Facile preparation and photophysics of near-infrared luminescent lanthanide(III) monoporphyrinate complexes

Article abstract of DOI:10.1021/ic034217g

The synthesis, characterization, and single crystal X-ray diffraction structures of a series of monoporphyrinate, trivalent lanthanide complexes with the monoanionic ligands hydridotris(1-pyrazolyl)borate (Tp) and (cyclopentadienyl)-tris(diethylphosphinito)cobaltate (L(OEt)) having the general formulas M(TPP)(L) (M = Yb, Tm, Er, Ho, Nd, Pr; TPP = 5,10,15,20-tetraphenylporphyrinate; L = Tp, L(OEt)) are described. The photophysical properties of these complexes are also presented including their absorption, emission, and transient absorption properties.

Full text of DOI:10.1021/ic034217g

Inorg. Chem. 2003, 42, 5023−5032
Facile Preparation and Photophysics of Near-Infrared Luminescent
Lanthanide(III) Monoporphyrinate Complexes
Timothy J. Foley, Benjamin S. Harrison, Alison S. Knefely, Khalil A. Abboud, John R. Reynolds,
Kirk S. Schanze,* and James M. Boncella*
Department of Chemistry and Center for Macromolecular Science and Engineering, UniVersity of
Florida, GainesVille, Florida 32611-7200
Received February 26, 2003
The synthesis, characterization, and single crystal X-ray diffraction structures of a series of monoporphyrinate,
trivalent lanthanide complexes with the monoanionic ligands hydridotris(1-pyrazolyl)borate (Tp) and (cyclopentadienyl)-
tris(diethylphosphinito)cobaltate (L(OEt)) having the general formulas M(TPP)(L) (M ) Yb, Tm, Er, Ho, Nd, Pr;
TPP ) 5,10,15,20-tetraphenylporphyrinate; L ) Tp, L(OEt)) are described. The photophysical properties of these
complexes are also presented including their absorption, emission, and transient absorption properties.
Introduction
The narrow band f f f emissions of the lanthanide ions
are a decidedly attractive optical property. However, direct
excitation of these transitions is difficult due to the low
optical cross section of lanthanide ions arising from the
forbidden nature of the 4f f 4f transitions.8 Since the
discovery that energy transfer from the triplet state of an
organic ligand can efficiently sensitize the emissive states
of lanthanide ions,9 there has been considerable effort devoted
to designing ligands that optimize this energy transfer and
thus give efficient lanthanide luminescence. While much of
There has been increasing interest in generating near-
infrared (NIR) emission from metal complexes through
photoluminescence1 or electroluminescence.2 Sources of
near-infrared emission are of interest for a variety of
biological and biomedical applications, including glucose
monitoring3 and immunoassay.4 Furthermore, there are also
potential uses for NIR sources in telecommunications5 and
defense applications.6 Complexes with lanthanide ions are
attractive candidates for such NIR devices because a number
of these ions display spectrally bright emission in this region.7
(3) (a) Muller, U. A.; Mertes, B.; Fischbacher, C.; Jageman, K. U.; Danzer,
K. Int. J. Artif. Organs 1997, 20, 285. (b) Robinson, M. R.; Eaton, R.
P.; Haaland, D. M.; Koepp, G. W.; Thomas, E. V.; Stallard, B. R.;
Robinson, P. L. Clin. Chem. 1992, 38, 1618. (c) Samann, A.;
Fischbacher, C.; Jagemann, K. U.; Danzer, K.; Schuler, J.; Papenkordt,
L.; Muller, U. A. Exp. Clin. Endocrinol. Diabetes 2000, 108, 406.
(4) (a) Boyer, A. E.; Lipowska, M.; Zen, J. M.; Patonay, G.; Tsang, V.
C. W. Anal. Lett. 1992, 25, 415. (b) Daneshvar, M. I.; Peralta, J. M.;
Casay, G. A.; Narayanan, N.; Evans, L.; Patonay, G.; Strekowski, L.
J. Immunol. Methods 1999, 226, 119.
* To whom correspondence should be addressed. E-mail: kschanze@
chem.ufl.edu (K.S.S.); boncella@chem.ufl.edu (J.M.B.).
(1) (a) Werts, M. H. V.; Hofstraat, J. W.; Geurts, F. A. J.; Verhoeven, J.
W. Chem. Phys. Lett. 1997, 276, 196. (b) Wolbers, M. P. O.; van
Veggel, F. C. J. M.; Snellink-Ruel, B. H. M.; Hofstraat, J. W.; Geurts,
F. A. J.; Reinhoudt, D. N. J. Chem. Soc., Perkin Trans. 2 1998, 2141.
(c) Klink, S. I.; Grave, L.; Reinhoudt, D. N.; van Veggel, F. C. J. M.;
Werts, M. H. V.; Geurts, F. A. J.; Hofstraat, J. W. J. Phys. Chem. A
2000, 104, 5457. (d) Werts, M. H. V.; Verhoeven, J. W.; Hofstraat, J.
W. J. Chem. Soc., Perkin Trans. 2 2000, 433. (e) Klink, S. I.; Alink,
P. O.; Grave, L.; Peters, F. G. A.; Hofstraat, J. W.; Geurts, F.; van
Veggel, F. C. J. M. J. Chem. Soc., Perkin Trans. 2 2001, 363. (f)
Werts, M. H. V. Ph.D. Thesis, University of Amsterdam, 2000.
(2) (a) Sun, R. G.; Wang, Y. Z.; Zheng, Q. B.; Zhang, H. J.; Epstein, A.
J. J. Appl. Phys. 2000, 87, 7589. (b) Harrison, B. S.; Foley, T. J.;
Bouguettaya, M.; Boncella, J. M.; Reynolds, J. R.; Schanze, K. S.;
Shim, J.; Holloway, P. H.; Padmanaban, G.; Ramakrishnan, S. Appl.
Phys. Lett. 2001, 79, 3770. (c) Slooff, L. H.; Polman, A.; Cacialli, F.;
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Yanagida, S. Jpn. J. Appl. Phys., Part 1 2001, 40, 350. (e) Hong, Z.
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10.1021/ic034217g CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/12/2003
Inorganic Chemistry, Vol. 42, No. 16, 2003 5023

Foley et al.
the focus has been on improvement of the quantum efficien-
cies of visible emitters such as Eu3+ (red) and Tb3+ (green),2g
recently effort has been directed toward investigating ligands
for efficient sensitization of the NIR emitting lanthanides.1,10
(Ln(TPP)Cl) complexes via nucleophilic displacement of
chloride ion from anhydrous LnCl3 by the TPP dianion.20 In
this paper, we report a high-yield method for the synthesis
of Ln(TPP) complexes, capped with multidentate ligands.
These synthetic procedures are readily scalable to produce
gram quantities of these materials and thereby provide easy
access to a variety of new complexes that are potential NIR
lumophores. The structures were confirmed using a combi-
nation of X-ray crystallography and NMR spectroscopy.
Photophysical characterization results are presented as
pertinent to the application of these complexes in NIR
emitting LEDs.
Porphyrins are promising ligands for efficient energy
transfer to NIR emitting lanthanide ions because their intense
Soret bands lead to high absorption cross sections and their
low energy triplet states can efficiently sensitize the NIR
emitting states of the lanthanide ions. While porphyrin
complexes of transition metals have been studied exten-
sively,11 comparatively few studies of lanthanide-porphyrin
complexes have been reported.12 The limited work in this
area has been directed toward their use as NMR shift
reagents,13 MRI contrast agents,14 and agents for photody-
namic therapy.15
Experimental Section
Materials and Reagents. Unless otherwise stated, all syntheses
were carried out on a double manifold Schlenk line under an
atmosphere of nitrogen, or in a N2 filled glovebox. Glassware was
oven dried prior to use. Methylene chloride, dimethoxyethane, and
chloroform were purchased from Fisher Scientific and distilled from
the appropriate drying agent.21 Toluene and pentane were purchased
from Aldrich Chemicals and dried by passage through a column
of activated alumina. Following dehydration, the solvents were
degassed and stored over 4 Å molecular sieves in resealable ampules
fitted with Teflon valves. The Ln(TPP)Cl(DME) complexes were
synthesized according to the literature procedure20 and stored in a
glovebox. Potassium hydridotris(1-pyrazolyl)borate (KTp)22 and
sodium (cyclopentadienyl)tris(diethylphosphinito)cobaltate(I) (NaL-
(OEt))23 were prepared according to literature procedures, dried
under vacuum for ∼3 h, and stored in a glovebox. Elemental
analyses were performed by Complete Analysis Laboratories, Inc.,
of Parsippany, NJ, or the University of Florida Spectroscopic
Services.
