Dispersed vs. Covalently Integrated Benzothioxanthene Emitters in Sustainable Luminescent Solar Concentrators

Herein, we present a comprehensive experimental and theoretical investigation of benzothioxanthene-based fluorophores embedded in recycled poly(methyl methacrylate) (rPMMA), comparing their performance when physically dispersed with that achieved through covalent integration via copolymerization. By deliberately employing high fluorophore loadings (up to 1000 ppm), we critically assessed aggregation tendencies, photophysical properties, and luminescent solar concentrator (LSC) performance across the two incorporation strategies. Remarkably, both systems exhibit nearly identical absorption and emission characteristics, high fluorescence quantum yields (≈85%-90%), comparable fluorescence lifetimes, and limited reabsorption losses, indicating excellent phase dispersion of the fluorophore within the acrylic matrix irrespective of the bonding approach. Consistently, LSCs fabricated from the two materials display very similar internal and external photonic efficiencies, concentration factors, and device efficiencies, with performance trends primarily governed by optical bandwidth and geometrical parameters rather than by fluorophore attachment. Density functional theory calculations support these findings, revealing a limited thermodynamic driving force for aggregation and a preserved monomer-like electronic structure in both solution and solid-state environments. This study shows that when fluorophore-polymer compatibility is intrinsically optimized, covalent integration does not improve performance over physical dispersion, highlighting a sustainable and scalable strategy for efficient LSCs based on BTX emitters in recycled PMMA.