Tunable phosphorescent NIR oxygen indicators based on mixed benzo-and naphthoporphyrin complexes

Article abstract of DOI:10.1021/ic100955z

A series of π-extended phosphorescent palladium(II) and platinum(II) porphyrin complexes were synthesized, in which additional benzene rings are fused radially onto at least one of the four peripheral benzo groups. The photophysical properties of the metalloporphyrins palladium(II)-meso-tetra-(4- fluorophenyl)mononaphthotribenzoporphyrin (Pd1NF), cispalladium(II)-meso-tetra- (4-fluorophenyl)dibenzodinaphthoporphyrin (Pd2NF), and palladium(II)-meso-tetra- (4-fluorophenyl)monobenzotrinaphthoporphyrin (Pd3NF) and the corresponding platinum(II) compounds (Pt1NF, cis-Pt2NF, Pt3NF) were investigated. The compounds under investigation absorb intensively in the near-infrared region (628-691 nm) and emit at room temperature at 815-882 nm. Phosphorescence quantum yields of the platinum(II) porphyrins range from 25 to 53% with luminescence decay times of 21 to 44 μs in deoxygenated toluene solutions at room temperature. The corresponding palladium(II) complexes exhibit quantum yields in the range of 7 to 18% with lifetimes of 106 to 206 μs. Density functional theory (DFT) calculations revealed nonplanar geometries for all complexes and corroborate the absorption characteristics. The subsequent π extension of the porphyrin system leads to near-infrared absorbing oxygen indicators with tailor-made luminescence properties as well as tunable oxygen sensitivity.

Full text of DOI:10.1021/ic100955z

Inorg. Chem. 2010, 49, 9333–9342 9333
DOI: 10.1021/ic100955z
Tunable Phosphorescent NIR Oxygen Indicators Based on Mixed
Benzo- and Naphthoporphyrin Complexes
,†
†
†
‡
§
€
Fabian Niedermair,* Sergey M. Borisov, Gunter Zenkl, Oliver T. Hofmann, Hansjorg Weber,
Robert Saf,|| and Ingo Klimant†
†Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, Stremayrgasse 18,
A-8010 Graz, Austria, ‡Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010
Graz, Austria, §Institute of Organic Chemistry, Graz University of Technology, Stremayrgasse 18, A-8010 Graz,
Austria, and ||Institute for Chemistry and Technology of Materials, Graz University of Technology,
Stremayrgasse 18, A-8010 Graz, Austria
Received May 13, 2010
A series of π-extended phosphorescent palladium(II) and platinum(II) porphyrin complexes were synthesized, in which
additional benzene rings are fused radially onto at least one of the four peripheral benzo groups. The photophysical
properties of the metalloporphyrins palladium(II)-meso-tetra-(4-fluorophenyl)mononaphthotribenzoporphyrin (Pd1NF), cis-
palladium(II)-meso-tetra-(4-fluorophenyl)dibenzodinaphthoporphyrin (Pd2NF), and palladium(II)-meso-tetra-(4-fluorophe-
nyl)monobenzotrinaphthoporphyrin (Pd3NF) and the corresponding platinum(II) compounds (Pt1NF, cis-Pt2NF, Pt3NF)
were investigated. The compounds under investigation absorb intensively in the near-infrared region (628-691 nm) and
emit at room temperature at 815-882 nm. Phosphorescence quantum yields of the platinum(II) porphyrins range from 25 to
53% with luminescence decay times of 21 to 44 μs in deoxygenated toluene solutions at room temperature. The
corresponding palladium(II) complexes exhibit quantum yields in the range of 7 to 18% with lifetimes of 106 to 206 μs.
Density functional theory (DFT) calculations revealed nonplanar geometries for all complexes and corroborate the
absorption characteristics. The subsequent π extension of the porphyrin system leads to near-infrared absorbing oxygen
indicators with tailor-made luminescence properties as well as tunable oxygen sensitivity.
Introduction
temperature near-infrared (NIR) phosphorescence.5,6 They
were successfully applied in OLEDs,2b,7 photovoltaics,2a,8
and optical oxygen sensors.9 Particularly, NIR oxygen indica-
tors overcome many drawbacks of the UV-vis indicators, such
as the adverse effects of autofluorescence and light scattering in
biological media.10 Additionally, NIR indicators are particu-
larly promising for subcutaneous glucose sensing (implantable
sensors or “smart tattoos”)11 which rely on oxygen transducers.
The class of π-extended porphyrins,1 in which the pyrrole
rings are fused with external aromatic fragments (e.g., tetra-
benzoporphyrins (TBP) and tetranaptho[2,3]porphyrins
(TNP)), continues to be intensively investigated in the fields
of materials research,2 biomedical imaging and sensing,3 and
photodynamic therapy.4 Platinum(II) and palladium(II) com-
plexes are of particular interest since they possess strong room
(5) Amao, Y. Microchim. Acta 2003, 143, 1–12.
*To whom correspondence should be addressed. Tel.: þ43 316 873 4329.
Fax: þ43 316 873 4324. E-mail: f.niedermair@tugraz.at.
(6) Papkovsky, D.; O’Riordan, T. J. Fluoresc. 2005, 15, 569–584.
(7) Sommer, J. R.; Farley, R. T.; Graham, K. R.; Yang, Y.; Reynolds,
J. R.; Xue, J.; Schanze, K. S. Appl. Mater. Interfaces 2009, 1, 274–278.
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Science 2008, 321, 226–228.
(1) Cheprakov, A. V.; Filatov, M. A. J. Porphyrins Phthalocyanines 2009,
13, 291–303.
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Chem. Soc. 2009, 131, 9281–9286. (b) Borek, C.; Hanson, K.; Djurovich, P.;
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(3) (a) Finikova, O.; Galkin, A.; Rozhkov, V.; Cordero, M.; Haggerhall,
C.; Vinigradov, S. J. Am. Chem. Soc. 2003, 125, 4882–4893. (b) Apraleva,
S. V.; Wilson, D. F.; Vinogradov, S. A. Appl. Opt. 2006, 45, 8547–8559.
(4) Friedberg, J. S.; Skema, C.; Baum, E. D.; Burdick, J.; Vinogradov,
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2001, 48, 105–107.
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2, 366–374. (b) Borisov, S.; Papkovsky, D.; Ponomarev, G.; DeToma, A.; Saf, R.;
Klimant, I. J. Photochem. Photobiol. A 2009, 206, 87–92. (c) Borisov, S. M.;
Nuss, G.; Klimant, I. Anal. Chem. 2008, 80, 9435–9442. (d) Dunphy, I.;
Vinogradov, S. A.; Wilson, D. F. Anal. Biochem. 2002, 310, 191–198. (e) Kumar,
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r
2010 American Chemical Society
Published on Web 09/14/2010
pubs.acs.org/IC

9334 Inorganic Chemistry, Vol. 49, No. 20, 2010
Niedermair et al.
a
Scheme 1.
a Reagents and conditions: (a1) CNCH2CO2Et, DBU, THF abs., reflux, 16 h (81%). (b1) NaOH, ethylene glycol, reflux, 1 h (92%). (a2) Na, t-BuOH,
Et2O, rt, 3 h (75%). (b2) (i) PhSCl, CH2Cl2; (ii) m-CPBA (56%). (c2) CNCH2CO2Et, t-BuOK, THF, reflux, 30 min (46%). (d2) NaOH, ethylene glycol,
reflux, 30 min (90%). (e, i) 4-F-ArCHO, BF3 Et2O, TEOAc, CH2Cl2 abs., 4 h, rt; (ii) DDQ, CH2Cl2, rt, 16 h (42% overall yield). 2NF is formed
3
exclusively as the cis isomer.
