A comparison of linear optical properties and redox properties in chalcogenopyrylium dyes bearing ortho-substituted aryl substituents and tert-butyl substituents

Article abstract of DOI:10.1021/jo026645u

A series of thiapyrylium pentamethine dyes (4 and 12-15) bearing 2,2′-di-tert-butyl-6,6′-diphenyl, 2,2′-di-tert-butyl-6,6′-bis(2,6-dimethylphenyl), 2,2′-di-tert-butyl-6,6′-bis(2-methylphenyl), 2,2′,6,6′-tetrakis(2,6-dimethylphenyl), and 2,2′,6,6′-tetrakis(2-methylphenyl) substituents, respectively, were prepared and their linear optical properties and electrochemical redox properties were measured and compared to thiapyrylium pentamethine dyes 3 and 5. The tert-butyl and 2,6-dimethylphenyl substituents give nearly identical chromophores with respect to values of λ_max, molar extinction coefficients (ε), bandwidths at half-height (ν_1/2), and lack of absorption in the visible spectrum. The 2-methylphenyl substituent imparts linear optical properties that are intermediate between those of the tert-butyl and phenyl substituents. The 2,6-dimethylphenyl and 2-methylphenyl substituents impart greater oxidative stability based on anodic shifts in oxidation potential.

Full text of DOI:10.1021/jo026645u

A Com p a r ison of Lin ea r Op tica l P r op er ties a n d Red ox P r op er ties
in Ch a lcogen op yr yliu m Dyes Bea r in g Or th o-Su bstitu ted Ar yl
Su bstitu en ts a n d ter t-Bu tyl Su bstitu en ts
J agannath Panda, Peter R. Virkler, and Michael R. Detty*
Department of Chemistry, University at Buffalo, The State University of New York,
Buffalo, New York 14260-3000
mdetty@acsu.buffalo.edu
Received November 1, 2002
A series of thiapyrylium pentamethine dyes (4 and 12-15) bearing 2,2′-di-tert-butyl-6,6′-diphenyl,
2,2′-di-tert-butyl-6,6′-bis(2,6-dimethylphenyl), 2,2′-di-tert-butyl-6,6′-bis(2-methylphenyl), 2,2′,6,6′-
tetrakis(2,6-dimethylphenyl), and 2,2′,6,6′-tetrakis(2-methylphenyl) substituents, respectively, were
prepared and their linear optical properties and electrochemical redox properties were measured
and compared to thiapyrylium pentamethine dyes 3 and 5. The tert-butyl and 2,6-dimethylphenyl
substituents give nearly identical chromophores with respect to values of λmax, molar extinction
coefficients (ꢀ), bandwidths at half-height (ν1/2), and lack of absorption in the visible spectrum. The
2-methylphenyl substituent imparts linear optical properties that are intermediate between those
of the tert-butyl and phenyl substituents. The 2,6-dimethylphenyl and 2-methylphenyl substituents
impart greater oxidative stability based on anodic shifts in oxidation potential.
In tr od u ction
dyes that have absorption maxima with large extinction
coefficients in this window.4,6 For many applications, the
near-infrared-absorbing dye should also be essentially
colorless in the visible spectrum, which severely limits
the types of substituents that can be incorporated along
the chromophore.
The tert-butyl substituent has been used in the 2- and
6-positions of various chalcogenopyrylium dyes to give
minimal absorption in the visible portion of the spectrum
and intense, narrow absorption in the near-infrared (with
typical bandwidths at half-height of e600 cm-1).6a,b,7 The
tert-butyl substituents also impart greater solubility to
the chalcogenopyrylium dyes in organic solvents and
minimize aggregationsproperties that tend to minimize
the formation of crystallites in coated films.
Commercial applications with inexpensive, near-
infrared-emitting diode lasers have created a demand for
near-infrared-absorbing dyes. Some of the more impor-
tant applications include thermal imaging,1 electropho-
tography,2 optical recording,3 photography, and lithog-
raphy.4 Near-infrared-absorbing dyes have also been used
as filter elements in conjunction with near-infrared-
emitting diode lasers.4,5 The 810-850-nm window is
where many of the commercially available gallium-
arsenide diode lasers emit. Chalcogenopyrylium dyes
derived from the condensation of 2-methyl and 4-methyl
chalcogenopyrylium salts with various carbonyl and
dicarbonyl equivalents give methine and polymethine
The tert-butyl substituent has one significant drawback
in near-infrared-absorbing chalcogenopyrylium dyes. Be-
cause alkyl substitituents are inductively electron donat-
ing,8 near-infrared-absorbing chalcogenopyrylium dyes
with 2,6-di-tert-butyl or other alkyl substituents are more
easily oxidized relative to dyes with aryl substituents.9
The ease of oxidation can lead to undesired redox
processes both in the ground (typically, reactions of the
dye with oxygen, ozone) and excited states (electron
transfer from electron-rich ground-state molecules to the
(1) For thermal imaging: (a) Yamaguchi, C.; Hiraoka, Y.; Kageyama,
T.; Ando, S.; Matsuoka, S.; Endo, T. J apanese Kokai Tokkyo Koho J P
62,257,890 [87,257,890], 1987 (Chem. Abstr. 1987, 107, 187518). (b)
Kellogg, R. F.; Laganis, E. D. U.S. Patent, US 5,019,549, 1991 (Chem.
Abstr. 1991, 115, 185546). (c) Burberry, M. S.; Tutt, L. W.; Detty, M.
R. U.S. Patent US 5,256,620, 1993 (Chem. Abstr. 1994, 120, 167007).
(d) Sansbury, F. H.; Oliff, D. B.; Grieve, D. M. A. European Patent
Application EP 764,878, 1995 (Chem. Abstr. 1997, 126, 310465).
