DFT and TD-DFT study of push-pull molecules with extended conjugated bridges: theoretical insight into organometallic...

This work presents a theoretical investigation of nine push-pull molecules featuring conjugated bridges composed of three distinct organometallic rings: Titanol, Chromol, Ferrol, Nickelol, and Zinkol. These bridges are connected at their ends to acceptor (NO₂) and donor (N(CH₃)₂) groups positioned on the α-sites of the aforementioned rings. In systems incorporating cyclic groups, it was found that placing Titanol and Nickelol rings between two Zinkol units enhances the nonlinear optical (NLO) response. A similar enhancement is observed when Chromol and Ferrol rings are positioned at the termini of the Zinkol units. Frontier orbital analysis reveals that the Zinkol rings exhibit electron-accepting characteristics, whereas the other rings act as electron donors. The two molecular systems conform to the architectures D-A-D-A-A (Titanol-Nichelol-Zinkol) and D-D-A-A-A (Chromol-Ferrol-Zinkol), respectively. Computed static β_tot values range from 142.71 to 512.07 × 10^-30 esu, while static |γav| values fall within 1.88 to 245.05 × 10⁻³⁵ esu. The study also includes an analysis of dynamic ${\beta }_{\left|\right|}^{\lambda }(-2\omega ;\omega ,\omega )$ values, which lie between 2478.43 and 1,036,410.00 × 10^-30 esu, and dynamic ${\gamma }_{\left|\right|}^{\lambda }(-2\omega ;\omega ,\omega ,0)$ values ranging from 26,017.87 to 193,013,000 × 10⁻³⁵ esu. Nonlinear refractive indices (n₂) were also evaluated, with values spanning from 5.11 × 10⁻¹⁵ cm²·W⁻¹ to 2.91 × 10⁻¹⁰ cm²·W⁻¹. Additionally, most of the investigated molecules exhibit absorption within the 450-900 nm range, both in vacuum and in various solvents.

All calculations were performed using Gaussian 16 program. The methods used are DFT and TD-DFT.Several functionals were treated: CAM-B3LYP, LC-ωPBE, LC-BLYP, M11, ωB97X, M08HX, M062X, MN12SX, MN15, M06HF.Several basis-sets was studied:6-31G(d,p), 6-31 +  + G(d,p), cc-pVDZ, AUG-cc-pVDZ, 6-311G(d,p), 6-311 +  + G(d,p), cc-pVTZ, AUG-cc-pVTZ and LanL2DZ. Implicit Solvation Model used are CPCM and SMD. Finally, NBO method is used also.