A TD-DFT investigation of the electronic optical and structural properties of tetracyanoethylene oxide for organic optoelectronic applications

The optical and electronic properties of Tetracyanoethylene oxide (TCNEO) were studied using DFT and TD-DFT methods to evaluate its potential for optoelectronic applications. Frontier molecular orbitals analyzed at the CAM-B3LYP/def2-TZVP level showed HOMO and LUMO energies of − 4.414 eV and − 1.551 eV, respectively, with a HOMO-LUMO gap of 2.863 eV. TD-DFT calculations at the PBE0/def2-TZVP level with CPCM water solvation predicted a highly active singlet transition S₁ at 329 nm (3.77 eV) with oscillator strength of 0.985, characterized primarily by HOMO→LUMO π→π* intramolecular charge transfer. Critically, no absorption was observed in the visible range (400–700 nm), indicating complete optical transparency. Chemical shift data confirmed sp²-hybridized carbon atoms and, importantly, revealed two distinct nitrile nitrogen environments arising from the molecular symmetry (near-C₂) rather than different functional groups, the calculated ¹⁵N NMR signals at δ ≈ 317 ppm and δ ≈ 359 ppm correspond to two sets of magnetically inequivalent nitrile groups within the same molecular framework. Reduced density gradient (RDG) analysis revealed extensive green surfaces corresponding to weak van der Waals dispersion interactions stabilizing the molecular configuration, with some red regions reflecting local steric repulsion between neighboring nitrile groups. TDOS and OPDOS analysis determined a band gap of 2.86 eV, with occupied states exhibiting bonding character (between − 13.6 and − 5.4 eV) and unoccupied states showing antibonding behavior. The calculated photoelectron spectrum (PES) showed the first ionization energy at 9.8 eV with no electronic states below 9.5 eV. These results indicate that TCNEO is a promising candidate for optoelectronic applications including UV protection, transparent optical windows, and non-linear optics, though further investigations of charge transport properties are recommended.