One way for shifting the absorption bands of transition
metal porphyrins into the lower energy region is the extension
of the porphyrin core by fusing it with external aromatic
fragments.1,12 This method results in the so-called “π-extended
porphyrins”. Tetra-annulated porphyrins like tetrabenzopor-
phyrins and tetranaphthoporphyrins and their metal com-
plexes have already been intensively studied due to their
attractive spectral features.13 However, the complexes of tetra-
naphthoporphyrins with palladium(II) or platinum(II) show
relatively low luminescence quantum yields12,14 as well as
extremely low photostability.15 In contrast to that, the corre-
sponding tetrabenzoporphyrin complexes exhibit moderate
photostability as well as high brightness.10
This work highlights the hybridization of both benzo- and
naphthoporphyrins resulting in novel functional chromo-
phores with interesting photophysical properties. The systema-
tic condensation of additional external aromatic fragments
leads to “tailor-made” NIR absorbing dyes, which cover the
complete region from 630 to 690 nm and, therefore, perfectly
match the commercially available laser diodes with excitation
wavelengths of 635, 650, and 670 nm, respectively. We demon-
strate that the extension of the aromatic system has a deep
impact on the luminescence decay times as well as quantum
yield of the corresponding palladium(II) and platinum(II)
complexes. In this context, our method opens up a powerful
tool to control the sensitivity to oxygen and at the same time to
provide optimal dynamics in most sensor materials.10
Results and Discussion
Synthesis. The synthesis of π-extended porphyrins is
based on the direct oxidative aromatization of porphyrins
annealed with nonaromatic saturated hydrocarbon
rings.1,12,13 The basic molecules such as the 4,5,6,7-tetrahy-
droisoindole as well as 4,9-dihydro-2H-benz[ f ]isoindole
were prepared according to literature methods (cf. Support-
ing Information).12,13 Porphyrin synthesis was accomplished
under optimized Lindsey conditions (cf. Scheme 1),16 intro-
ducing the “benzo” component 4,5,6,7-tetrahydroisoindole
and the “naphtho” component 4,9-dihydro-2H-benz-
[ f]isoindole in a molar ratio of 1.1/1 (10-2 M) in dry and
deoxygenated CH2Cl2. The reaction mixture was protected
from light, and 4-fluorobenzaldehyde was added in an
equimolar amount (10-2 M). After stirring the reaction
(11) (a) Russell, R. J.; Pishko, M. V.; Gefrides, C. C.; McShane, M. J.;
Cote, G. L. Anal. Chem. 1999, 71, 3126–3132. (b) Chinnayelka, S.; McShane,
M. J. Diabetes Technol. Ther. 2006, 8, 269–278. (c) Brown, J. Q.; McShane,
M. J. Biosens. Bioelectron. 2006, 21, 1760–1769.
mixture at room temperature for 10 min, BF3 Et2O (10-3
3
~
(12) Finikova, O. S.; Aleshchenkov, S. E.; Brinas, R. P.; Cheprakov,
M, 0.2 equiv) was added as a catalyst. After 1 h of reaction
time, the water scavenger triethylorthoacetate (10-2 M) was
added, which significantly improved the yield (approxi-
mately 10%). Subsequent addition of the catalyst leads to
A. V.; Carroll, P. J.; Vinogradov, S. A. J. Org. Chem. 2005, 70, 4617–4628.
(13) Finikova, O. S.; Cheprakov, A. V.; Beletskaya, I. P.; Carroll, P. J.;
Vinogradov, S. A. J. Org. Chem. 2004, 69, 522–535.
ꢀ ꢁ
(14) Lebedev, A. Y.; Cheprakov, A. V.; Sakadzic, S.; Boas, D. A.; Wilson,
D. F.; Vinogradov, S. A. Appl. Mater. Interfaces 2009, 1, 1292–1304.
(15) (a) Kobayashi, N.; Konami, H. J. Porphyrins Phthalocyanines 2001,
5, 233–255. (b) Mack, J.; Asano, Y.; Kobayashi, N.; Stillman, M. J. J. Am. Chem.
Soc. 2005, 127, 17697–17711.
(16) Shanmugathasan, S.; Edwards, C.; Boyle, R. W. Tetrahedron 2000,
56, 1025–1046.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9335
a
Scheme 2.
a Reagents and conditions: (a) M = Pd: PdCl2(PhCN)2, THF, reflux, 30 min, N,N-dimethyldiisopropylamine; M = Pt: PtCl2(PhCN)2, 1,2,4-
trimethylbenzene, reflux, 40 min, N,N-dimethyldiisopropylamine. (b) M = Pd = Pt: DDQ, THF, reflux, 15 min. Yields: M = Pd: 48-53%; M = Pt:
21-32%. The synthesis of M-2NF (cis isomer) is shown as a representative example for the synthesis of all complexes.
complete conversion after 4 h. The reaction mixture was
allowed to stir overnight at room temperature in the presence
of an excess of 2,3-dichloro-5,6-dicyano-p-benzoquinone
(DDQ), which then was removed by extraction with aqueous
Na2SO3 and water. After purification by column chroma-
tography on neutral alumina, the three main fractions, 1NF,
2NF, and 3NF, were isolated (overall yield, 42%; thereof,
3NF approximately 37%; 2NF approximately 34%; 1NF
approximately 29%) and characterized by 1H NMR,
UV-vis, and MALDI-TOF analysis (cf. Supporting In-
isomer. In fact, for the trans isomer, only two signals would
be expected in this region due to symmetry reasons, which
correspond to the two Ph3 carbon signals of 4-fluorobenzal-
dehyde at around 118 ppm.18 In this context, the signals
for 2NF at 116.4 and 116.2 ppm reveal a coupling constant
JC-2,F = 21.9 Hz, consistent with the corresponding coupling
constant of 4-fluorobenzaldehyde (JC-2,F = 22.4 Hz).17
meso-Tetra(4-fluorophenyl)tetracyclohexenoporphyrin
(B) was isolated as a side product and not further char-
acterized. The formation of meso-tetra(4-fluorophenyl)-
tetranaphthoporphyrin (4NF) could not be observed for
these optimized reaction conditions with a “benzo” to
“naphtho” ratio of 1.1 to 1. In this context, it should be
mentioned that the product distribution can potentially be
modified by applying a different initial ratio of the “benzo”
and “naphtho” starting materials. Moreover, 4-fluoroben-
zaldehyde was used in the synthesis because fluorine sub-
stitution of the phenyl groups in the meso position results in
metalloporphyrins with improved photophysical properties,
such as increased luminescence quantum yield as well as
higher photostability.10 The title compounds Pd1NF,
Pd2NF, and Pd3NF and Pt1NF, Pt2NF, and Pt3NF were
prepared by the reaction of the corresponding ligand and the
palladium and platinum precursors (MCl2(PhCN)2, M =
Pd, Pt), respectively, and subsequent oxidation with DDQ
(cf. Scheme 2). Palladation reactions proceeded smoothly in
refluxing THF with 2 equiv of the Pd precursor. For
platination reactions, harsher conditions were applied, using
a Pt precursor to ligand ratio of 3:1 in 1,2,4-trimethylbenzene
under reflux conditions (180 °C). Purification was accom-
plished by column chromatography using neutral Al2O3
(eluent: toluene for all complexes) as well as by recrystalliza-
tion from CH2Cl2/MeOH after the removal of Al2O3 by
filtration. Yields of analytically pure compounds ranged
from 48 to 53% for the palladium(II) complexes and from
21 to 32% for the platinum(II) porphyrins, respectively. The
complexes show good solubility in CHCl3, THF, diethy-
lether, and acetone but are hardly soluble in methanol. The
metalloporphyrins are air-stable in solution and in the solid
1
formation). The H NMR spectra of the corresponding
ligands display the correct number of proton signals, and
the mass spectra confirm the molecular mass of the corre-
sponding ligand (cf. Experimental Section). In this context, it
is noteworthy that a complete oxidation of the naphtho
moieties had taken place already during oxidative aromati-
1
zation with DDQ. According to UV-vis and H NMR
spectroscopy, the fraction of 2NF was isolated as a single
isomer. Further evidence for the nature of the isomer could
be retrieved from additional NMR studies. The 19F NMR
spectrum of 2NF exhibits two distinct signals at -109.5 and
-113.6 ppm (cf. Supporting Information Figure S4),
whereas the latter signal represents two fluorophenyl moi-
eties. In our hands, these peaks altogether indicate three
chemically nonequivalent fluorophenyl groups, which evi-
dence the presence of the cis isomer. For the corresponding
trans isomer, only one signal would be expected due to its
higher symmetry compared to the cis isomer. The 2D 1H/13C
NMR-HMBC spectrum (cf. Supporting Information Fig-
ure S5) at peak positions 8.24/164.5 ppm and 8.24/162.5
ppm, respectively, reveals the characteristic one-bond car-
bon fluorine coupling constant JC-1,F = 249 Hz, which is
comparable to the corresponding coupling constant of
4-fluorobenzaldehyde (JC-1,F = 255 Hz).17 The 2D 1H/13C
NMR-HSQC spectrum (cf. Supporting Information Fig-
ure S6) gives additional information about the nature of the
fluorophenyl protons. The signals at around 8.23/135.0 ppm
represent the meta protons bound to the Ph3 carbons. The
ortho protons bound to the Ph2 carbons reside at around
7.54/114.9 ppm. According to the 13C NMR spectrum (cf.
