Luminescent Zn and Pd tetranaphthaloporphyrins

Article abstract of DOI:10.1021/ic034257k

Zn and Pd complexes of meso-tetraphenyltetranaphthaloporphyrins (Ph4TNP) exhibit strong infrared absorption bands and luminesce in solutions at room temperature. S1 → S0 fluorescence (λ_max = 732 nm, φ = 5.3%) is the predominant emission in the

Full text of DOI:10.1021/ic034257k

Inorg. Chem. 2003, 42, 4253−4255
Luminescent Zn and Pd Tetranaphthaloporphyrins
Vladimir V. Rozhkov, Mazdak Khajehpour, and Sergei A. Vinogradov*
Department of Biochemistry and Biophysics, UniVersity of PennsylVania,
Philadelphia, PennsylVania 19104
Received March 9, 2003
Zn and Pd complexes of meso-tetraphenyltetranaphthaloporphyrins
(Ph4TNP) exhibit strong infrared absorption bands and luminesce
hand, are studied only minimally,5 although their synthesis
has also been recently improved.6 In this work, we report
on Zn and Pd tetraphenyltetra[2,3]naphthaloporphyrins
(Ph4TNPs), which possess remarkably red-shifted absorption
Q-bands and exhibit considerable room temperature emission,
suggesting applications in PDT and biological oxygen
sensing by phosphorescence quenching.
The symmetrical tetraphenyltetra[2,3]naphthaloporphyrins
(MPh4TNPs; M ) Zn (1), Pd (2)) studied in this work are
shown in Scheme 1 together with the homologous tetraphen-
yltetrabenzoporphyrin (MPh4TBP).
Synthesis of Ar4TNPs was originally proposed by
Kopranenkov et al.7 It was based on the template condensa-
tion of 2,3-naphthalenedicarboximide with phenylacetic acids
in the presence of Zn salts. A much improved higher yield
synthesis of Ar4TNPs has been recently developed by Ono
et al.,6 allowing for the introduction of substituents in the
meso-phenyl rings, but requiring rather elaborate synthesis
of the precursor compounds. In this work, we followed the
older method, which has an advantage of a simpler single-
in solutions at room temperature. S1 f S0 fluorescence (λmax
)
732 nm, φ ) 5.3%) is the predominant emission in the case of
ZnPh4TNP (1). This emission is in part due to the delayed
fluorescence (φ ) 1.1%). Phosphorescence (T1 f S0) of 1 (λmax
) 973 nm) is very weak (φ ) 0.04%) and occurs with lifetime of
about 440 µs in deoxygenated DMF. In the case of PdPh4TNP
(2), almost no S1 f S0 fluorescence could be observed, while
the main emission detected was T1 f S0 phosphorescence (λmax
) 938 nm). The phosphorescence of 2 occurs with lifetime of
about 65 µs and (φ)6.5%) in deoxygenated DMF solution.
Metalloporphyrins 1 and 2 are promising near infrared dyes
biomedical applications.
Interest in porphyrins fused with external aromatic rings
has been steadily increasing in the past several years.1
Symmetrically extended porphyrins, such as tetrabenzopor-
phyrins (TBPs), exhibit particularly red-shifted absorption
bands and strong infrared luminescence and possess interest-
ing nonlinear optical properties, suggesting applications in
biomedicine2 and various branches of optical technology.3
meso-Tetraarylated tetrabenzoporphyrins (Ar4TBPs) and tet-
ranaphthaloporphyrins (Ar4TNPs) have an advantage of
increased solubility and relative ease of derivatization.
Considerable progress has been achieved lately in the
synthesis of functionalized Ar4TBPs,4 and some of their
applications have been described.2b-f,3 Ar4TNPs, on the other
(3) (a) Brunel, M.; Chaput, F.; Vinogradov, S. A.; Campagne, B.; Canva,
M.; Boilot, J. P. Chem. Phys. 1997, 218, 301-307. (b) Chen, P. L.;
Tomov, I. V.; Dvornikov, A. S.; Nakashima, M.; Roach, J. F.; Alabran,
D. M.; Rentzepis, P. M. J. Phys. Chem. 1996, 100, 17507-17512.
(c) Ono, N.; Ito, S.; Wu, C. H.; Chen, C. H.; Wen, T. C. Chem. Phys.
2000, 262, 467-473. (d) Srinivas, N.; Rao, S. V.; Rao, D.; Kimball,
B. K.; Nakashima, M.; Decristofano, B. S.; Rao, D. N. J Porphyrins
Phthalocyanins 2001, 5, 549-554. (e) Ohkuma, S.; Yamashita, T. J.
