Engineering Long-Lived Blue Photoluminescence from InP Quantum Dots Using Isomers of Naphthoic Acid

Abstract

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.

Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal–Molecular Hybrids

“…Since the initial reports of triplet sensitization using nanocrystals, many other semiconductor nanocrystal sensitizers have been reported in the literature, including PbS, ,− InP, , CuInS 2 , and recently lead halide perovskites in both the bulk − and nanocrystal morphology. For sensitization with perovskite NCs, several studies have identified a two-step Dexter-type triplet energy transfer as the primary mechanism of interaction. ,, For example, in the case of CsPbBr 3 interacting with surface-adsorbed tetracene carboxylic acid derivative (TCA), a hole transfer step from excited CsPbBr 3 generated the TCA cation radical, followed by an electron transfer step to generate the TCA triplet state .…”

Thermally Activated Bright-State Delayed Blue Photoluminescence from InP Quantum Dots

“…35,36 The transmission electron microscopy images of the prepared InP dots used here feature a narrow size distribution. 32 The calculated TTET rates using the decay rates of the InP GSB across different wavelengths in the UFTA spectra are also nearly constant. Collectively, our data suggest that the Stokes shift observed in these InP QDs likely results from strong electron−phonon coupling.…”

“…31 Previous work from our laboratory established deterministic TADPL decay kinetics from InP/1-and 2-naphthoic acid (1-NA and 2-NA) constructs. 32 Unfortunately, the electron trap states in these hybrid nanomaterials effectively trapped the triplet excitons, leading to the observation of TADPL emanating from low-energy trap states having energies below that of the band edge bright state. We therefore questioned whether it was possible to generate bright-state TADPL from InP QDs by circumventing population of these electron trap states.…”

“…The collective results suggest that the nearly quantitative quenching of the PL emanating from the InP QDs results from concerted Dexterlike TTET such that InP QDs donate energy to the triplet states of surface-anchored organic chromophores from tripletlike excitonic "dark" states, which lie <15 meV below optically allowed "bright states", 1,12,13,43,44 consistent with what was observed with naphthoic acid-derivatized InP dots. 32 Using the transient absorbance difference spectra, the quantum efficiency for this interfacial energy transfer process was estimated to be 95% (see the Supporting Information for experimental details). The resulting long-lived surface-bound molecular triplets readily sensitize 1 O 2 phosphorescence at 1270 nm (Figure S12), whereas the as-synthesized InP QDs were unable to promote such bimolecular TTET.…”

“…Overall, these data support the notion that rTTET serves to quench the phosphorescence of the QCA triplets through repopulation of the InP nanocrystal excitonic states that ultimately generate bright-state TADPL. 29,30,32,46 To quantify the efficiency of the rTTET process, the intensity of the TADPL extracted from the PL spectra (Figure S10A) was plotted as a function of time, with 5 μs set as the time zero point because this is the time delay past which the PL is purely "InP-like". The decay curve was fitted with a stretched exponential function as described in the Supporting Information.…”