Synthesis and photoelectrochemical performance of chalcogenopyrylium monomethine dyes bearing phosphonate/phosphonic acid substituents

Article abstract of DOI:10.1021/jo401280s

Chalcogenopyrylium monomethine dyes were prepared via condensation of a 4-methylchalcogenopyrylium compound with a chalcogenopyran-4-one bearing a 4-(diethoxyphosphoryl)phenyl substituent (or the phosphonic acid derivative). The dyes have absorbance maxima of 603-697 nm in the window where the solar spectrum is most intense. The dyes formed H-aggregates on TiO₂, increasing the light-harvesting efficiency of the dyes. Shortcircuit photocurrent action spectra were acquired to evaluate the influence of dye structure on the photoelectrochemical performance.

Full text of DOI:10.1021/jo401280s

Note
pubs.acs.org/joc
Synthesis and Photoelectrochemical Performance of
Chalcogenopyrylium Monomethine Dyes Bearing Phosphonate/
Phosphonic Acid Substituents
Matthew A. Bedics, Kacie R. Mulhern, David F. Watson,* and Michael R. Detty*
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, United States
S
* Supporting Information
ABSTRACT: Chalcogenopyrylium monomethine dyes were prepared via condensation of a 4-methylchalcogenopyrylium
compound with a chalcogenopyran-4-one bearing a 4-(diethoxyphosphoryl)phenyl substituent (or the phosphonic acid
derivative). The dyes have absorbance maxima of 603−697 nm in the window where the solar spectrum is most intense. The
dyes formed H-aggregates on TiO2, increasing the light-harvesting efficiency of the dyes. Shortcircuit photocurrent action spectra
were acquired to evaluate the influence of dye structure on the photoelectrochemical performance.
anocrystalline TiO2 is a wide-bandgap semiconductor1−5
photoelectrochemistry on nanocrystalline TiO2, which include
absorbance at >700 nm.
6−8
Nused in dye-sensitized solar cells (DSSCs).
Effective
Dyes 1−8 (Chart 1) were prepared as representative
chalcogenpyrylium dyes to examine the effect of the chalcogen
atoms on the wavelengths of absorbance of light, the
effectiveness of the phosphonate as a linking group, and the
photoelectrochemical performance of DSSCs containing the
dyes. Dyes 7 and 8 have bulky substituents to mimimize
aggregation, allowing the impact of aggregation on TiO2 on
photoelectrochemical performance to be assessed directly.
Condensation of a phosphonate-containing chalcogenopyr-
anone 9−11 with a 4-methylchalcogenopyrylium salt 12−16
(prepared following literature procedures)18,20,29 should give
1−8 (Chart 1) on the basis of literature precedent.19,21 While
phosphonate-containing chalcogenopyranones 9−11 have not
been described, 4-bromophenyl-substituted chalcogenopyra-
nones 17 or 18 (Scheme 1) seem to be appropriate precursors
for introduction of the phosphonate group via Pd-catalyzed
coupling of diethyl phosphite.30 Addition of the elements of
H2S or H2Se to 1,5-diaryl-1,4-pentadiyn-3-one 19 formally
allows the preparation of 17 and 18.31 Pentadiynone 19 can be
prepared from addition of a metal phenylacetylide to the
known 4-bromophenylpropargyl aldehyde (20)32 followed by
oxidation of the intermediate 1,5-diaryl-1,4-pentadiyn-3-ol 21
that is formed.31,33,34
DSSCs require dyes to adhere to and persist on the
semiconductor surface and to absorb light efficiently, inject
electrons into the semiconductor, and oxidize an electron
donor in the electrolyte.7−10 More efficient DSSCs absorb light
available in the near-infrared (NIR) region of the solar
spectrum, which contains approximately half of the sun’s
usable energy,11 and use a sensitizer absorbing in the NIR with
a cosensitizer with high efficiency in the visible spectrum.12
Sensitizer aggregation, which broadens the electronic spectrum,
can be beneficial to the overall efficiency of the DSSC.13−17
Chalcogenopyrylium dyes absorb into the NIR,18−20 and X-
ray structural analysis has shown that chalcogenopyrylium
monomethine dyes have an essentially planar structure.18 The
contributions of the chalcogen atoms to the electronic structure
of these compounds (particularly with respect to HOMO and
LUMO levels) has been examined in detail.18 Chalcogeno-
pyrylium compounds form H- and J-aggregates in polymer
films and are effective photosensitizers in electrophotographic
applications.21−23 In order to evaluate chalcogenopyrylium
compounds in DSSCs, anchoring groups must be introduced
that persist on TiO2. Phosphonate anchoring groups have
surface-adduct formation constants to TiO2 that are much
greater than those for carboxylic acids.15,24−28 Herein, we
describe the synthesis of several chalcogenopyrylium mono-
methine dyes containing a phosphonate linker for attachment
to nanocrystalline TiO2 and preliminary results of their
Received: June 20, 2013
Published: July 30, 2013
© 2013 American Chemical Society
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Note
Chart 1
Scheme 2. Scrambling of Chalcogenopyrylium Rings in the
Synthesis of 4
was the expected 4 with m/z 741.0552 for C39H34O3P80Se2
(calcd m/z 741.0576) and a “methine” CH signal at δ 7.015.
