Synthesis, Structure, and optical properties of the platinum(II) complexes of indaphyrin and thiaindaphyrin

Article abstract of DOI:10.1021/ic802041z

The novel free base meso-di(5′-methylthien-2′-yl) thiaindaphyrin, 10, was prepared from the corresponding meso- tetra(thien-2-yl)porphyrin using a methodology analogous to that for the preparation of known meso-diphenylindaphyrin, 5: ββ′- Dihydroxylation

Full text of DOI:10.1021/ic802041z

Inorg. Chem. 2009, 48, 4067-4074
Synthesis, Structure, and Optical Properties of the Platinum(II)
Complexes of Indaphyrin and Thiaindaphyrin
Kimberly S. F. Lau,†,‡ Shengxian Zhao,‡ Claudia Ryppa,‡ Steffen Jockusch,§ Nicholas J. Turro,§
Matthias Zeller,| Martin Gouterman,† Gamal E. Khalil,† and Christian Bru¨ckner*,‡
Department of Chemistry, UniVersity of Washington, Box 351700,
Seattle, Washington 98195-1700, Department of Chemistry, UniVersity of Connecticut,
Unit 3060, Storrs, Connecticut 06269-3060, Department of Chemistry,
Columbia UniVersity, New York, New York 10027, and Department of Chemistry,
Youngstown State UniVersity, One UniVersity Plaza,
Youngstown, Ohio 44555-3663
Received October 24, 2008
The novel free base meso-di(5′-methylthien-2′-yl)thiaindaphyrin, 10, was prepared from the corresponding meso-
tetra(thien-2-yl)porphyrin using a methodology analogous to that for the preparation of known meso-diphenylindaphyrin,
5: ꢀ,ꢀ′-Dihydroxylation of the porphyrin is followed by oxidative diol cleavage. The resulting aldehyde moieties
undergo an acid-catalyzed intramolecular Friedel-Crafts alkylation of the adjacent meso-thienyl groups with
concomitant oxidation. Insertion of Pt(II) into either of the chromophores is facile, producing 5Pt and 10Pt. The
crystal structure of 5Pt, the first for any indaphyrin, shows that the conformation of the indaphyrinato ligand is
strongly ruffled, while the N4 donor set that coordinates the central Pt(II) maintains a near-perfect square-planar
¯
coordination geometry around the central metal ion (crystal data for C44H24N4O2Pt: triclinic space group P1 with a
) 8.8735(4) Å, b ) 12.9285(6) Å, c ) 14.3297(6) Å, R ) 88.785(1)°, ꢀ ) 82.248(1)°, γ ) 72.422(1)°; Z ) 2).
The UV-vis and emission spectra, triplet yields, and lifetimes of the Pt(II) complexes 5Pt and 10Pt were determined.
Both complexes luminesce (in EtOH at 77 K) in the NIR (5Pt: λmax-emission ) 864, 974 nm, lifetime 2 µs; 10Pt:
λmax-emission ) 990, 1112, 1276 nm) with modest to low quantum yields (Φp ∼ 1% and ∼ 6 × 10-3 %,
respectively).
Introduction
One particularly well-studied class of compounds for
oxygen sensing applications is that of the Pt(II) porphyrins,
such as [meso-tetraphenylporphyrinato]Pt(II) (1Pt) and re-
lated compounds.1,4-7 In Pt(II) and Pd(II) porphyrins, ligand-
based emissions are observed (λmax-emission for 1Pt ) 650, 712
The triplet oxygen-mediated quenching of the triplet
excited-state of many chromophores (Stern-Volmer
quenching) allows a correlation between the degree of
quenching and a particular oxygen partial pressure.1 This
gives rise to the development of optical oxygen sensors
that find applications in medicine, engineering, and
chemical and environmental analyses.1-3
(4) Xiang, H.-F.; Li, C.-N.; Yu, S. C.; Che, C.-M.; Lai, P. T.; Chui, P. C.
Proc. SPIE Int. Soc Opt. Eng. 2004, 5519, 218–225.
(5) Vinogradov, S. A.; Lo, L.-W.; Wilson, D. F. Eur. J. Chem. 1999, 5,
1338–1347.
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J. Am. Chem. Soc. 2005, 127, 11851–11862.
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Y. Inorg. Chem. 2006, 45, 4735–4742.
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E. G.; Cerny, R. L. J. Am. Chem. Soc. 1989, 111, 3702–3707.
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Callis, J. B.; Dalton, L. R. Sens. Actuators, B 2003, 96, 304–314.
(10) Gouterman, M.; Callis, J.; Dalton, L.; Khalil, G.; Mebarki, Y.; Cooper,
K. R.; Grenier, M. Meas. Sci. Technol. 2004, 15, 1986–1994.
(11) Khalil, G. E.; Costin, C.; Crafton, J.; Jones, G.; Grenoble, S.;
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97, 13–21.
* To whom correspondence should be addressed. Phone: (860) 486-
2743. Fax: (860) 486-2981. E-mail: c.bruckner@uconn.edu.
†
University of Washington.
University of Connecticut.
Columbia University.
Youngstown State University.
‡
§
|
(1) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.;
Springer: New York, 2006.
(2) Gouterman, M. J. Chem. Educ. 1997, 74, 697–702.
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Papkovsky, D. B.; O’Riordan, T.; Soini, A. Biochem. Soc. Trans. 2000,
28, 74–77.
10.1021/ic802041z CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 9, 2009 4067
Published on Web 04/02/2009

Lau et al.
nm).2 This allows a modulation of the excitation and
emission wavelengths through alterations of the porphyrinic
chromophore. Examples include the use of the Pd(II) and
Pt(II) complexes of porpholactones, 2Pt,8-11 ꢀ-oxo-porphy-
rins,12 or benzoporphyrins, such as complex 3Pt.13
ꢀ-carbons have become ketone moieties that are fused to
the o-position of the neighboring meso-phenyl rings, thus
giving rise to the formation of indanone moieties.17,18 It was
computed that the short linkage forces the indanone groups
into near coplanarity with the mean plane of the greatly
ruffled porphyrinoid chromophore, thus allowing for exten-
sive conjugation between the two π systems.18 This, and the
two conjugated ketone functionalities, rationalize the unusual
UV-vis spectra of indaphyrins (λmax-absorption ) 810 nm) when
compared to those of porphyrins (λmax-absorption ∼ 650 nm).18
Now, the question arises whether the Pt(II) complexes of
indaphyrin, 5, can be prepared, whether they are emissive
in the NIR, and whether they can be used as oxygen sensors.
