Extending the Scope of Bis(acyl)phosphane Oxides: Additional Derivatives

Article abstract of DOI:10.1002/ejic.201700140

A series of new bis(acyl)phosphane oxide (BAPO) photoinitiators has been synthesized and tested with respect to their efficiency in the initiation step of radical photopolymerizations. The transient absorption spectra of the phosphanoyl radicals obtained upon laser-flash photolysis reveal maxima at ca. 450–460 nm. Rate constants for the addition of these radicals to the double bonds of butyl acrylate, methyl methacrylate, 1-vinyl-2-pyrrolidone, and styrene have been determined. All phosphanoyl radicals have been found to react the most rapidly with styrene and the most slowly with butyl acrylate. Low fluorescence quantum yields of 0.1–0.3 % reveal that the studied BAPOs undergo efficient intersystem crossing, followed by α-cleavage. The heat profiles of selected photopolymerizations have been observed using a high-resolution infrared camera. Thermal-imaging experiments show substantial monomer-dependent exothermicity. All BAPO derivatives can additionally act as electron acceptors, as indicated by cyclic voltammetry and EPR spectroscopy.

Full text of DOI:10.1002/ejic.201700140

A Journal of
Accepted Article
Title: Extending the Scope of Bis(acyl)phosphane Oxides: New
Derivatives
Authors: Anna Eibel, Max Schmallegger, Michal Zalibera, Alex Huber,
Yasmin Bürkl, Hansjörg Grützmacher, and Georg Gescheidt
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700140
Link to VoR: http://dx.doi.org/10.1002/ejic.201700140

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
Extending the Scope of Bis(acyl)phosphane Oxides: New
Derivatives
Anna Eibel,[a] Max Schmallegger,[a] Michal Zalibera,[a], [b] Alex Huber,[c] Yasmin Bürkl,[a] Hansjörg
Grützmacher,*[c] and Georg Gescheidt*[a]
Abstract: A series of novel bis(acyl)phosphane oxide (BAPO)
photoinitiators has been synthesized and tested with respect to their
efficiency in the initiation step of radical photopolymerizations. The
transient absorption spectra of the phosphanoyl radicals obtained
upon laser-flash photolysis reveal maxima at ca. 450 – 460 nm. Rate
constants for the addition of these radicals to the double bonds of butyl
acrylate, methyl methacrylate, 1-vinyl-2-pyrrolidone and styrene have
been determined. All phosphanoyl radicals have been found to react
most rapidly with styrene and slowest with butyl acrylate. Low
fluorescence quantum yields of 0.1–0.3% reveal, that the studied
BAPOs undergo efficient intersystem crossing followed by α-cleavage.
The heat profiles of selected photo-polymerizations have been
observed using a high-resolution infrared camera. Thermal imaging
experiments show substantial monomer-dependent exothermicity. All
BAPO derivatives can additionally act as electron acceptors as
indicated by cyclic voltammetry and EPR spectroscopy.
spectra, α-cleavage reactions, the kinetics of their addition to
double bonds, reduction potentials, and the EPR spectra of
selected one-electron reduced species.
Scheme 1. Photolysis of BAPO derivatives 1–5 to give phosphanoyl radicals
1P–5P and the mesitoyl radical Mes. For the substituents R, see Scheme 2.
Results and Discussion
Synthesis and Characterization of BAPOs 1–5
The new BAPO derivatives 1–5 were synthesized as shown in
Scheme 2 using a synthesis method which we reported briefly in
a previous communication.[5] The readily available sodium
Introduction
Bis(acyl)phosphane oxides (BAPOs) have been among the most
successful initiators for photo-induced radical polymerizations.[1–
Photolysis of BAPOs leads to the formation of a phosphanoyl
and a mesitoyl radical via triplet-state -cleavage with high
quantum yields (Scheme 1).[6,7] Both radicals are efficient in
initiating radical polymerizations. Still, enhancing the scope of
BAPOs in terms of specific excitation wavelengths and solubility
bis(mesitoyl)phosphide, Na[P(COMes)2] (Mes
=
2,4,6-
trimethylphenyl) is reacted with a hydrocarbon halide, R-X, in
dimethoxyethane (DME) as solvent in a temperature range
between 25 °C and 60 °C to give cleanly the corresponding
bis(acyl)phosphanes, R-P(COMes)2, which are characterized by
their characteristic 31P NMR chemical shifts in the range from 40
– 70 ppm [R = 1-phenylethyl: 31P NMR δ = 71.1 ppm; R = 1-
5]
naphtylmethyl: 31P NMR
δ
=
52.9 ppm;
R
=
2-(2-
remains
a challenge. To this end, several modifications,
methoxyethoxy)ethyl: 31P NMR δ = 44.9 ppm; R = 3-bromopropyl:
31P NMR δ = 48.5 ppm; R = 3-(triethoxysilyl)propyl: 31P NMR δ =
50.8 ppm]. In some cases, longer reaction times are needed in
particularly at the phenyl substituents of the benzoyl moieties
have been introduced.[1] Advanced synthetic protocols however
allow to attach various groups directly at the phosphorus atom of
BAPOs.[5,8–11] Here, we introduce five novel BAPO derivatives and
besides describing their synthesis, we report on their optical
order
to
achieve
complete
conversion.
These
bis(acyl)phosphanes were subsequently oxidized without prior
isolation to give the bis(acyl)phosphane oxides 1–5 in mostly
excellent overall yields. The oxidation of (EtO)3Si-(CH2)3-
P(COMes)2 with H2O2 requires a solvent change from DME to
toluene and careful removal of sodium iodide by extraction of the
organic with aqueous potassium carbonate in order to achieve a
satisfactory yield (63%) of 5 as wax-like yellow solid. The BAPO
derivatives 1 and 2 are yellow solids with melting points at 178 °C
and 119 °C, respectively, while 3–4 are obtained as yellow
viscous oils. All compounds are thermally stable at least up to
150 °C.
[a]
Anna Eibel, Max Schmallegger, Yasmin Bürkl, Dr. Michal Zalibera,
Prof. Georg Gescheidt
Institute of Physical and Theoretical Chemistry
Technische Universität Graz
Stremayrgasse 9/I, 8010 Graz, Austria
E-mail: g.gescheidt-demner@tugraz.at
Dr. Michal Zalibera
Institute of Physical Chemistry and Chemical Physics, Slovak
University of Technology in Bratislava, Faculty of Chemical and
Food Technology, Radlinského 9, 81237 Bratislava, Slovakia
Dr. Alex Huber, Prof. Hansjörg Grützmacher
Laboratory of Inorganic Chemistry
[b]
[c]
The molecular structure of the 1-phenylethylderivative 1 was
determined by X-ray diffraction with single crystals. A plot is
shown in Figure 1. The unit cell of 1 contains both enantiomers of
which only the R-enantiomer is shown. These two molecules
interact via intermolecular π-stacking between the mesityl rings
ETH Zurich
Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
which are at about 3.7 Å distance from each other. As also
observed for other BAPOs[5] and the commercially available
Irgacure® 819[12] the distances between the carbon centers of the
COMes groups and the phosphorus atom are unusually long [P1-
C11 1.905(2) Å, P1-C1 1.895(1) Å] and even longer than the P-
C21 bond [1.832(2) Å] although the latter contains a sp3 valence
electron hybridized carbon center while the acyl groups contain
sp2 carbons to which shorter bonds are expected. In contrast to
other BAPO derivatives which show skewed arrangements
between the P=O unit and the COMes groups, the COMes groups
in 1 are in almost parallel arrangement and point to the opposite
direction with respect to the central P=O unit.
