Enhancement of Two-Photon Initiating Efficiency of a 4,4'-Diaminostyryl-2,2'-bipyridine Derivative Promoted by Complexation with Silver Ions

We report on the two-photon-induced polymerization (TPIP) ability of a new class of free radical two-photon initiator based on a cationic silver(I) complex incorporating 4,4′-diaminostyryl-2,2′-bipyridine (DES) derivatives as ligands. Coordination with Ag+ induces a strong increase of the charge transfer character at excited state, which enhances the two-photon absorption properties of the complex with respect to that of the free ligand. A comparative analysis of the photophysical properties of DES and DES2Ag+ shows that the presence of silver cation increases the efficiency for the generation of radical cations (DES*+), which can be used as hydrogen abstractor in free radical photopolymerization. We show that the addition of an aliphatic amine used as hydrogen donor also opens a parallel route for the regeneration of DES. The improvement of the two-photon polymerization efficiency is then evidenced by the fabrication of microstructures. We finally demonstrate that the use of DES2Ag+ as two-photon initiator offers new opportunities for the fabrication of functional nanostructures composed of metal-polymer nanocomposites.