A red shift of the excitation or luminescence spectra into
the red or NIR range (λmax-emission > 750 nm) is desirable for
a number of applications, particularly in the life sciences.14
By utilizing red to near-infrared (NIR) wavelengths, an
increase in the sensitivity of luminescence-based assays in
biological systems measurements can be achieved because
no natural chromophore emits in this region. The NIR is also
the region of the “spectroscopic window” in tissue, and
chromophores emitting in this range may allow the detection
of events deep in the tissue. Last, longer wavelengths are
scattered less in opaque media than shorter ones, increasing
the resolution of the emission images obtained.
This emission red shift was the driving force behind
the development of π-extended porphyrins such as 3Pt
(λmax-emission ) 745 nm)15 or the bimetallic complex of an
N-confused calyx[6]phyrin 4Pt2 (λmax-emission ) 1010 nm).16
An ideal sensor molecule should fulfill other key require-
ments such as high extinction coefficients and high
emission quantum yields (i.e., possessing high brightness),
and excellent photostability. Ancillary properties such as
nonaggregation in a polymer matrix, good processability,
and a large Stokes shift further improve their applicability.
We reported recently the synthesis of a novel class of
porphyrin derivatives, the indaphyrins, 5. This class of
compounds, synthesized from meso-tetraphenylporphyrin,
contains a ꢀ,ꢀ′-ring-cleaved pyrrole moiety. The former
In unrelated studies, we, and others, reported that meso-
thienyl-porphyrins and corroles possess red-shifted electronic
spectra.19,20 This observation was attributed to the smaller
ring size of thiophenes compared to that of phenyl groups,
which allows for their greater degree of coplanarity with the
porphyrin chromophore. This prompts the question of
whether meso-thienyl substitution and an indaphyrin-type
linkage can be combined to achieve a bathochromic shift in
the as-yet unknown meso-thienylporphyrin-derived thiain-
daphyrins, and their Pt(II) complexes, as compared to their
phenyl analogues.
This contribution will demonstrate that these questions can
largely be answered in the affirmative. We report here on
the preparation, photophysical characteristics, and oxygen-
sensing abilities of the Pt(II) complexes of indaphyrin and
thiaindaphyrin, 5Pt and 10Pt, respectively. We will also
report the X-ray single-crystal structure of [meso-phenylin-
daphyrinato]Pt(II) (5Pt), the first structural characterization
of any indaphyrin, proving their predicted highly ruffled
chromophore structure.
(17) McCarthy, J. R.; Hyland, M. A.; Bru¨ckner, C. Chem. Commun. 2003,
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(18) McCarthy, J. R.; Hyland, M. A.; Bru¨ckner, C. Org. Biomol. Chem.
2004, 2, 1484–1491.
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Birge, R. R.; Crundwell, G. Phys. Chem. Chem. Phys. 2006, 8, 2402–
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(12) Papkovsky, D. B.; Ponomarev, G. V.; Trettnak, W.; O’Leary, P. Anal.
Chem. 1995, 67, 4112–17.
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V. V.; Khajehpour, M.; Vinogradov, S. A. Inorg. Chem. 2003, 42,
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2005, 70, 9562–9572.
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4392–4400. (c) Friedlein, R.; Kieseritzky, F. v.; Braun, S.; Linde, C.;
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4068 Inorganic Chemistry, Vol. 48, No. 9, 2009

Pt(II) Complexes of Indaphyrin and Thiaindaphyrin
Table 1. Selected Crystallographic Data and Structure Refinement
Details for 5Pta
Experimental Section
Instruments and MaterialssSynthesis. All solvents and re-
agents were used as received. meso-Tetraphenylporphyrin (1),21
diolchlorin (7),22 free-base indaphyrin (5),18 and meso-tetra(5′-
methylthien-2′-yl)porphyrin (6)19 were prepared as described before.
The analytical thin-layer chromatography (TLC) plates (aluminum-
backed, silica gel 60, 250 µm thickness), preparative TLC plates
(20 × 20 cm, glass-backed, silica gel 60, 500 or 1000 µm thickness),
and flash column silica gel (standard grade, 60 Å, 32-63 µm) used
were provided by Sorbent Technologies, Atlanta, Georgia. 1H and
13C NMR spectra were recorded on a Bruker DRX400 spectrometer.
The NMR spectra are expressed on the δ scale and were referenced
to residual solvent peaks or internal Me4Si (for copies of the NMR
spectra, see the Supporting Information). IR spectra were recorded
on a Thermo Nicolet Nexus 670 spectrometer. Mass spectra were
provided by the Mass Spectrometry Facilities at the Department
of Chemistry, University of Connecticut or the Department of
Chemistry and Biochemistry, University of Notre Dame.
Instruments and MaterialssPhotophysical Characterizations.
UV-vis spectra were recorded on a Cary 50 spectrophotometer
and the fluorescence spectra on a Cary Eclipse spectrofluorometer
(both Varian Inc.). NIR emission spectra were recorded, at 77 K,
of samples dissolved in the solvents specified and contained in
5-mm-diameter Pyrex NMR tubes using a modified SPEX Fluorolog
2 spectrometer (J. Y. Horiba, Edison, NJ), equipped with a liquid-
nitrogen-cooled Ge diode detector (EO817L; North Coast Scientific
Corp.). A 450 W Xe lamp (Osram), in conjunction with a double-
grating monochromator, served as the excitation source. The
emission spectra reported were not corrected for the wavelength-
dependent sensitivity of the detector.
empirical formula
fw, g/mol
space group
λ, Å
C44H24N4O2Pt
835.76
P1 (No. 2)
0.71073
8.8735(4)
j
a, Å
b, Å
c, Å
12.9285(6)
14.3297(6)
R, deg
88.7850(10)
82.2480(10)
72.4220(10)
1552.50(12)
1.788
ꢀ, deg
γ, deg
volume, Å3
dcalcd, g/cm3
Z
2
µ, mm-1
4.569
transmission coeff
final R indices [I > 2σ(I)]
R indices (all data)
0.663, 0.377
R1 ) 0.0247, wR2 ) 0.0628
R1 ) 0.0260, wR2 ) 0.0635
a The weighted R factor wR and goodness of fit are based on F2,
conventional R factor R is based on F, with F set to zero for negative F2.