Supporting Information Figure S3), the signals ranging from
116.6 to 115.0 ppm further indicate the presence of the three
chemically nonequivalent fluorophenyl groups of the cis
1
state and were characterized by H NMR, UV-vis spec-
troscopy, and MALDI-TOF. The H NMR spectra of all
compounds display the correct number of proton signals,
1
(18) The 13C NMR spectrum in CDCl3 of 4-fluorobenzaldehyde from
Sigma-Aldrich was taken as a reference.
(17) Roberts, J. D.; Weigert, F. J. J. Am. Chem. Soc. 1971, 93, 2361–2369.

9336 Inorganic Chemistry, Vol. 49, No. 20, 2010
Niedermair et al.
Table 1. Photophysical Properties of the Platinum(II) and Palladium(II) Porphyrin Complexes at Room Temperature in Diluted Toluene Solutions
complex
abs, λmax, λ [nm] (ε [10-3 cm-1 M-1])
emission, λmax [nm]
τ [μs]
Φ [%]
Pt1NF
Pt2NF
Pt3NF
Pd1NF
Pd2NF
Pd3NF
434 (272), 583 (25.6), 628 (147), 638 (140)
438 (106), 594 (14.2), 652 (108)
441 (108), 618 (17.2), 635 (21.9), 667 (83.5), 678 (78.9)
450 (202), 601 (12.7), 641 (74.0), 654 (72.6)
452 (190), 608 (102), 666 (142)
815
835
870
849
868
∼882
44
28
21
203
138
106
53
27
25
18
12
7
456 (138), 630 (17.0), 652 (22.0), 681 (63.8), 691 (60.0)
and the mass spectra of all complexes confirm the molecular
mass of the corresponding parent complex (cf. Experimental
Section). As already shown for the 2NF ligand, the corre-
sponding complexes are present as the cis isomers.
Photophysical Properties. Electronic Absorption Spectros-
copy. The absorption spectra of all complexes measured in
diluted toluene solutions at room temperature under ambient
conditions show a subsequent bathochromic shift the more
naphtho moieties are annealed to the porphyrin system. For
the platinum(II) and palladium(II) complexes, the molar
absorption coefficients are very high (cf. Table 1). In contrast
to the minor shift of the Soret band, the Q band shifts
significantly from 654 to 691 nm for the palladium(II) com-
plexes and from 638 to 678 nm for platinum(II) porphyrins
(cf. Table 1; Figure 1). In addition to the already literature-
known tetra-annulated porphyrins palladium(II)-meso-tetra-
(4-fluorophenyl)tetrabenzoporphyrin (PdTPTBPF; λmax,abs
443 and 629 nm, solvent: toluene),10 palladium(II)-meso-
tetraphenyltetranaphthoporphyrin (PdTPTNP; λmax,abs 463
and 705 nm, solvent: benzene),19 platinum(II)-meso-tetra-
(4-fluorophenyl)tetrabenzoporphyrin (PtTPTBPF; λmax,abs
430 and 615 nm, solvent: toluene),10 and platinum(II)-meso-
tetraphenyltetranaphthoporphyrin (PtTPTNP; λmax,abs 436
and 689 nm, solvent: toluene),7 these “hybrid” porphyrins
completely cover the spectral range between 615 and 705 nm.
As a result, tailor-made near-infrared excitable porphyrin
dyes are available for NIR oxygen sensing applications. These
chromophores are particularly attractive materials for differ-
ent multiplexing applications, e.g., simultaneous glucose and
oxygen detection in enzymatic sensors. It should be empha-
sized that each additional naphtho moiety results in a red shift
of the Q band of approximately 20 nm. Moreover, it should be
noted that the Q-band absorption exhibits a slight red shift of
approximately 2 nm in polymeric films containing 1 wt % of
the indicator in polystyrene (cf. Supporting Information
Figure S16).
A comparative photophysical study as well as some
theoretical calculations have been recently published in
the work of Kobayashi et al.20 for reduced symmetry
peripheral fused-ring-subtituted zinc phthalocyanines. In
this context, the splitting observed in the Q bands of the
trans isomer is significantly greater than is the case with
the cis isomer despite the fact that the trans complex is the
higher symmetry complex. The Q bands of Pd2NF and
Pt2NF show a similar splitting like the zinc phthalocya-
nines cis isomer.20 In summary, extension of the conju-
gated system has only little effect on the Soret band but
shifts the Q band significantly to lower energy. A question
arises whether the differences in the absorption properties
Figure 1. Absorption spectra of palladium(II) porphyrin complexes in
toluene (*Q-band data from ref 19, c ∼ 10-3 M).
of these mixed benzo- and naphthoporphyrins are caused
by differences in planarity of these systems, by the
electronic effects of naphtho vs benzo moieties or by a
combination of both of these factors. According to
Finikova et al.,12 the Q-band transitions are mainly
affected by the extension of π conjugation, which is in
fact a substitution of the β-pyrrole carbons.