Dye 2221 displayed m/z 605 for C35H2580Se2 and a “methine”
CH signal at δ 6.97. The third product 23 gave m/z 877.0837
for C43H43O6P280Se2 (calcd m/z 877.0865) and a “methine”
CH signal at δ 7.05. In order to confirm the 1H NMR
assignments given for the “scrambled” products, pure 4
(described below) was spiked with ∼10 mol % of authentic
22 with the methine signal of 22 appearing at higher field than
that of 4 (Supporting Information).
The reaction was repeated with 0.11 M 10 and 0.10 M 13 in
Ac2O at 105 °C for 2 min. Dye 4 was isolated in 83% yield, and
neither 22 nor 23 was detected in the reaction mixture. These
concentrations were employed at 105 °C in the preparation of
the remaining dyes with the 4-methylchalcogenopyrylium
compound as limiting reactant. No “scrambled” products
were observed, and yields are compiled in Table 1. Reaction
a
Scheme 1. Synthesis of Chalcogenopyranones 9−11
Table 1. Synthetic Yields, Absorption Maxima (λmax), and
Molar Extinction Coefficients (ε) in CH2Cl2, and Saturation
Surface Coverages (Γ0) on Nanocrystalline TiO2 for Dyes
a
1−5, 7, and 8
compd % yield λmax, nm
ε, M−1 cm−1
Γ0, mol cm−2
1
89
79
93
83
56
65
88
88
630
655
651
677
697
653
603
625
(1.31 0.03) × 105
(1.18 0.03) × 105
(1.27 0.02) × 105
(1.27 0.02) × 105
(1.29 0.01) × 105
∼1.0 × 105
(6.8 1.7) × 10−8
(4.2 0.2) × 10−8
(5.5 0.6) × 10−8
(7.3 1.0) × 10−8
(4.1 0.4) × 10−8
2
3
a
4
Reagents: (a) PhCCMgBr, THF; (b) MnO2, CH2Cl2; (c) (1)
NaOEt, EtOH, (2) Na2S or Na2Se; (d) HP(O)(OEt)2, Pd(OAc)2,
dppf, KOAc, Et3N, THF; (e) Me3SiCl, NaI, CH3CN/CH2Cl2.
5
b
6/6a
(1.0−1.5) × 10−7
7
8
(1.08 0.02) × 105
(1.18 0.01) × 105
(3.7 1.1) × 10−8
(4.3 0.8) × 10−8
Addition of PhCCMgBr (deprotonation of phenyl-
acetylene with EtMgBr) to 20 gave diynol 21 (Scheme 1),
which was oxidized with MnO2 in CH2Cl2 to give 19 in 78%
overall yield. Sodium ethoxide catalyzed addition of EtOH to
19 to give an unisolated mixture of enol ethers,31 to which was
then added Na2S or Na2Se to give 17 or 18. Pd(OAc)2-
catalyzed coupling of diethyl phosphite to 17 and 18 gave 9 and
10.30 Phosphonate 10 was converted to phosphonic acid
derivative 11 using iodotrimethylsilane generated in situ from
chlorotrimethylsilane and NaI in CH2Cl2/CH3CN.35−37
While condensation of 12−16 with 9−11 should lead
directly to dyes 1−8, “scrambling” of the chalcogenopyrylium
rings can occur if concentrations of reactants are too high,
reaction times are too long, or the chalcogenopyranone is
limiting reagent.38 As shown in Scheme 2, 0.2 M 10 and 0.2 M
13 were heated 10 min at 105 °C in Ac2O to give a mixture of 4
(63%), known tetraphenyl derivative 2221 (24%), and 23 with
two phosphonate groups (13%) upon workup. The products in
the mixture were identified by mass spectrometry and 1H NMR
spectroscopy (Supporting Information). The major product
a
Error limits are standard deviations based on a minimum of 4 films/
b
measurement. Assumes ε of ∼1.0 × 105 for both 6 and 6a in a 60:40
mixture of 6 to 6a.
times were a function of chalcogen atom and steric bulk at the
2- and 6-positions. Condensations were slowest with
thiopyrylium compounds 15 (with two tert-butyl substituents,
30 min reaction time), 12 (15 min), and 16 (15 min).
Condensations with selenopyrylium compound 13 were
complete after 2 min and with telluropyrylium compound 14,
after 1 min.
Dye 6 (Chart 1) was prepared from 11 and 12 by heating at
105 °C in AcOH for 5 min as an equal volume of Ac2O was
added slowly and then for an additional 25 min. Dye 6 was
isolated as a 60:40 mixture of 6 and its zwitterionic form 6a,
with an absorbance maximum (λmax) for the mixture of 653 nm,
in 65% combined yield. Attempts to isolate the zwitterionic
form 6a were unsuccessful, as were attempts to protonate and
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Note
isolate only 6. Consequently, other phosphonic acid derivatives
were not prepared for study.
solution, the extent of H-aggregation by 1, 7 and 8 upon
adsorption to TiO2 can be varied (Figure S3, Supporting
Information).
