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 center dot+), 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.