We report spectroscopic and quantum-chemical investigations comparing the two-photon absorption (TPA) properties of a bis(dioxaborine)-substituted derivative of biphenyl with those of a bis(dioxaborine) carbazole derivative. The former molecule is close to linear and centrosymmetric, while the dioxaborine groups of the latter are in a V-shaped arrangement, due to their linkage to the 3 and 6 positions of the bridging group. For both systems, we find sizable TPA cross sections (on the order of 360-530 x 10(-50) cm(4) s/photon). Interestingly, while the TPA response in the biphenyl-based system can be well described on the basis of the traditional three-state model, a significantly larger number of excited states needs to be considered for the carbazole derivative. We present a detailed comparison of the convergence of the theoretical approaches and an analysis of the various channels that contribute to the TPA response in molecules with low effective symmetries.