The threshold expression of F2 > 2σ(F2) is used only for calculating R
factors.
KR radiation with the Ω scan technique in the range from θ )
1.43 to 28.28°; the limiting indices were -11 e h e 11, -17 e k
e 16, and -19 e l e 19. A total of 16 206 reflections were
collected, with 7670 independent reflections (Rint ) 0.0188),
completeness to θ ) 28.28°, 99.6%. The SADABS multiscan
absorption correction was applied.25a The data were collected using
SMART,25b and the data integration and unit cell determination
were made using SAINT+.25a The structure was solved by direct
methods and refined by full-matrix least-squares against F2 using
SHELXTL.25c The goodness-of-fit on F2 was 1.074; the largest
differential peak and hole were 1.879 and -0.940 e ·Å-3. A full-
matrix refinement method on the least-squares on F2 was applied.
Data, restraints, and parameters were 7670, 0, and 460. Non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters. All hydrogen atoms were placed in calculated positions
and were isotropically refined with a displacement parameter of
1.2 times that of the adjacent carbon atom. The refinement
converged satisfactorily. The crystal structure and refinement data
for 5Pt are summarized in Table 1. Selected bond lengths and
distances are tabulated in Table 2.
Phosphorescence lifetimes were measured at 77 K using the
pulses from a Lambda Physik dye laser (FL3002; Laser dye:
Stilbene 3), which was pumped with a Lambda Physik Excimer
laser (Lextra). The phosphorescence was collected and isolated
using lenses and monochromators (H10 for visual spectral range
and 1681B for NIR spectral range; Jobin-Yvon Inc.) and focused
into Hamamatsu photomultiplier tubes (PMT; R928 for visual
spectral range and H9170-45 for NIR spectral range). The photo-
current from the PMT was amplified (SR 560, Stanford Research
Systems) and stored on a digital oscilloscope (TDS 360, Tektronix).
Oxygen-Sensing Experiments. Complex 5Pt (5 mg) was
dissolved in a solution of silicon-polycarbonate LR 3320 (500 mg,
General Electric, Fairfield, CT) in CH2Cl2 (20 mL). The sensor
film was cast and tested following a standard procedure.23,24 In an
alternative approach, the PtDPI was dispensed directly onto 1 × 2
cm TLC plates (500 µm silica on glass).
[meso-Diphenylindaphyrinato]Pt(II) (5Pt). To a solution of
free-base indaphyrin, 5 (59 mg, 0.09 mmol), in PhCN (15 mL)
was added bis-2,4-pentanedionate [Pt(acac)2] (108 mg, 0.28 mmol,
3 equiv). The reaction mixture was refluxed and monitored by TLC
and UV-vis until the starting material was exhausted (5 h). The
solvent was removed in vacuo. The mixture was passed through a
plug of silica with CH2Cl2. The residue was further purified by
preparative TLC (silica-CH2Cl2/n-hexane 4:1) and recrystallized
from CHCl3/EtOH to give 5Pt as a purple solid (50 mg, 0.06 mmol,
65%). Rf (silica- CH2Cl2): 0.42. UV-vis (CH2Cl2) λmax (log ε):
391 (3.86), 462 (sh), 495 (sh), 525 (4.16), 632 (3.54), 677 (3.48)
nm. IR (neat) νmax: 1706 (CdO) cm-1. 1H NMR (400 MHz, CDCl3):
X-Ray Diffractometry of 5Pt.25 A dark green needle-shaped
crystal of 5Pt of the approximate dimensions 0.43 × 0.12 × 0.09
mm was obtained by the slow evaporation of a CH2Cl2/CH3CN
solution. Diffraction data were collected on a Bruker AXS SMART
APEX CCD diffractometer at 100(2) K using monochromatic Mo
(21) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour,
J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476.
(22) Bru¨ckner, C.; Rettig, S. J.; Dolphin, D. J. Org. Chem. 1998, 63, 2094–
2098.
3
3
7.37 (t, J ) 7.6 Hz, 1H), 7.50-7.60 (br s, 1H), 7.67 (t, J ) 7.6
3
3
Hz, 2H), 7.75 (br t, 3H), 7.90 (d, J ) 7.6 Hz, 1H), 8.26 (d, J )
7.6 Hz, 1H), 8.43 (s, 1H), 8.66 (d, 3J ) 5.2 Hz, 1H), 9.25 (d, 3J )
5.2 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): 117.2, 125.0, 126.2,
126.7, 127.0, 128.3, 129.0, 129.1, 131.4, 132.3, 136.3, 136.4, 137.1,
137.9, 138.6, 140.1, 146.2, 187.2 ppm. MS (ESI+, 100% CH3CN):
m/z 835 (M+). HRMS (EI, 30 eV): m/z calcd for C44H25N4O2Pt:
(M+) 835.1547. Found: 835.1546. Anal. calcd for C44H24N4O2Pt:
C, 63.23; H, 2.89; N, 6.70. Found: C, 63.19; H, 2.88; N, 6.68.
(23) Khalil, G.; Gouterman, M.; Ching, S.; Costin, C.; Coyle, L.; Gouin,
S.; Green, E.; Sadilek, M.; Wan, R.; Yearyean, J.; Zelelow, B. J.
Porphyrins Phthalocyanines 2002, 6, 135–145.
(24) Gamal, K. E.; Thompson, E. K.; Gouterman, M.; Callis, J. B.; Dalton,
L. R.; Turro, N. J.; Jockusch, S. Chem. Phys. Lett. 2007, 435, 45–49.
(25) (a) Bruker AdVanced X-ray Solutions SAINT, version 6.45; Bruker
AXS Inc.: Madison, WI, 1997-2003. (b) Bruker AdVanced X-ray
Solutions SMART for WNT/2000, version 5.628; Bruker AXS Inc.:
Madison, WI, 1997- 2002. (c) Bruker AdVanced X-ray Solutions
SHELXTL, version 6.10; Bruker AXS Inc., Madison, WI, 2000.