The first reported synthesis of lanthanide monoporphyri-
nates involved distillation of acetylacetone from a Ln(acac)3
complex in the presence of tetraphenylporphyrin (at 220 °C)
to give lanthanide monoporphyrinate acetylacetonate com-
plexes in 10-30% yields.16 The low yields arise because
the complexes hydrolyze during the required chromato-
graphic purification step. This method also limits the choice
of anionic axial ligand, because of the manner in which the
complexes are produced. The coordinated diketonate can be
replaced in subsequent reactions, but high boiling solvents
are again required and low isolated yields are typical.17
Recently, efforts to form lanthanide tetraphenylporphyrin
(TPP) and other porphyrin complexes have focused on
amine elimination reactions of neutral Ln amides or alkyls
with free base porphyrins,18 or similar reactions between
Li{Ln[N(SiMe3)2]3Cl} and substituted TPPs.19
NdTPP(I)(DME). A round-bottomed flask was charged with
NdI3(THF)4 (0.5 g, 0.615 mmol) and Li2TPP(DME) (0.499 g, 0.696
mmol) in a drybox. After addition of 40 mL of toluene, the flask
was removed from the glovebox, and the purple solution was
refluxed under N2. The progress of the reaction was monitored by
UV-vis, and after 4 h of reflux, the Soret band at 415 nm had
disappeared and was replaced by one at 425 nm indicating complete
metalation of the porphyrin. The solution was filtered via cannula
while still hot. The residue was then extracted with CHCl3 which
was filtered and combined with the toluene solution. The combined
extracts were reduced in volume to ca. 10 mL. This solution was
then layered with pentane. After 12 h, filtration gave a red/purple
solid (0.443 g, 0.455 mmol) in 74% yield. X-ray quality crystals
were grown from a concentrated THF solution layered with pentane.
Anal. Calcd for C48H38N4NdIO2: C, 59.19; H, 3.93; N, 5.75.
We have recently communicated the high-yield synthesis
of a series of lanthanide(III) chloride tetraphenylporphyrinate
(10) (a) de Sa, G. F.; Malta, O. L.; Donega, C. D.; Simas, A. M.; Longo,
R. L.; Santa-Cruz, P. A.; da Silva, E. F. Coord. Chem. ReV. 2000,
196, 165. (b) Veiopoulou, C. J.; Lianidou, E. S.; Ioannou, P. C.;
Efstathiou, C. E. Anal. Chim. Acta 1996, 335, 177. (c) Gao, X. C.;
Cao, H.; Huang, C. H.; Umitani, S.; Chen, G. Q.; Jiang, P. Synth.
Met. 1999, 99, 127.
(11) The Porphyrin Handbook. Volume 3, Inorganic, Organometallic and
Coordination Chemistry; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; Academic Press: San Diego, CA, 2000.
(12) (a) Hiroshi, T.; Satoshi, S. Chem. ReV. 2002, 102, 2389. (b) Wong,
W.-K.; Zhang, L.; Wong, W.-T.; Xue, F.; Mak, T. C. W. J. Chem.
Soc., Dalton Trans. 1999, 615. (c) Spyroulias, G. A.; Despotopoulos,
A.; Raptopoulou, C. P.; Terzis, A.; Coutsoleolos, A. G. Chem.
Commun. 1997, 783. (d) Radzki, S.; Giannotti, C. Inorg. Chim. Acta
1993, 205, 213.
(13) Horrocks, W. D.; Wong, C. P. J. Am. Chem. Soc. 1976, 98, 7157.
(14) (a) Shahbazi-Gahrouei, D.; Williams, M.; Rizvi, S.; Allen, B. J. J.
Magn. Reson. Imag. 2001, 14, 169. (b) Hofmann, B.; Bogdanov, A.;
Marecos, E.; Ebert, W.; Semmler, W.; Weissleder, R. J. Magn. Reson.
Imaging 1999, 9, 336.
(15) (a) Sessler, J. L.; Dow, W. C.; O’Connor, D.; Harriman, A.; Hemmi,
G.; Mody, T. D.; Miller, R. A.; Qing, F.; Springs, S.; Woodburn, K.;
Young, S. W. J. Alloys Compd. 1997, 249, 146. (b) Sessler, J. L.;
Miller, R. A. Biochem. Pharm. 2000, 59, 733. (c) Parise, R. A.; Miles,
D. R.; Egorin, M. J. J. Chromatogr., B 2000, 749, 145. (d) Mody, T.
D.; Sessler, J. L. J. Porphyrins Phthalocyanines 2001, 5, 134.
(16) (a) Wong, C. P.; Venteicher, R.; Horrocks, W. D. J. Am. Chem. Soc.
1974, 96, 7149. (b) Wong, C. P. Inorg. Synth. 1983, 22, 156.
(17) (a) Spyroulias, G. A.; de Montauzon, D.; Maisonat, A.; Poilblanc, R.;
Coutsolelos, A. G. Inorg. Chem. Acta 1998, 276, 182. (b) Spyroulias,
G. A.; Coutsolelos, A. G.; Raptopoulou, C. P.; Terzis, A. Inorg. Chem.
1995, 34, 2476. (c) Jiang, J. Z.; Mak, T. C. W.; Ng, D. K. P. Chem.
Ber. 1996, 129, 933.
1
Found: C, 57.28; H, 3.97; N, 5.52. H NMR in CD2Cl2: δ 8.95
(ν1/2 ) 5.78, 8H, H-pyrrole), δ 8.12 (ν1/2 ) 17.33, 4H, o-C6H5 TPP),
δ 7.56 (ν1/2 ) 19.32, 4H, m-C6H5 TPP), δ 7.31 (ν1/2 ) 5.71, 4H,
p-C6H5 TPP), δ 6.92 (ν1/2 ) 19.49, 4H, m-C6H5 TPP), δ 4.90 (ν1/2
) 18.72, 4H, o-C6H5 TPP), δ -5.42 (ν1/2 ) 217, 5H, H-DME).
(18) (a) Schaverien, C. J.; Orpen, A. G. Inorg. Chem. 1991, 30, 4968. (b)
Schaverien, C. J. Chem. Commun. 1991, 458.
(19) (a) Wong, W. K.; Zhang, L. L.; Wong, W. T.; Xue, F.; Mak, T. C.
W. J. Chem. Soc., Dalton Trans. 1999, 615. (b) Wong, W. K.; Zhang,
L.; Xue, F.; Mak, T. C. W. J. Chem. Soc, Dalton Trans. 1999, 3053.
(20) Foley, T. J.; Abboud, K. A.; Boncella, J. M. Inorg. Chem. 2002, 41,
1704.
(21) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; Wiley: New
York, 1972.
(22) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288.
(23) Klaui, W.; Dehnicke, K. Chem. Ber. 1978, 111, 451.
5024 Inorganic Chemistry, Vol. 42, No. 16, 2003

NIR Luminescent Ln(III) Monoporphyrinates
PrTPP(I)(DME). In the same fashion as NdTPPI(DME),
PrTPPI(DME) was synthesized by refluxing PrI3(THF)4 (0.5 g,
0.617 mmol) and Li2TPP (DME) (0.501 g, 0.699 mmol) in toluene
for 4 h. The purple solid was isolated in 74% yield (0.44 g, 0.451
mmol). Anal. Calcd for C48H38N4PrIO2: C, 59.39; H, 3.95; N, 5.77.
reacting to give 0.255 g of Ho(TPP)Tp (85%). Anal. Calcd for
C53H38BN10Ho: C, 64.26; H, 3.87; N, 14.14. Found: C, 63.75; H,
3.77; N, 13.75. 1H NMR (C6D6, 294 K, ppm ): 40.30 (ν1/2 ) 139.20
Hz, 3H, H-Tp), 8.90 (ν1/2 ) 84.74 Hz, 4H, o-C6H5 TPP), 4.62 (ν1/2
) 40.08 Hz, 4H, m-C6H5 TPP), 3.11 (ν1/2 ) 95.88 Hz, 3H, H-Tp),
2.43 (ν1/2 ) 26.86 Hz, 4H, p-C6H5 TPP), 1.36 (ν1/2 ) 38.59 Hz,
3H, H-Tp), -1.90 (ν1/2 ) 43.16 Hz, 4H, m-C6H5 TPP), -14.98
(ν1/2 ) 113.24 Hz, 8H, H-pyrrole), -19.90 (ν1/2 ) 121.76 Hz, 4H,
o-C6H5 TPP).
1
Found: C, 58.99; H, 3.96; N, 5.84. H NMR in CDCl3: δ 7.73
(ν1/2 ) 16.19, 4H, o-C6H5 Tpp), δ 6.81 (ν1/2 ) 18.68, 4H, m-C6H5
Tpp), δ 6.29 (ν1/2 ) 5.07, 4H, p-C6H5 Tpp), δ 5.53 (ν1/2 ) 5.73,
8H, H-pyrrole), δ 5.33 (ν1/2 ) 18.79, 4H, m-C6H5 TPP), δ 0.78
(ν1/2 ) 17.79, 4H, o-C6H5 TPP).
