2 research outputs found
Porphyrin dyes for TiO2 sensitization
A series of six new free base porphyrins were synthesized for use as photosensitizers in TiO2 dye-sensitized
photo-electrochemical cells. The porphyrin sensitizers are attached to the TiO2 photoelectrode by phosphonic
or carboxylic acid anchoring groups. These anchoring groups were placed on different substitution positions on
the porphyrin moiety. The new dyes were fully characterized by absorption and emission spectroscopies,
electrochemistry and photo-electrochemical spectroscopy. The photo-electrochemical performances of the
sensitizers are discussed and compared to the known 5,10,15,20-tetra(4-carboxyphenyl)porphyrin sensitizer. In
this study, we show that the nature of the anchoring group (phosphonic or carboxylic acids) has little impact
on the photo-electrochemical performance of the cell. However, the substitution position of the anchoring
group on the porphyrin strongly influences the monochromatic photon-to-electron conversion efficiency of the
resulting cell. The results indicate that the electronic coupling of this type of dye with the d-band of the
semiconductor is one of the key parameters in the design of efficient sensitizers
Hole-Transfer Dyads and Triads Based on Perylene Monoimide, Quaterthiophene, and Extended Tetrathiafulvalene
Two families of dyad and
triad systems based on perylene monoimide
(PMI), quaterthiophene (QT),
and 9,10-bis(1,3-dithiol-2-ylidene)-9,10-
dihydroanthracene (extended tetrathiafulvalene,
exTTF) molecular components
have been designed and synthesized.
The dyads (D1 and D2) are of
the PMI–QT type and the triads (T1
and T2) of the PMI–QT–exTTF type.
The two families differ in the saturated
or unsaturated nature of the linker
groups (ethynylene in D1 and T1, ethylene
in D2 and T2) that bridge the
molecular components. The dyads and
triads have been characterized by electrochemical,
photophysical, and computational
methods. Both the experimental
and the computational (DFT)
results indicate that in the unsaturated
systems strong intercomponent interactions
lead to substantial perturbation
of the properties of the subunits. In
particular, in T1, delocalization is particularly
effective between the QT and
exTTF units, which would be better
viewed combined as a single electronic
subsystem. For the dyad systems, the
photophysics observed following excitation
of the PMI unit is solvent-dependent.
In moderately polar solvents (dichloromethane,
diethyl ether) fast
charge separation is followed by recombination
to the ground state. In toluene,
slow conversion to the chargeseparated
state is followed by intersystem
crossing and recombination to
yield the triplet state of the PMI unit.
The behavior of the triads, on the other
hand, is remarkably similar to that of
the corresponding dyads, which indicates
that, after primary charge separation,
hole shift from the oxidized QT
component to exTTF is quite inefficient.
This unexpected result has been
rationalized on the basis of the anomalous
(simultaneous two-electron oxidation)
electrochemistry of exTTF and
with the help of DFT calculations. In
fact, although exTTF is electrochemically
easier to oxidize than QT by
around 0.6 V, the one-electron redox
orbitals (HOMOs) of the two units in
triad T2 are almost degenerate