Spatial energy transfer with observation of bimolecular singlet oxygen emission using quantum dots as donors and zinc‐phthalocyanine as acceptors

Abstract

This study reports the influence of CdSe–ZnS core–shell quantum dots (QDs) for formation of singlet oxygen using zinc‐phthalocyanine (ZnPc) dyes in colloidal solutions. Using a microluminescence surface scan technique it was possible to measure accurately the photon diffusion length, or photon mean free path, inside the medium. Analyses were performed for a range of QD concentrations. Photon diffusion length was assigned to the bimolecular singlet oxygen emission at 707 nm. Related singlet oxygen emission was predicted by observing quenching of the photon diffusion length measured at the specific oxygen emission as a function of QD concentration, being a nontrivial phenomenon related to the QD donors. Diffusion length measured at 707 nm increased with QD concentration; in the absence of QDs, as in pure ZnPc samples, the emission peak at 707 nm was not observed.

Colloidal Quantum Dots as an Emerging Vast Platform and Versatile Sensitizer for Singlet Molecular Oxygen Generation

“…43,55−60,69−71 Forster Resonance Energy Transfer (FRET). The concept of indirect 1 O 2 generation can be better explained by a study performed by Monte et al 71 The authors developed a system of CdSe/ZnS QDs as an energy donor and zinc-phthalocyanine (ZnPc) as an energy acceptor, which is a sensitizer of 1 O 2 generation (Figure 12). The FRET efficiency of the QD-ZnPc was measured by the relative decrease in the photon diffusion length at an emission wavelength of 630 and 707 nm, using the microluminescence scan surface technique (MSST).…”

“…FRET, being a resonant dipole coupling process, depends upon the dipole orientation between the donor and acceptor typically approximated as 2/3. , Additionally, FRET also depends upon the lifetime and QYs of the donor and the quenching efficiency of the acceptor . The energy transfer efficiency ( E ET ) of FRET can be determined by using the ratio between fluorescence intensities and the decay lifetime of the D in the presence and absence of the A, as expressed by following eq E ET = 1 − I DA I D = 1 − τ DA τ D where I DA and I D are the fluorescence intensities and τ DA and τ D the decay lifetimes of the D in the presence and absence of the A, respectively.…”

“…Jablonski diagram of energy migration from the triplet excited state of QDs to the ground state of molecular oxygen, modified from refs , , (a), reduction of oxygen at the CB and oxidation of superoxide O 2 – • at the VB to produce 1 O 2 , modified from ref (b), energy transfer from the QDs donor to the triplet state of the molecular acceptor, modified from refs − (c); and energy transfer from the QDs donor to molecular acceptor via either FRET or DET/sequential charge transfer (d,e), respectively, modified from refs , , .…”

“…Semiconductor QDs have been shown to be highly efficient sensitizers for 1 O 2 production either individually or functionalized with other inorganic materials or molecular sensitizers. ,,− Individually, QDs can be light activated to produce 1 O 2 via triplet energy transfer (TET) ,− or charge transfer ,,, or energy transfer from dopant defects to dioxygen. On the other hand, QDs functionalized with molecular acceptors involve QDs energy transfer to a molecular acceptor which subsequently sensitizes 1 O 2 production. ,− ,− Thus, QDs offers distinct advantages over the conventional molecular and inorganic nanosensitizers (i.e., polymeric NPs, plasmonic NPs, metallic NPs, lanthanide NPs, etc.) in terms of versatile sensitization of 1 O 2 generation by various mechanisms and fine-tuning of their optoelectronic properties by multiple parameters in the wide UV–vis and NIR-I (700–900 nm) and NIR-II (1000–1700 nm) regions. ,,,,,,,, …”

“…This review focuses on the recent developments in the QD-assisted emerging strategies for enhanced photosensitized 1 O 2 generation via different mechanisms: (i) direct energy transfer from the dark states/triplet states of QDs to ground-state oxygen producing 1 O 2 , ,− (ii) charge transfer from the QDs conduction band (CB) to dioxygen forming O 2 – • which subsequently interacts with the valence band (VB) to produce 1 O 2 , ,,, and (iii) QD–PS conjugates involving the QDs energy transfer to the PS via Förster resonance energy transfer (FRET), ,− ,− Dexter-like energy transfer (DET), or sequential triplet–triplet energy transfer (TTET), − which subsequently sensitize 1 O 2 generation. ,,− …”