DFT calculations were performed for all complexes
and reveal nonplanar equilibrium geometries in a “sad-
dle”-like geometry. The calculated nonplanar structures
(cf. Supporting Information) of the title compounds are
in good agreement with the structure determinations
(crystallographic data) for similar compounds described
in the literature.7,12-14 The distortion from planarity
observed for the metalloporphyrins can be attributed to
steric repulsion between the 4-fluorophenyl groups in the
meso position and the macrocycle, respectively. Calcula-
tions for the ligand 1NF also remain nonplanar, whereas
naphtho annulated porphyrins without the 4-fluorphenyl
groups in the meso position return to a flat geometry. In
agreement with the experiment, we find in all cases that
the strongest excitation occurs in the 420 nm region
(approximately 429 nm for Pd1NF and 420 nm for
Pt1NF) and does not shift much with increasing number
of naphtho moieties. It should be stressed in this context
that the Soret band in fact consists of several optical
transitions which are all found between ∼350 and ∼420
nm. In this context, we will only comment on the strongest
excitation in this region. In contrast, the spectral position
of the Q band changes significantly. For Pd1NF, TD-
DFT predicts two peaks of similar intensity located at 594
and 610 nm, however, significantly blue-shifted with
respect to the experimental peaks (641 nm, 654 nm). In
the case of Pd2NF, the cis and trans isomers were
(19) Rogers, J. E.; Nguyen, K. A.; Hufnagle, D. C.; McLean, D. G.; Su,
W. J.; Gossett, K. M.; Burke, A. R.; Vinogradov, S. A.; Pachter, R.; Fleitz,
P. A. J. Phys. Chem. A 2003, 107, 11331–11339.
(20) Kobayashi, N.; Mack, J.; Ishii, K.; Stillman, M. J. Inorg. Chem. 2002,
41, 5350–5363.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9337
calculated. The optical spectra of both compounds are
markedly different: while for the trans isomer the double-
peak shape of the Q band is retained, in the cis isomer
these two transitions coincide at the same energy, 619 nm.
Thus, the optical spectra corroborate the results from
NMR measurements which indicate the formation of the
cis isomer. By adding yet another naphtho moiety, the
double peak structure of the Q band is recovered. The
TD-DFT calculation for Pd3NF predicts two peaks at
wavelengths of 630 and 648 nm, i.e., again red-shifted
with respect to the smaller conjugated systems. In total,
between Pd1NF and Pd3NF, DFT finds a shift of 36 and
40 nm for the two Q-band peaks, in excellent agreement
with the experimental findings of 40 and 37 nm, respec-
tively. The Pt derivatives show the same trends;includ-
ing the near-degenerated excitation in cis-Pt2NF;as the
Pd molecules, but the transitions occur at somewhat
larger energies, in accordance with the experiment. In
order to discern the influence of increased conjugation
and geometry changes induced by the addition of the
naphtho groups, we have recalculated all molecules in a
planar conformation. In all cases, this induces a rigid
blue-shift with respect to the equilibrium geometry of
about 10-20 nm. The blue-shift affects all transition
rather equally; i.e., the Soret band is shifted as well as
the Q band. In the cis-M2NF systems, the near-degen-
eracy of the two Q-band transitions is not lifted, under-
lining the stability of this result. In the planar geometries,
we find the shift of the Q-band peaks between Pd1NF and
Pd3NF to be 40 and 41 nm, i.e., only slightly larger than in
the equilibrium geometries. It can thus be concluded that
the shift is indeed based on the π extension rather than
geometrical distortions, as predicted by Finikova et al.12
Comparative theoretical calculations have been recently
described for Zn and Pd complexes of symmetrically
extended porphyrins, which revealed that the influence
of nonplanar distortion is much smaller on the red shifts
of the optical transitions than that of the π conjugation.19
This behavior can be rationalized by looking at the
corresponding orbitals (cf. Figure 2). The energetically
lower lying excitation of the Q band corresponds mainly
to a HOMOfLUMO transition, while the energetically
higher lying Q-band excitation mainly involves HOMOf
LUMOþ1. As Figure 2 illustrates, LUMO and LUMOþ1
are almost degenerated in Pt2NF, resulting in (almost)
degenerated excitation energies. In Pt1NF and Pt3NF,
LUMO and LUMOþ1 are different energetically, giving
rise to the characteristic double-peak shape. Within the
series, both LUMO and LUMOþ1 vary only very little in
energy, and hence the strong shift of the Q band to higher
wavelength is dominated by the energy increase of the
HOMO, triggered by the larger size of the conjugated
system. In contrast, the main contributions to the Soret
band include the HOMO-1 orbital. Unlike the HOMO,
the HOMO-1 shows hardly any lobes on the naphtho
moieties. It is thus unaffected by the extension of the π
system and remains at practically the same energy,
thus leading to constant transition energies for all three
molecules.
Figure 2. Energies and isodensity representations of the Kohn-Sham
orbitals HOMO-1, HOMO, LUMO, and LUMOþ1 calculated for the
platinum(II) porphyrins.
Figure 3. Emission spectra of platinum(II) porphyrins measured in
toluene at room temperature.
compounds revealed emission maxima in the range of
815 to 870 nm (cf. Table 1, Figure 3). Compared to the
emission maxima of the tetra-annulated porphyrins
palladium(II)-meso-tetra(4-fluorophenyl)tetrabenzoporphyrin
(PdTPTBPF; λmax,em 803 nm, solvent: toluene),10 palladium-
(II)-meso-tetraphenyltetranaphthoporphyrin (PdTPTNP;
Luminescence Spectroscopy. Palladium(II) complexes
emitted in toluene solutions under ambient conditions
with maxima ranging from 849 to 882 nm (cf. Supporting
Information Figure S17), and the corresponding platinum(II)
λ
max,em 937 nm, solvent: benzene),19 platinum(II)-meso-tetra-
(4-fluorophenyl)tetrabenzoporphyrin (PtTPTBPF; λmax,em

9338 Inorganic Chemistry, Vol. 49, No. 20, 2010
Niedermair et al.
enable better comparison with literature data.10 In the
case of the heterogeneous luminescent oxygen-sensing
films, the Stern-Volmer plots are not linear, which is in
contrast to the behavior in solutions. This nonlinear
behavior is common for most oxygen-sensitive materials,
including benzoporphyrins in polystyrene.9b,c The so-
called two-site model is used to describe the quenching
plots.22 It assumes localization of an oxygen-sensitive
chromophore in two environments originating from mi-
croinhomogeneities in the polymeric film (e.g., in crystal-
linity). Since these areas of the polymer possess different
gas permeabilities, two Stern-Volmer constants KSV1
and KSV2 are obtained for the same chromophore:
I0
I
1
¼
ð1Þ
P
1 - P
þ
1 þ KSV1pO 1 þ KSV2
p
O2
2
where P is the partition coefficient, i.e., the fraction of the
chromophore located in the first environment, with 1 - P,
respectively, for the second environment. The simplified
equation (KSV2 is set as 0) is found to excellently fit the
nonlinear Stern-Volmer plots, also for the decay time
(correlation coefficient >0.998). It should be mentioned
here that the two-site model approximation physically
makes sense only for the luminescence intensity fit. In
contrast, in the presence of oxygen, the decay times are
expected to become substantially different in both envi-
ronments, and the overall signal is not monoexponential.
However, the decay times obtained in the frequency
domain are averaged to the certain extent which can
explain why the fit with the equation from the “two-site
model” is adequate. The Stern-Volmer constants KSV as
well as the quenching constants kq calculated from the
Stern-Volmer plots (obtained from the decay time plots)
are summarized in Table 2. The KSV values in polystyrene
films (1% of the indicator, w/w) and in toluene solution
are consistent with the luminescence decay times. Oxygen
sensitivity in polystyrene decreases moving Pd1NF with a
Figure 4. Stern-Volmer plots for the Pt(II) complexes embedded in
polystyrene (at 25 °C). Curve fitting is performed according to eq 1
(KSV2 = 0).
773 nm, solvent: toluene),10 and platinum(II)-meso-tetraphe-
nyltetranaphthoporphyrin (PtTPTNP; λmax,em 883 nm, sol-
vent: toluene),7 these “hybrid” porphyrins complement the
NIR emission spectral range between 773 and 937 nm. As a
result, not only absorption but also emission wavelengths are
tunable by systematic extension of the aromatic porphyrin
framework.
