Fluorescent heteroacenes with multiply-bonded phosphorus

Article abstract of DOI:10.1021/om400838g

An air-stable primary phosphine, 2,6-diphosphinonaphthalene-1,5-diol (4), has been synthesized and structurally characterized. A series of π-conjugated heteroacenes containing two phosphaalkene (P=C) units, 2,7-R ₂-naphtho[1,2-d:5,6-d′]bi(soxaphosphole)s [R₂-NBOP, R = ^tBu (5a), Ad (5b), and Ph (5c)], have been synthesized from reactions of 4 and benzimidoyl chlorides. These novel fluorescent analogues of organic acenes were characterized by multinuclear NMR, UV-vis, and fluorescence spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction experiments.

Full text of DOI:10.1021/om400838g

Article
pubs.acs.org/Organometallics
Fluorescent Heteroacenes with Multiply-Bonded Phosphorus
Feng Li Laughlin,† Nihal Deligonul,† Arnold L. Rheingold,‡ James A. Golen,§ Brynna J. Laughlin,∥
Rhett C. Smith,∥ and John D. Protasiewicz*,†
†Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, United States
‡Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
§Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747,
United States
∥Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson
University, Clemson, South Carolina 29634, United States
S
* Supporting Information
ABSTRACT: An air-stable primary phosphine, 2,6-diphosphino-
naphthalene-1,5-diol (4), has been synthesized and structurally
characterized. A series of π-conjugated heteroacenes containing two
phosphaalkene (PC) units, 2,7-R2-naphtho[1,2-d:5,6-d′]bi-
t
(soxaphosphole)s [R2-NBOP, R = Bu (5a), Ad (5b), and Ph
(5c)], have been synthesized from reactions of 4 and benzimidoyl
chlorides. These novel fluorescent analogues of organic acenes
were characterized by multinuclear NMR, UV−vis, and fluo-
rescence spectroscopy, cyclic voltammetry, and single-crystal X-ray
diffraction experiments.
entacene and related acenes have been intensely
investigated for uses as organic semiconductors, for they
direct conjugation with carbocyclic ring systems should be
accessible.
Chart 1 highlights representative examples of PC-
containing materials that have at least three annulated
conjugated rings. Phosphaanthracenes I and phosphaphenan-
threnes II, III, and IV can be isolated as stable compounds,
P
show high mobilities and on/off ratios in thin-film transistors
for p-type semiconductors.1 The electronic properties of
pentacenes arise from the conjugated nature of the fused ring
system that constitute these structures. While the electronic
properties of acenes can be altered by the addition of various
substituents, the integration of heteroatoms into carbocyclic
frameworks is an interesting route to influence HOMO and
LUMO orbital energetics and HOMO−LUMO gaps, and to
modulate UV−vis absorption and fluorescence emission.2,3
Replacement of carbon atoms in pentacenes and other acenes
by π-bonded heteroatoms provides an even greater opportunity
to directly influence the inherent nature of acene π-systems.
Changes in the nature of the π-system could also affect the
arrangement of molecules (e.g., π−π stacking) in the solid state.
Heteroacenes have thus been attracting the attention of
synthetic chemists. N-Heteroacenes, for example, are now an
established class of compounds with their own attractive
properties.4
Chart 1
There are now a growing number of heteroacenes
incorporating phosphorus atoms.5,6 Most of these materials
feature 1H-phospholes having three-coordinate phosphorus
centers. Phosphorus-containing acenes that possess phosphaal-
kene units (two-coordinate doubly bonded phosphorus
centers) within the π-conjugated extended acene framework
are much rarer, however. Because of the similarities of PC
and CC bonds, analogues of acenes having PC bonds in
Received: August 20, 2013
© XXXX American Chemical Society
A
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especially when substituted with additional phenyl groups.7−15
Compound V is an unusual example of a formally antiaromatic
compound.16,17 Compounds VI−IX feature additional three-
coordinate N and P atoms.18−21
We have recently been exploring the chemistry and
photochemistry of 1,3-benzoxaphospholes and 2,6-benzobis-
(oxaphosphole)s (R-BOPs and R2-BBOPs, respectively; Chart
2).22−24 Unlike other materials featuring phosphaalkene groups,
solid 2,6-diphosphinonaphthalene-1,5-diol (4) in 95.6% yield.
