Photophysical properties of ionic liquid-assisted porphyrin nanoaggregate–nickel phthalocyanine conjugates and singlet oxygen generation

Abstract

In this report, we demonstrate the formation of ionic liquid (IL)-assisted zinc octaethylporphyrin (ZnOEP) nanoaggregates which is confirmed by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) studies. A large red shifted emission of ZnOEP nanoaggregates in comparison to ZnOEP in DCM confirmed the H aggregation which is due to intermolecular porphyrin–porphyrin (such as π–π/hydrophobic) interactions. The steady state and time resolved spectroscopic studies unambiguously confirm the H-aggregation formation of porphyrin molecules during nanoaggregate formation. The significant quenching of the fluorescence spectrum and the shortening of decay time of porphyrin nanoaggregates imply an efficient (89%) energy transfer from porphyrin nanoaggregates to phthalocyanine. Furthermore, the emission band observed at 1270 nm unambiguously confirms the singlet oxygen (¹O₂) generation from ZnOEP nanoaggregates which opens up further prospects in designing new IL-assisted porphyrin nanoaggregates for their application in photodynamic therapy.