J.S. Aguirre-Araque et al. / Polyhedron 182 (2020) 114513
3
2H) 7.80 (dd, J = 5.80, 1.22 Hz, 1H) 7.86 (dd, J = 5.65, 0.76 Hz, 2H)
5. Theoretical calculations
7.91 (td, J = 7.78, 1.53 Hz, 2H) 8.39 (s, 1H) 8.57 (d, J = 7.93 Hz, 2H)
8.63 (s, 1H) 9.04 (s, 2H) 9.79 (d, J = 5.80 Hz, 1H). Calcd(Found) for
[Ru(Hmctpy)(dmbpy)(H3 tmt)](PF6)2ꢂ12H2O, C31H50F12N8O14P2-
RuS3: C 29.88 (29.43); H 4.05 (3.87); N 8.99 (9.02).
Theoretical calculations were carried out on a preliminary basis,
for help understanding of the electronic structure and spectra.
Although DFT and TDTFD theoretical calculations were initially
performed using the ORCA software, the molecular complexity of
the complexes demanded more than 10 days of computational pro-
cessing, and were frequently aborted for technical problems after
such a long computational time. For this reason, the ZINDO-S
semiempirical method from the Hyperchem 8.05 computational
package was here preferred.13 As demonstrated by Gorelski and
Lever [14] and according to our own experience, there is a reason-
able agreement between the two methods; however, the last one
requires only few seconds to perform on a lap top computer. As a
normal procedure, atomic dipoles were initially used to start the
MM+ geometry optimization, and then replaced by the atomic
charges obtained from the ZINDO-S method, with a convergence
limit of about 10ꢀ5 kcal Åꢀ1 molꢀ1. The electronic distribution
was generated from single CI excitations in an active space involv-
ing 20 frontier molecular orbitals (10 highest occupied and 10 low-
est unoccupied MOs). After many cycles of MM+/ZINDO-S
geometry optimization up to the convergence point, the final elec-
tronic spectra and the molecular orbitals involved were plotted as
2D energy contours.
2.6. Spectrophotometric titration
The complex [RuII(Hmctpy)(dmbpy)(H3tmt)](PF6)2ꢂ12H2O was
spectrophotometric titrated employing a H2O/MeOH 20:1 solution
containing 0.5 mol Lꢀ1 of NaCl supporting electrolyte in order to
maintain and control the ionic force. All of the spectra were col-
lected at room temperature (25 °C) by starting at pH 13 and acid-
ifying stepwise with HCl (3 mol Lꢀ1) solution until pH 2.
2.7. Preparation of [RuII(mctpy)(dmbpy)(Hxtmt)]n deprotonated
species
Spectrophotometric titration afforded three pKa values in the
pH window employed. In this way, the deprotonated species,
[RuII(mctpy)(dmbpy)(Hxtmt)]n were prepared by adjusting the pH
with (Bu4N)OH and precipitated upon addition of diethyl ether.
3. DSSC assembly
6. Results and discussion
DSSCs were assembled by employing a sandwich format. In the
anode, TiO2 nanoparticles paste were deposited by spin coating
forming working areas averaging 0.25 cm2 onto FTO/glass optically
transparent electrode and then sintered at 450 °C for 30 min. The
dyes were adsorbed on TiO2 surface by immersing the anode in
dye solution for 24 h before mounting the cells. The FTO/glass
counter electrode was coated with Pt by treating with H2PtCl6
solution and heating at 450 °C for 30 min. The cells were put
together using SurlynÒ as spacer and gluer, and sealed at 110 °C
for ten minutes. Through a predrilled hole in the counter electrode,
the Iꢀ/Iꢀ3 based electrolyte (0.5 M tert-butylpyridine, 0.6 M tetra-
butylammonium iodide, 0.1 M LiI, 0.1 M I2 in methoxypropioni-
trile) was injected after applying vacuum, and then the hole was
sealed with a coverslip glass using SurlynÒ as glue. The electrolyte
was let to accommodate on the DSSC unity for 24 h before making
the measurements.
6.1. NMR spectra
The first hint about the low spin Ru(II) center in [Ru(mctpy)Cl2-
H2O] was given by its 1H NMR spectrum (Fig. 2 top). Five well-
defined, symmetric signals can be observed, and the lack of broad-
ening is typical of a diamagnetic metal center, exhibiting slower
nuclear relaxation times in contrast with the paramagnetic species
[15]. This supported the assignment of a highly symmetrical Ru(II)
complex and the singlet in 8.98 ppm enabled the integration of
every signal acting as reference. The coupling constants permitted
the correlation between nuclei thanks to the -orto, -meta and -para
values.
Although the 1H NMR spectra gave us a hint about the oxidation
state of the ruthenium center, spin delocalization across the whole
complex may be poor enough to enable a good NMR signal [16].
The complex formed by the coordination of the tridentate ligand
terpy and its analogues is commonly reported as being RuIII(tpy)
Cl3. It is assumed that due to the lack of a reducing agent in the
reaction media, the ruthenium center does not undergo a redox
process during the complex formation [17–20]. However, EPR mea-
surement provided no signals of unpaired electrons as expected for
4d5 Ru(III) [21], indicating a low spin Ru(II) center
The quantification of the loaded complexes on the DSSC anode
was performed by treating with 0.1 mol Lꢀ1 NaOH aqueous solu-
tion, and monitored spectrophotometrically after diluting with
deionized water. Based on the absorption spectra of the complex,
the surface coverage was estimated as 9.3 ꢁ 1016 molecules cmꢀ2
.
4. Instrumentation
1H NMR spectrum of the [RuII(Hmctpy)(dmbpy)Cl]Cl complex
afforded 13 signals between 2.37 and 9.99 ppm expected for a
symmetric terpy with 5 signals and a unsymmetrical dmbpy ligand
due to the electronic trans influence of the chloride to one of the
pyridyl rings, making them magnetically distinct. Therefore, every
ring in dmbpy gives rise to four signals each, as shown in Fig. 2
middle. In the figure, the labeling has been kept for mctpy for com-
parison purposes and another labeling was adopted for dmbpy
hydrogens.
The electronic spectra of the complexes were obtained using a
Hewlett-Packard, model HP-8453-A diode array spectrophotome-
ter in the 200–1100 nm range. 1H NMR spectra were recorded on
a Bruker AIII 500 MHz equipment. Low resolution mass spectra
were obtained using a Esquire 3000 Plus Bruker Daltonics, and high
resolution spectra were collected on a MicroTof Bruker Daltonics
spectrometer. Cyclic voltammetry was carried out with an Autolab
PGStat30 instrument, using a glassy carbon working electrode. An
Oriel Spectral Luminator, whose power at cell position was con-
trolled (1 and 2 mW cmꢀ2) with a standard Si photodiode (1830-
C Newport Optical Power Meter), was used for the IPCE measure-
ments. The I-V curves were registered using an ABB class Oriel
solar simulator (AM 1.5, IEC, JIS, ASTM) calibrated with a Si cell
(VLSI standards, Oriel P/N 91150 V), interfaced to a computer-con-
trolled Keithley 2400 instrument.
The spectrum of the [RuII(Hmctpy)(dmbpy)(H3tmt)](PF6)2 com-
plex is shown in Fig. 2 bottom. Due to the use of a protic solvent
(MeOD-d4), isotopic exchange takes place with the thiol residues
making the hydrogens non visible in the spectrum. Nevertheless,
chemical shifts for the eleven signals found between 6.94 and
9.79 ppm differ substantially from those found for the
[RuII(Hmctpy)(dmbpy)Cl]+ precursor as observed in Fig. 2, allowing