Photopolym. Sci. Technol. 2002, 15, 23-27. (f) Karotki, A.; Drobizhev,
M.; Kruk, M.; Spangler, C.; Nickel, E.; Mamardashvili, N.; Rebane,
A. J Opt. Soc. Am. B 2003, 20, 321-332.
(4) (a) Vicente, M. G. H.; Tome, A. C.; Walter, A.; Cavaleiro, J. A. S.
Tetrahedron Lett. 1997, 38, 3639-3642. (b) Ito, S.; Murashima, T.;
Uno, H.; Ono, N. Chem. Commun. 1998, 1661-1662. (c) Ito, S.; Ochi,
N.; Murashima, T.; Uno, H.; Ono, N. Heterocycles 2000, 52, 399-
411. (d) Ito, S.; Uno, H.; Murashima, T.; Ono, N. Tetrahedron Lett.
2001, 42, 45-47. (e) Finikova, O.; Cheprakov, A.; Beletskaya, I.;
Vinogradov, S. Chem. Commun. 2001, 261-262.
(5) (a) Dashkevich, S. N.; Kaliya, O. L.; Kopranenkov, V. N.; Luk’janets,
E. A. Zh. Prikl. Spektrosk. 1987, 47, 144-148. (b) Sapunov, U. V.;
Soloviev, K. N.; Kopranenkov, V. N.; Dashkevich, S. N. Teor. Eksp.
Khim. 1991, 27, 105-108. (c) Kobayashi, N.; Nevin, W. A.;
Mizunuma, S.; Awaji, H.; Yamaguchi, M. Chem. Phys. Lett. 1993,
205, 51-54. (d) Roitman, L.; Ehrenberg, B.; Kobayashi, N. J.
Photochem. Photobiol., A 1994, 77, 23-28. (e) Vinogradov, S. A.;
Wilson, D. F. AdV. Exp. Med. Biol. 1997, 411, 597-603.
* Corresponding author. E-mail: vinograd@mail.med.upenn.edu.
(1) For review see: (a) Lash, T. D. Synthesis of Novel Porphyrinoid
Chromophores. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Chapter
10. (b) Senge, M. O. Highly Substituted Porphyrins. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: New York, 2000; Chapter 6.
(2) (a) Lavi, A.; Johnson, F. M.; Ehrenberg, B. Chem. Phys. Lett. 1994,
231, 144-150. (b) Vinogradov, S. A.; Wilson, D. F. J. Chem. Soc.,
Perkin Trans. 2 1994, 103-111. (c) Vinogradov, S. A.; Lo, L.-W.;
Jenkins, W. T.; Evans, S. M.; Koch, C.; Wilson, D. F. Biophys. J.
1996, 70, 1609-1617. (d) Friedberg, J. S.; Skema, C.; Baum, E. D.;
Burdick, J.; Vinogradov, S. A.; Wilson, D. F.; Horan, A. D.;
Nachamkin, I. J. Antimicrob. Chemother. 2001, 48, 105-107. (e)
Finikova, O.; Galkin, A.; Rozhkov, V.; Cordero, M.; Ha¨gerha¨ll, C.;
Vinogradov, S. J. Am. Chem. Soc. 2003, 125, 4882-4893. (f) Rietveld,
I. B.; Kim, E.; Vinogradov, S. A. Tetrahedron 2003, 59, 3821-3831.
(6) Ito, S.; Ochi, N.; Uno, H.; Murashima, T.; Ono, N. Chem. Commun.
2000, 893-894.
(7) Kopranenkov, V. N.; Vorotnikov, A. M.; Dashkevich, S. N.; Luk’yanets,
E. A. Zh. Obshch. Khim. 1985, 803-809.
10.1021/ic034257k CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/07/2003
Inorganic Chemistry, Vol. 42, No. 14, 2003 4253

COMMUNICATION
Scheme 1
Figure 1. Absorption spectra of porphyrins 1 and 2 in DMF solutions.
