On the Convergence of the Physicochemical Properties of [<i>n</i>]Helicenes

The results of a series of DFT and DFT−D calculations are reported with the aim to predict the physicochemical properties (equilibrium structures, stabilization energies, redox potentials, excitation and CD spectra, electronic conductivity, and elasticity) of elongating helical structures (i.e., [n]helicenes, n = 1−14). It was shown that many of them are converged at [14]helicene with an interpitch distance of Rpitch = 3.75 Å, an incremental stabilization energy of ΔGn = 11 kJ mol-1 (thus suggesting the inherent destabilization of the growing helical structures), an S0−S1 energy difference to the estimated band gap of 2.60 eV, and redox potentials, corresponding to the reduction of [n]helicenes, of E0 = −2.2 V. The elasticity was shown to decrease as a linear function of m (i.e., k ≈ m) with k = 0.01056 a.u. for [14]helicene. Moreover, the conductivity properties were discussed in terms of hole and excess electron densities. Possible implications of the calculated data in nanoscience are discussed.