Quantum yields (Φ) of the complexes were measured in
deoxygenated toluene solutions, and palladium(II)-meso-
tetraphenyltetrabenzoporphyrin (PdTPTBP) was used as
the standard. For the palladium complexes, the observed
luminescence quantum yields are 18% for Pd1NF, 12% for
Pd2NF, and 7% for Pd3NF. The obtained values are con-
sistent with the quantum yields known for PdTPTBPF
(Φ = 23%) and PdTPTNP (Φ = 6.5%).10,20 Platinum
complexes possess significantly higher luminescence quan-
tum yields (53, 27, and 25%, respectively, for Pt1NF, Pt2NF,
and Pt3NF), and the corresponding values for PtTPTBPF
(Φ = 60%) and PtTPTNP (Φ = 22%)7,10 are consistent
with our results. Luminescence lifetimes are in agreement
with the corresponding tetrabenzoporphyrin complexes
(297 μs for PdTPTBPF, 50 μs for PtTPTBPF)10 and tetra-
naphthoporphyrin complexes (65 μs for PdTPTNP,20 8.5 μs
for PtTPTNP7), respectively. Similar to meso-tetraaryl-
tetranaphtho[2,3]porphyrins (Ar4TNP) described byFinikova
et al.,12 every additional fused naphtho moiety enhances
radiativeless deactivation of the triplet states, which is
most probably caused by lower energy levels. However,
room temperature phosphorescence quantum yields of the
metalloporphyrins presented in this work render these phos-
phorescent dyes very suitable for incorporation into near-IR
light-emitting devices.2b,7
KSV1 of 0.60 kPa-1 to Pd3NF with a KSV1 of 0.47 kPa-1
Palladium(II)-meso-tetraphenyltetrabenzoporphyrin
.
(PdTPTBP)10 exhibits the highest sensitivity (KSV1
=
0.92 kPa-1), which corroborates the trend in this series.
Platinum(II) porphyrins show significantly lower sensi-
tivity than the respective palladium(II) complexes (which
correlates with the shorter decay times of the former), but
a similar trend for the KSV1 values is observed. Platinum-
(II)-meso-tetraphenyltetrabenzoporphyrin (PtTPTBP)10
completes the series revealing the same trend as for the
corresponding palladium compounds in solution as well
in polymeric film. Interestingly, the quenching con-
stants kq in polymer films (kq,film) and in toluene solution
(kq,solution) show the following trends: PdTPTBP <
Pd1NF < Pd2NF < Pd3NF and PtTPTBP < Pt1NF <
Pt2NF < Pt3NF, which correlate well with the increased
radii of the metalloporphyrin molecules. The increase in
the indicator size should result in a higher probability of
the collision between the excited indicator and molecular
oxygen. The obtained data (cf. Table 2) clearly show
that these “hybrid” porphyrin complexes are suitable as
Oxygen Quenching. Phosphorescence of all complexes
was found to be efficiently quenched by oxygen both in
toluene solutions and in polystyrene films (cf. Figure 4).
Polystyrene was chosen as a rigid polymer with good
optical properties and moderate diffusion and partition
coefficients for oxygen,5,21 as well as a model matrix to
(21) Papkovsky, D. B.; Olah, J.; Troyanovsky, I. V.; Sadovsky, N. A.;
Rumyantseva, V. D.; Mironov, A. F.; Yaropolov, A. I.; Savitsky, A. P.
Biosens. Bioelectron. 1992, 7, 199–206.
(22) Carraway, E. R.; Demas, J. N.; DeGraff, B. A.; Bacon, J. R. Anal.
Chem. 1991, 63, 337–342.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9339
Table 2. Quenching Constants (kq), Stern-Volmer Constants (KSV), and Partition Coefficients (P) of the Porphyrin Complexes in Polystyrene (1% of the Indicator, w/w)
and in Toluene Solution
complex
KSV1,film [kPa-1
]
P
kq,film [Pa-1 -1
s
]
KSV,solution [kPa-1
]
kq,solution [Pa-1 -1
s ]
PdTPTBP
Pd1NF
Pd2NF
Pd3NF
PtTPTBP
Pt1NF
0.92 ( 0.01a
0.60 ( 0.02
0.50 ( 0.03
0.47 ( 0.01
0.17 ( 0.01a
0.13 ( 0.01
0.11 ( 0.01
0.08 ( 0.01
0.87a
0.88
0.92
0.92
0.87a
0.84
0.80
0.66
2.6 ( 0.1a
3.6 ( 0.2
4.2 ( 0.2
4.8 ( 0.2
3.0 ( 0.1a
3.7 ( 0.2
3.9 ( 0.2
4.8 ( 0.2
15.8 ( 0.3
15.4 ( 0.2
10.4 ( 0.2
85 ( 4
114 ( 6
118 ( 6
2.8 ( 0.1
2.4 ( 0.1
1.9 ( 0.1
69 ( 3
93 ( 5
98 ( 5
Pt2NF
Pt3NF
a Data from ref 10.
indicators for use in optical oxygen sensors. Considering
the sensitivity, the materials based on the platinum(II)
complexes are excellently suitable for most biological
applications, and the more sensitive palladium(II) por-
phyrin-based sensors are more adequate for measure-
ments under anoxic conditions.
Photostability. The photostability of oxygen indicators
is of particular interest for practical applications, espe-
cially in those cases where high light densities are applied
or long-term measurements are performed. As theoreti-
cally predicted by Kobayashi et al.,15 π-ring expansion
results in the destabilization of the third LUMOs and the
first HOMOs of the porphyrins, and therefore, they
become unstable against oxidation and reduction. In this
work, the photostability of all complexes is investigated in
solution as well as in the polystyrene films. For photo-
stability measurements in solution, PdTPTBP and
PtTPTBP were used as reference materials. The photo-
stability of the complexes in DMF solution was deter-
mined by continuously irradiating the samples with a red
LED array (λmax = 638 nm, www.led-tech.de, Flux:
6200 μmols-1 m-2 μA at 5.0 W). Data presented in Figure
5 indicate that the photostability of the hybrid systems is
significantly lower than that of PtTPTBP. In fact, after 1 min
of irradiation, 4% of Pt1NF, 14% of Pt2NF, and 25% of
Pt3NF, respectively, is destroyed compared to 0.2% of
PtTPTBP. The decrease in photostability correlates well with
the number of naphtho moieties annealed to the porphyrin
system. Photobleaching rates for the palladium(II) and the
platinum(II) complexes are comparable (photodegradation
after 1 min: 6% for Pd1NF, 15% for Pd2NF, 30% for
Pd3NF, and 0.6% for PdTPTBP; cf. Supporting In-
formation). The nature of the solvent has a pronounced
influence on the photobleaching rates. For example, the
photodegradation of the platinum complex Pt3NF was
further investigated with toluene as the solvent. After 5 min
of irradiation, the absorption of Pt3NF in toluene remained
unchanged. In contrast to that, 52% of Pt3NF was destroyed
under the same irradiation conditions with DMF as a solvent
(cf. Supporting Information Figure S35). Finally, it should be
emphasized that irradiation of the complexes in solution
results in a complete degradation of the porphyrin system,
and no additional chromophores are formed.
Figure 5. Photodegradation curves for the platinum(II) porphyrins in
DMF solution at room temperature. Irradiation is performed with a red
LED array at 638 nm (flux: 6200 μmols-1 m-2 μA).
photostability compared to the “dinaphto” (Pd2NF, Pt2NF)
and “trinaphtho” complexes (Pd3NF, Pt3NF). In fact, after
30 min of irradiation, 18% of Pd2NF is destroyed (cf. Figure
6), compared to 3% of Pd1NF (cf. Supporting Information).
