Accurate Prediction of HOMO–LUMO Gap Using DFT Functional and Application to Next-Generation Organic Telluro[n]Helicenes Materials

The present work purposes and establishes an accurate prediction of HOMO–LUMO energies of thiophene-, selenophene-, and tellurophene-based helicenes using 15 different DFT methodologies. DFT functionals used in this work are PBE, PBE0, B3LYP, B3LYP-D, B3LYP-D3, M06, MN15, HSE06, LC-BLYP, CAM-B3LYP, LC-ωPBE, ωΒ97XD and B2PLYP. DFT HOMO–LUMO gaps are compared with the fundamental gaps calculated at the CCSD(T) level of theory. The LANL2DZ basis set is used for tellurium atoms, and the 6–311++G(d,p) basis set is used for other elements. Statistical error analysis suggests that the HOMO–LUMO energy gaps can be accurately obtained using ωB97XD functional, with geometry optimization performed at the same theoretical level. However, geometry optimization using the B3LYP functional, followed by single-point energy calculation with the ωB97XD functional, provides a more cost-effective method with similar accuracy for energy gap prediction. HOMO–LUMO gaps of telluro[n]helicenes ([n]TeH) are redshifted compared with their S- and Se-analogs. Tellurophene-based helicenes ([n]TeH) systems are easy to oxidize in contrast to their S- and Se-analogs. Dimerization studies have found that substituted [7]TeH^•+ is more stable in dichloromethane than its S- and Se-analogs. The CAM-B3LYP and ωΒ97XD functionals are used in conjunction with the TDDFT procedure to explore the excited states of [n]TeH radical cations. These radical cation systems showed better absorption in the infrared range than S- and Se-systems. Overall, our benchmarking studies lead to an accurate prediction of HOMO–LUMO gaps of [n]TeH. Further, this study demonstrates the potential of Te-based helical structures to create versatile next-generation organic materials.