Structure, Stability and Spectral Properties of Seleno[n]helicenes (n=1-10)
Structure, energy and spectral properties of neutral end substituted seleno[n]helicenes (n=1-10) are presented. Equilibrium structures are calculated applying B3LYP-D/6-311++G(d,p) method in DCM solvent considering a macroscopic solvent model. Single point energy calculations are also performed at MP2 level to improve the energy parameters. The study reveals that non-planar structures are preferred for neutral seleno[n]helicenes, n=3-10 and selenohelicene has helical structure with one complete turn. Excited state calculations are performed using Time-Dependent Density Functional Theory (TDDFT) to predict UV-Visible spectra in DCM solvent. Calculations suggest that dimerization of end substituted neutral selenohelicene system is not a favourable process; unsubstituted systems have a fair chance of dimerization though. Similar calculations are extended to radical cation of end substituted seleno[n]helicenes (n=1-10). Similar to neutral selenohelicene systems, it is predicted that radical cation of seleno[n]helicenes does prefer a non-planar structure leading to helical structure for n ≥ 3. In the charged system also one turn of helicality gets completed in case of selenohelicene radical cation. Excited state studies suggest that seleno[n]helicene radical cations have strong absorption in the range of far IR to near IR. Energy parameters clearly indicate that dimerization of even radical cation of end substituted selenohelicene system is not a favorable process in DCM solvent. Presence PF6- counter ion in DCM solvent also does not have much effect on dimerization. Overall, this study explores the effect of charge, size and substitution on the molecular and electronic properties of seleno[n]helicenes in search of Se based suitable material for applications as near infrared (NIR) electronic devices.