Nd(TPP)Tp. To a stirred solution of NdTPP(I)(DME) (0.152
g, 0.16 mmol) in DME was added KTp (0.041 g, 0.16 mmol). The
solution was stirred for an additional 12 h at room temperature.
The solvent was then removed in Vacuo, and the residue was
extracted with approximately 30 mL of CH2Cl2, leaving a white,
insoluble solid. The volume of the red/purple solution was then
reduced to 10 mL and layered with pentane. After being cooled to
-10 °C for 12 h, the solution was filtered, leaving a crystalline,
purple solid. The filtrate was then concentrated and cooled to -10
°C affording a second crop of crystals. Recrystallization of the
combined solids from CH2Cl2/pentane gave X-ray quality crystals
of Nd(TPP)Tp in 64% yield (0.093 g, 0.0962 mmol). Anal. Calcd
Yb(TPP)Tp. A solution of YbTPP(Cl)(DME) (0.300 g, 3.29 ×
10-1 mmol) in DME (ca. 65 mL) was stirred vigorously while
potassium hydridotris(1-pyrazolyl)borate (KTp) (0.084 g, 3.33 ×
10-1 mmol) was added. Following addition, the solution was
allowed to stir at room temperature for 12 h. The solvent was then
removed in Vacuo, and the purple residue was extracted with ca.
30 mL of methylene chloride, leaving behind a brown residue. The
solution was then filtered, reduced to ca. 10 mL, and layered with
ca. 30 mL of pentane. Purple crystals formed on standing overnight.
The supernatant was filtered, concentrated, and cooled to -78 °C
whereupon an additional amount of product precipitated. The
isolated solids were then combined, dissolved in ca. 20 mL of
methylene chloride, and cooled to -78 °C. Crystals then formed,
which were isolated by cannula filtration giving 0.265 g of product
(88%). Single crystals of X-ray diffraction quality were grown by
slow evaporation of a benzene solution of Yb(TPP)Tp in an inert
atmosphere. Anal. Calcd for C53H38BN10Yb: C, 63.73; H, 3.83;
for C53H38BN10Nd: C, 65.27; H, 3.95; N, 14.44. Found: C, 65.67;
1
H, 3.96; N, 14.33. H NMR (C6D6, 294 K, ppm): 14.65 (ν1/2
)
5.61 Hz, 3H, H-Tp), 7.97 (ν1/2 ) 15.05 Hz, 4H, o-C6H5 TPP), 7.82
(ν1/2 ) 4.25 Hz, 8H, H-pyrrole), 6.93 (ν1/2 ) 5.08 Hz, 7H, m-C6H5
TPP, H-Tp), 6.47 (ν1/2 ) 3.25 Hz, 4H, p-C6H5 TPP), 5.75 (ν1/2
)
16.88 Hz, 4H, m-C6H5 TPP), 2.88 (ν1/2 ) 15.66 Hz, 4H, o-C6H5
TPP), -6.23 (ν1/2 ) 22.41 Hz, 3H, H-Tp).
1
N, 14.02. Found: C, 64.23; H, 3.91; N, 13.89. H NMR (C6D6,
294 K, ppm): 22.71 (ν1/2 ) 53.24 Hz, 3H, H-Tp), 15.48 (ν1/2
)
Pr(TPP)Tp. Following the procedure used to generate Nd(TPP)-
Tp, PrTPP(I)(DME) (0.160 g, 0.155 mmol) and KTp(0.041 g, 0.16
mmol) were combined together in dry DME and allowed to react
for 12 h. After recrystallization, 0.073 g of Pr(TPP)Tp was collected
(0.076 mmol, 49%). Anal. Calcd for C53H38BN10Pr: C, 65.85; H,
3.96; N, 14.49. Found: C, 66.30; H, 3.91; N, 14.23. 1H NMR (C6D6,
294 K, ppm): 18.08 (ν1/2 ) 4.89 Hz, 3H, H-Tp), 8.13 (ν1/2 ) 14.81
Hz, 4H, o-C6H5 TPP), 6.63 (ν1/2 ) 5.09 Hz, 7H, m-C6H5 TPP,
H-Tp), 5.90 (ν1/2 ) 3.97 Hz, 4H, p-C6H5 TPP), 5.36 (ν1/2 ) 3.69
Hz, 8H, H-pyrrole), 4.64 (ν1/2 ) 17.51 Hz, 4H, m-C6H5 TPP), -0.47
(ν1/2 ) 14.09 Hz, 4H, o-C6H5 TPP), -13.87 (ν1/2 ) 11.23 Hz, 3H,
H-Tp).
40.81 Hz, 4H, o-C6H5 TPP), 13.88 (ν1/2 ) 25.90, 8H, H-pyrrole),
9.73 (ν1/2 ) 39.55 Hz, 4H, m-C6H5 TPP), 8.77 (ν1/2 ) 26.74, 4H,
p-C6H5 TPP), 8.09 (ν1/2 ) 43.17 Hz, 4H, m-C6H5 TPP), 7.83 (ν1/2
) 44.39 Hz, 4H, o-C6H5 TPP), 4.62 (ν1/2 ) 23.34 Hz, 3H, H-Tp),
-3.03 (ν1/2 ) 23.81 Hz, 3H, H-Tp).
Tm(TPP)Tp. The procedure used to generate this complex was
the same as that used for Yb(TPP)Tp with TmTPP(Cl)(DME)
(0.300 g, 3.33 × 10-1 mmol) and KTp (0.084 g, 3.33 × 10-1 mmol)
reacting to give 0.244 g of Tm(TPP)Tp (81%). X-ray diffraction
quality single crystals of Tm(TPP)Tp were obtained by slow
evaporation of a chloroform solution under an inert atmosphere.
Anal. Calcd for C53H38BN10Tm: C, 64.00; H, 3.85; N, 14.08.
Found: C, 64.52; H, 3.83; N, 14.11. 1H NMR (C6D6, 294 K,
ppm): 122.96 (113.08 Hz, 3H, H-Tp), 55.33 (58.73 Hz, 4H, o-C6H5
TPP), 38.92 (ν1/2 ) 38.16 Hz, 8H, H-pyrrole), 22.81 (ν1/2 ) 31.80
Hz, 4H, m-C6H5 TPP), 16.11 (ν1/2 ) 22.84 Hz, 4H, p-C6H5 TPP),
11.97 (ν1/2 ) 30.49 Hz, 4H, m-C6H5 TPP), 7.28 (ν1/2 ) 79.37 Hz,
3H, H-Tp), 3.72 (ν1/2 ) 25.72 Hz, 3H, H-Tp), -55.91 (ν1/2 ) 30.92
Hz, 4H, o-C6H5 TPP).
Er(TPP)Tp. The procedure used to generate this complex was
the same as that used for Yb(TPP)Tp with ErTPP(Cl)(DME) (0.300
g, 3.33 × 10-1 mmol) and KTp (0.084 g, 3.33 × 10-1 mmol)
reacting to give 0.271 g of Er(TPP)Tp (90%). Anal. Calcd for
C53H38BN10Er: C, 64.10; H, 3.86; N, 14.11. Found: C, 63.85; H,
3.12; N, 14.69. 1H NMR (C6D6, 294 K, ppm): 61.76 (ν1/2 ) 493.43
Hz, 3H, H-Tp), 32.13 (ν1/2 ) 94.73 Hz, 4H, o-C6H5 TPP), 20.90
(ν1/2 ) 72.68 Hz, 8H, H-pyrrole), 15.14 (ν1/2 ) 30.38 Hz, 4H,
m-C6H5 TPP), 11.84 (ν1/2 ) 18.77 Hz, 4H, p-C6H5 TPP), 9.63 (ν1/2
) 28.32 Hz, 4H, m-C6H5 TPP), 7.66 (ν1/2 ) 55.83 Hz, 4H, o-C6H5
TPP), 2.82 (ν1/2 ) 48.22 Hz, 3H, H-Tp), -24.79 (ν1/2 ) 59.67 Hz,
3H, H-Tp).
Yb(TPP)(L(OEt)). A solution of YbTPP(Cl)(DME) (0.150 g,
1.65 × 10-1 mmol) in DME (ca.50 mL) was stirred vigorously
while solid sodium (cyclopentadienyl)tris(diethylphosphinito)-
cobaltate(I) (NaL(OEt)) (0.088 g, 1.57 × 10-1 mmol) was added.
