Linear and Nonlinear Optical Properties of All-cis and All-trans Poly(p-phenylenevinylene)

Abstract

Poly(p-phenylenevinylene) (PPV) is a staple of the family of conjugated polymers with desirable optoelectronic properties for applications including light-emitting diodes (LEDs) and photovoltaic devices. Although the significant impact of olefin geometry on the steady-state optical properties of PPVs has been extensively studied, PPVs with precise stereochemistry have yet to be investigated using nonlinear optical spectroscopy for quantum sensing, as well as light harvesting for biological applications. Herein, we report our investigation of the influence of olefin stereochemistry on both linear and nonlinear optical properties through the synthesis of all-cis and all-trans PPV copolymers. We performed two-photon absorption (TPA) using a classical and entangled light source and compared both classical TPA and entangled two-photon absorption (ETPA) cross sections of these stereodefined PPVs. Whereas the TPA cross section of the all-trans PPV was expectedly higher than that of all-cis PPV, presumably because of the larger transition dipole moment, the opposite trend was measured via ETPA, with the all-cis PPV exhibiting the highest ETPA cross section. DFT calculations suggest that this difference might stem from the interaction of entangled photons with lower-lying electronic states in the all-cis PPV variant. Additionally, we explored the photoinduced processes for both cis and trans PPVs through time-resolved fluorescence upconversion and femtosecond transient absorption techniques. This study revealed that the sensitivity of PPVs in two-photon absorption varies with classical versus quantum light and can be modulated through the control of the geometry of the repeating alkenes, which is a key stepping stone toward their use in quantum sensing, bioimaging, and the design of polymer-based light-harvesting systems.

Enhanced Exciton Coherence Time and Correlation with Probability of Absorption of Classical and Entangled Light in Quantum-Confined Systems

“…There has been a large need of molecules for nonlinear optical materials that can be used with low-intensity lasers, image processing, high coherent time, etc. − Organic materials have attracted much attention due to their good nonlinear optical properties. − Scientists are interested in organic materials because they show many applications in various fields such as optical electronic devices , and sensors , . One of the important categories of organic materials is organic dyes due to their high photospectral properties. − Organic dyes such as the family of rhodamine dyes, , DTP-TD, and coumarin are the most explored dyes for their nonlinear optical properties and have been used in optical devices. , Among all the dyes, rhodamine-B (Rh-B) (C 28 H 31 ClN 2 O 3 ) has attracted considerable attention due to its spectral properties , such as high absorption cross-sections, high fluorescence quantum efficiencies, − and high photostability in the visible range.…”