The effect of electron-donating substituents on tuning the nonlinear optical properties of pyrene-core arylamine derivatives: DFT calculations

Using the LC-DFT/M06 functional, we elucidate the structure-property relationship for the effect of electron-donating substituents on tuning the nonlinear optical (NLO) and optical properties of a series of pyrene-core (PY) arylamine derivatives. After successfully synthesizing N1,N1,N3,N3,N6,N6,N8,N8-octakis(4-methoxyphenyl)pyrene-1,3,6,8-tetraamine (PYOMe), its crystallographic data and photophysical properties were reported. By substituting/removing the terminal –OMe donors in PYOMe with groups with different electron donation abilities, we systematically designed novel derivatives with adjusted optical and NLO properties. Comparison between the obtained results and those of the prototypical NLO chromophore p-nitroaniline (pNA) were performed. The experimental data from PYOMe and pNA allowed us to validate the applied DFT functional among six tested functionals. Charge transfer descriptors, such as the charge transfer distance (DCT), the amount of charge transferred (qCT), and dipole moment change (μCT), and other indices (H and t) were investigated. The trend observed for the βtot amplitudes was justified by the parameters in the two-level model and by the total term Δμf/ΔE3 for two crucial transitions of the investigated systems. Our investigation reveals that substitution of these systems results in larger βtot amplitudes compared to that of the unsubstituted system. However, their βtot amplitudes are smaller than that of pNA, except that of PY substituted with phenoxy groups. Additionally, our results indicate that optimal combinations of the different (optical) parameters involved in two-level approximation affects the NLO properties of the systems under investigation to a larger extent. Keywords: Pyrene-core arylamine, Electron-donating substitution, Nonlinear optical properties, First hyperpolarizabilit

Can Short- and Middle-Range Hybrids Describe the Hyperpolarizabilities of Long-Range Charge-Transfer Compounds?

The hyperpolarizabilities of five prototypical and four recently synthesized long-range charge-transfer (CT) organic compounds are calculated using short- and middle-range (SR and MR) hybrid functionals. These results are compared with data from MP2 and other DFT methods including GGAs, global hybrids, long-range corrected functionals (LC-DFT), and optimally tuned LC-DFT. Although it is commonly believed that the overestimation of hyperpolarizabilities associated with CT excitations by GGA and global hybrid functionals is the result of their wrong asymptotic exchange potential, and that LC-DFT heals this issue, we show here that SR and MR functionals yield results similar to those from LC-DFT. Hence, the long-range correction per se does not appear to be the key element in the well-known improved description of hyperpolarizabilities by LC-DFT. Rather, we argue that the inclusion of substantial amounts of Hartree-Fock exchange, which reduces the many-electron self-interaction error, is responsible for the relatively good results afforded by range separated hybrids. Additionally, we evaluate the effects of solvent and frequency on hyperpolarizabilities computed by SR and MR hybrids and compare these predictions with other DFT methods and available experimental data