Thermally activated delayed photoluminescence from pyrenyl-functionalized CdSe quantum dots

Abstract

The generation and transfer of triplet excitons across semiconductor nanomaterial-molecular interfaces will play an important role in emerging photonic and optoelectronic technologies, and understanding the rules that govern such phenomena is essential. The ability to cooperatively merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is therefore paramount. Here we show that 1-pyrenecarboxylic acid-functionalized CdSe quantum dots undergo thermally activated delayed photoluminescence. This phenomenon results from a near quantitative triplet-triplet energy transfer from the nanocrystals to 1-pyrenecarboxylic acid, producing a molecular triplet-state 'reservoir' that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet-triplet energy transfer. The photoluminescence properties are systematically and predictably tuned through variation of the quantum dot-molecule energy gap, temperature and the triplet-excited-state lifetime of the molecular adsorbate. The concepts developed are likely to be applicable to semiconductor nanocrystals interfaced with molecular chromophores, enabling potential applications of their combined excited states.

Near‐Infrared Optogenetic Genome Engineering Based on Photon‐Upconversion Hydrogels

“…Elongated photoluminescence lifetimes have been observed for metal complexes and quantum dots modified with chromophoric groups that have aslightly lower triplet energy level than the parent materials. [7] In those works,the lifetime extension is explained by intramolecular energy transfer (IMET) processes and succeeding excited-state equilibration. Theequilibrium constant K eq for these processes is estimated by the following relationship:…”

“…It has been reported that the triplet lifetime of sensitizers can be elongated by excited-state thermal equilibrium with covalently attached aromatic moieties with long triplet lifetime. [7] We successfully developed the new potential of this strategy to overcome the issue of limited molecular diffusion in viscous oxygen-blocking matrices.P erylene chromophores were covalently attached to Os bisterpyridine complex through phenyl linkages,giving anew complex Os(peptpy) 2 2+ ( Figure 2a). This sensitizer showed ar emarkably long phosphorescence lifetime of 23 mst hat is long enough for triplet sensitization even in av iscous,b iocompatible hydrogel formed from Pluronic F127.…”

Designed Long‐Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface‐Bound Chromophore

“…Moreover, a luminescent response for molecular oxygen can be implemented with nanocrystals that are inherently insensitive to O 2 . The strategy presented here provides opportunities for fundamental research on as‐yet poorly investigated triplet energy transfer in inorganic–organic nanoconjugates,4a and discloses new perspectives for tailoring optical properties in a wealth of nanomaterials 18…”

Semiconductor Quantum Dots as Components of Photoactive Supramolecular Architectures

“…[75] PCA was chosen as the chromophore because of the inherent properties of its lowest triplet state ( 3 ππ*; τ T � 10 ms, E T = 2.1 eV) and the efficient coordination of its carboxylate group to the surface of nanocrystals. [76] Although the pyrenyl ligand did not affect either the energy or the shape of the QD emission, significant changes in the luminescence lifetime were observed for samples CdSe-2/PCA and CdSe-3/PCA. Specifically, a component in the 100-μs domain appeared in their emission decay monitored at room temperature in deoxygenated heptane (Figure 14, a and b).…”

“…To verify this hypothesis, we prepared four samples of CdSe QDs with different size (diameter from 2.6 to 5.7 nm) and decorated them with 1‐pyrenecarboxylic acid (PCA) (Figure ) . PCA was chosen as the chromophore because of the inherent properties of its lowest triplet state ( 3 ππ*; τ T ≈10 ms, E T =2.1 eV) and the efficient coordination of its carboxylate group to the surface of nanocrystals …”