Spectroscopic Investigations
Absorption and Emission Spectra.
Figure 2 displays the UV-VIS absorption spectra of compounds
1–5 with intense π-π* absorptions around 315 -320 nm (1-4) and
around 300 nm (5) and with distinct weak bands above 350 nm.
The latter ones are attributable to n-π* transitions, responsible for
an α-cleavage between the P(O)–C(O) bond leading to
phosphanoyl (1P•–5P•) and mesitoyl (Mes•) radicals (Scheme 1).
Derivative 1 exhibits a band at 375 nm and the highest-
wavelength n-π* transition at 435 nm, higher than that of the well-
established commercially available BAPO 6 (ca. 420 nm).[2]
Naphthalene derivative 2 shows a somehow similar spectral
shape as 1 whereas 3–5 possess less structured broad bands
reaching to 430 nm. This observation shows that the substitution
with a π system, which is separated from the P atom by a non-
conjugating methylene group has a slight but not extended
influence on the long-wave absorption of BAPOs. The
substituents connected to the phosphorus center in 3–5 via sp3
carbon atoms behave essentially in an identical way (Figure 2,
top). To test if the π substituents in 1 and 2 alter the photophysical
reaction pathways in terms of allowing an extended reactivity in
the singlet state, we have measured fluorescence spectra. Using
an excitation wavelength of 373 nm, 1–4 show fluorescence with
almost identical Stokes shifts at ca. 455 nm and very low quantum
yields substantially below 0.4% (Figure 2, bottom and Table 1).
Scheme 2. Synthesis and skeletal diagrams of BAPOs 1–5 and of commercially
available BAPO Irgacure® 819 (6).
Figure 2. Top: UV-Vis absorption spectra of compounds 1–5 (two weak peaks
in the spectrum of compound 5 at 486 nm and 582 nm are due to spectrometer
artifacts); bottom: fluorescence emission spectra in acetonitrile normalized by
absorbance at the excitation wavelength (373 nm). For fluorescence
measurements, the absorbance of the solutions was kept at ca. 0.1 to avoid
inner filter effects.
In contrast to 1–4, BAPO 5 showed no detectable fluorescence,
indicating that the excited singlet state of 5 preferentially reacts
via intersystem crossing to the excited triplet state, or via internal
conversion. Table 1 summarizes the fluorescence quantum yields
(ΦF) of 1–4 determined by comparison with the known quantum
yield of 9,10-diphenylanthracene (ΦST = 0.95 in cyclohexane)
according to standard procedure.[13] These results correspond to
Figure 1 Plot of the structure of 1. Thermal ellipsoids are shown at a 50%
probability level. For clarity, hydrogen atoms are omitted. Selected bond lengths
[Å] and angles [º]: P1-O1 1.476(1), P1-C21 1.832(2), P1-C11 1.905(2), P1-C1
1.895(1), O2-C1 1.217(2), O3-C11 1.214(2), O1-P1-C21 115.82(8), O1-P1-C11
114.89(8), O1-P1-C1 118.13(8), O3-C11-P1 115.5(1), O2-C1-P1 114.7(1), C21-
P1-C11 102.54(8), C21-P1-C1 102.66(8), C11-P1-C1 100.42(8); torsion angles:
O2-C1-P1-O1 165.3(1), O3-C11-P1-O1 172.3(1), O2-C1-P1-C21 36.6(2), O3-
C11-P1-C21 45.8(2).
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
those obtained for related BAPOs and mono(acyl)phosphane
oxides (MAPOs).[6] Accordingly, for 1–5 efficient intersystem
crossing and subsequent α-cleavage can be expected.
Exponential fitting of the time decay traces obtained at various
quencher concentrations, which were significantly higher than
those of the radicals, yielded the pseudo-first-order rate constants
(kexp).[7] The second order addition rate constants (kmonomer) are
obtained from the slopes of their linear dependence on the
monomer concentration. The corresponding curves are shown in
Figure 4 for 1P• (for 2P•–5P• see the Supporting Information).
Table 1. Fluorescence quantum yields (ΦF) of 1–5 in acetonitrile solutions
(A ≤ 0.1)
Compound]
Fluorescence quantum yield ΦF (%)
0.314 ± 0.026
1
0.105 ± 0.001
2
0.286 ± 0.003
3
0.199 ± 0.005
4
5[a]
–
[a] no detectable fluorescence
Phosporous-centered Radicals and their Reactivity.
Figure 3 shows transient optical absorption spectra obtained upon
irradiation of 1–5 with a Nd-YAG laser at 355 nm.
Figure 4. a) Decay traces for radical 1P• in the presence of methyl methacrylate
at three different concentrations (0.1 M, 0.3 M and 0.5 M) recorded following
LFP of argon-saturated solutions of 1 in acetonitrile (excitation wavelength: 355
Figure 3. Transient optical absorption spectra (absorbance change ΔA versus
wavelength) of phosphanoyl radicals 1P•–5P• recorded 200 – 300 ns after laser
excitation (355 nm, 8 ns) of 1–5 in argon-saturated acetonitrile solutions
(absorbance at 355 nm ~ 0.3).
nm, monitoring wavelength: 465 nm; absorbance at 355 nm
~ 0.3).
Experimental rate constants are obtained from exponential fitting of the time
traces. b) Plots of the experimental rate constants kexp of 1P• versus monomer
concentrations. Second order addition rate constants kmonomer are obtained from
the slopes.
The bands centred at ca. 450 nm with lifetimes at a microsecond
time scale are attributable to the phosphanoyl radicals 1P•–5P•.
Benzoyl-derived radicals like the mesitoyl radical Mes• do not
reveal distinct absorptions in the VIS range and can only be
observed by time-resolved IR and EPR spectroscopy.[14,15] The
absorption peaks around 450 – 460 nm are in agreement with the
spectra of related BAPO-based phosphanoyl radicals.[7,16]
The distinct absorptions of the phosphorus-centered radicals
1P•–5P• allowed us to determine the rate constants for their
addition to butyl acrylate, methyl methacrylate, 1-vinyl-2-
pyrrolidone and styrene via pseudo-first-order kinetic analysis.
The addition rate constants for 1P•–5P• are summarized in Table
2 and Figure 5. Generally, the reactivity toward the monomers
increases in the following order: butyl acrylate < methyl
methacrylate < 1-vinyl-2-pyrrolidone < styrene. The highest
reactivity with the most electron-rich alkene (styrene) suggests
that phosphanoyl radicals show electrophilic behavior and prefer
to react with electron rich quenchers.
In Table 2, the data for the novel compounds 1P•–5P• are
compared with the rate constants previously determined for
radicals 6P• and Ph2P(O)•, which are obtained by photolysis of
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
commercially available Irgacure® 819 and Lucirin TPO®,
respectively.
recorded in the 50 ns time regime.[7,14,17,22] The phosphorus
centred radical 1P• gives rise to a doublet signal with a 31P hfc of
24.3 mT (g = 2.0042; calc. 31P hfc: 21.6 mT, see Supporting
Information), whereas the mesitoyl radical Mes• appears as a
rather narrow unresolved signal (g = 2.0005) in between the lines
of the 31P doublet (Figure 6).
