Dissolved oxygen-assisted enhancing room temperature phosphorescence of palladium-porphyrin in micelle-hybridized supramolecular gels under UV irradiation

Abstract

In general, dissolved oxygen in luminescent systems is a typical quencher for phosphors and usually needs to be removed from the system. In this work, we reported enhancing room temperature phosphorescence (RTP) assisted by dissolved oxygen. Herein, meso-tetra (carbonyl phenyl) palladium-porphyrin (Pd-TCPP) was used as phosphor and encapsulated within micelle-hybridized supramolecular gels formed by gelator N, N′-dibenzoyl-l-cysteine (DBC) and Gemini surfactant dodecyl-α, ω-bis (N, N-dimethyl-N-dodecylammonium bromides, G12-12-12). After UV irradiation for 10 min, RTP intensity of the gel system was found to be ∼100 times higher than that of the gel without UV irradiation. RTP enhancing mechanism involved the role of singlet oxygen generated from the dissolved oxygen under UV irradiation. Due to the disulfide group of DBC was oxidized by the singlet oxygen to sulfonic acid group, two types of interaction were caused. One of them was electrostatic interactions between the negatively charged moiety of sulfonic group and positively charged moiety of G12-12-12. Another was stronger hydrogen bonding between sulfonic groups of DBC aggregates. Under these two interactions, the supramolecular 3D network structure of the gel system became denser. The freedom and the probability of non-radiation transition of Pd-TCPP was more restricted, leading to RTP enhanced. Moreover, the RTP can be readily regulated by varying the time and power of UV irradiation.