Theoretical study of geometric, optical, nonlinear optical, UV–Vis spectra and phosphorescence properties of iridium(III) complexes based on 5-nitro-2-(2′,4′-difluorophenyl)pyridyl

Remarkable enhancement of the nonlinear optical behavior towards asymmetric substituted D-π-A dithiophene-based compounds

CONTEXT

Nonlinear optics (NLO) is an interesting field that discloses the interaction between intense light and matter, leading to a deeper understanding of NLO phenomena. Organic chromophores are considered as promising materials for NLO due to their exceptional structural versatility, ease of processing, and rapid response to NLO effects. Functional materials based on thiophene have been indispensable in advancing organic optoelectronics. Specifically, dithiophene-based compounds display weaker aromaticity, reduced steric hindrance, and additional sulfur-sulfur interactions. Hence, by utilizing dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DTBDT) as the core structure, designing of a set of organic compounds with D1-π-D2-π-A-type framework, namely ZR1D1-ZR1D8, was carried out in this study. The analysis of frontier molecular orbitals (FMOs) revealed that compound ZR1D2 has the lowest band gap of 1.922 eV among all the investigated chromophores. The correlation of global reactivity parameters (GRPs) with the band gap values indicates that ZR1D2 displays a hardness of 0.961 eV and a softness of 0.520 eV-1. Among the studied compounds, ZR1D2 demonstrated a broad absorption spectrum that extended across the visible region. The maximum absorption wavelengths were observed at 766.470 nm for ZR1D2 and 749.783 nm for ZR1D5. These DTBDT-based dyes exhibit a remarkable NLO response with exceptionally high first hyperpolarizability (βtot) values. Among them, compound ZR1D2 stands out with the highest average linear polarizability (⟨α⟩ = 3.0 × 10-22 esu), first hyperpolarizability (βtot = 4.1 × 10-27 esu), and second hyperpolarizability (γtot = 7.5 × 10-32 esu) values. In summary, this investigation offers valuable insights into the potential use of DTBDT-based organic chromophores, particularly ZR1D2, for advanced applications in NLO. These findings suggest promising opportunities for researchers to synthesize these molecules and utilize these compounds in hi-tech NLO-based applications.

METHODOLOGY

The density functional theory computations were performed at the M06/6-311G(d,p) functional to explore their structural effects on electronic and NLO findings. Various analyses like highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, absorption maxima, density of states, open circuit voltage, binding energies of electrons and holes, and transition density matrix are employed to investigate photovoltaic efficiencies of the derivatives. Different software packages like Avogadro, Multiwfn, Origin, GaussSum, PyMOlyze, and Chemcraft were used to deduce conclusions from the output files.

Nonlinear optical properties of azo sulfonamide derivatives

CONTEXT

The present work deals with the linear and nonlinear optical properties such as the dipole moment, polarizability, total hyperpolarizability, electric field-induced second harmonic generation, and hyper-Rayleigh scattering first hyperpolarizability of four heterocyclic azo compounds containing the sulfonamide group considered promise in nonlinear optic. The obtained polarizability and hyperpolarizability were supported by the frontier molecular orbital analysis. The properties have been effectively estimated and thoroughly examined to shed light on the nonlinear optical activity based on the density functional theory. The observed results show a high total first hyperpolarizability β tot up to 2503 a.u. and a low energy gap E g less than 1.41 eV. An inverse relationship has been obtained between the β tot and E g . The calculated E g values confirm that charge occurs within the azo sulfonamides. The new study provides a promising avenue for the development of these azo sulfonamides as novel NLO materials.

METHODS

The molecular modeling and the theoretical studies were performed with Gaussian software packages. The B3LYP/6-311 + G** level was used for optimization. All the linear and nonlinear optical properties reported here are obtained using the DFT. The optimized structures and their frontier molecular orbitals were plotted using the GaussView 5.1 program.

Theoretical Investigation of Iridium Complex with Aggregation-Induced Emission Properties

The mechanism of aggregation-induced emission (AIE) for the bis(1-(2,4-difluorophenyl)-1H-pyrazole)(2-(20-hydroxyphenyl)-2-oxazoline)iridium(III) complex, denoted as Ir(dfppz)2(oz), was investigated with use DFT and the TD-DFT level of theory. The mechanism of radiationless deactivation of the triplet state was elucidated. Such a mechanism requires an additional, photophysical triplet channel of the internal conversion (IC) type, which is activated as a result of intramolecular motion deforming the structure of the oz ligand and distorting the iridium coordination sphere. Formally, the rotational movement of the oxazoline relative to the C-C bond in the oz ligand is the main active coordinate that leads to the opening of the triplet channel. The rotation of the oxazoline group and the elongation of the Ir-Nox bond cause a transition between the luminescent, low-lying triplet state with a d/π→π* characteristic (T1(eq)), and the radiationless d→d triplet state (T1(Ir)). This transition is made possible by the low energy barrier, which, based on calculations, was estimated at approximately 8.5 kcal/mol. Dimerization, or generally aggregation of the complex molecules, blocks the intramolecular movement in the ligand and is responsible for a strong increase in the energy barrier for the T1(eq)⇝T1(Ir) conversion of triplet states. Thus, the aggregation phenomenon blocks the nonradiative deactivation channel of the excited states and, consequently, contributes to directing the photophysical process toward phosphorescence. The mechanism involved in locking the nonradiative triplet path can be called restricted access to singlet-triplet crossing (RASTC).

Theoretical investigation on orange-emitting cyclometalated platinum (II) complexes containing organosilyl/organocarbon-substituted 2-(2-thienyl)pyridine ligands

This paper presents a theoretical investigation of structural, optical, and phosphorescence properties of four cyclometalated Pt(II) complexes containing substituted 2-(2-thienyl)pyridine ligands using DFT and TD-DFT methods. Geometrical parameters of ground states were calculated and compared with available experimental data. Electronic absorptions were studied and assigned in terms of natural transition orbitals. Phosphorescence spectra have been simulated with adiabatic Hessian and adiabatic shift approaches according to the Franck-Condon approximation. Theoretical and experimental results agree and show that the four complexes exhibit two intense bands in orange region. Main normal modes involved in phosphorescence bands were analyzed and assigned.