DFT calculations indicate that P-centered radicals 2P•–5P•
possess electronic structures rather closely resembling those of
1P• (see Supporting Information). We therefore assume that the
differences of the addition constants for 1P•–5P• (Figure 5) can
be traced back to steric factors. Radical 1P• is very likely the
sterically most congested radical, caused by the methyl and
phenyl substituent at the sp3 carbon center next to the
phosphorus atom, contributing to the lower reactivity toward
double bonds.
Table 2. Second-order rate constants for the addition of phosphanoyl
radicals 1P•–5P• to monomers and comparison with radicals 6P• and
Ph2PO•. Errors are reported as twice the standard deviation from least
squares analysis of the data.
k monomer / 107 (M-1 s-1)
methyl
methacrylate
1-vinyl-2-
pyrrolidone
butyl acrylate
styrene
1P•
2P•
3P•
4P•
5P•
0.58 ± 0.02
1.28 ± 0.02
0.92 ± 0.10
0.93 ± 0.05
0.94 ± 0.01
1.1[a]
1.01 ± 0.01
2.73 ± 0.02
1.63 ± 0.02
2.88 ± 0.06
2.19 ± 0.01
1.83 ± 0.04
5.42 ± 0.04
3.23 ± 0.06
6.07 ± 0.08
3,64± 0.07
4.45 ± 0.02
12.0 ± 0.10
6.19 ± 0.04
11.1 ± 0.13
8.69 ± 0.09
6P•
–
–
–
–
–
–
0.87 ± 0.02[b]
2.8[a]
Ph2PO•
1.98 ± 0.06[b]
[a] Reference [7]. [b] Reference [17]
Figure 6. TR-EPR spectrum observed between 200-300 ns after laser flash
photolysis (355 nm) of 1 (15 mM solution in toluene), 31P hfc: 24.3 mT
(microwave frequency: 9.474 GHz).
The α-cleavage of the photoinitiators 1–5 and the corresponding
follow-up reactions can be conveniently followed using 31P CIDNP
spectroscopy. This NMR-based method provides information
about reaction products formed via radical pairs.[22] Radical-pair-
based phenomena lead to enhanced absorptive or emissive NMR
signals of reaction products, caused by a non-Boltzmann
population of magnetic energy levels. Figure 7 illustrates the
products detected via 31P CIDNP after photolysis of 2.
Figure 5. Second-order rate constants kmonomer for the addition of the
phosphanoyl radicals 1P•–5P• to butyl acrylate, methyl methacrylate, 1-vinyl-2-
pyrrolidone, and styrene.
TR-EPR and 31P CIDNP-NMR Spectroscopy.
The structure-reactivity relationship of phosphanoyl radicals is
influenced by the s-orbital character at the phosphorus center as
well as by steric factors.[7,17–20] The 31P hyperfine coupling
constants (hfc), determined by (time-resolved) EPR, present
insights into the s-orbital of the P center. Generally, the bigger the
31P hfc gets, the higher the s-orbital character of the spin carrying
orbital and the more efficient is the addition of the P-centered
radical to an acrylate double bond. This can be traced back to a
correlation between the s-orbital character of the P-centered
radical and the 31P hfc.[17,21] BAPOs with alkyl substituents at the
phosphorus atom generally reveal 31P hfcs of ca. 25–27 mT.[17]
Upon laser-flash photolysis (355 nm) of 1, we have obtained the
time-resolved EPR (TR-EPR, CIDEP) spectrum shown in Figure
6. It closely resembles the CIDEP spectra of related BAPOs
Figure 7. 31P CIDNP-NMR spectrum of 2 in argon-saturated C6D6 (30° RF
pulse; laser excitation at 355 nm, 60 mJ/pulse, 4 ms inter-pulse delay).
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
Figure 8. a,b) Glass vial containing a 1 mM solution of 3 in acetonitrile and butyl
acrylate (1:1 v/v ratio) before (a) and after (b) 10 s irradiation with a Hg-Xe UV
lamp. The line in the middle of the sample is caused by reflection. c) Plots of
temperature change ΔT versus time t (ΔT = Tt – Tinitial). The three line styles
represent the temperatures at the top, the center and the bottom of the sample
volume, where the temperature was sampled. The irradiation times are
indicated in the plot.
The radical pair Mes•/P2• can recombine regenerating the parent
compound 2. The benzoyl and the phosphanoyl radical may also
form product a via P–O bond formation. Two phosphanoyl
radicals P2• either yield b or c when reacting either via P,P or P,O
recombination (Scheme 3). This reactivity pattern is general for all
derivatives 1–5 (see Supporting Information for further spectra)
and follows that reported for related photoinitiators.[4,23]
For comparison, a reference sample containing only butyl acrylate
in acetonitrile was prepared, showing a basically uniform low
temperature upon irradiation (see the Supporting Information).
However, when the sample contains the photoinitiator and butyl
acrylate, substantial heating is detected (red, yellow color, Figure
8a,b). The corresponding heat profiles (temperature change vs.
time, Figure 8c) show an increase in temperature with increasing
irradiation periods (1s, 5s and 10s). Three positions in the solution
volume (top, center and bottom) were chosen to monitor the
temperature change. Figure 8c shows that the heat distribution
within the sample is almost uniform. This might be due to the short
light path of approximately 2 cm. The temperature changes are
significantly more pronounced for the sample containing butyl
acrylate than for methyl methacrylate, which is in line with the
enthalpy for the addition of butyl acrylates to C-centered radicals
being higher than for methyl methacrylate.[25] This indicates that
the observed heat development is mainly caused by the
exothermic polymerization chain growth rather than by the
initiating process.
Scheme 3. Reaction pattern of the primary radicals P• and Mes•.
Following Polymerizations with a Thermal Camera
Another approach to explore the reactivity of BAPOs 1–5 was to
follow the development of heat produced during polymerization
reactions using a high-resolution infrared camera.[24] Argon-
saturated samples were successively irradiated with UV light
pulses (1s, 5s and 10s) while thermal videos were recorded. The
lamp was positioned above the sample to avoid the heating of the
glass vial along the path of the camera. Selected thermograms of
the polymerization of butyl acrylate initiated by compound 3 are
shown in Figure 8a,b.
One-Electron Reduction Reactions of 1-5.
Beside serving as photoinitiators, BAPO and MAPO derivatives
have been shown to serve as electron-transfer-active agents, in
particular revealing (quasi) reversible one-electron reductions.[26]
Accordingly, we have recorded cyclic voltammograms of 1–5 (see
Figure 9 and the Supporting Information). For all derivatives, we
were able to observe quasi-reversible reduction steps (except 5,
see Table 3), whereas no distinguishable signals occurred in the
oxidative region.
Figure 9. Cyclic voltammogram of 1 (1 mM in acetonitrile, supporting electrolyte:
0.1 M tetrabutylammonium tetrafluoroborate), recorded using a Pt working
electrode, Pt counter electrode and Ag pseudo-reference electrode (100 mVs–1
scan rate). Potentials are given vs. Fc+/Fc. The direction of the potential sweep
is indicated by the arrow.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
The one-electron reduction potentials of 1–4, leading to the
formation of the corresponding radical anions reveal a rather
narrow range between -1.75 V and –1.81 V (vs. Fc+/Fc).
Accordingly, the aromatic substituents, which are separated by
sp3 C-centers from the P atom hardly influence the electron
donating/accepting properties of BAPOs.
