Photoinduced Formation of Bithiophene Radical Cation via a Hole-Transfer Process from CdS Nanocrystals

Year: 2013

Authors: Iagatti A., Flamini R., Nocchetti M., Latterini L.

Autors Affiliation: Dipartimento di Chimica and Centro Eccellenza Materiali Innovativi Nanostrutturati (CEMIN), Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy

Abstract: The exciton dynamics in semiconductor nanocrystals can be strongly affected by coupling the nanocrystals to organic ligands. A deeper understanding of the interactions in semiconductor-organic hybrid systems is important for the design of functional devices. In the present work, the interactions between CdS quantum dots and bithiophene molecules have been investigated. In particular, the photophysical behavior of CdS nanocrystals has been investigated in n-heptane in the presence of increasing bithiophene concentration by use of steady-state and time-resolved measurements. Bithiophene is a well-known electron donor (or hole acceptor), and it has a good affinity with CdS surface for the presence of sulfur atoms. The nanocrystal luminescence was efficiently quenched upon addition of increasing concentration of the thiophene derivative, and modifications in the emission decay profiles of CdS were observed; the analysis of luminescence data suggests that quenching is mainly due to static interaction able to modify the dynamics of the exciton states of the hybrid nanomaterials. The transient absorption measurements enable to detect the bithiophene radical cation upon CdS excitation, thus revealing the occurrence of an efficient hole transfer process from the nanocrystals to the organic ligand, for which a quantum efficiency of 36% has been measured. The dependence of transient signal on bithiophene concentration and the formation of tetrathiophene intermediates indicate that CdS exciton states are able to photosensitize the polymerization of bithiophene after the hole transfer processes. The data indicate that in the investigated system the decay of charged species is not determined by back-reactions.


Volume: 117      Pages from: 23996  to: 24002

More Information: We are grateful to Danilo Pannacci (Dipartimento di Chimica, Universita di Perugia) for the technical help with the analysis of photoproducts. The authors gratefully acknowledge the support of the University of Perugia. L.L. thanks the financial support of Minister per l\’Università e la Ricerca Scientifica e Tecnologica (Rome, Italy) under the project PRIN 2010-2011, 2010FM738P.
KeyWords: quantum dots; hole transfer; spectroscopy; small semiconductor crystallites; thiophene oligomers
DOI: 10.1021/jp406072n

Citations: 15
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