End-Substituted Thiahelicenes For Electronic Device Applications

Minimum energy structures of neutral and radical cations of end-substituted thia[n]helicenes (n = 1-10) in DCM solvent are reported. For both neutral and radical cations of these helicenes, calculated structures are nonplanar for n = 3 to 10. Helical structures are obtained for higher helicenes, and the thia[8]helicene system has a helical structure with one complete turn. Equilibrium structures are predicted by using B3LYP-D/6-311++G(d,p) method in conjunction with the solvation model based on solute density. Single-point energy calculations are also performed at the MP2 level to improve certain energy parameters. Excited-state calculations are performed using time-dependent density functional theory formalism to predict UV-Visible spectra of neutral and radical cations of thia[n]helicenes in DCM solvent. Thia[n]helicenes radical cation have strong absorption in the near-infrared region. Calculations also suggest that dimerization is not a favorable process in the DCM solvent for the end-substituted neutral and radical cation of thia[7]helicene. The present theoretical study examines the molecular and electronic properties of thia[n]helicenes in search of near-infrared electronic devices.