Table 4. 31P hfcs and g factors determined for 1•––5•–compared to 6•–
1•–
2•–
3•–
4•–
5•–
6[a]
31P hfc
[mT]
2.24
2.29
2.19
2.18
2.22
2.20
2.004
±0.001
2.004
±0.001
2.004 ±
0.001
2.004 ±
0.001
2.004 ±
0.001
2.004
g factor
[a] Taken from ref.[26]
.
Table 3. Reduction potentials and CV peak separations for 1–5 and
comparison with BAPO 6 (all values vs. Fc+/Fc)
1
2
3[c]
4
5 [d]
6[c]
E1/2 [V vs.
Fc+/Fc][a]
ΔEp [V] [b]
–1.80
–1.77
–1.81b
–1.80
–
–
–1.86
Conclusions
0.10
0.16
0.097b
0.14
0.089
We have shown that the presented synthetic procedure allows a
very convenient access to a variety of new P-substituents in
bis(acyl)phosphane oxides. This approach can be used to adjust
the hydrophilicity or lipophilicity of BAPO derivatives or allows
introducing groups which can be utilized as anchors to specific
environments (e.g. polyoxyethylene groups, Si-containing
[a] E1/2 =(Epc + Epa)/2, Epc and Epa are cathodic and anodic peak potentials,
respectively. [b] ∆Ep =(Epa– Epc). [c] Data from ref.[26] [d] Reduction waves
are not clearly distinguishable.
Reductions with a K-metal mirror in THF under high vacuum led
to well distinguishable EPR spectra attributed to 1•––5•– (Figure
10 and Supporting Information). The spectra are dominated by
31P hfc of ca. 2.2 mT for all radical anions (Table 4). These values
substituents, possibly intercallating
π
systems). These
modifications do not deteriorate the excellent photoinitiating and
electron-donating properties of this class of compounds,
sustaining the character of 1P•–5P• being decisive for their role
as polymerization initiating P-centered radicals. The substitution
patterns presented in this work have a slight effect on the
positioning and the extinction coefficients of the n-π* bands,
however a systematic behavior cannot be established. We plan
now to investigate how to utilize the (photo)chemistry of the
conveniently accessible radical anions 1•––5•–.
closely resemble those obtained for 6 and related derivatives.[26]
.
This reveals that, as in the case of the P-centered radicals 1P•–
5P•, the delocalization of the charge and the spin in 1•––5•– is
basically confined to the acyl (mesitoyl) substituents and
character of the additional substituents at the P(V) center does
not have a marked effect on the electronic properties in 1–5 at the
radical-anion stage.
Experimental Section
General Instrumentation. NMR spectra were recorded on Bruker Avance
500 MHz spectrometer with respect to 1H. Chemical shifts are reported in
ppm relative to TMS and residual chemical shifts of the solvent as the
1
secondary standard (for H and 13C) and 85% H3PO4 (for 31P). Coupling
constants (J) are given in Hertz (Hz) as absolute values. The multiplicity of
the signals is indicated as s, d, t, or m for singlets, doublets, triplets, or
multiplets, respectively.
IR-spectra were measured on a Perkin-Elmer-Spectrum 2000 FT-IR-
Raman spectrometer using the ATR technique. The relative intensities of
the signals are indicated as s = strong, m = medium and w = weak.
UV/VIS spectra were measured on
a UV/VIS/NIR Lambda 19
spectrometer in 10 mm Quarz cuvettes (200 – 800 nm).
Mass spectra were taken by the MS-service center of the Institute of
Organic Chemistry (LOC) of the ETH Zürich on a ESI-Q-TOF system
(maXis, Brucker Baltonics, Germany) coupled to an Agilent 1200 system
(Agilent Ltd., Deutschland). The data were analyzed and evaluated using
the Data Analysis 4.0 software package of Bruker Daltonics, Germany.
Highly resolved mass spectra confirm the purity of 1–5, since elemental
analysis did not give satisfactory results for BAPO derivatives.
The thermal properties of the compounds were investigated with
simultaneous thermogravimetry (TG) and differential thermoanalysis
(DTA) using a NETZSCH STA 409 apparatus. The measurements were
performed under an atmosphere of argon in an Al2O3 crucibles. The
heating rate was 2.0 or 10.0 °C/min within a temperature range from 20 to
500 °C.
Figure 10. EPR spectrum of 2 obtained after K-metal reduction in THF (T = 200
K), together with its simulation (microwave frequency: 9.473 GHz).
Single crystals suitable for X-ray diffraction were protected with
polyisobutylene oil in glovebox then transferred to the goniometer of an
Oxford XCalibur, a Bruker SMART APEX or a Bruker APEX diffractometer;
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
MoKɑ radiation (0.71073 Å). The structure was solved and refined using
filtration and evaporation of all volatiles under vacuum (oil pump, 1 mbar)
3.900 g (8.083 mmol, 82 % yield) of BAPO 2 are obtained as yellow solid.
1H-NMR (300.13 MHz, C6D6): δ = 8.43 (d, J = 8.43 Hz, 1H, Naph), 7.69–
7.60 (m, 3H, Naph), 7.44–7.18 (m, 3H, Naph), 6.55 (s, 4H, Mes), 4.23 (d,
J = 12.31 Hz, 2H, PCH2), 2.20 (s, 12H, o-Me), 2.00 (s, 6H, p-Me). 
13C{1H}-NMR (75.5 MHz, C6D6): δ = 216.3 (d, J = 51.3 Hz, CO), 140.9
(Mes-C4), 136.4 (d, J = 40.8 Hz, Mes-C1), 136.2 (d, J = 0.6 Hz, Mes-C2),
134.1 (d, J = 2.1 Hz, Naph), 132.8 (d, J = 4.0 Hz, Naph), 129.8 (d, J = 6.3
Hz, Naph), 129.2 (Mes-C3), 128.4 (Naph), 128.2 (Naph), 127.1 (d, J = 8.5
Hz, Naph), 126.4 (Naph), 125.9 (Naph), 125.3 (d, J = 3.2 Hz, Naph), 125.2
(d, J = 1.2 Hz, Naph), 30.5 (d, J = 49.7 Hz, PCH2), 20.7 (p-CH3), 19.5 (o-
CH3).  31P{1H}-NMR (121.5 MHz, C6D6): δ = 22.9.  31P-NMR (121.5 MHz,
C6D6): δ = 22.9 (t, J = 12.2 Hz).  IR (ATR [cm-1]): 2922.7 (w), 1663.6 (m),
1634.9 (w), 1605.3 (m), 1509.0 (w), 1419.4 (w), 1377.3 (w), 1295.2 (w),
1264.0 (w), 1214.4 (m), 1195.9 (s), 1148.4 (w), 1030.8 (w), 965.0 (w),
893.0 (w), 857.4 (m), 820.4 (m), 795.1 (m), 775.9 (s), 743.9 (m), 730.2 (w),
720.2 (m), 707.8 (w), 678.0 (w), 660.8 (w), 621.6 (w).  UV/VIS (ACN [nm],
ε [lmol-1cm-1]): 417 (269, shoulder), 396 (486, shoulder), 368 (757, max),
319 (3810, max), 292 (11676, shoulder), 282 (13081, max), 250 (9287,
shoulder), 243 (11594, max), 239 (11588, max), 220 (60579, max), < 215
(< 60000, max). MS (ESI): m/z = 483.2084 (MH+).  DTA/TG: melting
point 119 °C, decomposition > 170 °C.