(2) For optical recording: (a) Gravesteijn, D. J .; Steenbergeen, C.;
Van der Veen, J . Proc. SPIE-Int. Soc. Opt. Eng. 1983, 420 (Opt. Storage
Media), 327-330. (b) Gravesteijn, D. J .; Van der Veen, J . Philips
Technol. Rev. 1983, 41, 325-331. (c) Oguchi, Y.; Takasu, Y. J apanese
Kokai Tokkyo Koho J P 62,132,690 [87,132,690], 1987 (Chem. Abstr.
1988, 108, 29515). (d) Fukui, T.; Oguchi, Y.; Miura, K. J apanese Kokai
Tokkyo Koho J P 63,168,393 [88,168,393], 1988 (Chem. Abstr. 1989,
110, 125550). (e) Oguchi, Y.; Fukui, T. J apanese Kokai Tokkyo Koho
J P 63,168,392 [88,168,393] 1988 (Chem. Abstr. 1989 110, 105091).
(3) For electrophotography: Canon, K. K. J apanese Kokai Tokkyo
Koho J P 58,220,143 [83,220,143], 1983 (Chem. Abstr. 1984, 101,
219727).
(6) (a) Simard, T. P.; Yu, J . H.; Zebrowski-Young, J . M.; Haley, N.
F.; Detty, M. R. J . Org. Chem. 2000, 65, 2236-2238. (b) Detty, M. R.;
Merkel, P. B.; Powers, S. K. J . Am. Chem. Soc. 1988, 110, 5920-
5927. (c) Detty, M. R.; Murray, B. J . J . Org. Chem. 1982, 47, 5235-
5239.
(4) For reviews: (a) Matsuoka, M., Ed. Infrared Absorbing Dyes;
Plenum Press: New York, 1990. (b) J u¨rgen, F.; Nakagumi, H.;
Matsuoka, M. Chem. Rev. 1992, 92, 1197-1226.
(5) Bugner, D. E.; Kan, H. C.; Haley, N. F.; Detty, M. R.; Bucks, R.
R. US Patent 5,403,686 1995 (Chem. Abstr. 1995 123, 127521).
(7) Detty, M. R.; Henne, B. Heterocycles 1993, 35, 1149-1156.
(8) (a) Wells, P. R. Chem. Rev. 1963, 63, 171-187. (b) Swain, C. G.;
Lupton, E. C., J r. J . Am. Chem. Soc. 1968, 90, 4328-4338.
(9) Detty, M. R.; McKelvey, J . M.; Luss, H. R. Organometallics 1988,
7, 1131-1142.
10.1021/jo026645u CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/30/2003
1804
J . Org. Chem. 2003, 68, 1804-1809

Substituted Chalcogenopyrylium Dyes
CHART 1
Resu lts a n d Discu ssion
Thiapyrylium pentamethine dye 3 was prepared ac-
cording to Scheme 1 in which 4-methylthiapyrylium3
hexafluorophosphate 6a was condensed with cyanine 7
in a one-to-one mixture of acetic acid/acetic anhydride
with catalytic sodium acetate as a base to give dye 3 in
78% isolated yield. The remaining dyes of this study were
prepared in a similar manner from the appropriate salt
6.
The 4-methylthiapyrylium salts 6b-f were prepared
according to Scheme 2. The addition of a lithium acetylide
to an arylpropargyl aldehyde 8 gave the corresponding
1,4-pentadiyn-3-ol 9, which was then oxidized to the
corresponding pentadiyn-3-one 10 with MnO2 in CH2Cl2.
The addition of Na2S to diynones 10 in NaOEt/EtOH
under controlled conditions7 gave thiapyranones 11.
Addition of MeMgBr to the carbonyl groups of 11 followed
by elimination with HPF6 gave the 4-methylthiapyrylium
hexafluorophosphate salts 6.
The preparation of arylpropargyl aldehydes 8b and 8c
from the addition of the lithium acetylides of 2,6-
dimethylphenylethyne11 and 2-methylphenylethyne12 to
methyl formate was not complicated by competitive
addition of the acetylide to the resulting arylpropargyl
aldehyde 8. Further addition to give the 1,5-diaryl-1,4-
pentadiyn-3-ol occurred only under more forcing condi-
tions with an excess of acetylide as described below. The
propargyl aldehydes 8b and 8c were isolated in 63% and
69% yields, respectively, as air-sensitive oils.
The addition of lithium tert-butylacetylide to com-
mercially available phenylpropargyl aldehyde (8a ) gave
diynol 9b in 92% isolated yield. The addition of stoichio-
metric lithium tert-butylacetylide to arylpropargyl alde-
hydes 8b and 9c gave diynols 9c and 9d in 78% and 57%
isolated yields, respectively. The addition of acetylides
derived from 2,6-dimethylphenylethyne or 2-methylphen-
ylethyne to arylpropargyl aldehydes 8b or 8c was more
sluggish and useful yields were realized when a 3-fold
excess of the acetylide was employed. Diynols 9e and 9f
were isolated in 78% and 70% yields, respectively. All of
the diynols 9 were prone to air oxidation to give the
corresponding diynones 10 so the diynols 9 were con-
verted directly to diynones 10 in 91-95% isolated yield
with MnO2 in CH2Cl2.
The addition of Na2S to the diynones 10 to give
thiapyranones 11 was somewhat problematic. While the
2-tert-butyl-6-phenylthiapyranone 11b was isolated in
68% yield, thiapyranones 11c-f were isolated in only
18-22% yield. The increased steric demands of 2-methyl
and 2,6-dimethyl substituents on the phenyl ring may
contribute to the lower yields. The major byproducts in
these reactions, while not fully characterized, were con-
sistent with the addition of Na2S across two diynone units
as well as oligomeric products from further additions.
