Structure–property analysis of julolidine-based nonlinear optical chromophores for the optimization of microscopic and macroscopic nonlinearity

Abstract

Four NLO chromophores with different acceptors and modified julolidine donors were facilely synthesized to tune their intramolecular charge-transfer energy gaps for the investigation of the structure-property relationships. The photophysical properties of the UV-Vis absorption spectra, fluorescence spectra and solvatochromism were measured and analyzed to understand the effect of electron-donating strength and electron-withdrawing strength on intramolecular charge-transfer. Density functional theory calculations were carried out to investigate the electron density of the frontier orbitals, energy gap, molecular microscopic dipole moment and hyperpolarizability. The change tendency of the microscopic hyperpolarizability in different dielectric environments in association with the solvatochromism in absorption was analyzed. Meanwhile, the macroscopic electro-optic performance in relation to molecular structure variation and microscopic properties was further analyzed, revealing that chromophores with a larger solvatochromism exhibited higher microscopic hyperpolarizability and macroscopic electro-optic coefficients. Our investigation of the structure-property relationship gave a reliable insight into molecular design for high performance nonlinear optical chromophores.

Tuning of Second-Order Nonlinear Optical Properties Based on [2.2]Paracyclophanes Isomer: the Relative Configuration and Polarizable Environment

“…In the last three decades, the interest in excellent nonlinear optical (NLO) , materials has grown enormously, which is mainly due to their potential applications in photoelectric switches, data storage, optical communications, signal processing, and many other areas. − For purely organic compounds, the most typical molecular engineering scheme among these investigations is based on the conventional donor–(π-conjugate bridge)–acceptor (D−π–A) structure, in which the intramolecular charge transfer (ICT) processes from D toward A moiety through a π electron conjugated path. Literature reports are replete with examples based on the D−π–A design that displays ICT upon excitation. − Various systems strategies have been investigated by experimentalists and theorists in recent years for their NLO activity. These strategies are devoted to optimizing the length and overall planarity of π electron systems, the strength of D/A, the bridging conduits with enhanced longitudinal CT, and the change of framework shape, etc. ,− Interestingly, it is observed that the optical polarizabilities increase with the length of the π electrons bridge and choosing a better D/A group. − Although many factors can be adjusted, the dipolar characteristics of D−π–A structures still have considerable drawbacks .…”

Molecular engineering of organic small-molecule photothermal agents by changing the donor group for photothermal therapy and photoacoustic imaging of tumors

“…On the other hand, as the process of photothermal conversion involves non-radiative inactivation of the excited state, the radiative transition of excited molecules should be avoided in order to design efficient PTAs. Push-pull dyes with stronger electron-withdrawing acceptors have been developed that previously had weak photoluminescence, 33,34 which are beneficial for applications as PTAs.…”

Investigating functional performance and substituent effect in modelling molecular structure, UV-visible spectra, and optical properties of D-π-A conjugated organic dye molecules: a DFT and TD-DFT study

“…Quantum chemical methods act as an excellent computational tool to predict the optical properties of these organic molecules and identify the structure-property relationship within these molecules [17]. Some computational research studies have been previously performed for DR1 molecule.…”