SHELXS.
Synthesis of 1-5. All manipulations with air or moisture sensitive
compounds were performed in a Standard vacuum line using dried glass
ware. All reactions were performed under an argon atmosphere in dried
and argon saturated solvents. Sodium/benzophenone was used for drying
toluene, diethylether and sodium, benzophenone, tetraglyme was used for
drying DME. Air sensitive compounds were stored and weighed in a glove
box from M Braun (Lab master 130 bzw. 150B-G). Chemicals were used
as purchased from ABCR, Acros, Aldrich or Fluka.
1-phenylethyl-PO(COMes)2 (1). 5.016 g Na[P(COMes)2] x 0.5 DME
(12.721 mmol) and 1.7 mL 1-phenylethylbromide (2.295 g, 12.401 mmol)
were dissolved in 10 mL DME in a 50 mL Schlenk flask. After heating the
reaction mixture to 60 °C for 24 h, a complete conversion to the
corresponding phosphane is indicated by 31P NMR spectroscopy (δ = 71.1
ppm). 10 mL toluene were added and the suspension was cooled in an ice
bath. Subsequently, 4.5 mL 30% H2O2 (approx. 4 equivalents) were added
to achieve the quantitative oxidation to the bis(acyl)phosphane oxide 1. 30
mL Dichloromethane (DCM) were added and the resulting mixture was first
extracted with 10 mL deionized water, then with 10 mL of a saturated
aqueous Na2CO3 solution, then with 10 mL of a saturated aqueous NaCl
solution, and finally again with 10 mL deionized water. The combined
aqueous phases were extracted with 20 mL DCM. Afterwards the
combined organic phases were dried over Na2SO4. After filtration and
evaporation of all volatiles under vacuum at 60 °C (oil pump, 1 mbar) 4.927
g (11.035 mmol, 87 % yield) of BAPO 1 are obtained as yellow solid. 1H-
NMR (400.13 MHz, C6D6): δ = 7.56–7.55 (m, 4H, Ph), 7.29–7.27 (m, 2H,
Ph), 7.08–7.05 (m, 4H, Ph), 6.68 (s, 4H, Mes), 6.53 (s, 4H, Mes), 4.38–
4.31 (m, 2H, CH), 2.50 (s, 12H, o-Me), 2.09 (s, 3H, p-Me), 2.04 (s, 12H, o-
MeO(CH2CH2O)2-PO(COMes)2 (3). 4.048 g Na[P(COMes)2] x 0.5 DME
(10.290 mmol) and 1.7 ml degassed bromodiethylene glycol (2.290 g,
11.885 mmol) were dissolved in 10 mL DME in a 50 mL Schlenk flask.
After stirring the reaction mixture at 80 °C for 5 days, 31P NMR
spectroscopy (δ = 44.9 ppm) indicates the complete conversion to the
corresponding phosphane. The suspension was concentrated under
vacuum (oil pump, 1 mbar), the residue suspended in 20 mL of ethanol,
and the reaction mixture cooled to 0 °C in an ice bath before 1.2 mL 30%
H2O2 (approx. 1 equivalent) were added to achieve quantitative oxidation.
The reaction mixture was concentrated to dryness under vacuum and
suspended in 20 mL of diethylether. Na2SO4 was added to remove residual
water, the mixture filtered, and the clear filtrate concentrated under
vacuum and 60 °C. The product 3 was obtained in 96 % yield (4.407 g,
3
3
Me), 1.98 (s, 3H, p-Me), 1.62 (dd, JHH = 7.20 Hz, JPH = 16.01 Hz, 3H,
CH3).  13C{1H}-NMR (100.6 MHz, C6D6): δ = 215.8 (d, J = 50.0 Hz, CO),
215.3 (d, J = 54.6 Hz, CO), 141.5 (Mes-C4), 141.2 (Mes-C4), 138.5 (d, J =
4.4 Hz, Ph-C1), 137.8 (d, J = 41.7 Hz, Mes-C1), 136.5 (d, J = 40.0 Hz, Mes-
C1), 137.6 (Mes-C2), 136.5 (Mes-C2), 130.1 (d, J = 6.3 Hz, Ph-C2), 129.8
(Mes-C3), 129.6 (Mes-C3), 129.1 (Ph-C4), 127.8 (d, J = 1.8 Hz, Ph-C3),
38.8 (d, J = 52.7 Hz, PCH), 21.3 (p-CH3), 21.2 (p-CH3),20.4 (o-CH3), 19.7
(o-CH3), 17.2 (d, J = 2.1 Hz, CCH3).  31P{1H}-NMR (162.0 MHz, C6D6): δ
= 31.1.  31P-NMR (162.0 MHz, C6D6): δ = 31.1 (dq, 3JPH = 8.8 Hz, 2JPH
=
15.7 Hz).  IR (ATR [cm-1]): 2961.2 (w), 2928.3 (w), 2361.8 (w), 1662.3
(m), 1606.5 (m), 1493.5 (w), 1452.0 (m), 1420.3 (w), 1378.1 (w), 1261.7
(w), 1196.7 (s), 1146.3 (m), 1094.4 (m), 960.3 (w), 880.8 (m), 849.3 (s),
783.4 (s), 768.0 (s), 741.5 (m), 705.2 (s), 649.5 (m), 616.8 (m).  UV/VIS
(ACN [nm], ε [l mol-1cm-1]): 416 (438, shoulder), 400 (469, max), 368 (790,
max), 318 (2945, max), 245 (6845, shoulder), < 200 (42063, max).  MS
9.915 mmol) as yellow oil. H-NMR (300.13 MHz, C6D6): δ = 6.68 (s, 4H,
1
Mes), 3.74 (dt, JPH = 15.31 Hz, JHH = 6.45 Hz, 2H, PCH2CH2), 3.34 (t, J =
4.95 Hz, 2H, CH2), 3.17 (t, J = 4.95 Hz, 2H, CH2), 3.11 (s, 3H, OMe), 2.59–
2.51 (m, PCH2), 2.51 (s, 12H, o-Me), 2.09 (s, 6H, p-Me).  13C{1H}-NMR
(75.5 MHz, C6D6): δ = 215.9 (d, J = 55.8 Hz, CO), 140.7, (Mes-C4), 136.5
(d, J = 41.7 Hz, Mes-C1), 136.4 (Mes-C2), 129.2 (Mes-C3), 71.5 (CH2OMe),
70.11 (CH2CH2OMe), 63.6 (d, J = 4.8 Hz, PCH2CH2), 58.2 (OMe), 28.2 (d,
J = 55.1 Hz, PCH2), 20.8 (p-Me), 19.9 (o-Me).  31P{1H}-NMR (121.5 MHz,
C6D6): δ = 25.0.  31P-NMR (121.5 MHz, C6D6): δ = 25.2–24.8 (m).  IR
(ATR [cm-1]): 2921.3 (w), 2868.2 (w), 1721.0 (w), 1672.8 (m), 1607.3 (s),
1451.8 (m), 1421.4 (m), 1380.4 (w), 1295.8 (w), 1245.8 (w), 1196.2 (s),
1105.1 (s), 1034.0 (m), 957.6 (w), 886.5 (m), 849.9 (s), 770.6 (m), 741.4
(m), 699.8 (w), 619.2 (m).  UV/VIS (ACN [nm], ε [lmol-1cm-1]): 394 (477,
shoulder), 361 (603, max), 316 (18689, max), 291 (8021, max), 239 (6221,
shoulder), < 200 (30299, max).  MS (ESI): m/z = 445.2157 (MH+). 
