A theoretical study on the second-order nonlinear optical properties of Pt(II) bis-acetylide complexes: substituent and redox effects

Density functional theory studies on the geometric and electronic structures, UV-vis absorption spectra, and second-order nonlinear optical (NLO) properties of four-coordinate Pt(II) bis-acetylide complexes, cis-[Pt(CNtBu)(ADC)(CCR)2] , have been employed. The effects of ligand variation and the single electron redox process on the structures and NLO response of complexes have also been investigated. It shows that the variations of the ligand and electron have little effect on the geometries of the complexes, but there is a significant effect on their electronic structures and NLO responses. The introduction of a single -NO2 group in acetylide ligands increases the first hyperpolarizability of complex 12 times, while one electron lost in five complexes enhances the first hyperpolarizability 496 times at the most. Both methods are considered effective ways for improving the NLO response of Pt(II) bis-acetylide complexes. Based on the analysis of the electronic and optical properties of fifteen studied complexes, the increase of NLO response is mainly ascribed to strong oscillator strengths, lower electron transition energy, and well-directed effective charge transfer. This work reveals some underlying relationships between the NLO responses and electronic structures of complexes, which is helpful for the design and synthesis of high-performance NLO materials of Pt(II) bis-acetylide complexes.

Quantum Chemical Exploration of A-π1-D1-π2-D2-Type Compounds for the Exploration of Chemical Reactivity, Optoelectronic, and Third-order Nonlinear Optical Properties

Organic compounds exhibit significant nonlinear optical (NLO) properties and can be utilized in various areas like optical parameters, fiber optics, and optical communication. Herein, a series of chromophores (DBTD1-DBTD6) with an A-π₁-D₁-π₂-D₂ framework was derived from a prepared compound (DBTR) by varying the structure of π-spacer and terminal acceptor. The DBTR and its investigated compounds were optimized at the M06/6-311G(d,p) level of theory. Frontier molecular orbitals (FMOs), nonlinear optical (NLO) properties, global reactivity parameters (GRPs), natural bonding orbital (NBO), transition density matrix (TDM), molecular electrostatic potential (MEP), and natural population analysis (NPA) were accomplished at the abovementioned level to describe the NLO findings. DBTD6 has the lowermost band gap (2.131 eV) among all of the derived compounds. The decreasing order of highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap values was DBTR > DBTD1 > DBTD2 > DBTD3 > DBTD4 > DBTD5 > DBTD6. The NBO analysis was carried out to describe noncovalent interactions such as conjugative interactions and electron delocalization. From all of the examined substances, DBTD5 showed the highest λ_max value at 593.425 nm (in the gaseous phase) and 630.578 nm (in chloroform solvent). Moreover, the β_tot and ⟨γ⟩ amplitudes of DBTD5 were noticed to be relatively greater at 1.140 × 10^-27 and 1.331 × 10^-32 esu, respectively. So, these outcomes disclosed that DBTD5 depicted the highest linear and nonlinear properties in comparison to the other designed compounds, which underlines that it could make a significant contribution to hi-tech NLO devices.

Substituent and redox effects on the second-order NLO response of Ru(ii) complexes with polypyridine ligands: a theoretical study

Modifying ligands in four studied Ru(II) complexes have slight influence on their static first hyperpolarizabilities (βtot) values. However, the βtot values of complexes 1+/−–4+/− are all enhanced and the largest βtot value is observed for complex 4−.

Two state “ON–OFF” NLO switch based on coordination complexes of iron and cobalt containing isomeric ligand: a DFT study

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values. Moreover, switchable NLO response is also important in coordination complexes. Herein, we report two state ON–OFF switchable NLO contrast of coordination complexes of Fe and Co containing isomeric ligands. The optical, UV-visible, and electronic properties besides the “ON–OFF” switching effect are calculated using the CAM-B3LYP/6-31+G (d) method. The NLO responses of ligand–metal isomers are qualitatively evaluated through variation in charge transference (CT) style through TD-DFT. The higher β_o in each isomeric pair is strongly dependent on the HOMO–LUMO gap. The isomer 4b with lowest HOMO–LUMO gap shows the highest NLO response. The charge transfer pattern in these complexes results in variation of their β_o values. The notable β_o contrast of 21.15 in isomeric pairs 3a and 3b makes these complexes a favorable material for genuine NLO switches. Hence, the outcome of the current investigation reveals that these ligand–metal isomeric complexes exhibit a two-state switch “ON–OFF” effect.

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values.

Second-order NLO properties and two-state switching effects of transition metal redox complexes of iron and cobalt: A DFT study

Designing switchable materials with large contrasts of nonlinear optical properties has been the focus of research in recent decades because of their widespread applications. Redox-active metal complexes due to charge transfer excitation are suitable to produce switchable nonlinear optical (NLO) material. In this regard, we present here the redox switchable NLO response of active metal complexes of iron and cobalt. The geometric, electronic, molecular absorption, nonlinear optical properties, and switch "ON/OFF" style of these metal complexes are studied at the CAM-B3LYP/6-31 + G(d) level of theory. NLO responses of these redox metal complexes are described in terms of change in the charge transfer (CT) patterns by time dependent density functional theory (TD-DFT). The highest β_o value of 301534 × 10^-30 esu is noticed in [Fe-ethynyl-ZnP]¹⁺ complex, because of obvious charge transfer transition from metal to ligand i.e meatal-ligand charge transfer (MLCT) in redox metal complex. In each redox metal isomeric pair, the greater hyperpolarizability value of individual isomer is quite consistent with its smaller energy gap (H-Lgap) between highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), low crucial excitation energy, and bathochromic shift of λ_max. The remarkable β_o contrasts of these isomeric redox complexes illustrate that they can be appropriate for effective redox-triggered NLO switches. Thus, the results reveal that these redox pair complexes show two-state switching "ON/OFF" effect.