Unraveling the Novel Furan-Based π-Conjugated Systems: Insights From Optimally Tuned Long-Range Corrected DFT...

This paper offers a reliable methodology to calculate HOMO-LUMO energy gaps in furan-fused helicenes ([n]FH) by employing 16 DFT functionals (B3LYP, B3LYP-D, B3LYP-D3, B3LYP-D3BJ, CAM-B3LYP, LC-BLYP, HSE06, LC-ωPBE, M06, MN15, PBE0, PBe0DH, ωB97XD, B2PLYP, B2PLYP-D3, and B2PLYP-D3BJ). The fundamental gaps (ΔE_CCSD(T) = IE - EA) are used as reference values for a reliable benchmark for energy gaps for oxa[n]helicenes ([n]FH, n = 1-4). [n]FH yields blue-shifted HOMO-LUMO gaps relative to sulfur-, selenium-, and tellurium-based analogues. A dimerization study reveals that oxa[n]helicenes are very resistant to dimerization in DCM solvent in neutral as well as cationic states. MD simulations using the COMPASSIII force field in DCM solvent demonstrate that oxa[n]helicenes are highly resistant to dimerization in cationic states in the presence of ${\mathrm{PF}}_6^{-}$ counter ions. Optimally tuned ω values for LC-ωPBE, LC-BLYP, and ωB97XD in DCM (SMD solvation model) are almost ~20 to 100 times less than those in the gas phase, with the HOMO-LUMO gaps in solvent much smaller. In addition, PBC-DFT calculations reveal that the band gap obtained at PBC-PBE0 and PBC-B3LYP levels is quite comparable to the energy gap obtained at optimally tuned ω values for LC-ωPBE, LC-BLYP, and ωB97XD in DCM solvent. HOMO-LSOMO gaps of oxa[n]helicene radical cations also blueshift compared to their S-, Se-, and Te-based counterparts. TDDFT calculation with CAM-B3LYP functional shows intense infrared absorption in furan-based helicene radical cations, reflecting optoelectronic potential. This research emphasizes that the accuracy in excited-state properties can be achieved with optimally tuned LC-ωPBE, LC-BLYP, and ωB97XD functionals, which are quite comparable to results obtained with the CAM-B3LYP functional for neutral and radical cations of oxa[n]helicenes. These radical cation systems showed comparable absorption in the infrared range like S-systems. Overall, our benchmarking studies lead to better predictions of HOMO-LUMO gaps of oxa[n]helicenes. This work offers the much-needed insights into the design of furan-based helicene, opening doors to future advanced organic materials for electronics and photonics technology.