Third-order nonlinear optical properties of molecules containing aromatic diimides: Effects of the aromatic core size and a redox-switchable modification

Electronic and Nonlinear Optical Properties of B(III)-Submonoazaporphyrin-π-Diimide Compounds: A Density Functional Theory Study

Three hypothetical complexes were designed using diimides (PMDI, NTCDI, and PTCDI) as the acceptor unit and B(III)-submonoazaporphyrin (1) as the donor unit. These complexes have smaller HOMO-LUMO energy gaps (3.39-3.96 eV) than pristine 1 (6.61 eV). Further, the energy gap can be tuned by changing the number of benzene rings of these diimides. Remarkably, these proposed complexes possess considerable first hyperpolarizabilities (β0) (4865-6921 a.u.), and the regularity of the β0 values remained the same in the gas phase and toluene solvent conditions. There is an inverse relationship between the energy gap and the polarizability/first hyperpolarizability. In addition, absorption spectra, frontier molecular orbitals, and hole electron distributions were obtained using time-dependent density functional theory calculations to emphasize the relationship between structure and properties. Ultraviolet-Visible absorption spectra reveals that all complexes show satisfying IR working regions. Further analysis of the first hyperpolarizability density reveals the nature of the excellent NLO properties of the studied systems. This study can provide valuable insights for the development of potential high-performance NLO molecules.

The Electronic Properties of Cadmium Naphthalene Diimide Coordination Complex

The computational simulations for electronic properties of cadmium (Cd) coordinated L-alanine NDI ligand (H₂-l-ala NDI) based complex are the focus of this research. For the first time, the Cd-NDI complex (monomer) has been produced using water as the solvent; this is a new approach to synthesizing the Cd-NDI complex that has not been reported yet. Along with crystallography and Hirsch field analysis, CAM-B3LYP/LANL2DZ and B3LYP/LANL2MB basis sets were used, and in-depth characterisation of the Cd-NDI complex by following DFT and TD-DFT hypothetical simulations. Hyperpolarizabilities, frontier molecular orbitals (FMOs), the density of states (DOS), dipole moment (µ), electron density distribution map (EDDM), transition density matrix (TDM), molecular electrostatic potential (MEP), electron-hole analysis (EHA), and electrical conductivity (σ) have all been studied regarding the Cd-NDI complex. The vibrational frequencies and types of interaction are studied using infrared (IR) and non-covalent interaction (NCI) analysis with iso-surface. In comparison to the Cd-NDI complex with 2.61, 2.42 eV E_g (using CAM-B3LYP/LANL2DZ and B3LYP/LANL2MB basis sets, respectively) and 376 nm λ_max, (in case of B3LYP/LANL2MB λ_max is higher), H₂-l-ala NDI have 3.387 eV E_g and 375 nm λ_max, metal-ligand coordination in complex dramatically altered charge transfer properties, such as narrowing band gap (E_g). Based on the electronic properties analysis of Cd-NDI complex, it is predicted that the Cd-NDI complex will have a spectacular (nonlinear optical) NLO response. The Cd-NDI complex is discovered to be advantageous for the creation of future nanoscale devices due to the harmony between the Cd metal and H₂-l-ala NDI, in addition to their influences on NLO characteristics.

ESIPT-based benzazole-pyromellitic diimide derivatives. A thermal, electrochemical, and photochemical investigation

This study describes the synthesis of new pyromellitic diimide (PMDI) derivatives obtained in good yields from the reaction between pyromellitic dianhydride and aminobenzazoles reactive to proton-transfer in the excited state (ESIPT). In this investigation, a non-ESIPT PMDI was also prepared for comparison. These compounds presented absorption maxima in the ultraviolet region attributed to the allowed ¹π-π* electronic transitions. Redshifted absorptions were observed for the ESIPT compounds (3b-3c) due to their π-extended conjugation if compared to the non-ESIPT dye (3a). The compounds presented fluorescence emissions between 300 and 600 nm, dependent on the solvent polarity and their chemical structures. While compound 3a presents a single emission, a dual fluorescence could be observed for compounds 3b-3c. As expected for ESIPT compounds, the emission at higher energies could be related to the excited enol conformer (E*), and the emission with a large Stokes shift was attributed to the keto tautomer (K*). All compounds presented fluorescence emission in the solid state, whereas the ESIPT derivatives presented redshifted emissions with a large Stokes shift, as expected. Cyclic voltammetry was employed to investigate the electrochemical properties of these compounds. The HOMO and LUMO energy levels were estimated at -5.40 to -5.00 eV and -2.84 to -2.62 eV, and good thermal stability (T_d > 150 °C) was observed. Quantum chemical calculationsusingTD-DFT and DFT were performed to investigate the electronic and photophysical features of the molecules.

Assembling of Perylene, Naphthalene, and Pyromellitic Diimide-Based Materials and Their Third-Order Nonlinear Optical Properties

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

Synthesis and third-order nonlinear optical properties of triphenylene derivatives modified by click chemistry

A series of asymmetric triphenylene derivatives containing typical D-π-A structures is successfully synthesized by means of [2+2] cycloaddition-cycloreversion click reactions. The photophysical and electrochemical properties, as well as the click reactions, are characterized by means of UV/Vis absorption spectroscopy, cyclic voltammetry, and DFT modulations. In addition, the third-order nonlinear properties, including the nonlinear absorption and the nonlinear susceptibilities, are investigated by using Z-scan techniques. A typical reverse saturable absorption-saturable absorption behavior is observed for the third-order nonlinear absorption, with the third-order nonlinear susceptibilities of the compounds being 1.05×10(-12) , -1.50×10(-12) , and -0.52×10(-12) esu, respectively.