Triplet Exciton Delocalization in Organic-Quantum Dots Hybrid Photo-Systems: A Pathway to Improved Phototherapy and Theragnostics

In this work, we engineered hybrid photo-assemblies consisting of an organic triplet chromophore (QDM) and core-shell CdSe/ZnS, CdZnS/ZnS, core CdZnS, or CdS quantum dots (QD). Photophysical data shows that the presence of the QD in the vicinity of the QDM enhances spin-orbit coupling (SOC), resulting in the depopulation of the singlet excited state to create the corresponding triplet transient species with an accelerated intersystem crossing (ISC) of rate constants in the range kISC = 8.6–18 x1010 s-1 and a three-fold increase of triplet lifetime for the hybrids. Further photophysical, electrochemical, and computational investigations revealed that the triplet state of QDM is delocalized into the QD bands, which explains the increased triplet lifetime of the hybrids. Moreover, triplet photosensitization of molecular oxygen (3O2) using the hybrids produced 1O2 with a Φ(1O2) of 67% (in toluene) and 64% (in water) for the hybrid photo-material(s) compared to that of QDM alone (52% in toluene and 28% in water). This enhanced quantum efficiency was corroborated in dendritic cell viability assays, with cell death rates as high as 97%. The inherent emissive properties of QD component(s) facilitated the use of our new hybrid photo-assemblies as multifunctional platforms for synergistic bio-imaging and phototherapy.