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- Title
Photoinduced relaxation processes in self-assembling complexes from CdSe/ZnS water-soluble nanocrystals and cationic porphyrins.
- Authors
Sagun, E.; Knyukshto, V.; Ivashin, N.; Shchupak, E.; Zhavnerko, G.; Karatai, N.; Agabekov, V.
- Abstract
Particular features and quenching mechanisms of exciton luminescence of water-soluble nanocomposites that are formed as a result of the interaction of surface charged semiconductor quantum dots (QDs) CdSe/ZnS ( d = 2.8 nm) and cationic porphyrins (HTMPyrP and ZnTMPyrP) have been studied theoretically and experimentally. It has been found that, in CdSe/ZnS⊕Porphyrin conjugates, there occurs long-range inductive resonance electronic excitation energy transfer from surface modified (with thioglycolic or mercaptoundecanoic acid) QDs to porphyrins, which is accompanied by quenching of the exciton luminescence of QDs and an increase in the fluorescence intensity of porphyrin. It has been shown that, when mercaptoundecanoic acid is used as a QD shell, the QD luminescence quenching efficiency by porphyrins follows the Förster-Galanin theory and depends on the overlap integral between the CdSe/ZnS luminescence band and the absorption spectra of free-base porphyrin HTMPyrP and its metal complex ZnTMPyrP. It has been revealed that, as the QDs ↔ Zn-porphyrin intercenter distance decreases from 39.1 (mercaptoundecanoic acid) to 30.1), a considerable QD luminescence quenching is observed; however, the energy transfer efficiency substantially decreases, from 55% in the former case to 23% in the latter one. Based on the spectral-luminescent data and quantum-chemical calculations, it has been found that the chemical change of HTMPyrP in the structure of the complex with CdSe/ZnS QDs passivated by thioglycolic or mercaptoundecanoic acid is caused by the formation of a metal complex ZnTMPyrP. Based on calculations of the redox-potentials, it has been concluded that the low luminescence quantum yield of CdSe/ZnS QDs passivated by residues of mercaptocarboxylic acids S(CH)COO and its dependence on the number of CH groups are related to the possibility of photoinduced electron transfer from the HOMO of passivating molecules to QDs (QD* ⇐ S(CH) nCOO hole transfer). It has been shown that the quenching of the exciton luminescence of QDs in heterogeneous structures CdSe/ZnS(thioglycolic acid)⊕ZnTMPyrP, which is complementary to the energy transfer, can be caused by the photoinduced electron transfer that involves the participation of the LUMO of the ZnTMPyrP molecule (QD* ⇒ ZnTMPyrP).
- Subjects
PORPHYRINS; NANOCRYSTALS; EXCITON theory; ENERGY transfer; QUANTUM theory; CHARGE exchange; ABSORPTION spectra; LUMINESCENCE
- Publication
Optics & Spectroscopy, 2012, Vol 113, Issue 2, p165
- ISSN
0030-400X
- Publication type
Article
- DOI
10.1134/S0030400X12060185