The addition of MeMgBr to the thiapyranones 11b-f
followed by dehydration with aqueous HPF6 gave the
4-methylthiapyrylium hexafluorophosphate salts 6b-f in
low-energy SOMO of the excited-state dye) in various
imaging applications, which can impact color reproduc-
tion and sensitometry.4 The 2,6-di-tert-butylthiapyrylium
and selenopyrylium analogues of squarylium dyes 1
(Chart 1) have absorption maxima of 804 and 847 nm,
respectively (ꢀ > 300 000 M-1 cm-1), but oxidation
potentials of +0.48 and +0.54 V vs the ferrocene/
ferricinium couple (Fc/Fc+, E° ) +0.40 V), respectively.6a,7
The pyrylium croconate 2 (Chart 1) has an absorption
maximum of 845 nm (ꢀ > 100 000 M-1 cm-1) but an
oxidation potential of +0.42 V vs Fc/Fc+.6a Thiapyrylium
pentamethine dye 3 (prepared according to Scheme 1)
has an absorption maximum of 821 nm (ꢀ ) 384 000 M-1
cm-1, Figure S1 in Supporting Information) and an
oxidation potential of +0.58 V vs Fc/Fc+.
In contrast to the tert-butyl group, the phenyl and other
aryl groups are inductively electron withdrawing5 due in
part to the greater electronegativity of the sp2-hybridized
carbons. As shown in Table 1 for thiapyrylium penta-
methine dyes 4 (prepared according to Scheme 1) and
53c in which two and four tert-butyl substituents, respec-
tively, have been replaced by phenyl substituents, oxida-
tion potentials are more positive (+0.65 and +0.73 V vs
Fc/Fc+ for 4 and 5, respectively). However, absorption
maxima are significantly longer for 4 and 5 relative to 3
(Table 1) and weak secondary bands are observed in the
absorption spectra of 4 and 5 in the 400-450-nm window
(Figures S2 and S3, respectively, in Supporting Informa-
tion).
The tert-butyl substituent does not extend the π-chro-
mophore in contrast to aryl substituents. As a logical ex-
tension, the electron-withdrawing character of aryl sub-
stituents could be used to tailor oxidation potentials
without extending the π-chromophore if the aryl group
were held orthogonal to the dye π-framework. Further-
more, the orthogonal aryl substituents should eliminate
secondary absorption bands in the visible spectrum. We
describe a series of thiapyrylium pentamethine dyes in-
corporating 2,6-dimethylphenyl or 2-methylphenyl sub-
stituents in the 2- and 6-positions of the thiapyrylium
ring whose linear optical properties are nearly identical
with those of thiapyrylium pentamethine dye 3, but
whose electrochemical oxidation potentials are more posi-
tive (anodic) than that of dye 3 with tert-butyl substitu-
ents.
(10) Leonard, K.; Nelen, M.; Raghu, M.; Detty, M. R. J . Heterocycl.
Chem. 1999, 36, 707-717.
(11) Eisch, J . J .; Shafii, B.; Odom, J .; Rheingold, A. L. J . Am. Chem.
Soc. 1990, 112, 1847-1853.
(12) Moroz, A. A.; Shvartsberg, M. S. Izv. Akad. Nauk SSSR, Ser.
Khim. 1973, 476-479.
J . Org. Chem, Vol. 68, No. 5, 2003 1805

Panda et al.
SCHEME 1
TABLE 1. A Com p a r ison of th e Lin ea r Op tica l a n d Electr och em ica l P r op er ties of Th iop yr yliu m Dyes 3-5 a n d 12-15
oxc,d
redc
a
b
λmax
,
log
ν1/2
,
Epa, V
Epc, V
Epa, V
dye
R1
R2
nm
ꢀa
cm-1
(vs Fc/Fc+)
(vs Fc/Fc+)
(vs Fc/Fc+)
∆E, V
3
4
5
12
13
14
15
t-Bu
t-Bu
Ph
t-Bu
t-Bu
t-Bu
Ph
Ph
2,6-Me2C6H3
2-MeC6H4
2,6-Me2C6H3
2-MeC6H4
821
855
893
831
836
841
855
5.58
5.44
5.40
5.38
5.30
5.54
5.38
593
738
748
623
687
608
752
+0.58
+0.68
+0.65
+0.73
+0.69
+0.84
+0.78
-0.56
-0.44
-0.40
-0.47
-0.52
-0.36
-0.39
-0.48
-0.36
-0.34
-0.39
-0.44
-0.30
-0.31
1.10
1.08
1.02
1.16
1.17
1.17
1.13
2,6-Me2C6H3
2-MeC6H4
a
In CH2Cl2. b Bandwidth at half-height. c In CH2Cl2 at a Pt-disk electrode with a scan rate of 0.1 V s-1 with 0.2 MBu4NBF4 as supporting
electrolyte with the ferrocene/ferricinium couple as the reference electrode. Irreversible peak potential. e Epa - E°.
d
from 3 to 13 and a 65-cm-1 increase from 13 to 15). The
SCHEME 2
linear optical properties of dye 15 with four 2-methylphen-
yl substituents are nearly identical with those of dye 4
with two tert-butyl and two phenyl substituents. Impor-
tantly, all of the dyes 12-15 have intense absorbance at
λmax with molar extinction coefficients, ꢀ, >180 000 M-1
cm-1
.
(b ) E lect r och em ica l Oxid a t ion a n d R ed u ct ion
P oten tia ls. Oxidation and reduction potentials for dyes
3-5 and 12-15 were determined by cyclic voltammetry
and values of Epa for the irreversible oxidation of the
thiapyrylium dye and values of E° for the reversible
cation/neutral radical couple are compiled in Table 1.
Substitution of either a 2,6-dimethylphenyl or a 2-meth-
ylphenyl group for a tert-butyl group gives an anodic
(positive) shift in the oxidation potential. In comparing
dyes 3, 13, and 15, each substitution of a 2-methylphenyl
substituent for a tert-butyl group gives a 10-mV anodic
shift. In comparing dyes 3, 12, and 14, sequential
substitution of a 2,6-dimethylphenyl substituent for a
tert-butyl group gives 15- and 11-mV anodic shifts.
72-84% isolated yields following recrystallization. The
condensation of the 4-methylthiapyrylium salts 6b-f
with cyanine 7 gave dyes 4 and 12-15 in 56-62%
isolated yield following recrystallization.
