Size scaling of intramolecular charge transfer driven optical properties of substituted polyenes and polyynes

The origin of dramatic variation in optical polarizabilities of push–pull conjugated chains with respect to the conjugation length is discussed. Ab initio calculations of intramolecular charge transfer (ICT)-driven dipole moment (μCT), polarizability (αCT), and first hyperpolarizability (βCT) show that the values of αCT/μCT and βCT/μCT change linearly and quadratically with respect to the conjugation length, respectively. The maximum ICT-driven coherence sizes of αCT and βCT are consistent with the time-dependent densities to the first (ρ(1)) and second (ρ(2)) orders of the electric field obtained from the collective electronic oscillators method.