Effect of decorating alkali metals (Li, Na, and K) on the enhancement of nonlinear optical and electronic responses of CTF-0 molecule: A DFT study

Covalent triazine frameworks (CTFs) have very recently been identified as attractive materials for application in nonlinear optical (NLO) due to their exceptional structural stability and variable electronic properties. In the current work, the impact of alkali metal decorations (Li, Na, and K) on the electronic and nonlinear optical properties of CTF-0 has been explored utilizing density functional theory (DFT) and time-dependent density functional theory (TD-DFT). From our study, it is evident that the introduction of the alkali metals improves the first hyperpolarizability of CTF-0 through effective intramolecular charge transfer and reduction in the HOMO-LUMO energy gap. Our theoretical studies suggest that among the studied systems, the enhancement in the NLO performance of CTF-0 is more significant for the Na and K decorated CTF-0 structures due to their effective electronic polarization. Moreover, it is also observed that the complexation of the alkali metals with CTF is a key factor for controlling the optical properties of the complexes. From the TD-DFT analysis, we can confirm that there are some noticeable red shifts in the absorption spectrum of the decorated complexes due to increased charge transfer effect.