The solution was then stirred at room temperature for 12 h, after
which time the DME was removed in vacuo leaving a purple,
amorphous solid. The solid was extracted twice with ca. 15 mL of
toluene, leaving behind a slight amount of brown residue. The two
extracts were filtered, combined, and reduced to ca. 10 mL to which
was added ca. 30 mL of pentane producing a small amount of brown
precipitate. The solution was filtered to remove the precipitate and
then cooled to -78 °C. Purple crystals of the product formed on
standing for 5 h and were isolated via cannula filtration. Residual
solvents were removed from the crystals in vacuo, giving 0.200 g
of product (96%). Anal. Calcd for C61H65CoN4O9P3Yb: C, 55.46;
1
H, 4.91; N, 4.20. Found: C, 55.40; H, 4.95; N, 4.23. H NMR
(C6D6, 294 K, ppm): 17.41 (ν1/2 ) 18.27 Hz, 4H, o-C6H5 TPP),
15.81 (ν1/2 ) 8.22, 8H, H-pyrrole), 10.68 (ν1/2 ) 8.03 Hz, 4H,
m-C6H5 TPP), 9.40 (ν1/2 ) 4.43 Hz, 7 Hz, 4H, p-C6H5 TPP), 8.91
(ν1/2 ) 17.09 Hz, 6H, OCH2CH3), 8.63 (ν1/2 ) 18.20 Hz, 4H,
Ho(TPP)Tp. The procedure used to generate this complex was
the same as that used for Yb(TPP)Tp with HoTPP(Cl)(DME) (0.300
g, 3.32 × 10-1 mmol) and KTp (0.084 g, 3.33 × 10-1 mmol)
o-C6H5 TPP), 8.45 (ν1/2 ) 28.34 Hz, 4H, m-C6H5 TPP), 7.67 (ν1/2)
29.31 Hz, 6H, OCH2CH3), 3.05 (ν1/2 ) 10.45 Hz, 18H, OCH2CH3),
-4.67(ν1/2 ) 4.10 Hz, 5H, CpH).
Inorganic Chemistry, Vol. 42, No. 16, 2003 5025

Foley et al.
Tm(TPP)(L(OEt)). The synthetic procedure used was the same
as that used for Yb(TPP)L(OEt) with TmTPP(Cl)(DME) (0.150 g,
1.65 × 10-4 mol) reacting with Na(L(OEt)) (0.088 g, 1.57 × 10-1
mmol) to give 0.133 g of Tm(TPP)(L(OEt)) (64%). Anal. Calcd
for C61H65CoN4O9P3Tm: C, 55.63; H, 4.82; N, 4.25. Found: C,
51.92; H, 5.45; N, 3.37. 1H NMR (C6D6, 294 K, ppm): 67.59 (ν1/2
) 49.68 Hz, 4H, o-C6H5 TPP), 52.41 (ν1/2 ) 34.64 Hz, 8H,
Hz, 4H, p-C6H5 TPP), 3.96 (ν1/2 ) 26.20 Hz, 4H, m-C6H5 TPP),
3.04 (ν1/2 ) 2.47 Hz, 8H, H-pyrrole), -2.16 (ν1/2 ) 13.98 Hz, 18H,
-OCH2CH3), -2.39 (ν1/2 ) 30.25 Hz, 6H, -OCH2CH3), -2.59
(ν1/2 ) 27.79 Hz, 6H, -OCH2CH3), -3.02 (ν1/2 ) 25.20 Hz, 4H,
o-C6H5 TPP).
X-ray Crystallographic Measurements. Data were collected
at 173 K on a Siemens SMART PLATFORM equipped with a CCD
area detector and a graphite monochromator utilizing Mo KR
radiation (λ ) 0.71073 Å). Cell parameters were refined using up
to 8192 reflections. A full sphere of data (1850 frames) was
collected using the ω-scan method (0.3° frame width). The first 50
frames were remeasured at the end of data collection to monitor
instrument and crystal stability (maximum correction on I was
<1%). Absorption corrections by integration were applied on the
basis of measured indexed crystal faces. All structures were solved
by direct methods in SHELXTL524 and refined using full-matrix
least-squares. The non-H atoms were treated anisotropically,
whereas the hydrogen atoms were calculated in ideal positions and
were riding on their respective carbon atoms, except the boron H
atom which was obtained from a difference Fourier map and refined
freely.
For the structure of Nd(TPP)I(THF)2, the asymmetric unit
consists of the complex and a disordered THF molecule. The THF
molecule could not be modeled properly; thus, program SQUEEZE,
a part of the PLATON package of crystallographic software, was
used to calculate the solvent disorder area and remove its contribu-
tion to the overall intensity data. The complex has its iodine and
two THF ligands disordered about a 2-fold rotation axis perpen-
dicular to the plane of the macrocycle, but only the iodine atom of
the minor part could be seen due to its small site occupation factor
(refined to 5% then fixed in the final cycles of refinement). A total
of 548 parameters were refined in the final cycle of refinement
using 21110 reflections with I > 2σ(I) to yield R1 and wR2 values
of 4.06% and 10.31%, respectively. Refinement was done using
F2.
For the structure of Yb(TPP)Tp, the asymmetric unit consists of
the complex and four benzene molecules. Two of the solvent
molecules were disordered in their respective planes, and each was
refined in two parts. The site occupation factors of the minor and
major parts in each disordered molecule were dependently refined
to 0.54(2) and 0.53(1) for the C80 and the C90 benzene molecules
major parts, respectively. The disordered molecules were restrained
to maintain equivalent geometries throughout the refinement, and
their C atoms were refined with isotropic thermal parameters. A
total of 797 parameters were refined in the final cycle of refinement
using 12598 reflections with I > 2σ(I) to yield R1 and wR2 values
of 2.69% and 6.50%, respectively. Refinement was done using F2.
For the structure of Tm(TPP)Tp, the asymmetric unit consists
of the Tm complex and two chloroform molecules of crystallization.
A total of 663 parameters were refined in the final cycle of
refinement using 10920 reflections with I > 2σ(I) to yield R1 and
wR2 values of 3.40% and 7.28%, respectively. Refinement was
done using F2.
H-pyrrole), 40.92 (ν1/2 ) 70.14 Hz, 6H, OCH2CH3), 35.49 (ν1/2
)
74.76 Hz, 6H, OCH2CH3), 27.22 (ν1/2 ) 21.01 Hz, 4H, m-C6H5
TPP), 18.95 (ν1/2 ) 19.63 Hz, 4H, p-C6H5 TPP), 14.72 (ν1/2 ) 21.20
Hz, 5H, CpH), 14.52 (ν1/2 ) 14.77 Hz, 18H, OCH2CH3), 11.58
(ν1/2 ) 23.59 Hz, 4H, m-C6H5 TPP), -55.78 (ν1/2 ) 14.47 Hz, 4H,
o-C6H5 TPP).
Er(TPP)(L(OEt)). The synthetic procedure was the same as that
used for Yb(TPP)(L(OEt)) with ErTPP(Cl)(DME) (0.150 g, 1.65
× 10-1 mmol) reacting with Na(L(OEt)) (0.088 g, 1.57 × 10-1
mmol) to give 0.155 g of Er(TPP)(L(OEt)) (75%). Anal. Calcd for
C61H65CoN4O9P3Er: C, 55.71; H, 4.83; N, 4.26. Found: C, 56.04;
1
H, 4.84; N, 4.08. H NMR (C6D6, 294 K, ppm): 46.29 (ν1/2
)
82.29 Hz, 4H, o-C6H5 TPP), 34.74 (ν1/2 ) 77.14 Hz, 8H, H-pyrrole),
27.39 (ν1/2 ) 170.34 Hz, 6H, OCH2CH3), 23.10 (ν1/2 ) 185.68
Hz, 6H, OCH2CH3), 20.08 (ν1/2 ) 22.69 Hz, 4H, m-C6H5 TPP),
14.73 (ν1/2 ) 16.91 Hz, 4H, p-C6H5 TPP), 11.92 (ν1/2 ) 20.65 Hz,
4H, m-C6H5 TPP), 10.23 (ν1/2 ) 52.65 Hz, 5H, CpH), 9.71 (ν1/2
)
32.28 Hz, 18H, OCH2CH3), -34.72 (ν1/2 ) 21.95 Hz, 4H, o-C6H5
TPP).
Ho(TPP)(L(OEt)). The synthetic procedure was the same as that
used for Yb(TPP)(L(OEt)), substituting HoTPP(Cl)(DME) (0.150
g, 1.66 × 10-1 mmol) and allowing it to react with Na(L(OEt))
(0.088 g, 1.57 × 10-1 mmol) to give 0.146 g of Ho(TPP)(L(OEt))
(71%). Anal. Calcd for C61H65CoN4O9P3Ho: C, 55.80; H, 4.84;
1
N, 4.26. Found: C, 55.67; H, 4.46; N, 4.65. H NMR (C6D6, 294
K, ppm): 40.39 (ν1/2 ) 65.17 Hz, 4H, o-C6H5 TPP), 6.77 (ν1/2
)
90.51 Hz, 5H, CpH), 3.10 (ν1/2 ) 28.32 Hz, 4H, m-C6H5 TPP),
0.61 (ν1/2 ) 16.20 Hz, 4H, p-C6H5 TPP), -4.63 (ν1/2 ) 29.23 Hz,
4H, m-C6H5 TPP), -7.98 (ν1/2 ) 60.87 Hz, 18H, OCH2CH3),
-17.77 (ν1/2 ) 478.58 Hz, 12 H, OCH2CH3), -20.81 (ν1/2 ) 125.81
Hz, 8H, H-pyrrole), -28.52 (ν1/2 ) 138.57 Hz, 4H, o-C6H5 TPP).