1
Compounds 2−4 were readily identified by H, 13C, and 31P
NMR spectroscopy. The 31P NMR shift for 4 (δ −156.3) is
comparable to that we reported previously for 3-phosphino-2-
naphthol (δ −148.3). Notably, compound 4 displays significant
air stability, paralleling the air stability of 3-phosphino-2-
naphthol.25 By contrast, 2-phosphinonaphthalene slowly
degrades in CDCl3 in the presence of air.30
The solid-state packing within crystals of 4 was revealed by
an X-ray diffraction study (Figure 1). Intermolecular O···HO
Chart 2
Figure 1. Structural diagrams showing the solid-state hydrogen-
bonding network for 4.
however, these types of compounds are unique in that they are
highly fluorescent and can have quite high quantum yields.
These initial discoveries have been expanded, and we have
found that 2-R-naphtho[2,3-d]oxaphospholes (R-NOPs; Chart
2) are also fluorescent and represent phosphaacenes.25 In this
work, we have achieved the synthesis and characterization of
fluorescent 2,7-R2-naphthobis(oxaphosphole)s (R2-NBOPs;
Chart 2) as new examples of extended heteroacenes bearing
multiple PC units.
bonding is indicated by short O···O contacts (2.74 Å), which
are represented by dashed lines in Figure 1. The two
independent molecules of 4 form columns (3.43 Å) bridged
by the hydrogen bonds within the lattice. No evidence for
intramolecular hydrogen bonding involving phosphorus atoms
is noted.
The reaction of compound 4 with several benzimidoyl
chlorides in refluxing THF produced 2,7-R2-naphtho[1,2-d:5,6-
d′]bis(oxaphosphole)s in good to modest yields (Scheme 2).
The synthetic route to R2-NBOPs begins with commercially
available naphthalene-1,5-diol (1). The reaction of 1 with
diethyl chlorophosphate in the presence of triethylamine in
THF produces brown solid tetraethyl naphthalene-1,5-diylbis-
(phosphate) (2) in 84.4% isolated yield (Scheme 1).
Compound 2 in the presence of LDA undergoes a double
anionic phospho-Fries rearrangement26−29 to give tetraethyl
1,5-dihydroxynaphthalene-2,6-diylbis(phosphonate) (3), which
was isolated in 89.0% yield. Reduction of 3 with lithium
aluminum hydride in THF at room temperature afforded white
Scheme 2
Scheme 1
The R2-NBOPs were isolated as white (5a, 5b) or yellow (5c)
1
solids. Compounds 5a−c were characterized by 31P, H, and
13C NMR spectroscopy. The phosphorus NMR chemical shifts
are consistent with the presence of the PC functionality and
are 6.7−7.9 ppm downfield from those of similarly substituted
R-NOPs. The 13C{1H} chemical shifts for the PC units of 5
are doublets (JPC = 55.3−63.6 Hz) located 3.9−5.5 ppm upfield
of those for comparably substituted R-NOPs. The new R2-
NBOPs displayed significant air stability, even in solution. For
example, in a solution of 5a in CDCl3 left open to the air for 60
days (which required addition of further CDCl3 as it
evaporated), approximately 80% of the 5a remained, as judged
B
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t
by 31P{1H} NMR spectroscopy. By contrast, Bu2-BBOP and
tBu-NOP were completely decomposed in CDCl3 after 5 and
28 days, respectively.
Single crystals of 5a and 5c suitable for an X-ray diffraction
study were obtained by slow evaporation of diethyl ether and
CH2Cl2 solutions, respectively. The results are portrayed in
Figure 2. The PC bond lengths of 1.705(1) Å for 5a and
Figure 4. (top) UV−vis absorption and (bottom) fluorescence
emission spectra for 5a−5c in CH2Cl2 (excitation wavelength = 387
nm).
Figure 2. Structural diagrams for compounds 5a (top) and 5c
(bottom).
1.729(3) Å for 5c are consistent with such distances found in p-
ClC6H4-BOP [1.712(7) Å] and Bu2-BBOP [1.694(1) Å].
The structure of 5c is essentially planar, and analysis of the
crystal packing revealed that the molecules of 5c are π-stacked
along the a axis with only 3.49 Å separating the molecules
(Figure 3). A packing diagram for 5a is available in Figure S1 in
the Supporting Information.
