Leveraging triplet excitons in semiconductor quantum dots (QDs) in concert with surface-anchored molecules to produce long-lifetime thermally activated delayed photoluminescence (TADPL) continues to emerge as a promising technology in diverse areas including photochemical catalysis and light generation. All QDs presently used to generate TADPL in QD/molecule constructs contain toxic metals including Cd(II) and Pb(II), ultimately limiting potential real-world applications. Here, we report newly conceived blue-emitting TADPL-producing nanomaterials featuring InP QDs interfaced with 1-and 2-naphthoic acid (1-NA and 2-NA) ligands. These constitutional isomers feature similar triplet energies but disparate triplet lifetimes, translating into InP-based TADPL processes displaying two distinct average lifetime ranges upon cooling from 293 to 193 K. The time constants fall between 4.4 and 59.2 μs in the 2-NA-decorated InP QDs while further expanding between 84.2 and 733.2 μs in the corresponding 1-NA-ligated InP materials, representing a 167-fold time window. The resulting long-lived excited states enabled facile bimolecular triplet sensitization of 1 O 2 phosphorescence in the near-IR and promoted sensitized triplet−triplet annihilation photochemistry in 2,5-diphenyloxazole. We speculate that the discovery of new nanomaterials exhibiting TADPL lies on the horizon as myriad QDs can be readily derivatized using isomers of numerous classes of surface-anchoring chromophores yielding precisely regulated photophysical properties.

Low toxicity indium phosphide (InP) quantum dots represent an attractive alternative to heavy-metal-based quantum dots (QDs) in numerous applications including lighting, displays, and photosensitization. However, low photoluminescence quantum yields (PLQYs) resulting from a high density of surface trap states ultimately limit the applications of as-synthesized InP QDs in commercial products. Postsynthetic treatment with Z-type ligands (two-electron acceptors) is often used to passivate the surface traps of the InP QDs, while approaches using X-type ligands (oneelectron donors) are less prevalent due to the lack of understanding of how the X-type ligands function to passivate the surface traps. In this study, we report a postsynthetic surface passivation utilizing benzoic acid (BZA) as an X-type surface ligand. To understand how BZA impacts their electronic structure, we conducted spectroscopic studies on InP QDs with various surface modifications, including in situ fluorination and postsynthetic BZA treatment. A comparison of a variety of time-resolved spectroscopic techniques reveals that BZA can selectively remove electron trap states in InP QDs by passivating unsaturated indium atoms at the QD surface. When the BZA treatment is used in combination with a well-established fluoride treatment, the PLQYs of these unshelled InP QDs exceeds 20%. This research advances our understanding of the function of X-type ligands at the InP QD surface and their role in the passivation of unsaturated indium atoms to reduce electron trap states.

Thermally activated delayed photoluminescence (TADPL) generated from organic chromophore-functionalized quantum dots (QDs) is potentially beneficial for persistent light generation, QD-based PL sensors, and photochemical synthesis. While previous research demonstrated that naphthoic acid-functionalized InP QDs can be employed as low-toxicity, blue-emissive TADPL materials, the electron trap states inherent in these nanocrystals inhibited the observation of TADPL emerging from the higher-lying bright states. Here, we address this challenge by employing the heterocyclic aromatic compound 8quinolinecarboxylic acid (QCA), whose triplet energy is strategically positioned to bypass the electron trap states in InP QDs. Transient absorption and photoluminescence spectroscopies revealed the generation of bright-state TADPL from QCA-functionalized InP QDs resulting from a nearly quantitative Dexter-like triplet−triplet energy transfer (TTET) from photoexcited InP QDs to surface-anchored QCA chromophores followed by reverse TTET from these bound molecules to the InP QDs. This modification resulted in a 119-fold increase in the average PL intensity decay time with respect to the as-synthesized InP QDs.

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