Nd(TPP)(L(OEt)). To a stirred solution of NdTPP(I)(DME)
(0.125 g, 0.128 mmol) in THF was added 0.075 g of K(L(OEt))
(0.125 mmol). The purple solution was stirred for 12 h at room
temperature. The solvent was then removed in vacuo, and the
product was extracted with 30 mL of toluene which was filtered,
concentrated to ca. 10 mL, and layered with pentane. After cooling
to -78 °C for 24 h, the purple precipitate was isolated by filtration
and recrystallized from CH2Cl2/pentane. The crystals were washed
with pentane to give 30% (0.05 g, 0.039 mmol). Anal. Calcd for
C61H63CoN4O9P3Nd: C, 56.70; N, 4.34; H, 4.91. Found: C, 55.13;
1
N, 3.81; H, 4.81. H NMR (C6D6, 294 K, ppm): 10.13 (ν1/2
)
3.28 Hz, 5H, H-Cp), 7.98 (ν1/2 ) 19.35 Hz, 4H, o-C6H5 TPP), 6.80
(ν1/2 ) 20.88 Hz, 4H, m-C6H5 TPP), 6.53 (ν1/2 ) 4.32 Hz, 8H,
H-pyrrole), 6.35 (ν1/2 ) 3.22 Hz, 4H, p-C6H5 TPP), 5.61 (ν1/2
20.32 Hz, 4H, m-C6H5 TPP), 2.02 (ν1/2 ) 20.63 Hz, 4H, o-C6H5
)
For the structure of Nd(TPP)Tp, the asymmetric unit consists of
two complexes and a pentane molecule disordered over a center of
inversion site. The disorder is resolved where only the methyl
groups are disordered. A total of 1208 parameters were refined
in the final cycle of refinement using 12451 reflections with I >
2σ(I) to yield R1 and wR2 of 3.69% and 6.42%, respectively.
Refinement was done using F2.
TPP), -0.26 (ν1/2 ) 47.23 Hz, 12H, -OCH2CH3), -0.83 (ν1/2
11.27, 18H, OCH2CH3).
)
Pr(TPP)(L(OEt)). The procedure developed for the synthesis
of Nd(TPP)(L(OEt)) was used to prepare Pr(TPP)(L(OEt)), from
PrTPP(I)(DME) (0.2 g, 0.206 mmol) and K(L(OEt)) (0.121 g, 0.206
mmol) giving 0.08 g of the complex (30%, 0.062 mmol). Anal.
Calcd for C61H53CoN4O9P3Pr: C, 56.84; N, 4.35; H, 4.93. Found:
Nuclear Magnetic Resonance Spectroscopy. Spectra were
recorded in 5 mm Kontes resealable NMR tubes. Proton NMR
1
C, 55.73; N, 3.84; H, 4.96. H NMR (C6D6, 294 K, ppm): 14.92
(ν1/2 ) 1.79 Hz, 5H, H-Cp), 7.96 (ν1/2 ) 23.50 Hz, 4H, o-C6H5
TPP), 6.28 (ν1/2 ) 26.26 Hz, 4H, m-C6H5 TPP), 5.45 (ν1/2 ) 3.21
(24) Sheldrick, G. M. SHELXTL5; Bruker-AXS: Madison, WI, 1998.
5026 Inorganic Chemistry, Vol. 42, No. 16, 2003

NIR Luminescent Ln(III) Monoporphyrinates
Scheme 1
spectra were measured at 300 MHz on a Varian Gemini 300, VXR
300, or Mercury 300 with C6D6 as the solvent unless otherwise
noted. Chemical shifts in the spectra were referenced to the residual
protons on the deuterated solvent and are reported in parts per
million downfield from tetramethylsilane (δ ) 0). For paramagnetic
complexes, the acquisition times were varied according to the
relaxation rate enhancement provided by the lanthanide, and the
spectral window width was determined by expanding the window
of the spectrum until the peak positions remained invariant to further
expansions. The number of transients collected for an individual
spectrum varied with the nature of the metal, with the minimum
being determined by the noise in the particular spectrum. COSY
spectra were collected using the standard parameters that ac-
companied the Varian operating software.
Photophysical Measurements. All photophysical studies were
conducted in 1 cm2 quartz cuvettes unless otherwise noted. All
absorption, emission, and lifetime measurements were made in
CH2Cl2 unless otherwise noted. Absorption spectra were obtained
on a double-beam Cary-100 UV-vis spectrometer. Fluorescence
spectra were measured on a SPEX Fluorolog-2 equipped with a
thermoelectric-cooled PMT detector or on a spectrometer consisting
of an ISA-SPEX Triax 180 spectrograph equipped with a liquid
N2 cooled CCD detector (Hamamatsu CCD, 1024 × 64 pixel, 400-
1100 nm). Near-IR measurements were measured on a SPEX
Fluorolog-2 equipped with a liquid N2 cooled InGaAs detector
(800-1600 nm). All measurements were corrected for detector
response. Emission quantum yields were measured by relative
actinometry with H2TPP (φ ) 0.11) or ZnTPP (φ ) 0.033). Near-
IR quantum yields were determined for Yb(TPP)Tp and Yb(TPP)-
(L(OEt)) on the CCD fluorescence system using the visible H2TPP
and ZnTPP actinometers. Then, the emission quantum yields for
the Nd and Er complexes were determined relative to Yb(TPP)Tp
using the SPEX Fluorolog-2 with the InGaAs detector.
tion,25 with the third harmonic of a Nd:YAG laser (355 nm, 10 ns
fwhm, 5 mJ pulse-1) as the excitation source. Samples were
thoroughly degassed with argon. Primary factor analysis followed
by first order (A f B) least-squares fits of the transient absorption
data was accomplished with SPECFIT global analysis software
(Spectrum Software Associates).
Results and Discussion
Synthesis and Structural Characterization. The syn-
thesis of the Ln(TPP)Tp and Ln(TPP)(L(OEt)) complexes
involved reaction of LnTPP(X)(DME) with the Tp or
(L(OEt)) anions under anhydrous, oxygen-free conditions as
summarized in Scheme 1. We believed that, by replacement
of the halide and DME ligands with a multidentate, monoan-
ionic ligand, the increased steric bulk around the lanthanide
complex would minimize interactions between the metal and
quenching agents and thereby enhance the photolumines-
cence yields in the NIR. This synthesis is somewhat different
from that of other Ln porphyrins found in the literature
because the complexes are always handled under inert
atmosphere and the procedure avoids the use of column
chromatography for purification. The use of recrystallization
facilitates the preparation of large quantities of these
complexes, and the reactions have been performed success-
fully on a 1-g scale with no loss in yield or purity. While
column chromatography is useful for the purification of
LnTPP complexes, the hydrolytic instability of the Ln-N
bonds leads to decomposition on the column giving dramati-
cally reduced isolated yields.
These complexes are stable in air in the solid state over
the course of several days, but we have observed that
demetalation of the porphyrin ligands becomes noticeable
over an extended period of time. Thus, the NIR photolumi-
nescence intensity decreases and the visible fluorescence
from free porphyrin impurities increases when the samples
are stored in air for several weeks, while samples which are
stored under an inert atmosphere have consistent NIR
emission intensities and weak or unobservable free porphyrin
emission. The degradation of these compounds over time is
Time-resolved emission decays were obtained by time-correlated
single photon counting on an instrument that was constructed in-
house. Excitation was effected by using either a pulsed LED source
or a blue-pulsed diode laser (IBH instruments, Edinburgh, Scotland).
The pulsed LED and diode laser sources have pulse widths of ca.
1 ns. Time-resolved emission was collected using a red sensitive,
photon-counting PMT (Hamamatsu R928), and the light was filtered
using 10 nm band-pass interference filters. Lifetimes were deter-
mined from the observed decays by using fluorescence lifetime
deconvolution software. Nanosecond transient absorption spectra
measurements were obtained on previously described instrumenta-
(25) Wang, Y. S.; Schanze, K. S. Chem. Phys. 1993, 176, 305.
Inorganic Chemistry, Vol. 42, No. 16, 2003 5027

Foley et al.