Table 1. Absorption and Emission Data for 5a−c in CH2Cl2
24,31
t
λmax (nm)
ε (M−1 cm−1
)
λF,max (nm)
ΦF
τ (ns)
5a
5b
5c
316
318
387
24600
24300
44800
386
387
422
0.07
0.08
0.63
0.82(5)
1.50(8)
1.04(1)
at varying concentrations are nearly identical to spectra
recorded in CH2Cl2. The emission spectra, however, show a
small additional band at 394 nm (see the Supporting
Information) in addition to a broad absorption around 413
nm that is concentration independent. These latter observa-
tions do not suggest that excimer emission is important.
This emission band of 5c in CH2Cl2 is also blue-shifted by
around 40 nm compared with that for previously reported Ph-
NOP (λF,max = 461 nm).24 The quantum yield of emission from
5c (Table 1) is about 8 times higher than those of the two
alkyl-NBOPs, paralleling the observed differences between
alkyl- and aryl-substituted BOP derivatives.24
Electrochemical experiments were performed on 5a and 5c
to probe their reduction potentials in THF. Compound 5a did
not show evidence for reduction within the electrochemical
window examined (to −2.5 V vs SCE) and thus behaves
similarly to alkyl-substituted R-BOPs and R-NOPs.23,25 By
contrast, 5c features an irreversible reduction wave (Epc at
−1.90 V vs SCE). The reduction of 5c occurs more readily than
for Ph-BOP (Epc = −2.02 V) and is close to that observed for
Ph-NOP (Epc = −1.92 V). Single-electron reductions of many
Ar-BOPs are reversible. The reasons for the irreversible
reduction of 5c, however, are unclear at this time. The easier
reduction of 5c relative to 5a or 5b is consistent with a lower
Figure 3. Packing diagram for compound 5c.
As shown in Figure 4, the nature of the absorption and
emission spectra for the alkyl- and aryl-substituted NBOPs in
CH2Cl2 are very different. In particular, the absorption
maximum for 5c is red-shifted by almost 70 nm relative to
λmax for 5a and 5b. Key absorption and photoluminescence data
are compiled in Table 1. All three compounds are notably
fluorescent under UV light, appearing blue. The fluorescence
emission spectra of 5a and 5b exhibit three emission peaks
around 352, 369, and 387 nm. In contrast, 5c displays only one
broad peak at 422 nm with high intensity. This shift is
presumably due to the extended conjugation of 5c relative to 5a
and 5b. The nature of the emission of 5c in CH2Cl2 does not
change upon dilution. The absorption spectra of 5c in hexanes
C
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prior to use for UV−vis and fluorescence measurements. All of the
substituted benzimidoyl chlorides were prepared by reported
procedures.32 NMR spectra (1H and 31P{1H}) were recorded in
CDCl3 on a Varian Inova AS-400 spectrometer operating at 399.7 and
161.8 MHz, respectively, and 31P{1H} NMR spectra were referenced
to 85% H3PO4. 13C{1H} NMR spectra were recorded in CDCl3 on a
Varian Inova AS-600 spectrometer operating at 150.9 MHz. UV−vis
and fluorescence spectra were recorded using a Cary 5G UV−vis−NIR
spectrophotometer and a Cary Eclipse spectrometer, respectively.
Anthracene in ethanol was used as the quantum yield standard (conc.
5.0 × 10−6 M). The excitation slit width for all of the measurements
was kept at the default setting (5 nm). Melting points were measured
on a Thomas-Hoover capillary melting-point apparatus. Elemental
analyses were performed by Robertson Microlit Laboratories (Ledge-
wood, New Jersey). High-resolution mass spectrometry was performed
by the University of Michigan Mass Spectrometry facility using a VG
(Micromass) 70-250-S magnetic sector spectrometer with the EI
technique at 70 eV. Single-crystal X-ray data were collected with a
Bruker AXS SMART APEX II CCD diffractometer using mono-
chromatic Mo Kα radiation with the ω scan technique.