Inorganic Chemistry, Vol. 48, No. 9, 2009 4069

Lau et al.
Table 2. Select Bond Lengths and Angles for 5Pta
(CHCl3) λmax (log ε): 444 (4.77), 478 (4.71), 722 (4.16) nm. IR
(neat) νmax: 1648, 1691 (CdO) cm-1. 1H NMR (400 MHz, CDCl3)
δ: 2.57 (s, 3H), 2.70 (s, 3H), 2.72 (s, 6H), 3.34 (br s, exchangeable
with D2O, 2H), 6.89 (s, 1H), 6.99 (d, J ) 2.8 Hz, 1H), 7.03 (d, J
) 2.7 Hz, 1H), 7.09 (d, J ) 2.4 Hz, 1H), 7.26 (signal hidden under
CHCl3 signal, as seen in H,H-COSY), 7.30 (d, J ) 2.8 Hz, 1H),
7.45 (d, J ) 2.7 Hz, 1H), 8.08 (d, J ) 4.6 Hz, 1H), 8.17 (d, J )
4.6 Hz, 1H), 8.24 (brs, 2H), 8.32 (d, J ) 4.9 Hz, 1H), 8.36 (d, J )
4.9 Hz, 1H), 9.28 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3) δ:
15.5, 15.6, 15.9, 16.0, 110.7, 119.6, 120.5, 121.1, 124.2, 124.4,
125.0, 125.1, 125.2, 126.3, 131.4, 131.6, 132.2, 133.4, 134.1, 134.8,
135.4, 137.2, 137.8, 138.2, 139.0, 140.4, 142.4, 143.7, 144.9, 154.0,
154.4, 161.3, 165.3, 181.3, 185.0 ppm. HRMS (ESI+) m/z calcd
for C40H29N4O2S4: (M + H)+ 725.1168. Found: 725.1163.
bond
length [Å]
bond
angle [deg]
C(1)-N(1)
C(1)-C(9)
1.360(3)
1.389(4)
1.504(4)
1.208(3)
1.486(4)
1.409(4)
1.489(4)
1.392(4)
1.384(3)
1.437(4)
1.354(4)
1.439(4)
1.383(3)
1.402(4)
1.402(4)
1.387(3)
1.431(4)
1.359(4)
2.004(2)
2.002(2)
2.000(2)
2.007(2)
N(1)-C(1)-C(9)
126.9(2)
108.8(2)
126.9(3)
127.5(3)
105.3(2)
124.6(2)
108.6(2)
126.8(2)
122.9(2)
109.1(2)
127.9(2)
107.6(2)
107.4(2)
125.2(2)
109.1(2)
125.2(2)
123.6(2)
125.3(2)
109.0(2)
125.7(2)
107.9(2)
107.1(2)
125.6(2)
109.4(2)
115.5(2)
106.7(2)
106.5(2)
89.67(9)
179.76(8)
90.29(9)
179.24(8)
C(9)-C(1)-C(2)
C(1)-C(2)
O(1)-C(2)-C(3)
C(2)-O(1)
C(2)-C(3)
C(3)-C(8)
C(8)-C(9)
O(1)-C(2)-C(1)
C(3)-C(2)-C(1)
C(1)-C(9)-C(10)
C(1)-C(9)-C(8)
C(9)-C(10)
C(10)-N(2)
C(10)-C(11)
C(11)-C(12)
C(12)-C(13)
C(13)-N(2)
C(13)-C(14)
C(14)-C(15)
C(15)-N(3)
C(15)-C(16)
C(16)-C(17)
N(1)-Pt(1)
N(2)-Pt(1)
N(3)-Pt(1)
N(4)-Pt(1)
C(10)-C(9)-C(8)
N(2)-C(10)-C(9)
N(2)-C(10)-C(11)
C(9)-C(10)-C(11)
C(12)-C(11)-C(10)
C(11)-C(12)-C(13)
N(2)-C(13)-C(14)
N(2)-C(13)-C(12)
C(14)-C(13)-C(12)
C(13)-C(14)-C(15)
N(3)-C(15)-C(14)
N(3)-C(15)-C(16)
C(14)-C(15)-C(16)
C(17)-C(16)-C(15)
C(16)-C(17)-C(18)
N(3)-C(18)-C(19)
N(3)-C(18)-C(17)
C(1)-N(1)-C(32)
C(13)-N(2)-C(10)
C(18)-N(3)-C(15)
N(3)-Pt(1)-N(2)
N(3)-Pt(1)-N(1)
N(2)-Pt(1)-N(1)
N(2)-Pt(1)-N(4)
meso-Di(5′-methylthien-2′-yl)thiaindaphyrin (10). Monoalde-
hyde 9 (100 mg, 0.14 mmol) was dissolved in 2%TFA/CH2Cl2 (25
mL). The solution was stirred at ambient temperature overnight
and then was washed twice with aqueous NaHCO3 and once with
H2O. The solution was dried over anhydrous Na2SO4 and evaporated
to dryness. The residue was separated by column chromatography
(silica gel-CHCl3). The purple compound 10 (33 mg, 33% yield)
was isolated. Rf ) 0.65 (silica-CHCl3). UV-vis (CHCl3) λmax (log
ε): 432 (4.54), 570 (4.31) nm. IR (neat) νmax: 1678, 1694 (CdO)
1
cm-1. H NMR (400 MHz, CDCl3) δ: 1.16 (s, 1H), 2.55 (s, 3H),
2.72 (s, 3H), 6.88 (s, 1H), 7.01 (d, J ) 3.0 Hz, 1H), 7.39 (d, J )
3.0 Hz, 1H), 8.35 (s, 1H), 8.61 (d, J ) 4.7 Hz, 1H), 8.64 (d, J )
4.7 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ: 15.5, 15.9, 114.6,
116.3, 119.7, 122.6, 124.8, 129.2, 131.4, 132.9, 133.9, 134.4, 138.7,
138.8, 142.7, 144.9, 148.2, 157.2, 161.8, 183.3 ppm. HRMS (ESI+)
m/z calcd for C40H27N4O2S4 (M + H)+ 723.1011. Found: 723.1003.
Anal. calcd for C40H26N4O2S4 ·1/2CHCl3: C, 62.16; H, 3.41; N, 6.80.
Found: C, 62.09; H, 3.38; N, 6.70.
