Resonant quenching of photoluminescence in porphyrin-nanocarbon agglomerates

Abstract

By adopting structural conformations with sub-nanometer precision, nature creates highly concentrated pigment-protein arrays to capture solar energy with high efficiency. Synthetic analogs of such systems exhibit concentration-dependent fluorescence quenching when approaching pigment concentrations of that seen in biological systems. Here, we report on systems of acid-functionalized multi-walled carbon nanotubes and aminophenyl tetraporphyrins that create a novel synthetic pigment-scaffold complex. The complex does not follow the trend of typical fluorescence quenching. Our steady-state and time-resolved data suggest an optimal concentration that offers a luminescence enhancement compared with the expected standard Stern-Volmer quenching relationship. The quenching is modified by controlling the pigment-distance via agglomerate size to near the upper limit for Dexter transfer of 10 Å as confirmed by dynamic light scattering measurements and chromophore-chromophore distance calculations. Our results highlight a synthetic complex with facile synthesis to investigate resonant electron transfer processes that do not follow traditional luminescence self-quenching relationships. • Facile synthesis of porphyrin-nanotube complexes with high attachment in solution • The system presents resonant, bio-analogous luminescence self-quenching • Nanoparticle agglomeration drives chromophore-chromophore transfer mechanism crossover • Interplay of distance-dependent Förster and Dexter transfer mechanism overlap Spencer et al. affix porphyrins to acid-functionalized carbon nanotubes to assess the concentration-based quenching of varying nanotube loadings, finding that agglomeration of the complexes limits energy transfer mechanisms and reduces luminescence quenching. This work reveals detail of a hard-to-study distance-dependent transfer regime change with flexible optical attachments.