π* orbital. This hypothesis was further corroborated by
theoretical DFT calculations (B3LYP/6-31G*) performed on
5c. The HOMO and LUMO showing the delocalized nature of
the π-system are presented in Figure 5 (see the Supporting
Tetraethyl Naphthalene-1,5-diylbis(phosphate) (2). Triethylamine
(26.3 g, 187 mmol) was added dropwise to a mixture containing
naphthalene-1,5-diol (10.0 g, 62.4 mmol) and diethyl chlorophosphate
(22.6 mL, 156 mmol) in 250 mL of THF. The solution was stirred for
12 h. Aqueous HCl (1.2 M, 100 mL) was added, and the mixture was
stirred for 30 min. Diethyl ether (250 mL) was added, and the organic
layer was separated and washed successively with degassed aqueous
HCl (1.2 M, 100 mL), aqueous NaOH (1 M, 250 mL), and distilled
water (500 mL). The solution was then dried over anhydrous sodium
sulfate and filtered, and the solvent was removed by rotary evaporation
to yield 2 as a brown oil (22.8 g, 84.4%). 1H NMR: δ 8.00 (d, 2H, 3JPH
= 8.0 Hz), 7.54 (m, 2H), 7.47 (m, 2H), 4.26 (m, 8H), 1.35 (t, 12H,
3JHH = 7.2 Hz). 31P{1H} NMR: δ −5.3 (s). 13C{1H} NMR: δ 146.8 (d,
Figure 5. Computed LUMO (top) and HOMO (bottom) for
compound 5c.
Information for other orbitals). The minimized structure also
shows PC bond lengths of 1.737 Å, in agreement with those
determined experimentally [1.729(3) Å]. For comparison,
calculations were undertaken for Me2-NBOP to model
compounds 5a and 5b. The LUMO for 5c (−1.97 eV) is
raised to −1.28 eV upon replacement of the phenyl groups with
methyl substituents. We previously established a working
model to predict the electrochemical activity of benzoxaphosp-
holes23 and found that those compounds with a computed
LUMO energy higher than −1.4 eV would not be easily
reduced in THF. The lack of reduction of compounds 5a and
5b thus conform to this model. The oxidation chemistry of 5a−
c was not examined because analyses of simpler analogues
showed no reversible electrochemistry and provided few
insights.23
JPC = 6.9 Hz), 128.0 (d, JPC = 6.9 Hz), 126.2, 118.7, 115.8 (d, JPC = 2.3
Hz), 65.0 (d, JPC = 6.1 Hz), 16.3 (d, JPC = 6.6 Hz). Mp: 73−74 °C.
Anal. Calcd for C18H26O8P2: C 50.01%, H 6.06%. Found: C 50.13%, H
6.01%.
Tetraethyl 1,5-Dihydroxynaphthalene-2,6-diylbis(phosphonate)
(3). To a solution of diisopropylamine (37.6 mL, 266 mmol) in 100
n
mL of THF at −78 °C was added BuLi (2.5 M in hexane, 102 mL,
266 mmol) by cannula. The mixture was stirred for 15 min, generating
a white slurry of lithium diisopropylamide (LDA). Tetraethyl
naphthalene-1,5-diylbis(phosphate) (2) (23.0 g, 53.2 mmol) was
dissolved in 100 mL of THF, and this solution was transferred to the
LDA solution by cannula. The resulting solution was stirred for 1 h at
−78 °C and then warmed to RT and stirred for an additional 2 h. The
reaction mixture was poured into an aqueous saturated ammonium
chloride solution (250 mL) and stirred until the precipitate was
dissolved. The mixture was extracted with three 200 mL portions of
methylene chloride. The combined organic layers were separated and
washed with three 300 mL portions of distilled water. The solution
was then dried over anhydrous sodium sulfate and filtered. The solvent
was removed by rotary evaporation to yield 3 as a brown solid (20.5 g,
CONCLUSION
■
The air-stable primary phosphine 2,6-diphosphinonaphthalene-
1,5-diol has been synthesized and fully characterized. This
phosphine allowed ready access to a series of heteroacenes, R2-
NBOPs, that possess two phosphaalkene units. These
conjugated compounds possess significant air and water
stability and exhibit significant blue fluorescence. Comparisons
of the optical and electrochemical properties to related
benzoxaphospholes and naphthoxaphospholes show that the
R2-NBOPs behave more like benzoxaphospholes than naph-
thoxaphospholes. Efforts are now underway to prepare systems
with a greater degree of π-conjugation.
1
89.0%). H NMR: δ 11.2 (s, 1H, OH), 7.87 (m, 1H), 7.36 (m, 1H),
4.11 (m, 4H), 1.33 (t, 6H, 3JHH = 7.2 Hz). 31P{1H} NMR: δ 23.6 (s).
13C{1H} NMR: δ 160.4 (d, JPC = 7.0 Hz), 128.5 (dd, JPC = 13.2 Hz, JPC
= 7.7 Hz), 126.0 (d, JPC = 7.0 Hz), 114.7 (d, JPC = 14 Hz), 104.2 (d,
JPC = 178 Hz), 63.0 (d, JPC = 4.6 Hz), 16.4 (d, JPC = 6.7 Hz). Mp:
141.0−141.5 °C. Anal. Calcd for C18H26O8P2: C 50.01%, H 6.06%.