Values of λmax (603−697 nm) for the electronic absorbance
spectra of 1−8 in CH2Cl2 solution are compiled in Table 1 and
fall in the window where the solar spectrum is most intense. In
the higher dielectric solvent CH3CN, blue shifts of 3−7 nm are
observed relative to CH2Cl2. Normalized absorbance spectra
for 1−8 in both solvents are shown in Figure S1 of the
Supporting Information. Values of the molar extinction
coefficient (ε) vary between 1.08 × 105 and 1.31 × 105 M−1
cm−1 (Table 1). Increasing the size of the chalcogen atom gives
a red-shift in λmax, which has been previously reported for
chalcogenopyrylium18,20 and chalcogenoxanthylium dyes39 as
well as in π-excessive heterocyclic systems such as the
polychalcogenophenes.40 Values of ε for dyes 1 and 3−5,
which vary in structure only in the heteroatoms, have no
significant differences among them. Dye 2, where Se has been
substituted for S, has a lower value of ε that is significantly
different from the other dyes 1 and 3−5. Lower values of ε with
Se substitution have been observed in other chalcogen-
containing systems.41 Oscillator strengths for dyes 1−8 fall in
the range 0.57−0.62 and are not different from one another in a
statistically significant way.
Nanocrystalline TiO2 films on FTO-on-glass electrodes
(TiO2/FTO) were functionalized with 1−8. Short-circuit
photocurrent action spectra [incident photon to current
efficiencies (IPCE) vs wavelength] were acquired to evaluate
the influence of dye structure on the photoelectrochemical
performance of DSSCs. Overlaid absorptance and photocurrent
action spectra are shown in Figure 2 for dyes 1, 7, and 8 and in
Films of TiO2 were functionalized by immersion in ∼2 mM
CH2Cl2 solutions of 1−8. Amounts of the adsorbed dyes per
projected surface area (surface coverages, Γ0, in mol cm−2)
were determined by quantifying the concentration of dye in
adsorption solutions before and after exposure to TiO2 films.42
Values of Γ0 are compiled in Table 1 for 1−8 and vary from 3.7
× 10−8 to 7.3 × 10−8 mol cm−2 for the diethyl phosphonates.
The phosphonic acid derivatives 6/6a gave somewhat greater
coverage [(1.0−1.5) × 10−7 mol cm−2] than the phosphonate
derivatives. Exact values cannot be ascertained because of the
6/6a mixture.
Figure 1 shows absorbance spectra of dyes 1, 7, and 8 on
TiO2 films compared to absorbance spectra in CH2Cl2. On
Figure 1. Normalized UV−visible absorption spectra for dyes 1, 7
(offset 1 au), and 8 (offset 2 au) in CH2Cl2 (dashed lines) and on
TiO2 (solid lines).
Figure 2. Absorptance (y-axis left) and IPCE (y-axis right) spectra for
dyes (a) 1, (b) 7, and (c) 8. Error bars are 1 standard deviation
based on a minimum of 3 runs.
TiO2, 1 has developed a higher energy band relative to the
solution spectrum, consistent with the formation of an H-
aggregate on the surface. Dyes 2−6 show similar formation of
H-aggregates (Figure S2, Supporting Information). Dye 7 with
bulky tert-butyl substituents has more limited H-aggregation,
presumably because of the steric hindrance of face-to-face
interactions, and the absorbance spectra on TiO2 and in
CH2Cl2 are similar. Dye 8, with a bulky 2,6-dimethylphenyl
substituent, also limits face-to-face interactions. Some H-
aggregation is observed with 8 on TiO2, but much less than
observed with 1. By varying the concentration of the adsorbing
Figure S4 (Supporting Information) for dyes 2−6. (Absorp-
tance equals the fraction of photons absorbed, or one minus the
transmittance.) For dyes 1−4, absorptance was ≥0.90 from
570−575 nm through 675−725 nm (95−150 nm-wide
regions). For dyes 7 and 8 with reduced aggregation,
absorptance was ≥0.90 over a smaller region: 590−625 nm
(35-nm wide) for 7 and 588−670 nm (82-nm wide) for 8. Dye
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Note
1
100.5 °C; IR (KBr) 3320 (OH), 2232 (CC) cm−1; H NMR (500
MHz, CDCl3) δ 7.50−7.46 (m, 4 H), 7.36−7.32 (m, 5 H), 5.57 (d,
1H, J = 12 Hz), 2.54 (d, 1 H, J = 11.5 Hz); 13C NMR (75.5 MHz,
CDCl3) δ 133.3, 131.9, 131.6, 128.9, 128.3, 132.2, 121.8, 120.9, 87.1,
85.68, 84.8, 83.5, 53.2; HRMS [ESI, high-resolution, double focusing
magnetic sector (HRDFMagSec)] m/z 309.9958 (calcd for
C17H11O79Br+ 309.9993).
5 displayed absorptance ≥0.90 between 600 and 750 nm, and
dye 6, between 540 and 755 nm (215 nm).
White-light photocurrent−photovoltage (J−V) data were
also acquired. Values of open circuit voltage (Voc), short-circuit
photocurrent density (Jsc), fill factor (FF), and global energy-
conversion efficiencies (η) were low (η < 0.1% for all films)
(Table S1, Supporting Information).
