©
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800101 (3 of 8)
www.advancedsciencenews.com www.mme-journal.de
2.6. Structure and Electronic Properties of Complex 1
LanL2DZ and 6–31G**(d,p) basis sets were used for Ag and
all other atoms, respectively. Time-dependent DFT (TD-DFT)
was used to compute the 30 lowest singlet states, taking into
account the effect of solvent (toluene) by continuum polariz-
able continuum model (PCM) single-point calculations. Natural
transition orbitals (NTO) analysis was performed on the six sin-
glet states showing strongest oscillator strength.
[31]
2.7. UV–vis Experiments
UV–vis spectra were recorded at room temperature on a Varian
spectrophotometer (cary50 bio) in the range of 250–800 nm.
2.8. Photopolymerization Experiments
For film polymerization experiments, the one or two photoini-
tiating systems based on DMPA or Ag complex were dissolved
into a bulk formulation based on trimethylolpropane triacrylate
(TMPTA from Cytec) with or without trithiol. Formulations
were deposited on a BaF
2
pellet (4 µm thick) and irradiated
under polychromatic light (Xe–Hg lamp, Hamamatsu, L8252,
150 W). The disappearance of the acrylate bonds was followed
by RT-FTIR at room temperature using a Thermo-Nicolet 6700
instrument. The RT-FTIR analyses were carried out under air
and laminated conditions. For the laminate experiments, a poly-
propylene film was laid on the top of the photosensitive layer to
prevent oxygen diffusion. The maximum UV light intensity at
the sample position was evaluated to be 15 mW cm
−2
.
2.9. TEM Experiments
Thin-film layers of polymer were prepared by cryo-ultrami-
crotome (thickness less than 100 nm) using a leica MZ6 with
a diamond knife. Both the knife and the specimen were cooled
to −90 °C. The microstructural observations were performed
by TEM with a 200 kV eld emission electron gun (FEG) TEM
(FEI TecnaiF20) with resolution 0.24 nm and equipped with
a complete EDS system (windowless Octane SDD detector,
129 eV resolution and 0.5 sr and TEAM software). The NP size
distribution and average size had been determined by statistical
analyses software called CSD.
[32]
Sample preparation for solution experiments was done by
dispersing and ultrasounding for a few second a photoirradi-
ated solution of [Ag](PPh
3
) in toluene; one drop of the later
solution was pipetted onto a holey carbon support film on a
3 mm copper grid for analysis.
2.10. Nanoindentation Tests
All nanoindentation and scratch tests were achieved using a
commercial nanoindenter (G200 from Agilent Technologies)
using a Berkovich tip (Micros Star Technologies). Twenty ve
nanoindentation tests were achieved on steel substrate coating.
Samples were loaded and unloaded at constant strain rate
(0.05 s
−1
) with the help of a home-made method.
[33]
The loading
stage was achieved with the continuous stiffness method (CSM)
until a 1 µm depth was obtained. The unloading stage was real-
ized after a hold load plateau of 60 s in the sake of achieving the
viscous response. Twenty parallel scratches face forward were
achieved with a load increasing from 0 to 100 mN on a 500 µm
length. The distance between two scratches was 200 µm.
2.11. Inductively Coupled Plasma (ICP)
The substrates containing Ag NPs had been incubated into
milliQ water for a few days at 150 rpm. Dissolved metals were
diluted by a factor 10 with HNO
3
(5%). Metal levels were deter-
mined by ICP optical mission spectroscopy (ICP-OMS), using
a SPECTRO BLUE ICP-OMS instrument (Spectro, Germany).
2.12. Antiadhesion Tests
Coatings were incubated into bacteria suspension within a
fixed concentration during 3, 6, and 48 h. The antiadhesion test
was carried out according to refs. [34].
3. Results and Discussion
3.1. DFT Calculations
The calculated absorption spectrum of complex [Ag](PPh
3
)
by TD-DFT calculations using PCM model for toluene nicely
matches experimental spectrum recorded in toluene, with elec-
tronic transitions located in a rather narrow range between 269
and 302 nm (Figure S4, Supporting Information). Analysis of
the molecular orbitals involved in the six transitions with highest
oscillator strength (at 302, 294, 293, 291, 287, and 279 nm) did
not reveal a clearly dominant component, leading us to perform
NTO analysis. The two major contributions (accounting for 85%
and 14%) of the singlet electronic transition occurring at 302 nm
are reported in Figure S5 in the Supporting Information. They
clearly reveal that absorption of [Ag](PPh
3
) is essentially due to
metal-to-ligand charge transfer from the core bimetallic (AgCl)
2
pattern to PPh
3
ligands. Another striking feature of this tran-
sition is the significant decrease of electron density between
Ag and P atoms when comparing “hole” and “particle”
[31]
(Figure S3, Supporting Information), thereby evidencing the
weakening of the Ag
P bond upon irradiation.
3.2. Photoreactivity of [Ag](PPh
3
)
The photoreactivity of the Ag complex under light activation
has been studied by ESR investigations. Figure 1 describes
the different radical photoadducts which are trapped by PBN
during light activation of [Ag](PPh
3
). Under argon atmos-
phere (Figure 1A), two kinds of radicals could be detected
i.e., phosphorus-centered radicals which are produced from
the P-Ph cleavage (•PPh
2
, aN = 14.2 G, aH = 3.1 G, and
Macromol. Mater. Eng. 2018, 303, 1800101