The two-photon absorption properties of a series of bis dialkylamino-or diarylamino-substituted diphenylpolyenes and bis(styryl)benzenes have been investigated. Two-photon absorption cross sections, δ, as large as 1420 × 10 -50 cm 4 s/photon-molecule have been observed for molecules with this general bis-donor structure. The effect of the type and length of the conjugated chain and of dialkylamino or diarylamino substitution on the position and magnitude of the peak two-photon absorptivity is reported. The transition dipole moments for the transitions between the ground state and the first excited singlet state (M ge ) and between the first and second excited singlet states (M ee′ ) have been estimated using experimental data from the oneand two-photon spectra. It was found that increases in chain length result mainly in an increase in M ge , whereas the addition of donor end groups or going from diphenylpolyene-to phenylene-vinylene-type bridges leads primarily to an increase in M ee′ . The trends in the energy of the lowest excited singlet states and in the transition moments for the diphenylpolyene series as a function of chain length are in agreement with those calculated by quantum mechanical methods. These results furnish a link between structural features in these classes of molecules and the electronic dipole couplings and state energies that control the strength of the two-photon absorption. In bis(aminophenyl)polyenes containing up to four double bonds (m) the lowest excited singlet state is a B u state, as opposed to the case of simple polyenes and diphenylpolyenes, for which it is an A g state for m > 2. The relationship of the state ordering in these systems with the observed values of the radiative and nonradiative decay rates is also discussed.