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 (mu(CT)), polarizability (alpha(CT)), and first hyperpolarizability (beta(CT)) show that the values of alpha(CT)/mu(CT) and beta(CT)/mu(CT) change linearly and quadratically with respect to the conjugation length, respectively. The maximum ICT-driven coherence sizes of alpha(CT) and beta(CT) are consistent with the time-dependent densities to the first (rho((1))) and second (rho((2))) orders of the electric field obtained from the collective electronic oscillators method. (C) 2003 American Institute of Physics.