Two-photon absorption (2PA) and subsequent processes may be localized in space with a tightly focused laser beam. This property is used in a wide range of applications, including three dimensional data storage. We report theoretical studies of 5 conjugated chromophores experimentally shown to have large 2PA cross-sections. We use the Time Dependent Density Functional Theory (TD-DFT) to describe the electronic structure. The third order coupled electronic oscillator formalism is applied to calculate frequency-dependent second order hyperpolarizability. Alternatively, the sum over states formalism using state-to-state transition dipoles provided by the
Tamm-Dancoff approximation is employed. It provides new venues for qualitative interpretation and rational design of 2PA chromophores.