Substitution-driven two-photon absorption modulation on an alternating triphenyamine-vinylpyrimidine series with a V-shaped quadrupolar symmetry.

A comparative photophysical investigation on the linear and nonlinear properties of twelve alternating triphenylamine-vinylpyrimidine quadrupoles is presented. Within this series, each V-shaped chromophore has been designed with the incorporation of distinctive donor/acceptor substituents which were specifically positioned on the electron donating triphenylamine branches and on the electron withdrawing pyrimidine core. Such structural changes clearly allow a fine regulation of the intramolecular charge transfer (ICT) efficiency within the π-conjugated backbone of the dyes resulting in various electronic effects in terms of transitions energy positioning, excited states dipole moments enhancement, polarity-driven large amplitude fluorescence changes and modulation of the two-photon absorption (2PA) cross-sections with maximum values (δMAX) range from 60 to 430 GM. All these photophysical properties have been methodically described and quantified. Of particular interest, we highlight a limitation in the ICT-driven 2PA amplification by increasing the electron donor ability on triphenylamine subunit. Counterintuitively, such a simple structural change leads to a strong collapse of δMAX by about 70% within our D-π-A-π-D series.