Platinum(II) porphyrins show comparable photodegrada-
tion values of 2% for Pt1NF and 19% for Pt2NF.Incontrast
to that, the luminescence decay times remained stable for all
complexes during 30 min of irradiation time (cf. Figure 6,
Supporting Information). Photostability measurements un-
der a nitrogen atmosphere revealed stable signals for lumi-
nescence intensity as well as decay time during 30 min of
irradiation time (cf. Figure 6, Supporting Information).
Thus, all the indicators perform well in the sensor material,
and no influence of photobleaching on the luminescence
decay times could be observed. In addition, no recalibration
is needed for these dyes; however, the signal-to-noise ratio
deteriorates under air. However, it should be mentioned that
a continuous irradiation time of 30 min corresponds to
36 000 measurement points when a short light pulse of 50
ms is applied.
In summary, the photostability of these mixed benzo-
and naphthoporphyrins can be a critical issue. For some
potential applications, especially for those where high
light intensities are used (e.g., microscopy, fiber optical
microsensors) or very long acquisition is applied, photo-
stability should be improved. Considering the signifi-
cantly higher photobleaching rates in the presence of
oxygen, the photo-oxydation by singlet oxygen is the
most probable photodegradation pathway. Therefore,
The photostability of the complexes in polystyrene under
synthetic air was estimated upon continuous irradiation of
the samples with a blue LED (λmax = 450 nm, Roithner
Lasertechnik; Vienna, Austria, Flux: 200 μmols-1 m-2 μA)
and monitoring the emission intensity as well as the decay
time. According to the obtained results, the “mononaphtho”
complexes Pd1NF and Pt1NF show a significantly higher

9340 Inorganic Chemistry, Vol. 49, No. 20, 2010
Niedermair et al.
Particularly, the emission bands shift bathochromically, the
luminescence lifetime becomes shorter, and the luminescence
quantum yields decrease. The sensitivity of the materials to
oxygen is also affected and gradually reduces upon substitu-
tion. Unfortunately, the substitution significantly increases
the photobleaching rates. In this context, our future synthetic
work concerning these hybrid systems will essentially focus on
the improvement of the photochemical stability via halogena-
tion of the porphyrin macrocycle.
Experimental Section
Materials and Methods. Ethyl isocyanoacetate, 1-nitro-1-cyclo-
hexene, and 2,3-dicyano-5,6-dichlorobenzoquinone (DDQ) were
purchased from Aldrich (www.sigmaaldrich.com). 4-Fluoroben-
zaldehyde, palladium(II) chloride, platinum(II) chloride, and
benzonitrile were purchased from ABCR (www.abcr.de). Dimethyl-
formamide, N,N-dimethyldiisopropylamine, and 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU) were obtained from Fluka (www.
sigmaaldrich.com). All other solvents were obtained from
Roth (www.carl-roth.de). The silica-gel 60 (0.063-0.200 mm)
was purchased from Merck (www.merck.de), and the neutral
aluminum oxide (50-200 μm) was purchased from Acros
Organics (www.acros.com). Polystyrene (mw: 250 000) was
obtained from Fischer Scientific (www.fishersci.com). Poly-
(ethyleneterephthalate)-Mylar-support was purchased from
Goodfellow. Nitrogen and synthetic-air (all of 99.999% purity)
were obtained from Air Liquide (www.airliquide.at). Unless
otherwise noted, all other materials were obtained from com-
mercial sources (Aldrich, Fluka, ABCR, and Acros) and were
used without further purification. PdCl2(PhCN)2 and PtCl2-
(PhCN)2 were prepared according to a literature procedure.23
The complexes palladium(II)-meso-tetraphenyltetrabenzopor-
phyrin (PdTPTBP) and platinum(II)-meso-tetraphenyltetra-
benzoporphyrin (PtTPTBP) were prepared according to a
technique reported elsewhere.10
Figure 6. Photodegradation curves for the metalloporphyrin Pd2NF
embedded in a polystyrene film (1% of the indicator, w/w; 2.5-μm-thick
film). Irradiation is performed with a blue LED (λmax = 450 nm, flux:
200 μmols-1 m-2 μA).
the photostability is expected to dramatically improve if
the hydrogen atoms are substituted by the halogens, e.g.,
fluorine or chlorine. Due to the electron-withdrawing
effect of the halogen atoms, such perhalogenated deriva-
tives are expected to be more difficult to oxidize and,
therefore, are likely to represent highly photostable in-
dicators. It should be mentioned here that more sophis-
ticated synthetic routes for the preparation of a new
precursor for naphthoporphyrins bearing a perchlori-
nated outer ring are possible.1 In addition to the im-
proved photostability, the chlorine atoms are expected to
further improve the solubility in organic solvents and in
polymers. Current efforts are directed at developing
efficient synthetic strategies for perchlorination.
1H NMR spectra were recorded on a Varian INOVA 500 MHz
spectrometer at 500 MHz or a Bruker Avance III 300 MHz
spectrometer at 300 MHz. 13C NMR, 19F NMR, 2D HMBC,
and 2D HSQC spectra were recorded on a Varian INOVA 500
MHz spectrometer at 500 MHz. UV-visible absorption spectra
were recorded on a Cary 50 Bio UV-visible spectrophotometer
and fluorescence spectra on a Hitachi F-7000 fluorescence spec-
trometer equipped with a red-sensitive photomultiplier, R 928,
from Hamamatsu. The emission spectra were corrected for the
sensitivity of the PMT, which was calibrated with a halogen
lamp.24,25 Relative luminescence quantum yields were determined
using a solution of PdTPTBP in toluene as a standard (Φ =
0.2110). The solutions of the dyes were thoroughly deoxygenated
by bubbling nitrogen through for 20 min. The quantum yields as
well as luminescence phase shifts in solution were determined
using a lock-in amplifier (PreSens, www.presens.de) equipped
with a silicon photodiode. Excitation of the complexes was
performed with a 435 nm LED (www.roithner-laser.com), which
was sinusoidally modulated at a frequency of 916 Hz (absorbances
at the excitation wavelength of 435 nm were 0.1 for all complexes).
The errors in measurement were estimated as (10% for lumines-
cence quantum yields and (5% for luminescence decay times,
respectively.
Conclusion
In conclusion, mixed benzo- and naphthoporphyrin com-
plexes of palladium(II) and platinum(II) have been prepared.
Absorbance and luminescence as well as lifetime measure-
ments in solution and in the solid state have been performed
to establish a qualitative relationship between structure and
luminescence properties. The compounds under investiga-
tion show tunable absorption in the near-infrared region
(628-691 nm) as well as controllable emission in the range of
815-882 nm. In addition, these metalloporphyrins are
strongly luminescent, with quantum yields up to 53% for
platinum(II) porphyrins and up to 18% for palladium(II)
complexes, respectively. DFT calculations revealed nonpla-
nar geometries for all complexes. The calculations corrobo-
rate that only the cis isomer was formed during the synthesis
according to Lindsey. Moreover, they also show a strong
bathochromic shift in the Q band, while the Soret band
remains almost constant. This behavior is rationalized by the
different energy evolution of the involved orbitals HOMO
and HOMO-1, respectively, with respect to the increased
size of the conjugated system. The systematic extension of the
conjugated system by annealing further naphtho moieties to
the porphyrin system results in “tailor-made” near-infrared
absorbing indicators for oxygen. These chromophores are
particularly promising candidates for different multiplexing
applications, e.g., simultaneous glucose and oxygen determi-
nation in enzymatic sensors. The enlargement of the aromatic
system has a significant impact on the photophysical properties.
