On the convergence of the physicochemical properties of [n]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 Rpit,h= 3.75 A, an incremental stabilization energy of Delta G(n) = 11 kJ mol(-1) (thus suggesting the inherent destabilization of the growing helical structures), an S-0-S-1 energy difference to the estimated band gap of 2.60 CV, and redox potentials, corresponding to the reduction of [n]helicenes, of E-0 = -2.2 V. The elasticity was shown to decrease as a linear function of m (i.e., k approximate to 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.