1-(4-Bromophenyl)-5-phenylpenta-1,4-diyn-3-one (19). 1-(4-
Bromophenyl)-5-phenylpenta-1,4-diyn-3-ol (20, 2.88 g, 9.26 mmol)
and MnO2 (8.05 g, 92.6 mmol) in CH2Cl2 (30 mL) were stirred for 1
h at ambient temperature. The mixture was filtered through Celite, and
the filtrate was concentrated to give 2.66 g (93%) of 19 as a pale
yellow solid that was used without further purification: mp 105.5−
The correspondence between absorptance and IPCE spectra
for dyes 1−8 indicates that 1−8 sensitized TiO2 through
excited-state electron injection. The impact of aggregation on
IPCE values was determined by examining the window for each
dye where values of IPCE are ≥10%. For 1−6, this region is a
plateau where IPCE values are comparable over both the
aggregate region and the unaggregated dye. For 1, IPCE was
≥10% between 475 and 710 nm; for 2, between 500 and 725
nm; for 3, between 500 and 735 nm; and for 4, between 550
and 725 nm (Figure S4, Supporting Information). Dye 5
displayed IPCE values ≥10% only over the 400−450-nm range,
but had IPCE ≥ 5% from 400 to 775 nm (Figure S4,
Supporting Information). Dye 6, in contrast, displayed values of
IPCE ≥10% over the 400−750-nm window (Figure S4,
Supporting Information). All six of these dyes formed an H-
aggregate. Dye 7, in contrast, displayed IPCE values ≥10% only
over the 570−625-nm range (Figure 2), consistent with little
H-aggregation on the film. Dye 8 displayed IPCE values ≥10%
over the 525−700-nm range (Figure 2), which includes some
aggregate formation.
We have devised a strategy to prepare chalcogenopyrylium
monomethine dyes bearing a phosphonate or phosphonic acid
group, which can function as a linker to semiconductor
surfaces. The chalcogenopyrylium monomethine dyes prepared
by this strategy efficiently harvest visible and NIR light.
Moreover, like chalcogenorhodamine dyes that we have
previously evaluated,13−16 dyes 1−6 show improved light-
harvesting efficiency and higher values of IPCE upon formation
of H-aggregates. In contrast, 7 and 8, which are less prone to
form aggregates, have reduced light-harvesting efficiency.
Aggregates of other dyes have been shown to have poorer
IPCEs than their monomeric counterparts,43 but orientation of
the aggregates relative to the semiconductor surface was not
well-defined.
106.5 °C; IR (KBr) 2207 (CC), 1615 (CO) cm−1; H NMR
1
(500 MHz, CDCl3) δ 7.65 (AA′BB′, 2 H, J = 8 Hz), 7.57 (AA′BB′,
2H, J = 8 Hz), 7.52−7.49 (m, 3 H), 7.42 (t, 2 H, J = 8.0 Hz); 13C
NMR (125 MHz, CDCl3) δ 160.5, 134.5, 133.3, 132.0, 131.3, 128.7,
126.1, 119.3, 118.3, 92.0, 90.0, 89.3; HRMS (ESI, HRDFMagSec) m/z
307.9836 (calcd for C17H9O79Br+ 307.9837).
2-(4-Bromophenyl)-6-phenyl-4H-thiopyran-4-one (17). Sulfur
(0.171 g, 5.34 mmol), NaBH4 (0.202 g, 5.34 mmol) and 0.25 M
NaOEt in EtOH (40.0 mL) were heated at reflux for 4 h. In another
flask, 21 (1.50 g, 4.85 mmol) was dissolved in THF (10.0 mL) and
then added to 0.25 M NaOEt in EtOH (40 mL). After stirring for 10
min, this mixture was then added to the S/NaBH4 mixture. This
resulting mixture was heated at reflux for 20 min and poured into 100
mL of water, and products were extracted with EtOAc (3 × 50 mL).
The combined organic extracts were washed with brine, dried over
MgSO4, and concentrated. The resulting solid was purified via
chromatography on SiO2 eluted with 20% EtOAc/CH2Cl2 (Rf 0.50) to
yield 0.97 g (58%) of 17 as an off-white solid: mp 179.0−180.0 °C; IR
(KBr) 1625 cm−1 (CO); 1H NMR (500 MHz, CDCl3) δ 7.65−7.63
(m, 4 H), 7.53−7.51 (m, 5 H), 7.23 (s, 1 H) 7.20 (s, 1 H); 13C NMR
(75.5 MHz, CDCl3) δ 182.1, 153.0, 151.8, 135.9, 134.9, 132.6, 130.8,
129.4, 128.3, 127.2, 127.1, 126.9, 125.3; HRMS (ESI, HRDFMagSec)
m/z 342.9777 (calcd for C17H11O179BrS + H+ 342.9787).
2-(4-Bromophenyl)-6-phenyl-4H-selenopyran-4-one (18).
Selenium (0.215 g, 2.72 mmol), NaBH4 (85.6 mg, 2.72 mmol) and
0.25 M NaOEt in EtOH (30 mL) were heated at reflux for 1.5 h. In
another flask, 21 (0.700 g, 2.26 mmol) was dissolved in THF (5.0
mL), added to 0.25 M NaOEt in EtOH (20 mL), and stirred for 10
min before addition to the Se/NaBH4 mixture. The resulting mixture
was heated at reflux for 20 min and poured into 100 mL of water, and
products were extracted with EtOAc (4 × 50 mL). The combined
organic extracts were washed with brine, dried over MgSO4, and
concentrated. The resulting solid was purified via chromatography on
SiO2 eluted with 20% EtOAc/CH2Cl2 (Rf 0.50) to yield 0.43 (49%) of
18 as a white solid: mp 165.5−167.0 °C; IR (KBr) 1605 cm−1 (C
The chalcogenopyrylium compounds can accommodate
great structural diversity and the results presented here suggest
that additional chalcogenopyrylium dyes should be designed
and evaluated in DSSCs for enhanced photoelectrochemical
performance. Similar chemistry can be used to facilitate
incorporation of the phosphonate/phosphonic acid linker on
compounds with absorbance even further into the infrared.