Phase angle measurements concerning oxygen sensitivity in
solution were performed with a 450 nm LED (www.roithner-laser.
com). For phase angle measurements in solution, the following
modulation frequencies were applied: 916 Hz for Pd1NF,
1831 Hz for Pd2NF, 2747 Hz for Pd3NF, 4578 Hz for Pt1NF,
(23) Borisov, S.; Klimant, I. Dyes Pigm. 2009, 83, 312–316.
(24) Argauer, R. J.; White, C. E. Anal. Chem. 1964, 36, 368–371.
(25) Emanuel, N. M.; Kuzmin, M. G. Experimental Methods of Chemical
Kinetics (in Russian); MGU: Moscow, 1985; pp 152-157.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9341
5493 Hz for Pt2NF, and 6409 Hz for Pt3NF. The polymer
“cocktails” for the sensor films were prepared by dissolving the
metal complex and polystyrene in chloroform (10% w/w of PS
in CHCl3). The “cocktails” were knife-coated on the Mylar
support to give, after solvent evaporation, phosphorescent
sensor films with a thickness of 2.5 μm. The films contained
∼1% (w/w) of the dye in the polymer. For phase angle measure-
ments in polymeric films, the following modulation frequencies
were applied: 1831 Hz for Pd1NF, 4578 Hz for Pd2NF and
Pd3NF, 6409 Hz for Pt1NF, 8240 Hz for Pt2NF, and 10986 Hz
for Pt3NF. Excitation of the complexes was performed with a
450 nm LED (www.roithner-laser.com). A BG 12 filter (Schott,
www.schott.com) was used for excitation and an RG 9 filter
(Schott) for emission for all phase angle measurements. Tem-
perature was controlled by a ThermoHaake DC50 cryostat at
25 °C. Gas calibration mixtures were obtained using a gas
mixing device (MKS, www.mksinst.com).
Photostability of the dyes in polymeric films was determined
using a lock-in amplifier from PreSens. Sensor foils were posi-
tioned at 30° relative to the photodiode and the light source.
Continuous irradiation was performed with the light of a 450 nm
LED (www.roithnerlaser.com, Flux: 200 μmols-1 m-2 μA)
filtered through a BG 12 filter. An RG 9 filter (Schott) was used
for the emission. The same modulation frequencies as for oxygen
sensitivity measurements were applied. The bleaching rates were
corrected for the amount of the absorbed light at 456 nm. Photo-
stability of the complexes in DMF solution was determined con-
Ligand Synthesis via the Lindsey Method. 4,5,6,7-Tetrahy-
droisoindole (529.8 mg, 4.37 mmol, 0.52 equiv) and 4,9-dihydro-
2H-benz[f]isoindole (673.5 mg, 3.98 mmol, 0.48 equiv) were
dissolved in dry CH2Cl2 (835 mL). The reaction mixture was
degassed for 20 min with N2. The stirred mixture was protected
from light and stirred under N2. 4-Fluorobenzaldehyde (896 μL,
1.04 g, 8.35 mmol, 1.0 equiv) was added, and the reaction
mixture was kept in the dark under N2 and stirred for 10 min.
BF3 Et2O (210 μL, 237 mg, 1.7 mmol, 0.2 equiv) was added in
3
one portion, and the mixture was allowed to react at room
temperature for 1 h. After 1 h, triethylorthoacetate (TEOAc;
1531 μL, 1355 mg, 8.35 mmol, 1.0 equiv) was added, and the
reaction mixture was stirred at room temperature for 30 min.
After 30 min, BF3 Et2O (40 μL, 45.2 mg, 0.32 mmol, 0.04 equiv)
3
was added, and the reaction mixture was stirred for an addi-
tional 30 min. Finally, one last portion of BF3 Et2O (40 μL, 45.2
3
mg, 0.32 mmol, 0.04 equiv) was added, and the reaction mixture
was stirred for 2 h. After an overall reaction time of 4 h, DDQ
(9.5 g, 41.8 mmol, 5.0 equiv) was added to the mixture in one
portion, and the mixture was stirred at room temperature over-
night. The resulting mixture was washed with 10% aq. Na2SO3
(2 ꢀ 100 mL) and with water (2 ꢀ 100 mL). The combined organic
phases were dried over Na2SO4. The solvent was evaporated, and
the resulting residue was purified by column chromatography on
neutral alumina (3NF: toluene, CH2Cl2/toluene = 1:1 (v/v),
CH2Cl2; 2NF: CH2Cl2 þ 1% THF; 1NF: CH2Cl2 þ 2% THF).
The three main fractions were isolated as green solids with an
overall yield of 42%.
tinuously irradiating the samples with a red LED array (λmax
=
638 nm, www.led-tech.de, Flux: 6200 μmols-1 m-2 μA at 5.0 W).
MALDI-TOF mass spectra were recorded on a Micromass
TofSpec 2E. The instrument is equipped with a nitrogen laser
(337 nm wavelength, operated at a frequency of 5 Hz) and a time
lag focusing unit. Spectra were taken in reflectron mode at an
accelerating voltage of þ20 kV. Analysis of the data was done
with MassLynx 3.4 (Micromass, Manchester, U.K.). Samples
were dissolved in THF (1 mg/cm3). Dithranol or retinoic acid
was used as the matrix (10 mg/cm3 in THF). Solutions were
mixed in the cap of a microtube in a ratio of 1:10 μL. A total of
0.5 μL of the resulting mixture was spotted onto the target and
air-dried.
Density functional theory calculations were performed using
the Turbomole 5.7 software suite.26 The B3LYP exchange
correlation functional27 was employed together with the SVP
basis set28 and relativistic effective core potentials for Pd and
Pt.29 Geometry optimizations were performed explointing sym-
metry where possible. After the optmization, frequency calcula-
tions without imaginary frequencies ensured that a true
minimum was reached. To obtain planar geometries, a biased
start geometry was constructed. The planarity was enforced by
increasing the symmetry point group accordingly. Frequency
calculations performed after the geometry optmization showed
four imaginary frequencies. Optical excitations were calculated
within the time-dependent DFT framework. For all molecules,
the 10 lowest lying excitations of each irreducible representation
were collected. Test calculations using the higher quality
TZVP30 basis set for the exitations only yielded the same general
shape of the spectra. The transitions were slightly red-shifted
and therefore in even better agreement with the experiment.
1NF. Yield: 254.8 mg, 29%. 1H NMR (δ, 20 °C, CDCl3, 300
MHz): 8.46-8.12 (m, 8H), 7.73-7.39 (m, 14H), 2.51-2.17 (m,
12H), 1.74-1.67 (m, 12H). MALDI-TOF: m/z 949.3837, calcd
949.3893. UV-vis, toluene, λmax nm (relative intensity): 460
(1.00), 548 (0.11), 586 (0.08), 628 (0.07), 690 (0.04).
2NF. Yield: 301.3 mg, 34%. 1H NMR (δ, 20 °C, CDCl3, 300
MHz): 8.33-8.08 (m, 8H), 7.72-7.39 (m, 20H), 1.69-1.47 (m,
8H), 2.54-2.24 (m, 8H). 13C NMR (δ, 20 °C, CDCl3, 500 MHz):
165.2, 164.8, 164.6, 164.5, 163.2, 162.8, 162.6, 162.5, 142.2,
138.7, 138.6, 137.88, 137.86, 137.43, 137.41, 136.5, 136.4,
136.0, 135.92, 135.88, 135.82, 131.7, 131.5, 130.78, 130.76,
130.3, 130.2, 129.4, 129.2, 128.3, 128.2, 126.98, 126.96, 126.7,
126.4, 126.2, 124.4, 123.7, 116.6, 116.5, 116.4, 116.2, 115.9,
115.8, 115.6, 115.2, 115.0, 29.9, 29.5, 27.8, 25.9, 25.8, 24.5,
23.6, 23.5. 19F NMR (δ, 20 °C, CDCl3, 500 MHz): -113.6
(2F), -109.5 (1F). MALDI-TOF: m/z 995.3709, calcd 995.3737.