[meso-Di(5′-methylthien-2′-yl)thiaindaphyrinato]Pt(II) (10Pt). A
solution of 10 (40 mg, 6 mmol) and [Pt(acac)2] (65 mg, 3 equiv)
in PhCN (10 mL) was heated until, using TLC and UV-vis reaction
control, the starting material was exhausted (either for 8 h at ∼160
°C or 5 h at reflux temperature). The solvent was evaporated under
high vacuum conditions, and the residue was separated by column
chromatography (silica gel-CHCl3). The red compound 10Pt (31
mg, 61% yield) was isolated. Rf ) 0.42 (silica-CHCl3). UV-vis
(CHCl3) λmax (log ε): 414 (4.02), 529 (4.23), 648 (3.62) nm. IR
(neat) νmax: 1680, 1696 (CdO) cm-1. 1H NMR (400 MHz, CDCl3):
δ 2.59 (s, 3H), 2.75 (s, 3H), 6.90 (br s, 1H), 7.04 (d, 3J ) 3.6 Hz,
1H), 7.41 (d, 3J ) 4.0 Hz, 1H), 8.39 (s, 1H), 8.64 (d, 3J ) 4.0 Hz,
1H), 8.67 (d, 3J ) 4.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3)
δ: 15.5, 16.0, 114.5, 116.6, 119.8, 122.6, 124.9, 129.2, 131.6, 133.0,
133.7, 134.4, 138.8, 138.9, 142.9, 144.9, 148.3, 161.8, 183.2 ppm.
MS (ESI+, 100% CH3CN): m/z 915 (M+). HRMS (EI, 30 eV) m/z
calcd for C40H24N4O2PtS4: (M+) 915.0430. Found: 915.0418.
a Each molecule of 5Pt is pseudo-2-fold symmetric; hence, only half
the data are presented. For a full data set, see the Supporting Information.
meso-Tetra(5′-methylthien-2′-yl)-2,3-cis-dihydroxy-2,3-chlorin (8).
Caution! The synthesis requires a rotary eVaporator in a well-
Ventilated fume hood as the particularly Volatile and toxic reagents
OsO4 and H2S are used! A solution of meso-tetra(5′-methylthien-
2′-yl)porphyrin, 6 (500 mg, 0.72 mmol), and OsO4 (250 mg, 0.98
mmol) in EtOH-stabilized chloroform/50% pyridine (120 mL) was
stirred at room temperature for 4 days. The reaction was quenched,
at ambient conditions, by purging with gaseous H2S for 5 min,
followed by stirring for an additional 30 min. The solution was
filtered through a plug of Celite. The filtrate was evaporated to
dryness by rotary evaporation, and the residue was separated by
column chromatography (silica-gel gradient of CHCl3/MeOH). Two
fractions were isolated: the first was recovered purple porphyrin 6
(224 mg, 45%; Rf ) 0.90 (silica-CHCl3)), and the second fraction
was the purple-brown chlorin 8 (193 mg, 26% yield). Rf ) 0.22
(silica-CHCl3). UV-vis (CHCl3) λmax (log ε): 428 (5.21), 528 (4.13),
560 (4.18), 607 (3.92), 660 (4.39) nm. 1H NMR (400 MHz, CDCl3)
δ: -1.63 (s, exchangeable with D2O, 1H), 2.75 (s, 3H), 2.78 (s,
3H), 3.55 (s, exchangeable with D2O, 1H), 6.53 (s, 1H), 7.08-7.11
(m, 2H), 7.51 (d, J ) 3.2 Hz, 1H), 7.60 (d, J ) 3.2 Hz, 1H), 8.59
(d, J ) 4.8 Hz, 1H), 8.74 (s, 1H), 8.94 (d, J ) 4.8 Hz, 1H) ppm.
13C NMR (100 MHz, CDCl3) δ: 15.6, 15.7, 74.3, 105.5, 116.2,
124.3, 124.7, 125.0, 128.4, 132.1, 132.7, 133.2, 136.6, 139.4, 140.1,
141.9, 142.1, 142.6, 154.2, 163.2 ppm. HRMS (ESI+) m/z calcd
for C40H33N4O2S4: (M + H)+ 729.1481. Found: 729.1488.
Results and Discussion
Synthesis of 5Pt, the Pt(II) complex of indaphyrin 5.
The synthesis of diphenylindaphyrin 5 proceeded along the
pathway described previously (Scheme 1).18 Thus, dihy-
droxylation of meso-tetraphenylporphyrin 122 was followed
by the oxidative diol cleavage of diol 7. The resulting
bisaldehyde underwent, in situ, an acid-catalyzed intramo-
lecular Friedel-Crafts alkylation with concomitant air oxida-
tion. Insertion of Pt(II) into porphyrins generally requires
the heating of a Pt(II) salt, such as the acetate, chloride, or
acetyl acetonate, in benzonitrile at reflux temperatures (191
meso-Tri(5′-methylthien-2′-yl)-1-formylthiaindaphyrin (9). A
solution of diol 8 (100 mg, 0.14 mmol) and excess NaIO4
heterogenized on silica gel18 (1.0 g) in CHCl3 (25 mL) was stirred
at room temperature overnight. The oxidant was removed by
filtration (glass frit M), and the filtrate was evaporated to dryness
by rotary evaporation. The residue was separated by column
chromatography (silica gel-CHCl3). The orange compound 9 (70
mg, 70% yield) was isolated. Rf ) 0.55 (silica-CHCl3). UV-vis
4070 Inorganic Chemistry, Vol. 48, No. 9, 2009

Pt(II) Complexes of Indaphyrin and Thiaindaphyrin
Scheme 1a
Figure 1. ORTEP representation (50% ellipsoids) and numbering scheme
of the molecular structure of 5Pt.
The spectroscopic and analytical data were all consistent
with the structure of 5Pt. In particular, its 1H and 13C NMR
spectra were very similar to those of free-base 5, an
indication that the insertion of Pt(II) did not lead to dramatic
structural changes. As detailed below, a single-crystal
structure analysis of 5Pt confirms its connectivity and
highlights its conformation. The optical properties of all
chromophores synthesized are discussed below.