Table 1. Crystal Data for Complexes
Nd(TPP)(I)(THF)2 Yb(TPP)Tp Tm(TPP)Tp Nd(TPP)Tp
empirical
formula
fw
C
56H52IN4NdO3
C
77H62BN10Yb C55H40BCl6- C108.50H82B2-
10Tm 20Nd2
N
N
1100.16
193(2)
1309.81
193(2)
1233.41
193(2)
1976.04
193(2)
T/K
wavelength/Å 0.71073
0.71073
triclinic
P1h
0.71073
monoclinic triclinic
P21/n P1h
18.4931(8) 12.6145(5)
14.6041(6) 13.7314(6)
19.4154(9) 27.843(2)
90
98.808(2)
90
5181.8(4)
4
0.71073
cryst syst
space group
a/Å
triclinic
P1h
12.4470(11)
14.5765(13)
14.6837(13)
69.585(2)
74.880(2)
89.225(2)
2401.5(4)
2
11.9673(5)
14.0070(6)
20.7721(8)
98.846(2)
100.017(2)
106.862(2)
3203.5(2)
2
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
84.067(2)
78.022(2)
74.461(2)
4539.5(3)
2
Z
D(calcd)
1.521
1.359
1.581
1.446
Mg/m3
Table 2. Selected Structural Data for Ln(TPP) Complexesa
M-Nporph
M-NTp
b
c
Figure 1. Thermal ellipsoid plot of the molecular structure of Nd(TPP)-
(I)(THF)2showing selected atom labels. All thermal ellipsoids are drawn at
the 50% probability level; all hydrogen atoms and solvent atoms in the
crystal structure have been omitted for clarity.
(av)
(av)
M-N4plane
M-N3plane
Yb(TPP)(Tp)
Tm(TPP)(Tp)
Nd(TPP)(Tp)
Nd(TPP)I(THF)2
2.348(5)
2.514(9)
2.501(2)
2.602(8)
1.156(3)
1.187(1)
1.302(4)
1.286(6)
1.796(6)
1.782(8)
1.891(7)
2.364(11)
2.438(17)
2.436(16)
a All measurements in ångstroms. b Distance from the metal atom to the
least squares plane defined by the four TPP N atoms. c Distance from the
metal atom to the plane defined by the three coordinated Tp N atoms.
prism being composed of three of the porphyrin N atoms
and the three ligating atoms of the remaining ligands, with
the final porphyrin N atom comprising the capping group.
As shown in Table 2, the metal-ligand distances vary
according to the size of the metal ions with Yb and Tm
having essentially the same ionic radii while Nd is ca. 0.1
Å larger. Because the metal ions do not fit into the cavity of
the porphyrin, the porphryin ring adopts a domed conforma-
tion to maximize the Ln-N interactions. The structures of
the Ln(TPP)Tp complexes confirm the notion that the Tp
ligand provides a sterically congested environment around
the metal center that should mimimize interactions between
the metal and solvent that could reduce the quantum yields
for luminescence.
Figure 2. Thermal ellipsoid plot of the molecular structure of Tm(TPP)-
Tp showing selected atom labels. All thermal ellipsoids are drawn at the
50% probability level; all hydrogens and two molecules of chloroform have
been excluded for clarity. Nonlabeled atoms are carbon.
NMR Spectroscopy. A combination of 1-D and 2-D
proton NMR techniques were used to characterize the
complexes in solution. In all cases, the spectra are consistent
with mononuclear structures that have the metal ion sand-
wiched between the porphyrin ligand and the capping Tp or
L(OEt) ligands, as is observed in the solid state. Uncertainty
about the magnitude of the contact and pseudocontact shift
in new paramagnetic complexes inhibits the a priori assign-
ment of their NMR spectra, but by utilizing the relative
integration of the peaks in the one-dimensional proton
spectrum coupled with simple two-dimensional experiments,
the spectrum can be assigned to the correct protons in the
structure.27 While this provides limited predictive power, it
affords the researcher a tool for the rapid analysis of the
purity of a previously characterized material, and the ability
to determine if a new material has the expected structure.
consistent with the slow hydrolysis of the Ln-NTPP bonds
under ambient conditions.26 Therefore, to maximize the shelf
life of these compounds, it is necessary that they be stored
in an anhydrous, oxygen free environment.
X-ray Crystallography. Single crystals of Nd(TPP)(I)-
(THF)2, Yb(TPP)(Tp), Tm(TPP)(Tp), and Nd(TPP)(Tp) were
obtained as described in the Experimental Section. Thermal
ellipsoid plots of Nd(TPP)(I)(THF)2 and Tm(TPP)(Tp) are
shown in Figures 1 and 2 while the crystal data and data
collection parameters for all four complexes are found in
Table 1. Solvent(s) of crystallization have been omitted from
Figures 1 and 2 for clarity. In general, all the structures share
the common feature that the metal ions are too large to fit
in the cavity of the porphyrin ring and sit above the plane
defined by the four N atoms of the porphyrin with the
remaining ligands completing the coordination sphere of the
metal. The coordination geometry of the metal centers is best
described as distorted capped trigonal prisms with the trigonal
(27) (a) Luchinat, C. Coord. Chem. ReV. 1996, 150, 185. (b) Bertini, I.;
Coutsolelos, A.; Dikiy, A.; Spyroulias, G. A.; Troganis, A. Inorg.
Chem. 1996, 35, 6308. (c) Spyroulias, G. A.; Coutsolelos, A. G. Inorg.
Chem. 1996, 35, 1382.
(26) Haye, S.; Hambright, P. Chem. Commun. 1988, 666.
5028 Inorganic Chemistry, Vol. 42, No. 16, 2003

NIR Luminescent Ln(III) Monoporphyrinates
Figure 3. One-dimensional proton NMR spectrum of Pr(TPP)Tp in C6D6. The structure with the positions labeled corresponding to the spectrum is presented
in the figure.
The one-dimensional proton NMR spectrum of Pr(TPP)-
Tp is shown in Figure 3. Assuming the rotation of the phenyl
rings on the porphyrin is slow on the NMR time scale,28
there should be nine proton resonances. Of these nine peaks,
five correspond to the protons from the phenyl rings and
have an integration of four protons each, three correspond
to the Tp protons and have an integration of three protons
each, and the ninth peak corresponds to the pyrrole protons
and has an integration of eight (the B-H proton is rarely
observed even in diamagnetic complexes due to quadrapolar
relaxation caused by boron). The spectrum of Pr(TPP)Tp,
however, only shows eight peaks with integration ratios of
3:4:7:4:8:4:4:3 (peaks A-H, Figure 3). Variable temperature
NMR studies ranging from 40° to 60 °C show that peak C
is composed of two overlapping peaks, Ca and Cb, with
relative integrations of four and three protons, respectively.
Using the integrations, peaks A, Cb, and H are assigned as
Tp protons while peaks B, Ca, D, F, and G are assigned to
the protons on the phenyl ring and peak E is assigned to the
protons on the pyrrole.
In the COSY spectrum of Pr(TPP)Tp (see Supporting
Information), there are cross-peaks between A and Cb, and
Cb and H, demonstrating that, as expected, those peaks are
in the same spin system, consistent with their assignment as
Tp ligand protons. Cross-peaks between peaks B and Ca,
Ca and D, D and F, and F and G confirm their assignment
as phenyl ring protons with peaks B and G being the ortho
protons, peaks Ca and F being the meta protons, and peak
D being the para proton. Similar experiments on the other
new compounds were used to generate the peak assignments
that are reported in the Experimental Section of the paper.
Photophysical Properties. Our interest in Ln porphyrin
complexes is focused on their application as near-IR emitters
in organic light emitting diodes. Each of the lanthanides used
in the course of the present synthetic investigation is known
to exhibit one or more spectrally narrow emission bands in
the 800-1600 nm region in the near-IR. Indeed, we and
others have already reported near-IR electroluminescence
from devices that contain Yb, Nd, and Er.2 Thus, to provide
a clear understanding of the photophysics and luminescence
properties of the new series of Ln porphyrins, each of the
complexes was characterized by absorption and room tem-
perature photoluminescence spectroscopy in CH2Cl2 solution.
In addition, nanosecond time-resolved absorption spectros-
copy was carried out on selected complexes in an effort to
characterize the nature of the luminescent excited states.
