Optimization of quadrupolar chromophores for molecular two-photon absorption

Multiphoton absorption is attracting considerable attention owing to applications in various fields including optical power limitation, and high resolution imaging of biological tissues. Within this framework, our aim has been the design of optimized NLO-phores with very high two-photon absorption (TPA) cross-sections in the visible and/or NIR region and high fluorescence quantum yield. Our strategy was based on the push–push or pull–pull functionalization of rigid conjugated cores built from a rigidified biphenyl or bithiophene moiety. A series of push–push and pull–pull elongated chromophores have been prepared and their nonlinear absorption properties investigated by determining their two-photon excited fluorescence (TPEF) characteristics. The TPA spectra of theses derivatives can be tuned and their TPA responses boosted by playing on the nature of the rigid core and electroactive end groups. As a result, quadrupolar molecules showing very large TPA cross-sections (up to 1.3×10−47 cm4 s photon−1) in the visible red and/or NIR region have been obtained. Such derivatives are promising for optical limitation applications as well as for TPEF imaging of cellular membranes.