The optical power limiting in the visible region of a series of two-photon absorbing quadrupoles built from conjugated backbones bearing electro-active peripheral groups was investigated. Nonlinear absorption experiments demonstrate that these molecules show marked nonlinear behaviour for short pulses (3 ns) in the ns regime. Structure-property relationships could be derived, emphasizing the role of the conjugated connectors and of the end-groups for improving the optical limiting efficiency. Push-push systems are more efficient than pull-pull systems, but at the expense of reduced transparency. Pyridine-At-oxides, terminal moieties which act in synergy as both donor and acceptor end-groups, lead to improved efficiency/transparency trade-off. (c) 2005 Elsevier B.V. All rights reserved.