets denote the orientational average over the molecules, and a 4 zz is 0.2 for linear conjugated polymer whose molecular chains are randomly oriented [9]; γ r(im) is the real (imaginary) part of second hyperpolarizability γ for the QEO effect.…”