Found: C 50.12%, H 6.02%.
2,6-Diphosphinonaphthalene-1,5-diol (4). Tetraethyl 1,5-dihy-
droxynaphthalene-2,6-diylbis(phosphonate) (3) (10.0 g, 23.1 mmol)
was slowly added to a solution of LiAlH4 (5.27 g, 139 mmol) in 150
mL of THF. The solution was stirred for 2 h. An aqueous solution of
saturated ammonium chloride was added dropwise to the reaction
mixture, and the mixture was extracted with chloroform (300 mL).
The organic layer was separated and filtered through Celite. The
solvent was removed by rotary evaporation to yield 4 as a white solid
EXPERIMENTAL SECTION
■
General. Experimental procedures for air- and water-sensitive
reactions were conducted under nitrogen using either Schlenk line
techniques or an MBraun drybox. Tetrahydrofuran, toluene, and
diethyl ether were dried by distillation from sodium and
benzophenone ketyl. Hexanes were dried by distillation from sodium
and benzophenone in the presence of tetra(ethylene glycol)dimethyl
ether. Methylene chloride was dried by distillation from calcium
hydride. Methylene chloride (99.99%) and methanol were degassed
(2.41 g, 95.6%). 1H NMR: δ 7.70 (d, 1H, 3JPH = 8.4 Hz), 7.52 (t, 1H,
4
3JPH = 8.4 Hz), 5.98 (d, 1H, OH, JPH = 4.0 Hz), 3.84 (d, 2H, JPH
=
D
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208 Hz). 31P{1H} NMR: δ −156.3 (s, 1P). 13C{1H} NMR: δ 154.9 (d,
JPC = 7.9 Hz), 133.2 (d, JPC = 19.3 Hz), 125.7 (d, JPC = 57.4 Hz), 114.2
(d, JPC = 7.7 Hz), 106.0 (d, JPC = 7.4 Hz). Mp: 140−145 °C. Anal.
Calcd for C10H10O2P2: C 53.59%, H 4.50%. Found: C 53.86%, H
4.53%.
AUTHOR INFORMATION
■
Notes
The authors declare no competing financial interest.
2,7-Di-tert-butylnaphtho[1,2-d:5,6-d′]bis(oxaphosphole) (5a).
2,6-Diphosphinonaphthalene-1,5-diol (4) (0.50 g, 2.2 mmol) and N-
phenylpivalimidoyl chloride (2.6 g, 13 mmol) were dissolved in 20 mL
of THF within a 100 mL round-bottom flask with a stir bar. The flask
was outfitted with a reflux condenser, and then the solution was
refluxed under nitrogen for 16 h. The reaction mixture was filtered
using a glass-fritted filter funnel. The solid was extracted two times
with THF (5 mL), and the combined filtrates were evaporated under
vacuum to yield a brown solid. Purification by column chromatog-
raphy (1:1 CH2Cl2/hexanes, Rf = 0.9) led to the isolation of white
ACKNOWLEDGMENTS
■
We thank the National Science Foundation for support (CHE-
1150721).
REFERENCES
■
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Appl. Chem. 2009, 81, 2203. (f) Nickel, B.; Fiebig, M.; Schiefer, S.;
solid 5a (0.21 g, 27%). 1H NMR: δ 8.24 (dd, 1H, 3JPH = 8.4 Hz, 3JHH
2.0 Hz), 8.03 (dd, 1H, 3JPH = 8.4 Hz, 3JHH = 2.0 Hz), 1.56 (d, 9H, 4JHH
= 1.2 Hz). 31P{1H} NMR: δ 81.8 (s). 13C{1H} NMR: δ 212.4 (d, JPC
=
̈
=
63.6 Hz), 156.3 (d, JPC = 3.2 Hz), 132.2 (d, JPC = 40.0 Hz), 126.0 (d,
JPC = 14.4 Hz), 121.0 (d, JPC = 1.5 Hz), 116.0 (d, JPC = 9.1 Hz), 38.1
(d, JPC = 11.3 Hz), 30.1 (d, JPC = 8.6 Hz). UV (CH2Cl2): λmax/nm (ε/
M−1 cm−1) 316 (24550). Fluorescence (CH2Cl2, 5 × 10−6 M): λem/
nm (int.) 368 (690). Quantum yield Φ (CH2Cl2): 0.067. Mp: 208−
212 °C. Anal. Calcd for C20H22O2P2: C 67.41%, H 6.22%. Found: C
67.40%, H 6.21%.