1
O); H NMR (500 MHz, CD2Cl2) δ 7.66−7.62 (m, 4 H), 7.52−7.50
(m, 5 H), 7.24 (s, 1 H), 7.22 (s, 1 H); 13C NMR (75.5 MHz, CDCl3)
δ 184.2, 155.3, 153.9, 137.5, 136.6, 132.6, 131.0, 129.4, 128.3, 128.3,
128.1; HRMS (ESI, HRDFMagSec) m/z 391.9148 (calcd for
C17H11O179Br80Se + H+ 391.9138).
Diethyl [4-(4-oxo-6-phenyl-4H-thiopyran-2-yl)phenyl]-
phosphonate (9). Triethylamine (0.102 mL, 0.732 mmol) was
added to palladium acetate (4.1 mg, 0.018 mmol), 1,1′-bis-
(diphenylphosphino)ferrocene (20.2 mg, 0.0364 mmol), KOAc (7.1
mg, 0.072 mmol) in THF (5.0 mL). The resulting solution was heated
at reflux for 15 min prior to the addition of diethyl phosphite (93 μL,
0.73 mmol) and 17 (0.250 g, 0.728 mmol). The resulting mixture was
heated at reflux for 24 h and then diluted with CH2Cl2 (10 mL) and
water (10 mL). The organic layer was dried over MgSO4 and
concentrated. The resulting oil was purified via chromatography on
SiO2 first using 40% EtOAc/CH2Cl2 and then 10% MeOH/EtOAc as
eluent (Rf 0.58) to yield 0.225g (77%) of 9 as an off-white solid: mp
128.5−129.5 °C; IR (KBr) 1613 cm−1 (CO); 1H NMR (500 MHz,
CD2Cl2) δ 7.92 (dd, 2H, J = 12.5, 7.5 Hz), 7.78 (dd, 2H, J = 8.0, 3.5
Hz), 7.70−7.68 (m, 2H), 7.55−7.53 (m, 3H), 7.21(s, 1H), 7.20 (s,
1H), 4.13 (m, 4H), 1.33 (t, 6H, J = 7 Hz); 13C NMR (75.5 MHz,
CDCl3) δ 182.0, 153.2, 151.8, 139.7, 135.8, 132.7, 132.5, 132.6, 132.5,
EXPERIMENTAL SECTION
■
1-(4-Bromophenyl)-5-phenylpenta-1,4-diyn-3-ol (21).
EtMgBr (3.0 M, 11.2 mL, 34 mmol) was added dropwise to a
tetrahydrofuran (THF, 60 mL) solution of phenylacetylene (3.94 mL,
35.9 mmol) at 0 °C. The resulting solution was stirred for 0.5 h at 0
°C and then for an additional 0.5 h at ambient temperature. The
solution was cooled to −78 °C, and 20 (4.95 g, 23.7 mmol), dissolved
in THF (30 mL), was added via cannula. After 1 h at −78 °C, the
reaction mixture was stirred for an additional 2 h at ambient
temperature. The reaction was quenched with 10 mL of MeOH and
then was poured into saturated NH4Cl (50 mL). Products were
extracted with CH2Cl2 (3 × 75 mL). The combined organic extracts
were washed with brine, dried over MgSO4, and concentrated. The
resulting oil was purified via chromatography on SiO2 with CH2Cl2 as
eluent (Rf 0.62) to yield 6.15 g (84%) of 21 as a white solid: mp 99.5−
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2
3
130.9, 130.0, 129.4, 128.0, 127.2, 127.0, 126.9, 126.8, 62.4 (d, JCP
=
16.5 (d, JCP = 6.8 Hz); HRMS (EI, HRDFMagSec) m/z 693.1119
(calcd for C39H34O3PS80Se+ 693.1126). Anal. Calcd for
C39H34O3PSSe·PF6: C, 55.92; H, 4.09. Found: C, 55.85; H, 4.42.
4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-seleno-
pyran-4-ylidene)methyl)-2,6-diphenylthiopyrylium hexafluor-
ophosphate (3). Selenopyran-4-one 10 (50.0 mg, 0.112 mmol), 4-
methyl-2,6-diphenylthiopyrylium hexafluorophosphate (12, 41.5 mg,
0.102 mmol), and Ac2O (0.500 mL) were heated at 105 °C for 15 min.
Workup as described for 1 gave 79.5 mg (93%) of 3 as a metallic dark
blue solid: mp 124.5−126 °C; 1H NMR (500 MHz, CD2Cl2) δ 8.20−
7.96 (m, 6 H), 7.80 (d, 6 H, J = 7.5 Hz), 7.73- 7.59 (m, 11 H), 6.96 (br
s, 1 H), 4.15 (m, 4 H), 1.35 (t, 6 H, J = 7.0 Hz); 13C NMR (125 MHz,
CD2Cl2) δ 158.2, 154.7, 153.3, 141.0, 137.6, 135.3, 133.25, 133.17,
132.7, 132.2, 131.7, 130.3, 130.2, 127.54, 127.42, 127.36, 127.3, 126.7,
3
4.7 Hz), 16.3 (d, JCP = 5.7 Hz); HRMS (ESI, HRDFMagSec) m/z
401.0971 (calcd for C21H21O4PS + H+ 401.0976).