UV-vis, toluene, λmax nm (relative intensity): 471 (1.00), 589
(0.09), 630 (0.13), 691 (0.04).
3NF. Yield: 324.2 mg, 37%. 1H NMR (δ, 20 °C, CDCl3, 300
MHz): 8.33-8.20 (m, 8H), 7.81-7.36 (m, 22H), 7.28-7.26 (m,
4H, ovelap with solvent), 2.55-2.41 (m, 4H), 1.68-1.54 (m,
4H). MALDI-TOF: m/z 1040.3414, calcd 1040.3502. UV-vis,
toluene, λmax nm (relative intensity): 475 (1.00), 558 (0.04), 599
(0.08), 641 (0.14), 718 (0.09).
Synthesis of the Pd(II) and Pt(II) Porphyrins. Pd1NF. An
excess of PdCl2(PhCN)2 (36.0 mg, 0.09 mmol, 2.0 equiv) was
added to a solution of porphyrin ligand 1NF (44.5 mg, 0.05
mmol, 1.0 equiv) in THF (20 mL), and the mixture was refluxed
for 15 min. N,N-dimethyldiisopropylamine (20 μL) was added
as a base, and the mixture was refluxed for an additional 15 min.
The conversion was monitored by UV-vis spectroscopy
(solvent: toluene). DDQ (106.0 mg, 0.47 mmol, 10 equiv) was
added, and the mixture was refluxed for 15 min. The oxidation
was monitored by UV-vis spectroscopy (solvent toluene). The
solvent volume was reduced to 20 mL under vacuum conditions.
CH2Cl2 (100 mL) was added, and the mixture was washed with
aqueous 10% Na2SO3. The organic phase was dried over
Na2SO4, and the solvent was evaporated. The crude product
was purified by column chromatography on Al2O3 (removal of
excess DDQ, eluent: n-hexane/toluene = 2:1 (v/v); elution of
Pd1NF, eluent: toluene). Final purification was accomplished
€
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(26) Ahlrichs, R.; Bar, M.; Haser, M.; Horn, H.; Kolmel, C. Chem. Phys.
Lett. 1989, 162, 165–169. TURBOMOLE 5.7. http://www.turbomole.com
(accessed Sept 2010).
(27) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Stephens,
P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98,
11623–11627.
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(28) Schafer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571–
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€

9342 Inorganic Chemistry, Vol. 49, No. 20, 2010
Niedermair et al.
by recrystallization from CH2Cl2/MeOH after the removal of
Al2O3 by filtration to yield the product as a green solid. Yield:
26.1 mg, 53%. 1H NMR (δ, 20 °C, CDCl3, 300 MHz): 8.30-8.20
(m, 8H), 7.74-7.49 (m, 14H), 7.31-7.12 (m, 12H, overlapped w/
solv). MALDI-TOF: m/z 1038.1804, calcd 1038.1761.
The preparation of Pd2NF was performed similarly to Pd1NF
starting from PdCl2(PhCN)2 (38.5 mg, 0.10 mmol, 2.0 equiv)
and 2NF (50.0 mg, 0.05 mmol, 1.0 equiv). Yield: 26.4 mg, 48%.
1H NMR (δ, 20 °C, CDCl3, 300 MHz): 8.35-8.19 (m, 8H),
7.75-7.50 (m, 20H), 7.30-7.19 (m, 6H, ovelapped w/solv),
7.14-7.11 (m, 2H). MALDI-TOF: m/z 1088.2034, calcd
1088.1919.
Pd3NF was synthesized analogously to Pd1NF starting from
PdCl2(PhCN)2 (37.9 mg, 0.10 mmol, 2.0 equiv) and 3NF (51.5
mg, 0.05 mmol, 1.0 equiv). Yield: 27.5 mg, 49%. 1H NMR (δ,
20 °C, CDCl3, 300 MHz): 8.35-8.24 (m, 8H), 7.75-7.49 (m,
26H), 7.31-7.19 (m, 4H, ovelapped w/solv). MALDI-TOF: m/z
1138.2065, calcd 1138.2075.
and the solvent was evaporated. The remaining material was purified
by column chromatography on Al2O3 (removal of excess of DDQ,
eluent: n-hexane/toluene = 2:1 (v/v); elution of Pt1NF, eluent:
toluene). Final purification was accomplished by recrystallization
from CH2Cl2/MeOH after the removal of Al2O3 by filtration to yield
1
the product as a green solid. Yield: 20.0 mg, 32%. H NMR (δ,
20 °C, CDCl3, 300 MHz): 8.30-8.19 (m, 8H), 7.73-7.50 (m, 14H),
7.32-7.26 (m, 7H, ovelapped w/solv), 7.20-7.17(m,1H),7.12-7.09
(m, 4H). MALDI-TOF: m/z 1128.2311, calcd 1128.2346.
The preparation of Pt2NF was performed similarly to that of
Pt1NF starting from PtCl2(PhCN)2 (79.0 mg, 0.17 mmol, 2.8
equiv) and 2NF (59.4 mg, 0.06 mmol, 1.0 equiv). Yield: 17.4 mg,
25%. 1H NMR (δ, 20 °C, CDCl3, 300 MHz): 8.35-8.19 (m, 8H),
7.73-7.51 (m, 20H), 7.31-7.08 (m, 8H, ovelapped w/solv).
MALDI-TOF: m/z 1178.256, calcd 1178.250.
Pt3NF was synthesized analogously to Pt1NF starting from
PtCl2(PhCN)2 (99.0 mg, 0.21 mmol, 3.0 equiv) and 3NF (50.0
mg, 0.07 mmol, 1.0 equiv). Yield: 18.5 mg, 21%. 1H NMR (δ,
20 °C, CDCl3, 300 MHz): 8.35-8.25 (m, 8H), 7.73-7.53 (m,
26H), 7.33-7.18 (m, 4H, ovelapped w/solv). MALDI-TOF: m/z
1228.2660, calcd 1228.2631.
Pt1NF. An excess of PtCl2(PhCN)2 (90.4 mg, 0.19 mmol,
3.6 equiv) was added to a solution of porphyrin ligand 1NF
(50.0 mg, 0.05 mmol, 1.0 equiv) in 1,2,4-trimethylbenzene (20 mL),
and the mixture was refluxed for 10 min. N,N-dimethyldiisopropy-
lamine (40 μL) was added as a base, and the mixture was refluxed for
an additional 30 min. The conversion was monitored by UV-vis
spectroscopy (solvent: toluene). The reaction mixture was cooled to
room temperature and filtered over neutral alumina to remove
colloidal platinum black. The solvent was evaporated, and the crude
product was dried. Oxidation was performed in THF (20 mL) with
DDQ (134.6 mg, 0.59 mmol, 12 equiv) by refluxing the mixture for
15 min. The oxidation was monitored by UV-vis spectroscopy
(solvent: toluene). The solvent volume was reduced to 20 mL.
CH2Cl2 (100 mL) was added, and the mixture was washed with
aqueous 10% Na2SO3. The organic phase was dried over Na2SO4,
Acknowledgment. Financial support by the Austrian Science
Fund (FWF; Research Project No. P21192-N17) is gratefully
acknowledged.
Supporting Information Available: Detailed synthetic proce-
dures, comprehensive photophysical data (tables, absorption,
excitation and emission spectra, oxygen quenching, photo-
stability), NMR spectra, MALDI-TOF data, orbitals, and
DFT calculated geometries. This material is available free of
charge via the Internet at http://pubs.acs.org.