Scheme 2
Table 1. Photophysical Properties of 1 and 2 in DMF Solutions at
Room Temperature
absorption
emission
Figure 2. Side views of the calculated structures of ZnPh4TBP and
ZnPh4TNP (1). dsad values indicate the magnitudes of the saddle type (B2u)
normal distortion modes, as calculated by NSD.13
λmax, nm
(log10 ꢀ)
type
λ
max (λex),b nm
φ,c %
τ, µs
1
2
720 (4.82)
659 (3.90)
494 (4.98)
Ra ) 2.3
S1 f S0
S1 f S0e
732, 809 (494)
732, 809 (494)
5.3 ( 0.7d
1.1 ( 0.2
442
438
respectively, while the Q-band peak of 2 is at 704 nm. The
red-shifted absorption of Ph4TBPs versus TPPs is due to the
π-extension12a and nonplanar distortion12b of the Ph4TBP
macrocycle. In the case of Ph4TNP versus Ph4TBP, however,
it is only the extra π-extension that causes the absorption
red-shift, which reaches 75 nm for Pd complexes and 63
nm for Zn complexes (λQmax ZnPh4TBP ) 657 nm).9 The
magnitudes of the predominant saddle type distortions (dsad’s)
are practically the same in 1 and in ZnPh4TBP, as seen from
the calculated structures, depicted in Figure 2, and evidenced
by the results of NSD (normal-coordinate structural decom-
position) analyses.13
Presently, no structural data are available for Ar4TNPs,
and only a few X-ray analyses are reported for Ar4TBPs.14
Therefore, making structural comparisons was possible only
by using computed structures. The geometries of the corre-
sponding Zn-complexes were optimized at the DFT B3LYP/
6-31G level. It has to be mentioned that the degree of the
saddle type distortion in the calculated ZnPh4TBP is higher
than that found in the reported14a experimental structure
ZnPh4TBP‚THF (dsad ) 2.34 Å).
T1 f S0
S1 f S0
973 (720)
715 (440)
0.04 ( 0.01
<0.02d
704 (5.01)
640 (4.12)
459 (4.98)
Ra ) 1.2
T1 f S0
938 (704)
6.5 ( 0.1
65
b
a R ) ISoret/IQ ) ratio of the integral intensities. λex ) wavelength used
for excitation, shown in parentheses. c φ ) emission quantum yield,
determined relative to the fluorescence of Zn tetraphenylporphyrin (ZnTPP)
in deaerated benzene, φ ) 3.3%.10 d Quantum yield is shown for combined
fast and delayed fluorescence in deoxygenated solution. e Delayed fluores-
cence due to thermal repopulation of singlet state.
step synthetic procedure. Our goal was to examine basic
photophysical properties of Ph4TNPs, for which the materials
were required only in minimal amounts. The synthesis is
shown in Scheme 2.
A similar synthesis of Ph4TBPs8 has been reported to give
mixtures of products, consisting of porphyrins with two to
four meso-phenyl rings.9 Although not directly demonstrated,
synthesis of Ph4TNPs is likely to suffer from the same
problem. As a consequence, a very tedious purification was
required to obtain pure ZnPh4TNP (1), which could be
isolated only in a very low yield (<1%). A much higher
yield (25%) has been reported originally,7 along with the
blue-shifted Q-band of 1 (λQmax ) 710 nm). For comparison,
λQmax of 1 in CH2Cl2, reported by Ono et al.,6 is 723 nm. It
is likely that the material obtained in ref. 7 contained
porphyrins with fewer meso-phenyl substituents, ZnPhnTNP
(n ) 2-4), whose presence resulted in the overall Q-band
blue-shift.
(8) Kopranenkov, V. N.; Dashkevich, S. N.; Luk’yanets, E. A. Zh. Obshch.
Khim. 1981, 51, 2165-2168.
(9) Ichimura, K.; Sakuragi, M.; Morii, H.; Yasuike, M.; Fukui, M.; Ohno,
O. Inorg. Chim. Acta 1990, 176, 31-33.
(10) Quimby, D. J.; Longo, F. R. J. Am. Chem. Soc. 1975, 97, 5111-5117.
(11) Eastwood, D.; Gouterman, M. J. Mol. Spectrosc. 1970, 35, 359-375.
(12) (a) Cheng, R. J.; Chen, Y. R.; Chuang, C. E. Heterocycles 1992, 34,
1-4. (b) Haddad, R. E.; Gazeau, S.; Pecaut, J.; Marchon, J. C.;
Medforth, C. J.; Shelnutt, J. A. J. Am. Chem. Soc. 2003, 125, 1253-
1268 and references therein.
(13) NSD (normal-coordinate structural decomposition) analysis was
performed using web-based software available at http://jasheln.
unm.edu/. (See Supporting Information for complete NSD results.)
Original NSD references: (a) Jentzen, W.; Song, X.-Z.; Shelnutt, J.
A. J. Phys. Chem. B 1997, 101, 1684-1699. (b) Jentzen, W.; Ma, J.
G.; Shelnutt, J. A. Biophys. J. 1998, 74, 753-763.
(14) (a) Cheng, R. J.; Chen, Y. R.; Wang, S. L.; Cheng, C. Y. Polyhedron
1993, 12, 1353-1360. (b) Finikova, O. S.; Cheprakov, A. V.; Carroll,
P. J.; Dalosto, S.; Vinogradov, S. A. Inorg. Chem. 2002, 41, 6944-
6946.
