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aP = 18.7 G, Figure 1A) and phenyl radicals
[35,36]
(Ph•, aN =
13.6 G and aH = 2.1 G, Figure 1A) according to Equation (1). In
aerated medium, the photolysis of [Ag](PPh
3
) demonstrates the
formation of oxygen-centered radicals,
[1,4]
i.e., peroxy radicals
(ROO•) or PhO• radicals (aN = 13.7 G and aH = 1.8 G, Figure 1B).
According to Buckler,
[37]
phosphorus compounds can act as
reductants of peroxy radicals, and a radical process has been
proposed for the autoxidation of triphenylphosphines under air
(Equations (2–5)).
Ag PPh (hv) Ag PPh
(1)
(2)
(3)
•O PhOO •
2
(4)
PhOO • PPh PhO• POPh
33
()
+→ +=
(5)
To complete and conrm the ESR results, LFP experiments
have been performed. Figure 1C shows the transient absorp-
tion spectrum of a solution of [Ag](PPh
3
) obtained by LFP. In
combination with our ESR results and Wan investigations on
tripheynlphosphines,
[37]
we can clearly observe the formation
of diphenylphosphinyl radical species in toluene solution at
a 320 nm maximum wavelength. This maximum is slightly
shifted to around 330 nm in polar solvent (like methanol) as
described by Wan and co-workers.
[38]
The primary radical-
forming process during [Ag](PPh
3
) photolysis is the cleavage
of the phosphorus–phenyl bond from PPh
3
to produce both
diphenylphosphinyl
[38]
and phenyl radical species. According
to LFP results, the lifetime of diphenylphosphinyl radi-
cals was evaluated at 61 ± 2.4 µs in argon-saturated solution
(Figure 1C), whereas in O
2
-saturated atmosphere, a pseudo
first-order decay was observed with a second-order rate constant
(k
add
(•PPh
2
/O
2
)) > 10
9
M
−1
s
−1
(Figure 1D).
3.3. Overcoming the Oxygen Inhibition Effects with
(DMPA/Ag Complex) Photoinitiating System and Evidence
of the Silver NPs Formation
According to the UV–vis spectra and epsilon values of Ag com-
plex ([Ag](PPh
3
)) and DMPA (Figure S6, Supporting Informa-
tion),
ε
([Ag](PPh
3
)) at its maximal wavelength absorption
(
λ
= 251 nm) was evaluated at 22687 L mol
−1
cm
−1
, whereas
DMPA displays two absorption bands which maximum were
evaluated at 251 and 340 nm with respectively,
ε
(251 nm) =
11990 L mol
−1
cm
−1
and
ε
(340 nm) = 275 L mol
−1
cm
−1
. As
the emission spectrum of the lamp used (a polychromatic
Xe–Hg lamp) perfectly ts with the UV absorption spectra of
both [Ag](PPh
3
) and DMPA, these photoinitiating species are
photolyzed, thus generating phosphorus-centered radicals,
benzoyl, and dimethoxybenzyl radicals. Even if triphenylphos-
phines could be generated as described in Equation (1), the
photolysis leads to the formation of phosphorus-centered
Macromol. Mater. Eng. 2018, 303, 1800101
Figure 1. ESR spectra of the radicals generated after illumination of a solution of [Ag](PPh
3
) A) under argon and B) under air and trapped by PBN in
tert-butylbenzene: 1 = Experimental and 2 = simulated spectra. C) Transition absorption spectra of the diphenylphosphinyl radicals recorded after laser
pulses at 0.1, 1, 10, and 100 µs of an argon-saturated toluene solution of Ag[PPh
3
] and D) decay traces of diphenylphosphinyl radicals at 320 nm after
a laser pulse (
λ
ex
= 300 nm) of argon- (1) and O
2
(2)-saturated toluene solution of [Ag](PPh
3
).