Zhonghua Peng

Conjugated photorefractive polymer

A novel type of photorefractive polymer, containing a conjugated backbone and a second order nonlinear optical chromophore, has been developed. It was expected that the conjugated backbone would absorb photons in the visible region and play the triple role of charge generator, charge transporter, and backbone. Several physical measurements demonstrated this expectation. Two beam coupling experiments clearly indicated an asymmetric optical energy exchange between two beams without applying an external electrical field. This is a conclusive signature for photorefractivity. Also, large optical gain, 5.7 cm−1, was observed under zero‐field condition.

Hybridized approach to new polymers exhibiting large photorefractivity

We report on a new photorefractive polymer that contains an ionic tri(bispyridyl) ruthenium complex as the charge generating species, a conjugated polymer backbone as the charge transporting channel, and a nonlinear optical chromophore. The ruthenium complex was introduced to utilize its efficient photoinduced metal‐to‐ligand charge transfer process. This polymer shows greatly enhanced photorefractive performance; a large net optical gain of about 200 cm−1 was obtained at a zero external electric field.

NEW PHOTOREFRACTIVE POLYMER BASED ON MULTIFUNCTIONAL POLYURETHANE

A new photorefractive polymer containing a photocarrier generator, a hole transporting compound, and a nonlinear optical chromophore covalently linked to the polymer backbone has been synthesized. Two‐beam coupling experiments have clearly demonstrated asymmetric energy exchange under zero‐field condition, a sign for photorefractivity and a maximum optical gain of 0.88 cm−1 was measured. Although it is not a net gain, the result reported here demonstrates the feasibility of rational designs of photorefractive polymers.

Novel porphyrin containing photorefractive polymers

Several novel photorefractive polymers based on the charge transfer properties in photosynthetic model compounds were synthesized. These polymers contain a prophyrin moiety, a second order nonlinear optical chromophore covalently linked to a polyimide backbone. High thermal stability of the second order nonlinear effect were observed at elevated temperatures. An asymmetric optical energy exchange was detected in two beam coupling experiments, indicating the photorefractive nature of the polymers. Large optical gains were deduced at zero-external electric filed (20 cm-1).

Novel photorefractive polymers: structure, design, and property characterization

To manifest a photorefractive effect, the polymer must possess a photocharge generator, a charge transporter, a charge trapping center and a nonlinear optical chromophore. We have synthesized two types of novel photorefractive (PR) polymers. The type I PR polymers contain the NLO chromophore, the charge generator and the transporting compound covalently linked to the polymer backbone. The type II photorefractive polymers contain a conjugated backbone and a second order NLO chromophore. The design idea behind the structure of the type II polymers is the expectation that they will possess photorefractivity. Since the conjugated backbone absorbs photons in the visible region and is photoconductive, it is expected to play the triple roles of charge generator, charge transporter and backbone. Thus, the four functionalities necessary to manifest the PR effect will exist simultaneously in a single polymer.

Rational designs of multifunctional polymers - conjugated photorefractive polymers

A novel type of photorefractive polymers, containing a conjugated backbone and a second order NLO chromophore, has been developed. A new polymerization method based on the Stille coupling reaction was explored to synthesize these materials. It was expected that the conjugated backbone would absorb photons in the visible region and play the triple role of charge generator, charge transporter and backbone. Several physical measurements demonstrated this expectation. Two beam coupling experiments clearly indicated an asymmetric optical energy exchange between two beams without applying an external electrical field. This is a conclusive demonstration for photorefractivity. Also, large optical gain of 5.7 cm -1 was observed under zero-field condition, which is comparable to most inorganic photorefractive materials. The versatility of the reaction makes possible the advancement of new polymer structures.

Rational synthesis of photorefractive polymers

We report a new photorefractive polymer that contains an ionic tri(bispyridyl) ruthenium complex as the charge generating species, a conjugated polymer backbone as the charge transporting channel and a nonlinear optical chromophore. The ruthenium complex was introduced to utilize its efficient light induced metal-to-ligand charge transfer process. This polymer shows greatly enhanced photorefractive performance; a large net optical gain of about 200 cm-1 was obtained at a zero external electric field.