Metal complexes of indaphyrins were described before.18
However, the Ni(II) complexes of indaphyrins are unstable
and form ring-opened products within days in solution,
though the larger ions Cu(II) and Zn(II) form stable inda-
phyrinato complexes.18 Complex 5Pt is stable in solution
for days and as a solid for at least 2 years.
a Reaction conditions: (i)22 1. OsO4/pyridine, CHCl3 (EtOH-stabilized),
ambient temperature, 4 d; 2. H2S; 3. chromatography. (ii)18 NaIO4 on silica
gel, CHCl3, ambient temperature, air. (iii) [Pt(acac)2], PhCN, reflux, 5h.
(iv) 2% TFA in CH2Cl2, ambient temperature, air.
X-Ray Structure of 5Pt. Figures 1 and 2 and Table 2
show the results of a single-crystal diffractometry analysis
of crystals of 5Pt. The structure, the first X-ray structure of
any indaphyrin, confirms the spectroscopically derived
connectivity of 5Pt. It shows the significant degree of ruffling
of the chromophore, with a root-mean-square (rms) deviation
from the average plane of the C20N4Pt core of 0.448 Å.28 In
comparison, an example of a severely nonplanar [morpholi-
nochlorinato]Ni(II) complex shows an rms deviation from
planarity of its C20N4Ni core of 0.468Å.22,29 As a result of
the ruffling, a 46° dihedral angle between the mean planes
of the two indanone moieties is observed.
The ruffling observed in Ni(II) porphyrins is caused by
the presence of the small metal ion.29-31 The ruffling
distortion mode allows for a shortening of the N-Ni bonds
without any deviation of the nitrogens from a square-planar
coordination sphere around the central metal. Indeed, in 5Pt,
the N4Pt bond lengths and angles are also nearly perfectly
square-planar (deviations from the C20N4Pt mean plane lie
between 0.006(2) Å for N1 and 0.148(2) Å for N2). In
°C) for extended periods of time (typically 12-24 h).26,27
Appreciable Pt(II) insertion into indaphyrin 5 already takes
place in benzonitrile at 140-160 °C. At reflux temperatures,
the reaction is completed within 3-5 h. We attribute this to
the much greater conformational flexibility of the indaphyrin
chromophore as compared to that of a porphyrin. Chroma-
tography, followed by recrystallization, produced Pt(II)
indaphyrin 5Pt in good yields.
(26) Buchler, J. W. In The Porphyrins; Dolphin, D., Ed.; Academic Press:
New York, 1978; Vol. 1, p 389-483.
(27) Dean, M. L.; Schmink, J. R.; Leadbeater, N. E.; Bru¨ckner, C. Dalton
Trans. 2008, 1341–1345.
(28) The contribution of the various non-planar conformational modes to
the overall conformation of a porphyrin can be computed using a
normal coordinate structural analysis, see: Shelnutt, J. A. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, CA, 2000; Vol. 7, pp 167-224. The
different macrocycle connectivity of indaphyrins, however, does not
allow their analysis along any porphyrin lowest-energy frequency mode
using the NSD Engine (http://jasheln.unm.edu/jasheln/content/nsd/
NSDengine/start.htm, accessed Mar 2009).
Inorganic Chemistry, Vol. 48, No. 9, 2009 4071

Lau et al.
Figure 3. Normalized UV-vis spectra of 7 (broken trace) and 8 (solid
trace) in CH2Cl2 + 0.1% of Et3N. For the spectra of these species in the
presence of TFA, see the Supporting Information.
Synthesis of the Dithienylthiaindaphyrin 10 and Its
Pt(II) Complex 10Pt. The synthetic methodology toward
indaphyrin 5 is perceivably transferable to any meso-
arylporphyrin with an ortho position on the meso-aryl group
that is susceptible to electrophilic aromatic substitution,
including also meso-thien-2-ylporphyrin, 6 (Scheme 1). Thus,
osmylation/reduction of the meso-tetra(4-methyl-thien-2-
yl)porphyrin,33 6, resulted in the formation of the corre-
sponding diol chlorin 8. Its HRMS (ESI+, m/z ) 729.1488
for [M + H]+) spectrum confirms its composition
(C40H33N4O2S4), and diagnostic peaks in the 1H and 13C NMR
spectrum confirm its structure. Moreover, the UV-vis
spectrum of 8 is a typical chlorin spectrum, with λmax at 658
nm the most intense of all side bands. It is, as expected,
based on the comparison of thienylporphyrins with phe-
nylporphyrins,19 ∼12 nm bathochromically shifted compared
to that of meso-phenyl-based chlorin 7 (Figure 3).22,34
Oxidative diol cleavage of diol 8 using NaIO4 hetero-
genized on silica gel results in the formation of a putative
bisaldehyde intermediate that, analogous to the reactivity of
its meso-phenyl analogue,17,18 spontaneously undergoes a
Friedel-Crafts alkylation with concomitant oxidation to form
monothiaindanone monoaldehyde 9. It is identified by the
Figure 2. Front view (top) along the N(1)-Pt(1)-N(3) bond axis and
(bottom) side view along the N(4)-Pt(1)-N(2) bond axis of the molecular
structure of 5Pt. Hydrogen atoms are omitted for clarity.
contrast to the Ni(II) porphyrins, however, the distortion is
intrinsic to the indaphyrin ligand. This is because the
conformation of the ligand in 5Pt is, albeit slightly more
pronounced, very similar to that computed for free-base 5
(rms deviation of the C20N4 core from planarity was
computed to be 0.39 Å).18 Interestingly, the observed N-Pt
bond lengths (average of 2.003(2) Å) are identical to those
observed in the slightly ruffled [porphyrinato]Pt(II) com-
plexes (2.005 Å in 1Pt at 295 K).32
The cleavage of the pyrrole and fusion of two indanone
units into the macrocycle results in a significant dissymmetry
of the bond lengths and angles within the porphyrinoid
macrocycle (Table 2). For instance, the N(1)imine-C(1)indanone
and the C(1)indanone-C(9)indanone bond lengths are significantly
shorter (1.360(3) and 1.389(4) Å, respectively) compared to
the corresponding and unusually long N(2 or 3)pyrrole-C(11/
13 or 15/18)pyrrole (average of 1.385(3) Å) and C(13/
15)pyrrole-C(14)meso bond lengths (1.402(4) Å), respectively.