(a ) Lin ea r Op tica l P r op er ties of Th ia p yr yliu m
P en ta m eth in e Dyes 3-5 a n d 12-15. The absorption
spectra of dyes 3-5 and 12-15 are shown in Figures
S1-S7, respectively, in the Supporting Information. The
wavelengths of the absorption maxima (λmax) and the
molar extinction coefficients (ꢀ) for dyes 3-5 and 12-15
are compiled in Table 1. The bandwidths at half-height
(ν1/2) for these dyes are also compiled in Table 1.
The substitution of a 2,6-dimethylphenyl substituent
for a tert-butyl substituent gives a 10-nm bathochromic
shift in λmax with minimal increase in ν1/2 in comparing
dyes 3, 12, and 14. In comparison, substitution of the
2-methylphenyl substituent for a tert-butyl substituent
gives 15-19-nm bathochromic shifts in λmax, but gives
significant increases in values of ν1/2 (a 94-cm-1 increase
In earlier work, we demonstrated that the energy of
the absorbed photon at λmax was directly proportional to
the energy difference, ∆E, between the oxidation and
reduction potentials for chalcogenopyrylium dyes.6 Not
surprisingly, values of ∆E for 12-15 (1.13-1.17 V, Table
1) are comparable to ∆E for dye 3 (1.10 V) and the anodic
shift observed in oxidation potentials upon substitution
of 2,6-dimethylphenyl and 2-methylphenyl substituents
for tert-butyl groups is accompanied by a corresponding
shift in the reduction potential.
(c) Sin glet -Oxygen Gen er a t ion b y Dyes 4 a n d
12-15. Self-sensitized generation of singlet oxygen in
solution is not a concern for the dyes of this study. The
quantum yields for singlet oxygen generation [φ(1O2)] for
4 and 12-15 were all <0.0005 [100% efficiency has
φ(1O2) ) 1.0] in MeOH solution.
1806 J . Org. Chem., Vol. 68, No. 5, 2003

Substituted Chalcogenopyrylium Dyes
20.1; IR (KBr) 1621 cm-1; HRMS (ES) m/z 273.1313 (calcd for
Su m m a r y a n d Con clu sion s
C
17H20OS + H: 273.1313). Anal. Calcd for C17H20OS: C, 74.95;
In conclusion, strong, narrow absorbance bands char-
acterize chalcogenopyrylium dyes bearing 2,6-di-tert-bu-
tyl substituents. In polymethine systems, the wave-
lengths of absorption extend into the near-infrared. Thia-
pyrylium pentamethine dye 3 has λmax ) 821 nm with a
molar extinction coefficient of 384 000 M-1 cm-1. While
dye 3 has excellent optical properties for compatibility
with near-infrared-emitting diode lasers, it is very easily
oxidized with Epa ) +0.58 V (vs Fc/Fc+), which limits
its utility. The 2,6-dimethylphenyl substituent is very
similar to the tert-butyl substituent with respect to
impact on λmax and band shape as measured by ν1/2, but
dyes bearing this substituent have more anodic (positive)
oxidation potentials relative to dyes with tert-butyl sub-
stituents. The 2-methylphenyl substituent is intermedi-
ate between the tert-butyl group and the phenyl group
with respect to optical properties, but also imparts more
anodic (positive) oxidation potentials relative to dyes with
tert-butyl substituents. Synthetically, the 2,6-dimeth-
ylphenyl and 2-methylphenyl substituents are easily
introduced into the thiapyrylium framework at the 2- and
6-positions.
H, 7.40. Found: C, 74.62; H, 7.48.
P r ep a r a tion of 2-(1,1-Dim eth yleth yl)-6-(2-m eth ylp h en -
yl)th ia p yr a n -4-on e (11d ). Diynone 10d (0.25 g, 1.1 mmol),
sulfur (0.043 g, 1.3 mmol), and NaBH4 (0.067 g, 1.8 mmol) were
treated as described for the preparation of 11b. Following
chromatography on SiO2 eluted with 20% EtOAc/hexanes,
thiapyranone 11d was isolated in 0.051 g (18%) yield as a
colorless oil: 1H NMR (300 MHz, CDCl3) δ 7.2 (m, 4 H), 7.03
(d, 1 H, J ) 1.2 Hz), 6.83 (d, 1 H, J ) 1.2 Hz), 2.34 (s, 3 H),
1.39 (s, 9 H); 13C NMR (75 MHz, CDCl3) δ 182.7, 166.9, 153.5,
136.0, 135.9, 131.1, 130.0, 129.4, 129.3, 126.3, 125.4, 38.6, 30.7,
20.1; IR (film, NaCl) 1613 cm-1; HRMS (ES) m/z 281.0959
(calcd for
16H18OS: C, 74.38; H, 7.02; Found: C, 74.19; H, 7.11.
P r ep a r a tion of 2,6-Bis(2,6-d im eth ylp h en yl)th ia p yr a n -
C16H18OS + Na: 281.0976). Anal. Calcd for
C
4-on e (11e). Diynone 10e (0.20 g, 0.69 mmol), sulfur (0.028
g, 0.84 mmol), and NaBH4 (0.44 g, 1.1 mmol) were treated as
described for the preparation of 11b. Following chromatogra-
phy on SiO2 eluted with 20% EtOAc/hexanes and recrystalli-
zation from CH3CN, thiapyranone 11e was isolated in 0.050
g (22%) yield as a white crystalline solid, mp 168-170 °C: 1H
NMR (300 MHz, CDCl3) δ 7.25 (t, 2 H, J ) 7.5 Hz), 7.13 (d, 4
H, J ) 7.5 Hz), 6.87 (s, 2 H), 2.29 (s, 12 H); 13C NMR (125
MHz, CDCl3) δ 183.0, 155.0, 136.5, 135.2, 130.5, 129.9, 128.4,
20.4; IR (CCl4) 1619 cm-1; HRMS (ES) m/z 343.1120 (calcd for
C
21H20OS + Na: 343.1133). Anal. Calcd for C21H20OS: C,
Exp er im en ta l Section
78.71; H, 6.29. Found: C, 78.73; H, 6.32.