Diethyl [4-(4-oxo-6-phenyl-4H-selenopyran-2yl)phenyl]-
phosphonate (10). Palladium acetate (3.6 mg, 0.016 mmol), 1,1′-
bis(diphenylphosphino)ferrocene (17.8 mg, 0.0321 mmol), KOAc
(6.3 mg, 0.064 mmol), THF (5 mL), Et3N (98 μL, 0.70 mmol),
diethyl phosphite (82 μL, 0.64 mmol) and 18 (0.250 g, 0.641 mmol)
were treated as described for the preparation of 9. The isolated oil was
purified by chromatography on SiO2 eluted first with 40% EtOAc/
CH2Cl2 and then with 10% MeOH/EtOAc (Rf 0.64) to yield 0.229 g
(80%) of 10 as an off-white solid: mp 99.5−100.5 °C; IR (KBr) 1608
cm−1 (CO); 1H NMR (500 MHz CD2Cl2) δ 7.94 (dd, 2 H, J = 13.0,
8.0 Hz) 7.69 (dd, 2 H, J = 8.5, 4.0 Hz) 7.61−7.59 (m, 2 H) 7.52−7.51
(m, 3 H), 4.18 (m, 4 H), 1.36 (t, 6 H, J = 7.5 Hz); 13C NMR (125
2
3
62.8 (d, JCP = 5.8 Hz), 16.5 (d, JCP = 6.6 Hz); HRMS (EI,
HRDFMagSec) m/z 693.1134 (calcd for C39H34O3PS80Se+ 693.1126).
Anal. Calcd for C39H34O3PSSe·PF6: C, 55.92; H, 4.09. Found: C,
55.85; H, 4.15.
4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-seleno-
pyran-4-ylidene)methyl)-2,6-diphenylselenopyrylium hexa-
fluorophosphate (4). Selenopyran-4-one 10 (50.0 mg, 0.112
mmol), 13 (46.3 mg, 0.102 mmol), and Ac2O (1.0 mL) were at 105
°C for 2.0 min. Workup as described for 1 gave 74.9 mg (83%) of 4 as
MHz, CDCl3) δ 184.0, 155.4, 153.8, 141.2, 137.3, 132.7, 132.6, 131.6,
2
130.7, 130.1, 129.3, 129.0, 128.1, 126.9, 126.7, 126.7, 62.3 (d, JCP
=
3
5.8 Hz), 16.2 (d, JCP = 6.6 Hz); HRMS (ESI, HRDFMagSec) m/z
449.0415 (calcd for C21H21O4P80Se + H+ 449.0421).
4-(4-Oxo-6-phenyl-4H-selenopyran-2-yl)phenylphosphonic
acid (11). Trimethylsilyl chloride (0.142 mL, 1.12 mmol) was added
dropwise to NaI (0.168 g, 1.12 mmol) in anhydrous CH3CN (2.0 mL)
and anhydrous CH2Cl2 (2.0 mL). After 0.5 h of stirring,
selenopyranone 10 (0.100 g, 0.224 mmol) was added, and the
resulting mixture was stirred overnight. The dark red mixture was
quenched with MeOH (2.0 mL) and poured into 1 M HCl (50 mL).
Potassium hydroxide pellets were added until the solution became a
light brown color. The mixture was washed with EtOAc (2 × 25 mL).
The pH of the aqueous solution was lowered to approximately 1 with
concentrated HCl, and products were extracted with EtOAc (3 × 25
mL). The combined organic extracts were dried over Na2SO4 and
concentrated. The product was precipitated from EtOAc with hexanes
to yield 61.2 mg (70%) of 11 as a light brown powder: mp 220−222
1
a metallic dark blue solid: mp 133−135 °C; H NMR (500 MHz,
CD2Cl2) δ 8.20- 8.07 (m, 4 H) 7.98 (dd, 2 H, J = 12.5, 8.0 Hz), 7.81
(dd, 2 H, J = 7.5, 3.0 Hz), 7.75−7.73 (m, 6 H), 7.69−7.60 (m, 9 H),
6.97 (s, 1 H), 4.15 (m, 4 H), 1.35 (t, 6 H, J = 6.5 Hz); 13C NMR (100
MHz, CD2Cl2) δ 163.2, 160.9, 158.3, 155.1, 153.7 141.2, 137.6, 137.4,
133.4, 133.3, 133.0, 132.6, 132.4, 131.1, 130.4, 130.3, 129.7, 128.1,
2
3
127.6, 127.5, 127.4, 62.8 (d, JCP = 5.6 Hz), 16.5 (d, JCP = 6.6 Hz);