DTA/TG: decomposition > 150 °C.
(ESI): m/z
= 447.2076 (MH+).  DTA/TG: melting point 178°C,
decomposition > 210°C  X-Ray Diffraction: CCDC 1536239.
1-naphtylmethyl-PO(COMes)2 (2). 3.893 g Na[P(COMes)2] x 0.5 DME
(9.896 mmol) and 1.726 g degassed chloromethylnaphthalin (9.771 mmol)
were dissolved in 10 mL DME in a 50 mL Schlenk flask. After stirring the
reaction mixture at room temperature for 4 hours, a complete conversion
to the corresponding phosphane is indicated by 31P NMR spectroscopy (δ
= 52.9 ppm). 10 mL toluene were added and the suspension was cooled
in an ice bath. Subsequently, 5 mL 30% H2O2 (approx. 5 equivalents) were
added. After
1 hour at 50 °C, the quantitative oxidation to the
bis(acyl)phosphane oxide 2 was achieved. After addition of 50 mL DCM,
the reaction mixture was first extracted with 20 mL deionized water, then
with 20 mL of a saturated aqueous Na2CO3 solution, then with 20 mL of a
saturated aqueous NaCl solution, and finally again with 20 mL deionized
water. The combined aqueous phases were extracted with 20 mL DCM.
Afterwards the combined organic phases were dried over Na2SO4. After
3-bromopropyl-PO(COMes)2 (4). 5.312 g Na[P(COMes)2] x 0.5 DME
(13.502 mmol) and
a tenfold excess of 15 ml degassed 1,3-
dibromopropane (29.835 g, 147.786 mmol) were dissolved in 20 mL DME
in a 50 mL Schlenk flask. After stirring the reaction mixture at 60 °C for 16
hours, 31P NMR spectroscopy (δ = 48.5 ppm) indicates the complete
conversion to the corresponding phosphane. Oxygen (5.0, Pangas) was
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
bubbled through the solution for 30 minutes at room temperature.
Subsequently, 50 mL of diethylether were added and this mixture was
extracted first with 15 mL distilled water, then two times with 15 mL of a
saturated aqueous Na2CO3 solution, and finally with 15 mL distilled water.
The combined aqueous phase was extracted once with 50 mL diethylether
and the combined organic phases were dried over Na2SO4. After filtration,
the filtrate was concentrated to dryness on the vacuum at 60 °C. The
residue was purified by flash-chromatography using hexane/ethylacetate
1:2 as eluent to give 5.2 g (83%) of product 5 as yellow oil. 1H-NMR
(300.13 MHz, C6D6): δ = 6.66 (s, 4H, Mes), 2.95 (t, J = 6.30 Hz, 2H, CH2Br),
2.46–2.30 (m, 2H, PCH2), 2.41 (s, 12H, o-Me), 2.15–1.98 (m, 2H,
PCH2CH2), 2.08 (s, 6H, p-Me).  13C{1H}-NMR (75.5 MHz, C6D6): δ = 216.4
(d, J = 54.0 Hz, CO), 141.0, (Mes-C4), 136.5 (d, J = 40.9 Hz, Mes-C1),
135.8 (Mes-C2), 129.3 (Mes-C3), 33.4 (d, J = 14.4 Hz, CH2Br), 25.1 (d, J =
54.1 Hz, PCH2), 25.0 (d, J = 3.4 Hz, PCH2CH2), 20.8 (p-Me), 19.6 (o-Me).
(5813, max), 243 (5486, shoulder), < 200 (33497 max).  MS (ESI): m/z =
547.2632 (MH+).  DTA/TG: melting point 37 °C, decomposition > 190 °C.
Materials and Solvents for Spectroscopic Investigations. The solvent
acetonitrile was obtained from Roth (purity ≥ 99.9 %). Butyl acrylate (purity
≥ 99.0 %), methyl methacrylate (≥ 99.0 %), 1-vinyl-2-pyrrolidone (≥ 97.0 %)
and styrene (≥ 99.5 %) were obtained from Fluka and used as received.
The photoinitiator Irgacure® 819 (6) was obtained from BASF. All
experiments were performed at ambient temperature.
Emission Spectroscopy. Solutions of the photoinitiators in acetonitrile
were prepared so that the absorbance at and above the excitation
wavelength was ≤ 0.1. The absorption spectra were recorded using a UV-
3101 PC UV-VIS-NIR spectrometer (Shimadzu, Japan). Fluorescence
emission spectra were recorded with a FluoroMax-2 spectral-fluorimeter
(Horiba Scientific, Japan) at the excitation wavelength of 373 nm.
Fluorescence quantum yields (ΦF) of 1–5 were determined by comparison
with the known quantum yield of 9,10-diphenylanthracene (ΦST = 0.95 in
cyclohexane).[13] Emission spectra were measured for each compound
and for the standard at four different concentrations. The wavelength
integrated intensities of these spectra were plotted versus the absorbance
at the excitation wavelength (A373). From the slopes of these plots, the

31P{1H}-NMR (121.49 MHz, C6D6): δ = 26.1.  31P-NMR (121.49 MHz,
C6D6): δ = 26.4–25.9 (m).  IR ATR [cm-1]): 2922.7 (w), 1735.7 (w), 1672.0
(m), 1607.3 (s), 1431.9 (m), 1378.6 (w), 1295.9 (w), 1241.6 (m), 1212.6
(s), 1193.9 (s), 1147.3 (m), 1035.5 (m), 958.6 (w), 888.0 (m), 849.7 (s),
757.1 (m), 736.9 (m), 619.0 (m).  UV/VIS (ACN [nm], ε [lmol-1cm-1]): 394
(466, shoulder), 364 (552, max), 315 (2330, max), 294 (7283, max), 241
(5858, shoulder), < 200 (30959, max).  MS (ESI): m/z = 463.1037 (MH+).
 DTA/TG: decomposition > 170 °C.
fluorescence quantum yields were calculated according to equation 1,[13]
퐼 퐴푆푇 휂2
퐼푆푇 퐴 휂푆2푇
Ф퐹 = Ф푆푇
(1)
Synthesis of 3-(triethoxysilyl)propyl-PO(COMes)2 (5). 4.995
g
Na[P(COMes)2] 0.5 DME (12.697 mmol) and 4.228 1,3-
x
g
where I is the integrated emission intensity, A the absorbance at 373 nm
and η the refractive index of the solvent (acetonitrile for the BAPOs and
cyclohexane for the standard ST).
iodopropyltriethoxysilane (4.228 g, 12.726 mmol) were dissolved in 20 mL
DME in a 50 mL Schlenk flask. After stirring the reaction mixture at 60 °C
for 2 hours, 31P NMR spectroscopy (δ = 50.8 ppm) indicates the complete
conversion to the corresponding phosphane. The suspension was
concentrated to dryness under vacuum and subsequently 10 mL toluene
and 10 mL Diethylether were added. The resulting suspension was
extracted two times with 10 mL of degassed aqueous K2CO3 (pH = 10).
