Probing the Strong Near-IR Two-Photon Transition in Supramolecular Triphenylamine-based Polymers by Nonlinear Absorption Spectroscopy

Abstract

Due to their capability of film formation and remarkable optical features, semiconductor polymers with high two-photon absorption (2PA) have been studied as potential candidates for the development of organic photonic platforms. Furthermore, there is a high demand for photonic devices operating in the near-infrared (IR) region. However, the magnitude of the nonlinear optical response of random coil polymers in the IR region is weak due to the loss of molecular structure caused by increasing the π-conjugated backbone. Thus, herein we aim to investigate the molecular structure and 2PA features relationship for four polymers with supramolecular (helical) rodlike structure. Such polymers have a rigid core based on triphenylamine groups connected to the chiral binaphthalene units and a strong electron-withdrawing group (EWG). This kind of structure allows a very high chromophore density, which was responsible for generating 2PA cross-section between 305 GM and 565 GM in the near-IR (900–1300 nm), depending on the EWG strength. in light of the two-level model within the sum-overstates approach, we estimated the degree of intramolecular charge transfer induced by 2PA in the IR region, and values as high as 50–70% were found. Such a critical outcome allows the 2PA cross-section in the IR region to remain high even though the ratio between the visible/IR-band 2PA cross-section increases as a function of EWG strength.