Ligand and Gold(I) Fluorescein-AIEgens as Photosensitizers in Solution and Doped Polymers

The synthesis of fluorescein propargyl diether (L) and two different dinuclear gold(I) derivatives containing a water-soluble phosphane [1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane (PTA) for complex 1 and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) for complex 2] has been successfully performed. All compounds display intrinsic emission from fluorescein, being less intense for gold(I) complexes due to the heavy-atom effect. All compounds aggregate in acetonitrile/water mixtures with the formation of larger aggregates for those samples containing more water content, as evidenced by dynamic light scattering and small-angle X-ray scattering experiments, in agreement with the absorption and emission data. The emission of the samples increases when they are used to obtain luminescent materials with four different organic matrices [poly(methyl methacrylate, polystyrene (PS), cellulose, and Zeonex]. The compounds display very high values of singlet oxygen (¹O₂) production in dichloromethane. Singlet oxygen production was also evaluated in the doped matrices, being the highest in PS and with an exciting increase on PS microspheres. Density functional theory (BP86-D3) and GFN2-xTB calculations were used to model the assembly of L and complexes 1 and 2 with the different organic matrices and rationalize the experimental findings based on the geometries, molecular electrostatic potential surfaces, and complementarity and HOMO-LUMO gaps.