Then the mixture was cooled in an ice bath and a small amount of K2CO3
was added to assure saturation with K2CO3. Afterwards 1.8 mL H2O2 (30%,
ca. 1.4 equiv.) were slowly added in order to oxygenate the phosphane to
5. 20 mL Diethylether were added before the suspension was extracted
with two times 20 mL saturated aqueous Na2CO3, two times 10 mL
saturated aqueous NaCl, and once with 10 mL of degassed aqueous
K2CO3 (pH = 10). The combined aqueous phase were extracted once with
20 mL diethylether, the combined organic phases were dried over Na2CO3,
all insoluble parts were filtered off, and the filtrate dried under vacuum at
60 °C. This treatment gave 4.367 g product 5 (7.988 mmol, 63%) in form
of a yellow wax.1H-NMR (400.13 MHz, C6D6): δ = 6.66 (s, 4H, Mes), 3.82
(q, J = 6.94 Hz, 6H, OCH2CH3), 2.55–2.45 (m, 2H, PCH2), 2.48 (s, 12H, o-
Me), 2.18–2.08 (m, 2H, PCH2CH2), 2.08 (s, 6H, p-Me), 1.23 (t, J = 7.00,
6H, OCH2CH3), 0.80 (t, J = 7.80 Hz, 2H, SiCH2).  13C{1H}-NMR (100.6
MHz, C6D6): δ = 217.5 (d, J = 53.4 Hz, CO), 141.0 (Mes-C4), 137.3 (d, J =
40.2 Hz, Mes-C1), 136.2 (Mes-C2), 129.6 (Mes-C3), 58.7 (OCH2CH3), 29.8
(d, J = 52.3 Hz, PCH2), 21.2 (p-CH3), 20.2 (o-CH3), 18.7 (OCH2CH3), 16.2
(d, J = 4.3 Hz, PCH2CH2), 12.9 (d, J = 12.4 Hz, SiCH2).  31P{1H}-NMR
(162.0 MHz, C6D6): δ = 29.0.  31P-NMR (162.0 MHz, C6D6): δ = 29.1–28.9
(m).  IR (ATR [cm-1]): 2974.5 (w), 2920.0 (w), 2878.6 (w), 2359.5 (w),
1669.6 (w), 1608.7 (m), 1441.2 (w), 138131 (w), 1293.9 (w), 1253.1 (w),
1211.2 (m), 1197.7 (m), 1164.7 (w), 1149.0 (m), 1075.8 (s), 1033.3 (m),
956.7 (m), 887.3 (m), 863.0 (w), 849.0 (m), 804.0 (m), 781.5 (m), 748.4
(m), 732.2 (m), 698.5 (w), 645.3 (w), 618.1 (m).  UV/VIS (ACN [nm], ε
[lmol-1cm-1]): 394 (359, shoulder), 365 (443, max), 303 (4643, max), 290
Laser Flash Photolysis Experiments. The experiments were performed
on a LKS80 Laser Flash Photolysis Spectrometer (Applied Photophysics,
UK). Samples were excited with the frequency tripled light from the
Spitlight Compact 100 (InnoLas, Germany) solid state Nd:YAG laser at 355
nm (pulse duration: 8 ns, energy: 10 mJ/pulse). The concentration of the
BAPOs in the acetonitrile solutions was adjusted to achieve the
absorbance of ~ 0.3 at 355 nm. The solutions were purged with argon for
10 minutes before the measurement. The transient absorption spectra
were recorded in a quartz cuvette (1 cm x 1 cm) using a flow system driven
by a peristaltic pump (0.012 L min-1). Rate constants for the addition of the
phosphanoyl radicals to the monomer double bonds were determined in
pseudo-first-order experiments; solutions of the compounds in acetonitrile
containing monomer-concentrations in the range of 0.5 M to 0.025 M and
providing absorbance of ~ 0.3 at 355 nm were prepared. Static solutions
were saturated with argon and then measured. The decay of the
phosphanoyl radicals was recorded at the absorption maximum
determined from the transient absorption spectra.
TR-EPR Spectroscopy. Continuous-wave time-resolved (TR) EPR
experiments were performed on a Bruker ESP 300E X- band spectrometer
(unmodulated static magnetic field) equipped with a 125 MHz dual channel
digital oscilloscope (Le Croy 9400). As the light source, the frequency
triplet light of a Nd:YAG laser was used (InnoLas Spitlight 400, 355 nm,
operating at 20 Hz, ca. 7 mJ/pulse, 8 ns). The setup is controlled by the
fsc2 software developed by Dr. J. T. Toerring (Berlin). Spectra were
recorded by acquiring the accumulated (50 accumulations) time responses
to the incident laser pulses at each magnetic field value of the chosen field
range (field steps: 0.5 G). Argon-saturated solutions in toluene (~ 15 mM
in photoinitiator concentration) were pumped through a quartz flat cell
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
M.Z. are grateful for the support of the Aktion Österreich –
Slowakei (Project 2016-05-15-003) We thank NAWI Graz, the
ETH Zürich, the Swiss National Science Foundation, and the
BASF company for support of this work.
positioned in the cavity of the EPR spectrometer using a flow system (flow
rate: 2-3 mL min-1).
31P CIDNP-NMR Spectroscopy. The experiments were carried out with a
200 MHz Bruker AVANCE DPX spectrometer equipped by a custom-made
CIDNP probe head. A Quantel Nd-YAG Brilliant B (355 nm, ∼60 mJ/pulse,
pulse length ∼8−10 ns) operating at 20 Hz served as light source. mJ/pulse,
pulse length ∼ 8−10 ns) operating at 20 Hz was employed as the light
source. The timing sequence of the experiment consists of a series of 180°
radiofrequency (RF) pulses (applied to suppress the normally present
NMR intensities), the laser flash, the 90° RF detection pulse and the
acquisition of the FID. The spectra were recorded with 1H decoupling and
“dummy” CIDNP spectra employing the same pulse sequence but without
the laser pulse were always measured. Samples were prepared in
deuterated benzene and deoxygenated by bubbling with argon before the
experiment.
Keywords: bis(acyl)phosphane oxides • photoinitiators • radical
photopolymerization
relationships
•
photochemistry
•
structure-reactivity
[1]
[2]
[3]
W. Rutsch, K. Dietliker, D. Leppard, M. Köhler, L. Misev, U. Kolczak,
G. Rist, Prog. Org. Coatings 1996, 27, 227–239.
K. Dietliker, T. Jung, J. Benkhoff, H. Kura, A. Matsumoto, H. Oka, D.
Hristova, G. Gescheidt, G. Rist, Macromol. Symp. 2004, 217, 77–98.
K. K. Dietliker, Chemistry and Technology of Uv and Eb Formulation
for Coatings, Inks & Paints, Volume 3: Photoinitiators for Free Radical
and Cationic Polymerisation, SITA Technology, London, 1991.
U. Kolczak, G. Rist, K. Dietliker, J. Wirz, J. Am. Chem. Soc. 1996,
118, 6477–6489.
[4]
[5]
Thermal Imaging. Thermographic experiments were conducted with the
VarioCAM high resolution infrared camera (InfraTec, Germany). Solutions
of the photoinitiators in acetonitrile were mixed with the monomers in a 1:1
v/v ratio. The samples were purged with argon for 15 minutes. The
polymerization was initiated by light pulses generated by a Hg-Xe-lamp
(Hamamatsu, Japan) positioned above the vial containing the sample (see
figure 5). Pulses of various durations (1s, 5s, 10s) were employed.