The corresponding bond lengths in metalloporphyrin 1Pt lie,
with an average N-CR length of 1.376 Å and an average
CR-Cmeso length of 1.388 Å, between the two extreme values
observed in 5Pt. The C-N-C bond angles within the pyrrole
units are with 107° within the range expected in a porphyrin,
whereas the bond angle of the imine-type linkage between
the indanone units is widened to 115°.
1
characteristic loss of symmetry in the H and 13C NMR
spectra; an ESI+ HRMS indicative of the expected composi-
tion for MH+ (C40H29N4O2S4); and the appearance of one
1
aldehyde signal in the H NMR (9.28 ppm, s, 1H) and two
carbonyl signals in the 13C NMR (181.1, 185.0 ppm) and
IR (ν ) 1691, 1648 cm-1) spectra. Product 9 possesses,
however, only limited stability in solution. Using 2% TFA
in CH2Cl2, this orange product is converted to a brown-purple
and slightly less polar product that could be identified as
the meso-di(5′-methylthien-2-yl)-substituted thiaindaphyrin
10. Its HR-MS spectrum indicates the loss of two hydrogens
The crystal is composed of offset columns of π-stacked
pairs of 5Pt that are held together by π-π interactions
between meso-phenyl groups. No major channels or cavities
are discernible. Complex 5Pt is chiral and crystallizes as a
j
racemate in the nonchiral space group P1.
1
compared to the composition of its precursor 9. Its H and
13C NMR spectra suggest a molecule of 2-fold symmetry
with diagnostic signals for the presence of an ortho-linked
(29) Bru¨ckner, C.; Hyland, M. A.; Sternberg, E. D.; MacAlpine, J.; Rettig,
S. J.; Patrick, B. O.; Dolphin, D. Inorg. Chim. Acta 2005, 358, 2943–
2953.
(30) Kratky, C.; Waditschatka, R.; Angst, C.; Johansen, J. E.; Plaquevent,
J. C.; Schreiber, J.; Eschenmoser, A. HelV. Chim. Acta 1985, 68, 1313–
1337.
(31) Barkigia, K. M.; Berber, M. D.; Fajer, J.; Medforth, C. J.; Renner,
M. W.; Smith, K. M. J. Am. Chem. Soc. 1990, 112, 8851–8857.
(32) Hazell, A Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1984,
40, 751. CSD code: CEZKEX.
(33) This particular thiophen-2-yl porphyrin derivative was chosen, as it
was characterized by a significantly red-shifted UV-vis spectrum
compared to the corresponding non-methylated compound, see ref 19.
(34) Interestingly, the unique acid-base dependency of the optical proper-
ties of chlorin 8 vs chlorin 7 is similar to the shifts observed for the
porphyrins, see ref 19. The spectra are shown in the Supporting
Information.
4072 Inorganic Chemistry, Vol. 48, No. 9, 2009

Pt(II) Complexes of Indaphyrin and Thiaindaphyrin
Figure 5. UV-vis absorption spectra (CH2Cl2, r.t.) of 1Pt (solid black
trace), 5Pt (solid green trace), and 10Pt (solid red trace) in CH2Cl2;
phosphorescence emission spectra (EtOH glass, 77 K) of 5Pt (dotted green
trace; λexcitation ) 524 nm) and 10Pt (dotted red trace; λexcitation ) 529 nm).
The emission spectra were confirmed using excitation emission scans.
Figure 4. UV-vis spectra of 5 (green trace), 9 (blue trace), and 10 (red
trace) in CH2Cl2 + 0.1% of Et3N.
aryl group,18 only three types of thienyl ꢀ-protons, and one
type of ketone functionality (183.3 ppm in the 13C NMR).
Further, a comparatively high-field-shifted signal assigned
to the NH protons can be discerned (1.16 ppm, br s, 1H),
another characteristic of indaphyrins that is likely a reflection
of the great distortion from planarity in these porphyrinoids.18
Taken together, the spectroscopic data confirm the structure
of 10. It is interesting to note that the formation of a
thiaindanone35 moiety in the target compound 10 appears
to be similarly facile as in the phenyl derivative 5, despite
the fact that the steric requirements of forming the indanone
moiety (one five- and six-membered fused ring) are different
from those for the formation of a thiaindanone unit (two
fused five-membered rings).
Figure 5 shows the absorption spectra of the Pt(II)
complexes 5Pt and 10Pt in comparison to that of 1Pt. The
main absorption bands of 5Pt and 10Pt are a Soret-like band
(for 5Pt at ∼ 525 nm; ε ) 14 500 M-1 cm-1) and two side
bands (at 632 and 677 nm, ε ) 3500 and 3000 M-1 cm-1,
respectively) with a vibrational spacing of 1070 cm-1,
assuming that the origin of the bands is similar to that of
1Pt. The absorption spectrum of 5Pt has little resemblance
to that of a platinum porphyrin complex (1Pt). It is much
broader, spanning almost the entire visible spectral region
up to ∼680 nm, albeit the extinction coefficients of the bands
are only ∼10% of those of 1Pt. A broad absorption spectrum
has the advantage that it allows for the use of many readily
available excitation light sources. As predicted, the absorption
spectrum of 10Pt is slightly bathochromically shifted com-
pared to that of 5Pt. Also reflecting the trend seen in the
free base thiaindaphyrin, the spectrum of 10Pt is relatively
broad.
The insertion of Pt(II) into 10 also proceeded smoothly,
and 10Pt could be isolated as a microcrystalline powder in
65% yield. It possesses all of the expected spectroscopic and
analytical properties. Aside from the disappearance of the
signals for the NH protons, only minor shifts in the 1H NMR
spectrum are observed upon the insertion of Pt(II) into free-
base 10. This is likely a testimony to the preservation of the
conformation of the free ligand in its complex. A Pt(II)
insertion into thiaindaphyrin monoaldehyde 9 failed due to
the instability of the ligand.