P r ep a r a tion of 2,6-Bis(2-m eth ylp h en yl)th ia p yr a n -4-
on e (11f). Diynone 10f (0.70 g, 2.5 mmol), sulfur (0.096 g, 3.0
mmol), and NaBH4 (0.15 g, 4.0 mmol) were treated as
described for the preparation of 11b. Following chromatogra-
phy on SiO2 eluted with 20% EtOAc/hexanes and recrystalli-
zation from CH3CN, thiapyranone 11f was isolated in 0.15 g
(22%) yield as a white crystalline solid, mp 144-146 °C: 1H
NMR (300 MHz, CDCl3) δ 7.2-7.35 (m, 8 H), 6.99 (s, 2 H),
2.39 (s, 6 H); 13C NMR (125 MHz, CDCl3) δ 182.2, 154.9, 136.2,
135.9, 131.5, 130.3, 130.4, 129.6, 126.7, 20.4; IR (KBr) 1614
cm-1; HRMS (EI) m/z 292.0904 (calcd for C19H16OS: 292.0922).
Anal. Calcd for C19H16OS: C, 78.05; H, 5.52. Found: C, 77.87;
H, 5.13.
Gen er a l Meth od s. 2,6-Di-tert-butyl-4-methylthiapyrylium
hexafluorophosphate 6a was prepared as described in ref 3a.
Quantum yields for singlet oxygen were measured in MeOH
at 25 °C, using methods we have previously described.14
P r ep a r a tion of 2-(1,1-Dim eth yleth yl)-6-p h en ylth ia p y-
r a n -4-on e (11b). Diynone 10b (5.13 g, 24.4 mmol) was
dissolved in a 0.25 M solution of NaOEt in EtOH (488 mL)
that was stirred at room temperature for 10 min and then
added to a solution of Na2S prepared from sulfur (0.94 g, 29.3
mmol) and NaBH4 (1.48 g, 39.0 mmol) in a 0.25 M solution of
sodium ethoxide in ethanol (488 mL). (These reagents were
heated at reflux until all sulfur was dissolved and the color of
the solution changed from green to white.) The reaction
mixture was stirred for 1 h at ambient temperature and was
first filtered through Celite and then concentrated. The
products were extracted from an aqueous workup with EtOAc
and the organic extracts were washed with brine, dried over
MgSO4, and concentrated. The product was purified via
chromatography on SiO2 eluted with EtOAc to give 4.05 g
(68%) of 11b as a yellow oil: 1H NMR (400 MHz, CDCl3):δ
7.57 (m, 2 H), 7.45 (m, 3 H), 7.10 (s, 1 H), 7.00 (s, 1 H), 1.40 (s,
9 H); 13C NMR (125 MHz CDCl3) δ 182.7, 165.9, 153.0, 136.3,
130.4, 129.1, 126.8, 126.2, 125.0, 38.3, 30.5; IR (film, NaCl)
1613 cm-1; HRMS (EI) m/z 244.0922 (calcd for C15H16OS:
244.0931). Anal. Calcd for C15H16OS: C, 73.73; H, 6.60.
Found: C, 73.38; H, 6.41.
P r ep a r a tion of 2-(1,1-Dim eth yleth yl)-6-(2,6-d im eth -
ylp h en yl)th ia p yr a n -4-on e (11c). Diynone 10c (0.44 g, 1.8
mmol), sulfur (0.070 g, 2.2 mmol), and NaBH4 (0.11 g, 2.9
mmol) were treated as described for the preparation of 11a b.
Following chromatography on SiO2 eluted with 20% EtOAc/
hexanes and recrystallization from CH3CN, thiapyranone 11c
was isolated in 0.105 g (20%) yield as a white crystalline solid,
mp 105-106 °C: 1H NMR (300 MHz, CDCl3):δ 7.24 (t, 1 H, J
) 7.5 Hz), 7.12 (d, 2 H, J ) 7.5 Hz), 7.02 (s, 1 H), 6.75 (s, 1 H),
2.23 (s, 6 H), 1.38 (s, 9 H); 13C NMR (125 MHz, CDCl3):δ 183.1,
167.5, 153.3, 136.4, 135.3, 129.5, 129.3, 128.0, 125.3, 38.6, 30.7,
Gen er a l P r oced u r e for th e P r ep a r a tion of 4-Meth yl-
th ia p yr yliu m Hexa flu or op h osp h a te Sa lts. P r ep a r a tion
of 2-(1,1-Dim eth yleth yl)-6-p h en yl-4-m eth ylth ia p yr yliu m
Hexa flu or op h osp h a te (6b). Thiapyranone 11b (4.05 g, 16.6
mmol) was dissolved in THF (70 mL) and cooled to 0 °C. A
solution of 1.4 M methylmagnesium bromide (60 mL, 84 mmol)
in ether was added and the reaction mixture was stirred at
room temperature for 15 min. The solution was then poured
into acetic acid and 5 mL of a 60% solution of HPF6 was slowly
added until the solution darkened. The reaction mixture was
then poured into water and the green crystals were collected
by filtration. The crude product was recrystallized from
CH3CN to give 6b in 4.64 g (72%) yield as a light green powder,
1
mp 178 °C: H NMR (500 MHz, CD3CN) δ 8.64 (s, 1 H), 8.56
(s, 1 H), 7.95 (d, 2 H, J ) 7.6 Hz), 7.76 (m, 1 H), 7.70 (m, 2 H),
2.88 (s, 3 H), 1.62 (s, 9 H); 13C NMR (125.5 MHz, CD3CN) δ
186.1, 169.0, 167.4, 134.8, 134.7, 134.7, 134.4, 131.2, 129.3,
42.5, 30.9, 26.0; λmax (CH2Cl2) 367 nm (ꢀ 41 400 ( 800 M-1
cm-1); MS (ES) m/z 243 (M+ for C16H19S, 243). Anal. Calcd for
C
16H19F6PS: C, 49.48; H, 4.93. Found: C, 49.27; H, 4.95.
