Quantum mechanics

Poling

Materials science

Orientation (vector space)

Stability (learning theory)

Economics

Molecule

Computer science

Intermolecular force

Ferroelectricity

Physics

Nonlinear system

Nanotechnology

Dipole

Organic chemistry

Dielectric

Mathematics

Optics

Terahertz radiation

Nonlinear optical

Nonlinear optics

Geometry

Chromophore

Chemistry

Finance

Optoelectronics

Order (exchange)

Hyperpolarizability

Machine learning

Dyes and Pigments

Compared with traditional inorganic second-order nonlinear optical (NLO) materials, organic second-order NLO materials have many advantages in bandwidth, dielectric constant, half-wave voltage, electro-optic (EO) coefficients, processability, and material cost. Due to their potential applications in telecommunications, computing, detection, terahertz generation, and construction of functional photonic crystals, organic NLO materials have been widely studied for several decades. Currently, the poling efficiency and long-term stability are the largest obstacles for the application of organic NLO materials. At the molecular level, these problems are mainly caused by the strong dipole–dipole intermolecular interactions between the NLO chromophores with D-π-A structures. In the molecular design of the polymer system, modification of the chromophores is considered to be an efficient pathway to solve this problem. Since 2009, many studies have been performed by our group to reduce the strong dipole–dipole intermolecular interactions between the chromophores. In this review, the development of organic NLO materials in recent years is summarized, including the following: 1) a brief introduction of organic second-order NLO materials, 2) the requirements of NLO materials for applications in devices, 3) optimization of the first-order hyperpolarizability of NLO chromophores, 4) the optimization of the chromophore loading parameters (N, <cos3θ>), and 5) improvements of the stabilities of organic NLO materials.

Progress in the enhancement of electro-optic coefficients and orientation stability for organic second-order nonlinear optical materials