A number of groups have previously characterized the
photophysics of Ln porphyrin complexes.29-34 However, in
most cases, due to synthetic limitations, studies of a specific
porphyrin ring system were limited to only a few lanthanides
and/or capping ligands. Nonetheless, the previous work has
revealed a number of important photophysical properties that
are characteristic of Ln porphyrins. First, Ln porphyrins
display absorption spectra that are typical for “regular
metalloporphyrins” (this terminology is derived from Gou-
terman’s original review of the field).35 Specifically, they
feature an intense B (Soret) band near 425 nm due to the
allowed S0 f S2 transition, and two weaker Q-bands (Q(1,0)
and Q(0,0)) in the 550-600 nm region arising from the
orbitally forbidden S0 f S1 transition.29,35 Porphyrin com-
plexes that contain Yb3+, Er3+, Nd3+, Ho3+, Pr3+, and Tm3+
typically display only weak fluorescence and/or phospho-
rescence in the visible region. This is because the Ln ions
introduce a manifold of low-lying f-states which rapidly
(29) Gouterman, M.; Schumaker, C. D.; Srivastava, T. S.; Yonetani, T.
Chem. Phys. Lett. 1976, 40, 456.
(30) (a) Solovev, K. N.; Tsvirko, M. P.; Kachura, T. F. Opt. Spectrosc.
1976, 40, 391. (b) Pyatosin, V. E.; Tsvirko, M. P.; Solovev, K. N.;
Kachura, T. F. Zh. Prikl. Spektrosk. 1981, 35, 268; J. Appl. Spectrosc.
(Engl. Transl.) 1982, 879. (c) Shushkevich, I. K.; Dvornikov, S. S.;
Kachura, T. F.; Solovev, K. N. Zh. Prikl. Spektrosk. 1981, 35, 647; J.
Appl. Spectrosc. (Engl. Transl.) 1982, 1109. (d) Tsvirko, M. P.;
Solovev, K. N.; Stelmakh, G. F.; Pyatosin, V. E.; Kachura, T. F. Opt.
Spectrosc. 1981, 50, 300. (e) Pyatosin, V. E.; Tsvirko, M. P.; Solovev,
K. N.; Kachura, T. F. Opt. Spectrosc. 1982, 52, 162. (f) Tsvirko, M.
P.; Stelmakh, G. F.; Pyatosin, V. E.; Solovev, K. N.; Kachura, T. F.;
Piskarskas, A. S.; Gadonas, R. A. Chem. Phys. 1986, 106, 467.
(31) Kaizu, Y.; Asano, M.; Kobayashi, H. J. Phys. Chem. 1986, 90, 3906.
(32) Korovin, Y.; Rusakova, N. ReV. Inorg. Chem. 2001, 21, 299.
(33) (a) Meng, J. X.; Li, K. F.; Yuan, J.; Zhang, L. L.; Wong, W. K.;
Cheah, K. W. Chem. Phys. Lett. 2000, 332, 313. (b) Wong, W.-K.;
Hou, A.; Guo, J.; He, H.; Zhang, L.; Wong, W.-Y.; Li, K.-F.; Cheah,
K.-W.; Xue, F.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 2001,
3092.
(34) Asano-Someda, M.; Kaizu, Y. J. Photochem. Photobiol., A 2001, 139,
161.
(28) Slow rotation of the phenyl rings on the NMR time scale is expected
because it has been previously reported in ref 16.
(35) Gouterman, M. In The Porphyrins, Vol. III; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. III, pp 1-165.
Inorganic Chemistry, Vol. 42, No. 16, 2003 5029

Foley et al.
Table 3. Absorption and Emission Spectral Properties for Ln(TPP)Tp Complexes in CH2Cl2
absorption λmax/nm (log ꢀ)
emission
Ln
B(1,0)
B(0,0)
Q(1,0)
Q(0,0)
vis λem
NIR λem
NIR φem
Ho3+
Pr3+
402(4.55)
402(4.87)
402(4.65)
402(4.67)
423(5.69)
425(5.71)
423(5.80)
424(5.74)
552(4.27)
554(4.31)
551(4.43)
553(4.32)
590(3.61)
593(3.86)
588(3.70)
592(3.76)
649, 715
652, 717
652, 718
651, 717
Tm3+
Nd3+
882, 900, 932, 1069,
1111, 1324, 1354
1485, 1531a
932, 954, 977, 990, 1002,
1014, 1022, 1037
0.0024
Er3+
402(4.68),
402(4.85)
422(5.60)
421(5.72)
551(4.21)
551(4.41)
590(3.63)
588(3.77)
653, 717
652, 718
0.0009
0.032
Yb3+
a Reported λem may be blue-shifted slightly from true λem due to falloff in InGaAs detector response for λ > 1550 nm.
Table 4. Absorption and Emission Spectral Properties for Ln(TPP)(L(OEt)) Complexes in CH2Cl2
absorption λmax/nm (log ꢀ)
emission
NIR λem
Ln
B(1,0)
B(0,0)
Q(1,0)
Q(0,0)
vis λem
NIR φem
Ho3+
Pr3+
405(4.63)
409(4.78)
405(4.62)
409(4.69)
427(5.72)
428(5.81)
426(5.71)
429(5.76)
558(4.30)
561(4.32)
557(4.27)
561(4.39)
597(3.85)
600(4.01)
595(3.76)
600(3.93)
614, 656, 717
656, 717
611, 655, 717
655, 718
Tm3+
Nd3+
829, 896, 947, 1069, 113,
1317, 1350, 1429
0.002
Er3+
406(4.68)
406(4.60)
427(5.68)
427(5.73)
558(4.34)
559(4.30)
596(3.79)
596(3.76)
611, 655 720,
612, 655, 719
1480, 1517,1537a
0.001
0.024
Yb3+
923, 956, 977, 1003, 1023, 1046
a Reported λem may be blue-shifted slightly from true λem due to falloff in InGaAs detector response for λ > 1550 nm.
quench the lowest singlet and triplet states of the porphyrin
ring.29-31 Finally, a few studies have been reported which
show that it is possible to use transient absorption spectros-
copy to distinguish the porphyrin localized triplet excited
state from the lanthanide f-centered excited states.30b,c,e
Tables 3 and 4 summarize important features concerning
the near UV-vis absorption and vis-NIR photolumines-
cence of the entire family of complexes. We first focus
attention on the absorption spectra. Band maxima and molar
absorptivities of the B- and Q-bands for each of the
complexes in CH2Cl2 solution are listed in the tables. In
addition, the absorption spectra of all of the complexes are
included in the Supporting Information section. As expected,
each of the complexes exhibit the characteristic features of
regular metalloporphyrins.29 Systematic trends in the absorp-
tion maxima as a function of the Ln are not seen, however,
close inspection of the data reveals that the B- and Q-bands
are systematically red-shifted when the capping ligand is
changed from Tp to L(OEt). The origin of this effect is
unclear, but the fact that the B- and Q-bands are shifted by
approximately the same energy suggests that it arises from
a slight ground state destabilization in the Tp complex
relative to the L(OEt) complex.
All of the Ln porphyrin complexes exhibit weak photo-
luminescence as several resolved bands in the 600-720 nm
region. The band maxima for the visible emissions are
tabulated in Tables 3 and 4. Interpretation of the visible
emissions observed is rendered difficult due to the fact that
it is believed that most of the samples contain a small amount
of free base TPP as an impurity. (Under our conditions, free
base TPP in CH2Cl2 features two fluorescence bands at 648
and 715 nm.) Inspection of the data for the Tp complexes in
Table 3 reveals that the only visible emission that is observed
arises from the free base TPP impurity. However, the visible
emission of the L(OEt) complexes (Table 4) is more
complicated, and importantly, in each case a weak emission
band is seen at ≈610 nm. This band is believed to be the
Q(0,0) fluorescence from the Ln(TPP)(L(OEt)) complexes.
The assignment is supported by the fact that excitation
spectra obtained while monitoring the 610 nm emission band
correspond to the absorption of the respective Ln(TPP)-
(L(OEt)) complexes. Our results are not unprecedented, as
other groups have also reported weak fluorescence from Ln
porphyrins. Specifically, in separate reports Gouterman and
co-workers29 and Kobayashi and co-workers31 document
weak Q(0,0) fluorescence from Yb(OEP)acac, Yb(OEP)OH,
and Er(TPP)OH (OEP ) octaethylporphyrin). Presumably,
1
the fluorescence arises from the lowest π,π* (Q) state of
the porphyrin in competition with intersystem crossing (ISC)
to the 3π,π* state. The fluorescence is weak because ISC is
likely very fast (kISC ≈ 1010-1011 s-1) due to strong spin-
orbit coupling promoted by the Ln ion.
Emission studies were carried out in the near-IR region
(800-1550 nm) on all of the complexes dissolved in
CH2Cl2 solution. Near-IR emission was observed for Yb3+,
Nd3+, and Er3+ complexes where the capping ligand is Tp
or L(OEt). No emission was observed for Ln ) Ho3+, Pr3+
or Tm3+ in this spectral range. Tables 3 and 4 list the maxima
of the emission lines observed for each of the near-IR
luminescent complexes, and Figure 4 illustrates emission
from the complexes. Quantum efficiencies (φem) were also
determined for the luminescence from the emitting com-
plexes, and the values are listed in the tables. First, the lack
of near-IR luminescence from Ho3+, Pr3+, and Tm3+
complexes in the 800-1550 nm region is not surprising.