Spin-orbit interactions with the coordinated 5d8 ion Pt(II)
increase the intersystem crossing rate of photoexcited Pt(II)
porphyrin, resulting in very high triplet yields.2 Subsequent
phosphorescence emissions are on the nanosecond to mi-
3
crosecond scale. Ideally, the observed lifetimes of the T1
Photophysical Properties of 5 and 10, and Their Pt(II)
Complexes. The UV-vis spectra of free-base meso-tri(thien-
2-yl)formylthiaindaphyrin, 9, and meso-di(thien-2-yl)thiain-
daphyrin, 10, in comparison to that of known meso-
diphenylindaphyrin, 5,18 are shown in Figure 4. The spectrum
of thienyl derivative 10 is, as hoped for, red-shifted compared
to that of the phenyl analogue 5, though the number and
relative intensities of the bands also vary slightly. This is a
reflection of the differing π systems of the two chromophores
and the differing conformation and conformational flexibility.
The relatively broad and far-into-the-red-reaching bands of
5 and 10 allow a prediction for ligand-based emissions in
the NIR for their Pt(II) complexes. The spectrum of the
formylated “half-thiaindaphyrin” 9 possesses larger extinction
coefficients and appears to be more “porphyrin-like”, an
observation also made for its phenyl analogue.18
state are above ∼10 µs, allowing ample opportunity for the
3
quenching of the triplet state by O2. In this triplet lifetime
regime, high sensitivity with respect to the oxygen-pressure
measurement can also be achieved through a time-resolved
recording of the luminescence.36
The phosphorescence emission spectra of 5Pt and 10Pt
in EtOH at 77 K are shown in Figure 5. The emission spectra
are two-band spectra that are strongly solvochromic (5Pt:
λmax-emission ) 850 and 965 nm in EtOH and λmax-emission
)
880 and 995 nm in methylcyclohexane, see Supporting
Information) with a minimum Stokes shift of 2880 cm-1.
No detectable spectral sharpening was detected for the 10-6
M solution of 5Pt in n-octane, a Shopl’skii-type matrix. The
emissions around 1000 nm are several hundreds of nanom-
eters red-shifted compared to those observed in Pt porphyrins
and related derivatives and are comparable to that of the
(35) The formal name for the resulting moiety is cyclopenta[b]thiophen-
4-one, also referred to as thiaindanone: Aparajithan, K.; Thompson,
A. C.; Sam, J. J. Heterocycl. Chem. 1966, 3, 466–469.
(36) Lippitsch, M. E.; Draxler, S.; Kieslinger, D. Sens. Actuators B 1997,
B38, 96–102.
Inorganic Chemistry, Vol. 48, No. 9, 2009 4073

Lau et al.
structurally more complex calyx[6]phyrin Pt2 complex 4Pt2.16
While the phosphorescence quantum yield for the phenyl
derivative 5Pt, at 77 K in an deoxygenated EtOH glass, is
∼1%, it is about 3 orders of magnitude less in the thio
analogue 10Pt (∼6 × 10-3 %). In comparison, the quantum
yield for 1Pt is near unity, and that of the 2Pt is 70%.23
This low quantum yield (and short triplet lifetime, see below)
are likely caused by a larger conformational flexibility of
the indaphyrin and the conjugated ketone oxygens. Consider-
ing the very low reported fluorescence yields for thienylpor-
phyrins, the low emission yield for 10Pt is not a surprise.22
The triplet lifetime of 5Pt was determined to be a relatively
short 2 µs. In comparison, the triplet lifetime for 1Pt is 120
µs, and that for 2Pt is 70 µs,9 while the Pt2 complexes of
calix[6]phyrin are characterized by two-digit nanosecond
lifetimes (at r.t.).16
Testing of 5Pt as Oxygen Sensor. One notable application
of oxygen sensors is in air flow visualization. In this
application, also referred to as phosphorescence barometry,
a sensor is incorporated into an oxygen-permeable polymer
matrix that is applied to a surface. The resulting thin layer
serves as a two-dimensional air pressure profile sensor for
objects exposed to wind flow.2,10,11
The oxygen sensitivity of 5Pt was first tested by incor-
porating it into a gas-permeable silicon-polycarbonate
copolymer matrix. Disappointingly, no oxygen sensitivity
was detected. Subsequently, 5Pt was dispensed directly onto
a silica TLC plate. TLC plates provide a chemically neutral
flat surface that is highly reflective, and serves as an open
configuration with a highly oxygen-permeable surface. Upon
irradiation with light of 520 nm, the oxygen partial pressure
dependency of the phosphorescence emission of 5Pt in the
range from 700 to 1400 nm was recorded. In the range from
0 to 100% O2, the intensity of the emission was quenched
by only 15% (see Supporting Information), indicating that
this dye is not a practical dye for O2 sensing. The low
sensitivity of 5Pt towards a variation of [O2] can likely be
attributed to the short phosphorescence lifetime of the Pt(II)
indaphyrin.
Summary and Conclusions
The Pt(II) complex of indaphyrin 5, 5Pt, forms readily
and is stable. Its nonplanar conformation was proven to be
most similar to the computed conformation of the free-base
ligand 5. Their meso-thienyl analogues, free-base thiainda-
phyrin 10 and its Pt(II) complex 10Pt, can also be formed
in acceptable yields. They are the first examples of non-
meso-phenylporphyrin-derived indaphyrins. Significantly, 5Pt
and 10Pt possess the expected NIR emission spectra, but
their short triplet lifetimes, relatively low emission yields,
and impractically low sensitivity of the emission intensity
variation with respect to changing oxygen partial pressure
render these complexes unsuitable as practical oxygen
sensors.
Acknowledgment. We thank Paul Foss for preliminary
work on the preparation of 8 and Pedro Daddario for
technical assistance. C.B. thanks the National Science
Foundation for financial support through grants NSF CHE-
0517782 and NSF CMMI-0730826. This work was also
supported by the Department of Defense Multi-Disciplinary
University Research Initiative (MURI) Center on Polymeric
Smart Skin Materials through the Air Force Office of
Scientific Research contract F49620-01-1-0364 (to G.E.K.).
The diffractometer was funded by NSF grant 0087210, by
Ohio Board of Regents grant CAP-491, and by YSU. S.J.
and N.J.T. thank the National Science Foundation for
financial support through grant NSF CHE-0717518.
Supporting Information Available: The X-ray crystallographic
1
file in CIF format for the reported structure 5Pt. H, 13C NMR,
and IR spectra of 5Pt, 8, 9, 10, and 10Pt and more details on the
photophysical investigations. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC802041Z
4074 Inorganic Chemistry, Vol. 48, No. 9, 2009