Triplet Exciton Delocalization in Organic-Quantum Dot Hybrids as Potential Agents for Photodynamic Therapy and Theragnostic Applications

In this work, we engineered hybrid photoassemblies consisting of a triplet organic chromophore (QDM) and core–shell CdSe/ZnS, CdZnS/ZnS, core CdZnS, or CdS quantum dots (QDs). Photophysical data shows that the presence of the QD in the vicinity of 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 × 1010 s–1 and a 3-fold increase of triplet lifetime for the hybrids. Further photophysical, electrochemical, and computational investigations revealed that the triplet state of QDM is delocalized across the QD bands, accounting for the increased triplet lifetime of the hybrids. Moreover, triplet photosensitization of molecular oxygen (3O2) using the hybrids produced 1O2 with a ΦΔ(1O2) of 67% (in toluene) and 64% (in water) for the hybrid photomaterial(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, where cell death rates reached 97%. The inherent emissive properties of QD component(s) facilitated the use of our hybrid photoassemblies as multifunctional platforms for synergistic bioimaging and phototherapy.