Intra-Molecular Electrical Field Regulated Nonlinear Catalyst Charge Transfer in the Organic Conjugated Molecular System

Quanjiang Li,Meishan Wang,Shenghui Chen,Jingang Wang,Li Wang,Yanli Liu,Di He

doi:10.3390/catal11111375

Abstract

The application of organic conjugated molecular systems to photocatalysis is based on the charge transition with different electronegative substituents and the electron–hole separation behavior of charge transfer under light excitation. In this work, the relationship between the intra-molecular electrical field and molecular second-order nonlinear optical properties is investigated theoretically by the sum-of-states (SOS) method. We use substituents with different electron affinity energy to construct internal electric fields with different properties in similar conjugated systems. The studies of these systems reveal the intra-molecular electric field strength and mode regulation of nonlinear optical coefficients and explain its physical mechanism. The intra-molecular charge recombination caused by the electrostatic potential multipole field of different substituents changes the transition behavior of one-photon, resulting in the enhancement of nonlinear optical properties (second-harmonic generation and sum-frequency coefficient) greater than 104.

Highlights

In recent years, organic molecules with conjugated systems have been widely used in many electronic devices [1,2,3,4]
Different functional groups have a great influence on nonlinear optical properties. This is because the introduction of functional groups changes the electric field distribution in the molecule or the system, which causes a large change in the molecular dipole moment or fragment dipole moment, causing a change in the nonlinear optical properties
Different from this, the hole density of the nitro system is distribu5teodf 9 on the nitro group and the electron density is distributed on the conjugated ring, indicating that the charge transfer is excited from the nitro group to anthracene, see Figure 4d

Summary

Introduction

Organic molecules with conjugated systems have been widely used in many electronic devices [1,2,3,4]. In specific application scenarios, researchers will make various chemical modifications to these conjugated molecules or materials It is embodied in the modification of different functional groups, which can significantly improve the performance of the material. This is because the introduction of functional groups changes the electric field distribution in the molecule or the system, which causes a large change in the molecular dipole moment or fragment dipole moment, causing a change in the nonlinear optical properties This is because the nonlinear optical properties are theoretically defined by the sum-of-state (SOS) [25,26] of the system dipole moment. The sum-frequency coefficients of different substituent molecular systems are shown. The regions with relatively large sum-frequency coefficients constitute concentric elliptical rings, while the number of elliptical rings of different substituent molecular systems is different. Because the range of the color bar4sofin the figure is the same, it can be intuitively found that the carboxyl system has a high sumfrequency coefficient and the cyano system is the lowest

Physical Mechanism and Transition Characteristic

Materials and Methods

Conclusions