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2,7-Diadamantylnaphtho[1,2-d:5,6-d′]bis(oxaphosphole) (5b).
2,6-Diphosphinonaphthalene-1,5-diol (4) (0.50 g, 2.2 mmol) and N-
adamantylbenzimidoyl chloride (3.1 g, 11 mmol) were dissolved in 25
mL of THF in a 100 mL round-bottom flask with a stir bar. The flask
was outfitted with a reflux condenser, and the solution was refluxed
under nitrogen for 3 h. The reaction mixture was filtered using a glass-
fritted filter funnel. The solid was extracted two times with THF (5
mL), and the combined filtrates were evaporated under vacuum yield a
brown solid. Purification by column chromatography (1:1 CH2Cl2/
hexanes, Rf = 0.9) led to isolation of white solid 5b (0.54 g, 47%). 1H
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́ ́
pati, T.; Sutherland, T. C.;
3
3
NMR: δ 8.25 (dd, 1H, JPH = 8.4 Hz, JHH = 1.6 Hz), 8.04 (dd, 1H,
́
3JPH = 8.4 Hz, JHH = 2.0 Hz), 2.17 (m, 9H), 1.86 (s, 6H). 31P{1H}
3
NMR: δ 80.5 (s). 13C{1H} NMR: δ 212.8 (d, JPC = 62.7 Hz), 156.1 (d,
JPC = 3.0 Hz), 132.0 (d, JPC = 40.0 Hz), 126.1 (d, JPC = 21.0 Hz),
121.0, 116.1 (d, JPC = 9.2 Hz), 42.4 (d, JPC = 8.9 Hz), 40.1 (d, JPC = 9.2
Hz), 36.7, 28.4. UV (CH2Cl2): λmax/nm (ε/M−1 cm−1) 318 (24336).
Fluorescence (CH2Cl2, 5 × 10−6 M): λem/nm (int.) 369 (786).
Quantum yield Φ (CH2Cl2): 0.080. Mp: 358−362 °C. Anal. Calcd for
C32H34O2P2: C 74.99%, H 6.69%. Found: C 74.00%, H 6.63%.
2,7-Diphenylnaphtho[1,2-d:5,6-d′]bis(oxaphosphole) (5c). 2,6-
Diphosphinonaphthalene-1,5-diol (4) (1.0 g, 4.5 mmol) and N-
phenylbenzimidoyl chloride (4.8 g, 22 mmol) were dissolved in 50 mL
of THF in a 250 mL round-bottom flask with a stir bar. The flask was
outfitted with a reflux condenser, and the solution was refluxed under
nitrogen for 21 h. The reaction mixture was filtered using a glass-fritted
filter funnel. The solid residue was collected and purified by flash
column chromatography (1:4 CH2Cl2/hexanes), leading to the
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1
isolation of yellow solid 5c (0.19 g, 11%). H NMR: δ 8.40 (d, 1H,
3
3JPH = 8.4 Hz), 8.15 (d, 3H, JPH = 8.0), 7.52−7.43 (m, 3H). 31P{1H}
NMR: δ 91.6 (s). 13C{1H} NMR: δ 196.0 (d, JPC = 55.7 Hz), 156.2,
134.7 (d, JPC = 13.0 Hz), 134.0, 129.8 (d, JPC = 4.5 Hz), 129.0, 126.3
(d, JPC = 21.4 Hz), 124.8 (d, JPC = 13.9 Hz), 121.5 (d, JPC = 2.9 Hz),
116.9 (d, JPC = 10.1 Hz). UV (CH2Cl2): λmax/nm (ε/M−1 cm−1) 387
(44834). Fluorescence (CH2Cl2, 5 × 10−7 M): λex/nm (int.) 422
(960). Quantum yield Φ (CH2Cl2): 0.626. Mp: 265−270 °C. HRMS
m/z: 396.0478 (calcd 396.0469).
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ASSOCIATED CONTENT
■
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* Supporting Information
Details for the UV−vis absorption and fluorescence emission
spectra, electrochemical measurements, DFT calculations,
crystallographic studies, and CIF files. This material is available
free of charge via the Internet at http://pubs.acs.org.
E
dx.doi.org/10.1021/om400838g | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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dx.doi.org/10.1021/om400838g | Organometallics XXXX, XXX, XXX−XXX