+
HRMS (EI, HRDFMagSec) m/z 741.0552 (calcd for C39H34O3P80Se2
741.0571). Anal. Calcd for C39H34O3PSe2·PF6·H2O:44 C, 51.90; H,
4.02. Found: C, 51.85; H, 3.80.
4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-thiopyr-
an-4-ylidene)methyl)-2,6-diphenyltelluropyrylium hexafluoro-
phosphate (5). Thiopyran-4-one 9 (50.0 mg, 0.112 mmol), 4-methyl-
2,6-diphenyltelluropyrylium hexafluorophosphate (14, 46.3 mg, 0.102
mmol), and Ac2O (1.0 mL) were heated at 105 °C for 1.0 min. The
solution was then diluted with diethyl ether, and the resulting solid was
isolated by filtration. Workup as described for 1 was followed by
purification by column chromatography eluted first with 10% EtOAc/
CH2Cl2 and then with 30% EtOAc/CH2Cl2 to yield 56.4 mg (56%) of
5 as a green solid: mp 144.5−147.5 °C; 1H NMR (500 MHz, CD2Cl2)
δ 8.17 (s, 2 H), 8.13 (s, 1 H), 8.07 (s, 1 H), 7.99 (dd, 2 H, J = 8.5, 12.5
Hz), 7.85 (dd, 2 H, J = 3.5, 8.5 Hz), 7.76 (d, 2 H, J = 8.5 Hz), 7.68−
7.57 (m, 13 H), 6.97 (s, 1H), 4.15 (m, 4 H), 1.35 (t, 6 H, J = 7.0 Hz);
13C NMR (75.5 MHz, CD2Cl2) δ 160.9, 156.4, 156.1, 154.3, 152.6,
1
°C; H NMR (500 MHz, (CD3)2SO) δ 11.38 (s, 2 H), 7.81−7.80
(m, 4 H), 7.74 (dd, 2 H, J = 1.5, 7.5 Hz), 7.56 (m, 3 H), 7.39 (s, 1 H),
7.29 (s, 1 H); 13C NMR (75 MHz, (CD3)2SO) δ 183.0, 154.1,
153.2, 139.0, 137.9, 136.8, 135.5, 131.6, 131.5, 131.0, 129.6, 128.0,
127.4, 126.7, 126.7, 126.5. HRMS (EI, HRDFMagSec) m/z 392.9805
(calcd for C17H13O4P80Se + H+ 392.9795).
General Procedure for the Preparation of Monomethine
Dyes 1−8. 4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-
thiopyran-4ylidene)methyl)-2,6-diphenylthiopyrylium hexa-
fluorophosphate (1). Thiopyranone 9 (50.0 mg, 0.125 mmol), 4-
methyl-2,6-diphenylthiopyrylium hexafluorophosphate (12, 46.4 mg,
0.114 mmol), and Ac2O (0.500 mL) were heated at 105 °C for 15 min.
The solution was diluted with Et2O (2.5 mL), and the resulting solid
was isolated by filtration. The solid was recrystallized from CH3CN/
ether to yield 71.8 mg (89%) of 1 as a metallic dark blue solid: mp
141.0, 138.7, 138.7, 135.3, 133.9, 133.1, 132.9, 132.3, 131.7, 131.4,
130.1, 130.0, 128.7, 127.2, 127.1, 127.0, 62.7 (d, JCP = 5.8 Hz), 16.2
2
1
124.0−125.5 °C; H NMR (500 MHz, CD2Cl2) δ 8.14−7.98 (m, 6
3
(d, JCP = 5.7 Hz); HRMS (EI, HRDFMagSec) m/z 743.1025 (calcd
H), 7.86 (dd, 2 H, J = 8.0, 3.5 Hz), 7.79 (t, 6 H, J = 7.0 Hz), 7.68−7.61
(m, 9 H), 6.85 (br s, 1 H) 4.15 (m, 4 H), 1.35 (t, 6 H, J = 7.0 Hz); 13C
NMR (75.5 MHz, CD2Cl2) δ 157.4, 155.9 (br), 154.5, 153.9 (br),
153.2, 139.1, 135.7, 135.5, 134.2, 133.3, 133.2, 132.6, 132.5, 131.8,
for C39H34O3PS130Te+ 743.1023). Anal. Calcd for C39H34O3PSTe·PF6·
H2O:44 C, 51.80; H, 4.01. Found: C, 51.51; H, 3.81.
2,6-Diphenyl-4-((2-phenyl-6-(4-phosphonophenyl)-4H-sele-
nopyran-4-ylidene)methyl)thiopyrylium hexafluorophosphate
(6). Acetic anhydride (3.0 mL) was slowly added over 5 min to 11
(70.0 mg, 0.203 mmol) and 12 (83.0 mg, 0.203 mmol) in AcOH (3.0
mL) at 105 °C. The resulting mixture was heated for an additional 25
min at 105 °C. Workup as described for 1 gave 89.8 mg (65%) of a
60:40 mixture of 6 and its zwitterionic form as a dark blue solid: mp
>260 °C; 1H NMR (500 MHz, 2:1 CD3OD:CD2Cl2) δ 8.24 (s, 2 H),
8.10 (s, 2 H), 7.95 (dd, 2 H, J = 8.0, 13.0 Hz), 7.79 (d, 6 H, J = 7.5
Hz), 7.71 (d, 2 H, J = 7 Hz), 7.64−7.52 (m, 9 H) 6.91 (s, 1 H);
HRMS (EI, HRDFMagSec) m/z 637.0521 (calcd for
C35H26O3PS80Se+ 637.0500). Anal. Calcd for [C35H26O3PSSe·
PF6]0.60·[C35H25O3PSSe]0.40: C, 58.13; H, 3.57. Found: C, 58.22; H.
3.55.
2
130.3,130.2, 127.6, 127.5, 127.4, 126.8, 123.6, 62.9 (d, JCP = 5.7 Hz),
3
16.5 (d, JCP = 6.9 Hz); HRMS (EI, HRDFMagSec) m/z 645.1694
(calcd for C39H34O3PS2+ 645.1692). Anal. Calcd for C39H34O3PS2·PF6:
C, 59.24; H, 4.33. Found: C, 59.11; H, 4.47.