P r ep a r a tion of 2-(1,1-Dim eth yleth yl)-6-(2,6-d im eth yl-
ph en yl)-4-m eth ylth iapyr yliu m Hexaflu or oph osph ate (6c).
Thiapyranone 11c (0.22 g, 0.80 mmol) was treated with 1.4 M
MeMgBr in ether (1.7 mL, 2.4 mmol) and HPF6 as described
1
for 6b to give 6c in 0.27 g (82%) yield, mp 152 °C: H NMR
(300 MHz, CDCl3) δ 8.63 (s, 1 H), 8.15 (s, 1 H), 7.39 (t, 1 H, J
) 7.5 Hz), 7.23 (d, 2 H, J ) 7.5 Hz), 3.04 (s, 3 H), 2.14 (s, 6 H),
1.69 (s, 9 H); 13C NMR (125.5 MHz, CD3CN) δ 189.6, 168.6,
168.1, 138.2, 137.4, 135.4, 133.3, 131.9, 128.9, 42.5, 30.5, 25.9,
20.3; HRMS (ES) m/z 271.1532 (calcd for C18H23S: 271.1520).
(13) Sadekov, I. D.; Ladatko, A. A.; Sadekova, E. I.; Minkin, V. I.
Khim. Geterotsikl. Soedin. 1980, 274-276.
(14) (a) Detty, M. R.; Merkel, P. B. J . Am. Chem. Soc. 1990, 112,
3845-3851. (b) Leonard, K. A.; Nelen, M. I.; Anderson, L. T.; Gibson,
S. L.; Hilf, R.; Detty, M. R. J . Med. Chem. 1999, 42, 3942-3952.
J . Org. Chem, Vol. 68, No. 5, 2003 1807

Panda et al.
Anal. Calcd for C18H23F6PS: C, 51.92; H, 5.97. Found: C,
51.77; H, 6.03.
by filtration and washed with 10% ethanol in ether to give
copper-bronze crystals. A final wash with hot ethyl acetate
removes the products of half reaction to give 2.67 g (90%) of
dye 3, mp 175-178 °C: 1H NMR (500 MHz, CDCl3) δ 8.13 (t,
2 H, J ) 13 Hz), 7.43 (br s, 4 H), 6.48 (t, 1 H, J ) 13 Hz), 6.25
(d, 2 H, J ) 13 Hz), 1.42 (s, 18 H); λmax (CH2Cl2) 822 nm [ꢀ
384 000 ( 7 000 M-1 cm-1). Anal. Calcd for C31H45F6PS2: C,
59.41; H, 7.24; S, 10.23. Found: C, 59.33; H, 7.28; S, 9.93.
P r ep a r a tion of 4-[4-[2-(1,1-Dim eth yleth yl)-6-(2,6-d i-
m et h ylp h en yl)]-4H -(t h ia p yr a n ylid en e)m et h yl]-1,3-b u -
t a d ien yl-2-(1,1-d im et h ylet h yl)-6-(2,6-d im et h ylp h en yl)-
th ia p yr yliu m Hexa flu or op h osp h a te (12). Sodium acetate
(0.016 g, 0.18 mmol), cyanine 7 (0.034 g, 0.093 mmol), and
4-methylthia-
P r ep a r a tion of 2-(1,1-Dim eth yleth yl)-6-(2-m eth ylp h en -
yl)-4-m eth ylth iapyr yliu m Hexaflu or oph osph ate (6d). Thia-
pyranone 11d (0.100 g, 0.39 mmol) was treated with 1.4 M
MeMgBr in ether (1.2 mL, 1.7 mmol) and HPF6 as described
1
for 6b to give 6d in 0.13 g (84%) yield, mp 147 °C: H NMR
(300 MHz, CD3CN) δ 8.62 (s, 1 H), 8.41 (s, 1 H), 7.3-7.7 (m,
4 H), 2.88 (s, 3 H), 2.35 (s, 3 H), 1.61 (s, 9 H); 13C NMR (125.5
MHz, CD3CN) δ 187.3, 168.9, 166.4, 137.3, 134.5, 132.6, 132.1,
131.2, 127.4, 127.1, 126.6, 30.4, 30.1, 25.6, 19.6; HRMS (ES)
m/z 257.1361 (calcd for C17H21S: 257.1364). Anal. Calcd for
C
17H21F6PS: C, 50.74; H, 5.26. Found: C, 50.92; H, 5.51.
P r ep a r a tion of 2,6-Bis(2,6-d im eth ylp h en yl)-4-m eth -
pyrylium hexafluorophosphate 6c (0.080 g, 0.17 mmol) were
heated at 95 °C for 10 min in 0.5 mL of Ac2O and 0.5 mL of
HOAc as described for the preparation of dye 4. Product yield
was 0.085 g (60%) of 12 as a dark blue solid, mp 130 °C: 1H
NMR (300 MHz, CDCl3) δ 8.10 (br s, 2 H), 7.52 (s, 1 H), 7.49
(s, 1 H), 7.33 (t, 2 H, J ) 7.5 Hz), 7.14 (d, 4 H, J ) 7.5 Hz),
7.12 (br s, 2 H), 6.62 (br t, 1 H, J ) 13 Hz), 6.38 (br d, 2H, J
) 13 Hz), 2.24 (s, 6 H), 2.18 (s, 6 H), 1.48 (s, 18 H); 13C NMR
(125 MHz, CDCl3) δ 167.7, 154.4, 151.7, 144.3, 137.1, 130.4,
129.5, 128.6, 124.8, 120.3, 117.1, 31.2, 30.1, 20.7 (one signal
overlapping); λmax (CH2Cl2) 831 nm (ꢀ 240 000 ( 3 000 M-1
cm-1) HRMS (ES) m/z 577.2968 (calcd for C39H45S2: 577.2963).
