jp406072n_si_001.pdf (367.6 kB)
Photoinduced Formation of Bithiophene Radical Cation via a Hole-Transfer Process from CdS Nanocrystals
journal contribution
posted on 2013-11-14, 00:00 authored by Alessandro Iagatti, Rebecca Flamini, Morena Nocchetti, Loredana LatteriniThe 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.