4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-thiopyr-
an-4-ylidene)methyl)-2,6-diphenylselenopyrylium hexafluoro-
phosphate (2). Thiopyranone 9 (50.0 mg, 0.125 mmol), 4-methyl-
2,6-diphenylselenopyrylium hexafluorophosphate (13, 51.7 mg, 0.114
mmol), and Ac2O (1.0 mL) were heated at 105 °C for 2.0 min.
Workup as described for 1 gave 75.6 mg (79%) of 2 as a metallic dark
1
blue solid: mp 142−144 °C; H NMR (500 MHz, CD2Cl2) δ 8.16−
8.10 (m, 4 H), 8.00 (dd, 2 H, J = 8.0, 12.5 Hz), 7.86 (dd, 2 H, J = 3.5,
8 Hz), 7.79 (d, 2 H, J = 7.5 Hz), 7.74 (d, 4 H, J = 7.5 Hz), 7.68−7.61
(m, 9 H), 6.95 (br s, 1 H), 4.15 (m, 4 H), 1.35 (t, 6 H, J = 7.0 Hz);
13C NMR (125 MHz, CD2Cl2) δ 161.7, 156.8, 154.7, 154.4, 153.8,
153.6, 138.9, 137.6, 135.5, 133.9, 133.3, 133.2, 132.7, 132.3, 130.3,
129.2, 128.4, 127.5, 127.5, 127.4, 126.7, 124.1, 62.9 (d, 2JCP = 5.7 Hz),
2,6-Di-tert-butyl-4-((2-(4-(diethoxyphosphorylphenyl)-6-
phenyl-4H-thiopyran-4-ylidene)methyl)thiopyrylium hexa-
fluorophosphate (7). Thiopyran-4-one 9 (0.100 g, 0.250 mmol),
2,6-di-tert-butyl-4-methylthiopyrylium hexafluorophosphate (15, 83.6
mg, 0.227 mmol), and Ac2O (1.0 mL) were heated at 105 °C for 3 h.
8889
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The Journal of Organic Chemistry
Note
Workup as described for 1 gave 0.151 g (88%) of 7 as a purple solid:
mp 211.5−213.5 °C; 1H NMR (500 MHz, CD2Cl2) δ 7.98 (dd, 2 H, J
= 8.5, 12.5 Hz), 7.92 (s, 2 H), 7.83 (m, 2 H), 7.74 (d, 2 H, J = 7.5 Hz),
7.63−7.58 (m, 3 H), 6.66 (s, 1 H), 4.14 (m, 4 H), 1.52 (s, 18 H), 1.34
(t, 6 H, J = 7.0 Hz); 13C NMR (125 MHz, CD2Cl2) δ 173.8, 155.8,
151.7, 133.27, 133.19, 132.1, 130.1, 127.3, 125.7, 122.5, 122.4, 62.9 (d,
IPCE data for dyes 2−6. These materials are available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: dwatson3@buffalo.edu; mdetty@buffalo.edu.
■
3
2JCP = 5.8 Hz), 40.7, 31.1, 16.5 (d, JCP = 5.6 Hz); HRMS (EI,
+
HRDFMagSec) m/z 605.2315 (calcd for C35H42O3PS2 605.2307).
Notes
Anal. Calcd for C35H42O3PS2·PF6: C, 55.99; H, 5.64. Found: 55.91; H,
5.48.
The authors declare no competing financial interest.
4-((2-(4-(Diethoxyphosphoryl)phenyl)-6-phenyl-4H-thiopyr-
an-4-ylidene)methyl)-2-(2,6-dimethylphenyl)-6-phenylthio-
pyrylium hexafluorophosphate (8). Thiopyran-4-one 9 (0.100 g,
0.250 mmol), 2-(2,6-dimethylphenyl)-4-methyl-6-phenylthiopyrylium
hexafluorophosphate (16, 99.1 mg, 0.227 mmol), and Ac2O (0.50 mL)
were heated at 105 °C for 15 min. Workup as described for 1 gave 81.7
ACKNOWLEDGMENTS
■
We thank the National Science Foundation (CHE-1151379)
for support of this work. K.R.M. acknowledges the financial
support provided by the Silbert Fellowship in Chemistry,
Department of Chemistry, University at Buffalo.
1
mg (88%) of 8 as a metallic dark blue solid: mp 133.5−135.5 °C; H
NMR (500 MHz, CDCl3) δ 8.231 (s, 1 H), 8.09−8.08 (m, 2 H), 7.98
(dd, 2 H, J = 13.0, 8.0 Hz), 7.89 (dd, 2 H, J = 8, 3.5 Hz), 7.78 (d, 2 H,
J = 7.0 Hz), 7.71−7.69 (m, 3 H), 7.61−7.53 (m, 6 H), 7.33 (t, 1 H, J =
7.5 Hz), 7.21 (d, 2 H, J = 7.5 Hz), 7.10 (s, 1 H), 4.23−4.09 (m, 4 H),
2.31 (s, 6 H), 1.36 (t, 6 H, J = 7.0 Hz); 13C NMR (100 MHz, CD2Cl2)
δ 159.0, 157.5, 156.7, 154.7, 154.5, 153.9,139.0, 136.9, 135.7, 135.5,
134.3, 134.1, 133.4, 133.3, 132.7, 132.6, 132.2, 131.2, 130.9, 130.3,
130.3, 128.7, 127.6, 127.53, 127.47, 123.3, 62.9 (d, 2JCP = 5.4 Hz), 20.5,
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