Each of these ions has a “ladder” of energetically closely
spaced states (e.g., separations of 2000-4000 cm-1) that are
3
below the energy of the π,π* state of the TPP ligand.36
Because of the close spacing of the states, nonradiative decay
(36) Dieke, G. H. Spectra and Energy LeVels of Rare Earth Ions in Crystals;
Crosswhite, H. M., Crosswhite, H., Eds.; Interscience: New York,
1968.
5030 Inorganic Chemistry, Vol. 42, No. 16, 2003

NIR Luminescent Ln(III) Monoporphyrinates
that φem of Yb(TPP)Tp only increases to 0.034 in CDCl3 (a
7% increase).
The near-IR emission from the Yb3+ complexes is shown
in Figure 4a. The single transition centered at 977 nm arises
2
2
from the F5/2 f F7/2 transition,29,36 and it is split into
multiple bands because of splitting by the ligand field.34 As
shown in Figure 4b, the Nd3+ complexes feature a rich array
of bands in the near-IR region. The luminescence consists
of three primary transitions, each of which is split by the
ligand field. The transitions are (in order of decreasing
4
4
4
4
4
4
36
energy): F3/2 f I11/2, F3/2 f I13/2, and F3/2 f I15/2
.
Finally, the Er3+ complexes exhibit only one weak emission
in the near-IR which corresponds to the I13/2
f
4I15/2
4
transition (Figure 4c).36 The emission is split into two
resolved bands presumably due to the ligand field, with the
strongest band (1531 nm) exhibiting a shoulder on the short-
wavelength side. Interestingly, this shoulder is resolved in
Er(TPP)(L(OEt)), where it appears as a resolved band at 1517
nm. This effect apparently reflects the different ligand field
presented by the Tp and L(OEt) ligands.
Transient absorption (TA) spectroscopy was carried out
on Yb(TPP)Tp, Yb(TPP)(L(OEt)), and Nd(TPP)Tp in order
to provide additional information concerning the electronic
structure and lifetime of the emitting states. In these
experiments, the complexes were excited by a 355 nm laser
pulse (10 ns duration, 5 mJ pulse-1), and transient absorption
difference spectra were recorded at various delay times
following the excitation. Figure 5 shows the TA difference
spectra for the three complexes over the 450-650 nm region,
which coincides with the Q-band ground state absorption
bands. In each of the three complexes, weak transient
absorption (bleaching) was observed, and the transients
decayed with lifetimes of 43, 32, and 44 µs for Yb(TPP)Tp,
Yb(TPP)(L(OEt)), and Nd(TPP)Tp, respectively. It is be-
lieved that the visible region transient absorption arises from
the influence of the f-f state localized on the lanthanide ion
on the porphyrin Q-bands. Consequently, the transient
absorption decays provide a measure of the lifetime of the
f-f state, which is also responsible for the near-IR emission.
The observed lifetimes are consistent those of other Yb3+
and Nd3+ complexes that have been previously reported.1,30
In each case, the TA spectra are dominated by bleaching
of the ground state Q(0,1) and Q(0,0) bands, and increased
absorption on the red and blue sides of each Q-band. This
pattern of transient absorption was reported in a previous
investigation of Yb(TTP) and Yb(etio) (where TTP )
1,5,10,15-tetra-p-tolylporphyrin and etio ) etioporphyrin)
and was attributed to broadening of the Q-bands caused by
the influence of the electronically excited Ln ion.30b,e The
broadening of the Q-bands may arise for one or more of the
following reasons. (1) The excited Ln ion may have a
different polarizability, and this may have an influence on
the bandwidth of the porphyrin π,π* transitions. (2) The
geometry of the complex may be slightly distorted when the
Ln ion is excited, and this may change the geometry of the
porphyrin ring. (3) There may be a charge transfer interaction
between the porphyrin and the excited state Ln ion which
induces broadening of the porphyrin π,π* transitions.30b,e
Figure 4. Near-IR photoluminescence spectra of Ln(TPP)L complexes.
Solid lines (s), L ) Tp, and dashed lines (- - -), L ) L(OEt): (a) Yb-
(TPP)L, (b) Nd(TPP)L, (c) Er(TPP)L.
via coupling to high frequency vibrations (e.g., C-H modes
of the ligands and the solvent) is rapid. The emission
quantum yields for the luminescent complexes follow the
trend Yb3+ > Nd3+ > Er3+, and the yields are not strongly
affected by the nature of the capping ligand. The trend in
emission quantum yields is consistent with observations on
other luminescent lanthanide complexes1 and reflects the fact
that that the efficiency of nonradiative decay increases as
the energy of the luminescent state decreases (energy gap
law). While the absolute emission quantum yields are
comparatively low, they are generally higher than yields of
other Yb, Nd, and Er complexes.1 The enhanced emission
yields for the Ln(TPP)Tp and Ln(TPP)(L(OEt)) complexes
are believed to arise because the coordination environment
provided by the TPP in combination with Tp or L(OEt)
effectively shields the Ln ion from interacting with solvent
(C-H) vibrational modes which enhance the rate of nonra-
diative decay. This premise is supported by the observation
Inorganic Chemistry, Vol. 42, No. 16, 2003 5031

Foley et al.
It is possible that in the case of the Nd porphyrin there is an
equilibrium population of the TPP-3π,π* produced via
4
thermally activated crossing from the Nd F3/2 state. Such
an equilibrium may be possible because the TPP-3π,π* level
4
is only ≈2000 cm-1 above the Nd F3/2 state. The energy
gap between the emitting f-state and the TPP-3π,π* level in
the Yb3+ complexes is >3500 cm-1, and the increased barrier
may preclude substantial population of the TPP-3π,π* level
to a significant extent. In summary, the TA spectroscopy
confirms that in each of the near-IR luminescent complexes
the TPP-3π,π* excited state is quenched by the lanthanide
ion, and the long-lived states have difference spectra that
are consistent with the Ln ion localized f-f state assignment.
Conclusions
A new synthetic method has been developed which
facilitates the high-yield and large scale preparation of Ln-
(TPP) complexes that are capped with various anionic
multidentate ligands. The synthesis is demonstrated for a
series of 12 complexes, where the lanthanide is Yb, Tm, Ho,
Pr, Er, and Nd and the capping ligands are Tp and L(OEt).
Each of the complexes is prepared in high yield from a
common precursor, Ln(TPP)(X)DME. X-ray structures of
three Tp complexes have been obtained, and they are
qualitatively similar, with the Ln ion occupying a position
that is above the plane defined by the TPP pyrrole nitrogens.
The complexes feature absorption spectra that are typical of
regular metallophorphyrins, and near-IR photoluminescence
is observed for the Yb, Nd, and Er complexes.
In ongoing work, we are exploring the properties of
electroluminescent devices fabricated using the Ln(TPP)Tp
and Ln(TPP)(L(OEt)) complexes as the active materials.
Results of this work will be reported in a forthcoming
report.38
Figure 5. Transient absorption spectra of Ln(TPP)L complexes in CH2-
Cl2 solution. Spectra are obtained at various delay increments following
the 355 nm laser excitation pulse, with the first spectrum acquired within
0.5 µs of the excitation: (a) Yb(TPP)(L(OEt)) (8 µs delay increments), (b)
Yb(TPP)Tp (8 µs delay increments), (c) Nd(TPP)Tp (16 µs delay incre-
ments).
Acknowledgment. We acknowledge the Army Research
Office and the Defense Advanced Research Projects Agency
(DAAD19-00-1-0002) for support of this work.
Supporting Information Available: Thermal ellipsoid plots
for Yb(TPP)(Tp) and Nd(TPP)(Tp) as well as positional and COSY
NMR spectrum for Pr(TPP)Tp, and absorption spectra for all of
the Ln(TPP)Tp and Ln(TPP)(L(OEt)) complexes. Crystallographic
data in CIF format. This material is available free via the Internet
at http://pubs.acs.org.
One final point of note is that the TA spectrum of
Nd(TPP)Tp features stronger excited state absorption in the
region between the Q and B bands (450-500 nm) compared
to that of the Yb complexes. Interestingly, this is the region
where the TPP-localized 3π,π* excited state absorbs strongly.37
IC034217G
(37) Tsvirko, M. P.; Sapunov, V. V.; Solovev, K. N. Opt. Spectrosc. 1973,
34, 635.
(38) Kang, T.-S.; Harrison, B. S.; Foley, T. J.; Knefely, A. S.; Boncella, J.
M.; Reynolds, J. R.; Schanze, K. S. AdV. Mater. 2003, 15, 1093.
5032 Inorganic Chemistry, Vol. 42, No. 16, 2003