Thermograms were recorded in order to monitor the heat profile of the
reactions (recording frequency: 10 Hz). The data were evaluated using the
IRBIS remote 3.0 software.
A. Huber, A. Kuschel, T. Ott, G. Santiso-Quinones, D. Stein, J. Bräuer,
R. Kissner, F. Krumeich, H. Schönberg, J. Levalois-Grützmacher, et
al., Angew. Chemie Int. Ed. 2012, 51, 4648–4652.
[6]
S. Jockusch, I. V. Koptyug, P. F. McGarry, G. W. Sluggett, N. J. Turro,
D. M. Watkins, J. Am. Chem. Soc. 1997, 119, 11495–11501.
S. Jockusch, N. J. Turro, J. Am. Chem. Soc. 1998, 120, 11773–11777.
J. Wang, G. Siqueira, G. Müller, D. Rentsch, A. Huch, P. Tingaut, J.
Levalois-Grützmacher, H. Grützmacher, Y. Habibi, L. A. Lucia, et al.,
Chem. Commun. 2016, 52, 2823–2826.
[7]
[8]
Cyclic Voltammetry. Cyclic voltammograms (CVs) were obtained with a
PG580 potentiostat (Uniscan, UK) using a standard three-electrode
electrochemical cell with platinum disk working (WE) and counter (CE)
[9]
S. Benedikt, J. Wang, M. Markovic, N. Moszner, K. Dietliker, A.
Ovsianikov, H. Grützmacher, R. Liska, J. Polym. Sci. Part A Polym.
Chem. 2016, 54, 473–479.
electrodes and
a
silver wire pseudoreference electrode (RE).
[10]
[11]
[12]
D. E. Fast, M. Zalibera, A. Lauer, A. Eibel, C. Schweigert, A.-M.
Kelterer, M. Spichty, D. Neshchadin, D. Voll, H. Ernst, et al., Chem.
Commun. 2016, 9917–9920.
Approximately 1mM sample solutions were prepared in acetonitrile with
0.1 M tetrabutylammonium tetrafluoroborate supporting electrolyte and
purged with argon for 10 min before each experiment. CVs were recorded
at 100 mV/s scan rate. All potentials are given vs. Fc+/Fc, which was used
as internal reference and are uncorrected from Ohmic drop.
G. Müller, M. Zalibera, G. Gescheidt, A. Rosenthal, G. Santiso-
Quinones, K. Dietliker, H. Grützmacher, Macromol. Rapid Commun.
2015, 36, 553–7.
H. Gruetzmacher, J. Geier, D. Stein, T. Ott, H. Schoenberg, R. H.
Sommerlade, S. Boulmaaz, J.-P. Wolf, P. Murer, T. Ulrich, Chimia
(Aarau). 2008, 62, 18–22.
EPR Spectroscopy. Radical anions of 1-4 were prepared in a special
three-compartment EPR sample tube connected to the vacuum line. K-
metal mirror was sublimated to the wall of the tube and THF (ca. 0.4 mL)
was freshly condensed to dissolve the investigated compound. The
sample was successively degassed by three freeze-pump-thaw cycles and
sealed under high vacuum. Reductions were performed by contact of the
THF solution of the parent molecule with the K-metal mirror in the
evacuated sample tube. A Bruker X-band spectrometers, ESP 300
(equipped with an ENDOR unit, 12.5 kHz field modulation), both with an
EUROTHERM temperature control unit, was used to record the cw-EPR
spectra. Typical experimental conditions for the EPR spectra were 2mW
microwave power and 0.03 mT field modulation. Spectra were analyzed
with WinEPR and SimFonia software provided by the manufacturer of the
spectrometer as well as with WinSim a public domain program.[27]
[13]
[14]
[15]
M. Montalti, A. Credi, L. Prodi, M. T. Gandolfi, Handbook of
Photochemistry, 3rd Ed., CRC Press, Taylor & Francis Group, 2006.
G. W. Sluggett, C. Turro, M. W. George, I. V Koptyugjs, N. J. Turro,
J. Am. Chem. Soc. 1995, 117, 5148–5153.
C. S. Colley, D. C. Grills, N. a. Besley, S. Jockusch, P. Matousek, A.
W. Parker, M. Towrie, N. J. Turro, P. M. W. Gill, M. W. George, J. Am.
Chem. Soc. 2002, 124, 14952–14958.
[16]
[17]
G. W. Sluggett, P. F. McGarry, I. V Koptyug, N. J. Turro, J. Am. Chem.
Soc. 1996, 118, 7367–7372.
I. Gatlik, P. Rzadek, G. Gescheidt, G. Rist, B. Hellrung, J. Wirz, K.
Dietliker, G. Hug, M. Kunz, J.-P. Wolf, J. Am. Chem. Soc. 1999, 121,
8332–8336.
[18]
[19]
[20]
C. Dursun, M. Degirmenci, Y. Yagci, S. Jockusch, N. J. Turro,
Polymer (Guildf). 2003, 44, 7389–7396.
Acknowledgements
G. W. Sluggett, P. F. Mcgarry, I. V Koptyug, N. J. Turro, J. Am. Chem.
Soc. 1996, 7863, 7367–7372.
M.Z. acknowledges the support of Scientific Grant Agency of the
Slovak Republic (Project VEGA 1/0041/15) and A.E., M.S. and
M. Spichty, N. J. Turro, G. Rist, J.-L. Birbaum, K. Dietliker, J. P. Wolf,
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
G. Gescheidt, J. Photochem. Photobiol. A Chem. 2001, 142, 209–
213.
[21]
[22]
[23]
G. W. Sluggett, P. F. McGarry, I. V Koptyug, N. J. Turro, J. Am. Chem.
Soc. 1996, 118, 7367–7372.
A. Yurkovskaya, O. Morozova, G. Gescheidt, in Encycl. Radicals
Chem. Biol. Mater., John Wiley & Sons, Ltd, 2012.
D. Neshchadin, A. Rosspeintner, M. Griesser, B. Lang, S. Mosquera-
Vazquez, E. Vauthey, V. Gorelik, R. Liska, C. Hametner, B. Ganster,
et al., J. Am. Chem. Soc. 2013, 135, 17314–17321.
R. Geier, C. Wappl, H. Freiszmuth, C. Slugovc, G. Gescheidt, Polym.
Chem. 2015, 6, 2488–2492.
[24]
[25]
[26]
[27]
G. Moad, D. H. Solomon, The Chemistry of Radical Polymerization,
Elsevier, 2006.
M. Zalibera, P.-N. Stébé, K. Dietliker, H. Grützmacher, M. Spichty, G.
Gescheidt, European J. Org. Chem. 2014, 2014, 331–337.
D. R. Duling, J. Magn. Reson. Ser. B 1994, 104, 105–110.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700140
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
FULL PAPER
Phosphorous-based Photoinitiators*
Anna Eibel, Max Schmallegger, Michal
Zalibera, Alex Huber, Yasmin Bürkl,
Hansjörg Grützmacher,* and Georg
Gescheidt*
Page No. – Page No.
Novel bis(acyl)phosphane oxide (BAPO) derivatives have been synthesized and
tested with respect to their efficiency as radical photoinitiators and electron
acceptors.
Extending the Scope of
Bis(acyl)phosphane Oxides: New
Derivatives
This article is protected by copyright. All rights reserved.