We demonstrate an ability to control the structures and photodynamics of porphyrin-based nanoassemblies via solvent mixture technique. Surfactants such as ethylene glycol (EG) derivatives with different chain lengths are employed to control the sizes and shapes of nanoparticles composed of meso-substituted tetracarboxyphenyl porphyrin [H2P(CO2H)4] in mixed H2O/THF solvent. With increasing the chain lengths, the diameters of H2P(CO2H)4/EG composite nanoparticles systematically increase in the range of 90-350 nm. In contrast with H2P(CO2H)4/EG composite nanoparticles, pristine H2P(CO2H)4 assemblies show long rod-shaped assemblies with micrometer scales. The porphyrin nanoparticles are stable in solution without precipitation for several days. The nanoparticles exhibit the following optical properties: a large bathochromic shift in the absorption spectra and an increase of the fluorescence quenching properties relative to those for the monomer porphyrin solution. The hierarchical clustering of H2P(CO2H)4 molecules within nanoparticles is caused by the hydrogen bonding and p-stacking effects. The efficient fluorescence quenching of H2P(CO2H)4 is mainly due to the effect of singlet-singlet annihilation of H 2P(CO2H)4 moieties within nanoassemblies. We further report the quenching processes of the excited triplet states of H 2P(CO2H)4 nanoassemblies. Efficient quenching properties of the excited triplet states of H2P(CO2H) 4 moieties are observed in the range of lifetime 26-100 ns, which is largely dependent on the sizes of nanoparticles. These quenching processes can be also analyzed by triplet-triplet annihilation theory.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films