Anal. Calcd for C39H45F6PS2: C, 64.80; H, 6.27. Found: C,
64.53; H, 6.27.
P r ep a r a tion of 4-[4-[2-(1,1-Dim eth yleth yl)-6-(2-m eth -
ylp h e n yl)]-4H -(t h ia p yr a n ylid e n e )m e t h yl]-1,3-b u t a d i-
e n yl-2-(1,1-d im e t h yle t h yl)-6-(2-m e t h ylp h e n yl)t h ia p y-
r yl-iu m Hexa flu or op h osp h a te (13). Sodium acetate (0.023
g, 0.28 mmol), cyanine 7 (0.044 g, 0.12 mmol), and 4-meth-
ylthiapyrylium hexafluorophosphate 6d (0.10 g, 0.25 mmol)
were heated at 95 °C for 10 min in 0.5 mL of Ac2O and 0.5 mL
of HOAc as described for the preparation of dye 4. Product
yield was 0.10 g (58%) of 13 as a dark blue solid, mp 144-146
°C: 1H NMR (500 MHz, CD3CN) δ 7.93 (t, 2 H, J ) 13 Hz),
7.5-7.2 (m, 12 H), 6.65 (t, 1 H, J ) 13 Hz), 6.50 (d, 2 H, J )
13 Hz), 2.36 (s, 6 H), 1.44 (s, 18 H); 13C NMR (125 MHz, CD3-
CN) δ 168.3, 153.5, 151.5, 149.5, 137.0, 136.7, 132.0, 131.3,
130.4, 129.5, 127.3, 125.4, 124.2, 120.1, 40.0, 30.6, 20.0; λmax
(CH2Cl2) 836 nm (ꢀ 198 000 ( 5 000 M-1 cm-1) HRMS (ES)
m/z 549.2650 (calcd for C37H41S2: 549.2656). Anal. Calcd for
ylth ia p yr yliu m Hexa flu or op h osp h a te (6e). Thiapyranone
11e (0.080 g, 0.25 mmol) was treated with 1.4 M MeMgBr in
ether (1.0 mL, 1.4 mmol) and HPF6 as described for 6b to give
6e in 0.09 g (78%) yield, mp 176 °C: 1H NMR (300 MHz, CDCl3)
δ 8.40 (s, 2 H), 7.39 (t, 2 H, J ) 7.5 Hz), 7.25 (d, 4 H, J )
7.5 Hz), 3.15 (s, 3 H), 2.22 (s, 12 H); 13C NMR (125.5 MHz,
CD3CN) δ 173.1, 170.6, 139.4, 137.2, 133.0, 132.3, 129.1, 26.4,
20.4; HRMS (ES) m/z 319.1530 (calcd for C22H23S: 319.1520).
Anal. Calcd for C22H23F6PS: C, 56.89; H, 4.99. Found: C,
56.83; H, 5.03.
P r ep a r a tion of 2,6-Bis(2-m eth ylp h en yl)-4-m eth ylth ia -
p yr yliu m Hexa flu or op h osp h a te (6f). Thiapyranone 11f
(0.080 g, 0.27 mmol) was treated with 1.4 M MeMgBr in ether
(1.0 mL, 1.4 mmol) and HPF6 as described for 6b to give 6f in
1
0.10 g (84%) yield, mp 156 °C: H NMR (300 MHz, CDCl3) δ
8.40 (s, 2 H), 7.0-7.6 (m, 8 H), 3.03 (s, 3 H), 2.49 (s, 6 H); 13
C
NMR (125.5 MHz, CD3CN) δ 176.5, 171.7, 142.7, 142.2, 138.8,
137.9, 137.4, 136.5, 132.6, 30.8, 24.8; HRMS (ES) m/z 291.1203
(calcd for C20H19S: 291.1207). Anal. Calcd for C20H19F6PS: C,
55.05; H, 4.39. Found: C, 54.83; H, 4.22.
Gen er a l P r oced u r e for t h e P r ep a r a t ion of P en t a -
m eth in e Dyes. P r epar ation of 4-[4-[2-(1,1-Dim eth yleth yl)-
6-p h en yl]-4H-(th ia p yr a n ylid en e)m eth yl]-1,3-bu ta d ien yl-
2-(1,1-d im eth yleth yl)-6-p h en ylth ia p yr yliu m Hexa flu or o-
p h osp h a te (4). Aniline (2.86 g, 30.0 mmol) and 1,1,3,3-
tetramethoxypropane (1.99 g, 12.1 mmol) were dissolved in
acetic acid (10 mL) and the solution heated to 80 °C for 15
min. The solution was removed from the heat and a 60%
solution of hexafluorophosphoric acid (2 mL) was slowly added.
The reaction mixture was then poured into water (200 mL)
and the hexafluorophosphate cyanine salt 7 was collected as
a yellow solid.13 Sodium acetate (0.023 g, 0.28 mmol), cyanine
7 (0.051 g, 0.14 mmol), and 4-methylthiapyrylium hexafluo-
rophosphate 6b (0.11 g, 0.28 mmol) were heated at 95 °C for
10 min in 0.75 mL of Ac2O and 0.75 mL of HOAc. The reaction
mixture was poured into water and the brown precipitate was
collected by filtration. The dye was recrystallized by dissolving
the crude dye in hot CH3CN, cooling to ambient temperature,
and then adding an equal volume of ether to induce crystal-
lization upon standing. The resulting copper crystals were
collected to give 4 in 0.058 g (62%) yield: mp 206.5-207.5 °C;
1H NMR (500 MHz, CD3CN) δ 7.92 (t, 2 H, J ) 13 Hz), 7.70
(m, 6 H), 7.53 (m, 8 H), 6.60 (t, 1 H, J ) 13 Hz), 6.46 (d, 2 H,
J ) 13 Hz), 1.42 (s, 18 H); 13C NMR (125 MHz, CD3CN) δ
167.1, 152.9, 151.7, 149.3, 136.8, 134.7, 132.2, 131.2, 130.5,
129.4, 127.8, 126.1, 40.1, 30.7; λmax (CH2Cl2) 855 nm (ꢀ 275 000
( 8 000) M-1 cm-1). Anal. Calcd for C35H37F6PS2: C, 63.05; H,
5.59. Found: C, 63.11; H, 5.52.
C
37H41F6PS2: C, 64.80; H, 6.27. Found: C, 64.53; H, 6.27.
