Photoinduced enhancement in the luminescence of hydrophilic quantum dots coated with photocleavable ligands.
In search of strategies to photoactivate the luminescence of semiconductor quantum dots, we devised a synthetic approach to attach photocleavable 2-nitrobenzyl groups to CdSe-ZnS core-shell quantum dots coated with hydrophilic polymeric ligands. The emission intensity of the resulting nanostructured constructs increases by more than 60% with the photolysis of the 2-nitrobenzyl appendages. Indeed, the photoinduced separation of the organic chromophores from the inorganic nanoparticles suppresses an electron-transfer pathway from the latter to the former and is mostly responsible for the luminescence enhancement. However, the thiol groups anchoring the polymeric envelope to the ZnS shell also contribute to the photoinduced emission increase. Presumably, their photooxidation eliminates defects on the nanoparticle surface and promotes the radiative deactivation of the excited quantum dots. This effect is fully reversible but its magnitude is only a fraction of the change caused by the photocleavage of the 2-nitrobenzyl groups. In addition, these particular quantum dots can cross the membrane of model cells and their luminescence increases by ~80% after the intracellular photocleavage of the 2-nitrobenzyl quenchers. Thus, photoswitchable luminescent constructs with biocompatible character can be assembled combining the established photochemistry of the 2-nitrobenzyl photocage with the outstanding photophysical properties of semiconductor quantum dots and the hydrophilic character of appropriate polymeric ligands.
Laboratory for Molecular Photonics, Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33146-0431, USA.
Stefania
S
Impellizzeri
Bridgeen
B
McCaughan
John F
JF
Callan
Françisco M
FM
Raymo
D000818:Animals; D016466:CHO Cells; D019187:Cadmium Compounds / Q000737:chemistry*; D002478:Cells, Cultured; D006224:Cricetinae; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D049449:Luminescence; D015394:Molecular Structure; D009578:Nitrobenzenes / Q000138:chemical synthesis / Q000737:chemistry*; D055668:Photochemical Processes; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
D019187:Cadmium Compounds; D008024:Ligands; D009578:Nitrobenzenes; D018036:Selenium Compounds; D013440:Sulfides; D017967:Zinc Compounds; C058667:cadmium selenide; C031238:zinc sulfide