Surface functionalization of twisted graphene C₃₂H₁₅ and C₁₀₄H₅₂ derivatives with alkalis and superalkalis for NLO response; a DFT study

Herein, we present the detailed comparative study on geometric, electronic, optical and non-linear optical response of alkalis and superalkalis doped twisted graphene. The results illustrate that alkali metals and superalkalis interact with the central ring of the twisted graphene through non-covalent interactions which demonstrate the stability of the resultant complexes. NBO charges indicate the transfer of electrons from dopant (alkali metal atoms and superalkalis) towards twisted graphene sheet. Superalkalis doped twisted graphene complexes exhibit higher first hyperpolarizability values compared to alkali metals analogues. Among superalkalis doped complexes, K₃O@C₁₀₄H₅₂ shows the highest β_o value of 1.68 × 10⁵ au. In frequency dependent first hyperpolarizability analysis, strong second harmonic generation (SHG) response of K₃O@C₃₂H₁₅ complex is observed at both selected resonance frequency values (532 nm and1064 nm) whereas EOPE value of K₃O@C₃₂H₁₅ complex shows higher induced response at 1064 nm wavelength. The static hyperpolarizability (β_o) further increases under the influence of applied electric field. Among all complexes, Li₃O@C₃₂H₁₅ graphene complex has the highest β_o value (1.40 × 10⁵ au) under applied electric field along x axis when sheet is in y-z plane. This analysis will be an important guideline for future studies on twisted graphene based NLO materials.