P r ep a r a tion of 4-[4-[2,6-Bis(2,6-d im eth ylp h en yl)]-4H-
(t h ia p yr a n ylid en e)m et h yl]-1,3-b u t a d ien yl-2,6-b is(2,6-
dim eth ylph en yl)th iapyr yliu m Hexaflu or oph osph ate (14).
Sodium acetate (0.016 g, 0.18 mmol), cyanine 7 (0.034 g, 0.093
mmol), and 4-methylthiapyrylium hexafluorophosphate 6e
(0.080 g, 0.17 mmol) were heated at 95 °C for 10 min in 0.5
mL of Ac2O and 0.5 mL of HOAc as described for the
preparation of dye 4. Product yield was 0.080 g (56%) of 14 as
a dark blue solid, mp 162-164 °C: 1H NMR (500 MHz, CDCl3)
δ 7.76 (t, 2 H, J ) 13 Hz), 7.48 (s, 2 H), 7.44 (s, 2 H), 7.16 (t,
4 H, J ) 7.5 Hz), 7.04 (d, 8 H, J ) 7.5 Hz), 6.66 (t, 1 H, J ) 13
Hz), 6.40 (d, 2 H, J ) 13 Hz), 2.18 (s, 24 H); λmax (CH2Cl2) 841
nm (ꢀ 348 000 ( 7 000 M-1 cm-1) HRMS (ES) m/z 673.2963
(calcd for C47H45S2: 673.2963). Anal. Calcd for C47H45F6PS2:
C, 68.93; H, 5.54. Found: C, 69.08; H, 5.39.
P r epar ation of 4-[4-[2,6-Bis(2-m eth ylph en yl)]-4H-(th ia-
p yr a n ylid e n e )m e t h yl]-1,3-b u t a d ie n yl-2,6-b is(2-m e t h -
ylp h en yl)th ia p yr yliu m Hexa flu or op h osp h a te (15). So-
dium acetate (0.023 g, 0.28 mmol), cyanine 7 (0.051 g, 0.14
mmol), and 4-methylthiapyrylium hexafluorophosphate 6f
(0.11 g, 0.28 mmol) were heated at 95 °C for 10 min in 0.5 mL
of Ac2O and 0.5 mL of HOAc as described for the prepara-
tion of dye 4. Product yield was 0.11 g (58%) of 15 as a dark
blue solid, mp 134-136 °C: 1H NMR (500 MHz, CD3CN) δ
7.70 (br t, 2 H, J ) 13 Hz), 7.34 (br s, 4 H), 7.7-7.0 (m, 12 H),
6.48 (t, 1 H, J ) 13 Hz), 6.30 (d, 2 H, J ) 13 Hz), 2.21 (s,
12 H); 13C NMR (125 MHz, CD3CN) 153.7, 150.5, 149.4,
P r ep a r a tion of 4-[4-[2,6-Bis(1,1-d im eth yleth yl)]-4H-
(t h ia p yr a n ylid en e)m et h yl]-1,3-b u t a d ien yl-2,6-b is(1,1-
d im eth yleth yl)th ia p yr yliu m Hexa flu or op h osp h a te (3).
2,6-Di-tert-butyl-4-methylthiopyrylium hexafluorophosphate
(6a , 4.04 g, 0.0110 mol), NaOAc (1.0 g, 0.012 mol), and cyanine
7 (1.84 g, 0.00500 mol) were heated to 90-95 °C in 25 mL of
acetic anhydride and 25 mL of acetic acid for 0.5 h. (Temper-
ature is critical, if the reaction reaches >100 °C, yields are
dramatically reduced.) The reaction mixture was poured into
300 mL of water and stirred for 1 h. The solid was collected
1808 J . Org. Chem., Vol. 68, No. 5, 2003

Substituted Chalcogenopyrylium Dyes
136.5, 135.6, 131.9, 131.2, 130.2, 130.1, 129.3, 127.2, 119.8,
Ack n ow led gm en t. J .P., P.R.V., and M.R.D. thank
the Eastman Kodak Company and Kodak Polychrome
Graphics for a grant in partial support of this work.
19.8; λmax (CH2Cl2) 854 nm (ꢀ 240 000 ( 3 000 M-1 cm-1
)
HRMS (ES) m/z 617.8852 (calcd for C43H37S2: 617.8859). Anal.
Calcd for C43H37F6PS2: C, 67.70; H, 4.89. Found: C, 67.33; H,
4.86.
Electr och em ica l P r oced u r es. The working electrode for
cyclic voltammetry was a platinum disk electrode (diameter,
1 mm). The auxiliary and reference electrodes were silver
wires. The reference for cyclic voltammetry was the Fc/Fc+
couple at +0.40 V at a scan rate of 0.1 V s-1. All samples were
run in HPLC-grade dichloromethane that had been stored over
3A molecular sieves and freshly distilled prior to use. Tetra-
butylammonium fluoroborate was recrystallized from ethyl
acetate-ether and then dried overnight at 80 °C before it was
used as supporting electrolyte at 0.2 M. Nitrogen was used
for sample deaeration.
Su p p or tin g In for m a tion Ava ila ble: Figures S1-S7 for
the absorption spectra of dyes 3-5 and 12-15 and experi-
mental procedures for the preparation of 2,6-dimethylphenyl-
ethyne, 2-methylphenylethyne, and compounds 8-10. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O026645U
J . Org. Chem, Vol. 68, No. 5, 2003 1809