The photophysical properties of ZnPh4TNP (1) and
PdPh4TNP (2) are summarized in Table 1. The absorption
spectra of 1 and 2 are shown in Figure 1.
The absorption Q-bands of both complexes are signifi-
cantly red-shifted, compared to those of tetraphenylporphy-
rins (TPPs) and Ph4TBPs. For example, the principal Q-band
peaks of PdTPP11 and PdPh4TBP2b are at 522 and 628 nm,
4254 Inorganic Chemistry, Vol. 42, No. 14, 2003

COMMUNICATION
nificant increases (up to 1660 cm-1) in the gaps between
fluorescence and absorption maxima.16 S1 f S0 fluorescence
quantum yield of 1 (φ ) 5.3%), is comparable to that of
ZnTPP (3.3%),10 and higher than that of ZnDPP (1%) and
ZnOETPP (0.3%).16 Interestingly, a large portion of fluo-
rescence (∼20%) is delayed. Phosphorescence of Zn complex
1 is very weak (φ ) 0.04%). The inset in Figure 3 shows
the delayed emission spectrum of 1 in deoxygenated DMF,
where both the phosphorescence and the fluorescence peaks
are clearly present. The time-resolved measurements at the
emission maxima (732 and 973 nm) resulted in practically
the same lifetimes, 442 and 438 µs, suggesting that emitting
S1 species are formed in this case as a result of thermal
equilibrium between T1 and S1 states. Delayed fluorescence
has been previously observed for metalloporphyrins by
Gouterman and co-workers.17
Because of the greatly enhanced intersystem crossing, S1
f S0 fluorescence of 2 (λmax ) 715 nm) is extremely weak
(φ < 0.02%). Instead, T1 f S0 phosphorescence constitutes
the major emission from this porphyrin, similar to what has
been previously observed for PdTPP11 and PdPh4TBP.2b The
quantum yield of this emission, φ ) 6.5%, is somewhat lower
than that reported for PdPh4TBP phosphorescence (φ )
8-12%).2b The phosphorescence lifetime of 2 in the absence
of oxygen is 65 µs, and in aerated solutions, the emission is
almost fully quenched. Considering the extremely strong
absorption Q-band of 2 (704 nm, log10 ꢀ ≈ 5.0), these
characteristics suggest that 2 can be very effective as a near
infrared phosphor for biological oxygen measurements.
Finally, we would like to point out that, upon excitation
at the Soret bands, both compounds 1 and 2 exhibit broad
and weak emissions (φ ) 0.1-0.3%) in the 520-570 nm
region, i.e., blue-shifted compared to the corresponding S1
f S0 bands. The excitation spectra showed that these peaks
were due to impurity (or impurities) with absorption bands
at 510-515 nm.
Figure 3. Corrected emission spectra of ZnPh4TNP (1) and PdPh4TNP
(2) in DMF. (1) Black line indicates fluorescence in aerated solution (λex
) 460 nm); green line indicates phosphorescence in deoxygenated solution
(λex ) 720 nm). Inset: Red line indicates emission in deoxygenated solution
(uncorrected); spectrum delayed by 50 µs (λex ) 494 nm). (2) Black line
indicates fluorescence (λex ) 440 nm); green line indicates phosphorescence
(λex ) 704 nm).
The Soret transitions are less affected by the macrocycle
extension/distortion than the Q-bands. For example, the red-
shift of the Soret band of 1 versus that of ZnTPP is only 71
nm (λSoret ZnTPP ) 423 nm), while for the corresponding
Q-bands this difference is more than 120 nm (λQ(0,0) ZnTPP
) 596 nm).10 Porphyrins 1 and 2 are, therefore, far surpassed
in terms of Soret red-shifts by, for instance, tetraaryltet-
raacenaphthoporphyrins, whose Soret bands reach as far as
550 nm and above.15 However, the locations of extremely
strong and narrow Q-bands make 1 and 2 almost ideally
suited for biological in vivo applications, such as PDT, where
absorption between 630 and 800 nm, in the so-called “near
infrared window of tissue”, is highly desirable. Another in-
teresting and useful feature of 1 and 2 is that, compared to
the corresponding TPPs and Ph4TBPs, they exhibit large
increases in the oscillator strengths (Iλ) of the Q-bands ver-
sus Soret bands. In the case of Pd complexes, for example,
the ratio ISoret/IQ (see Table 1) changes from PdTPP to
PdPh4TBP to 2 as 13.8 f 2.6 f 1.2. In fact, the extinction
at the Q-band peak of 2 is higher than that at the Soret peak,
offering a possibility for very effective near infrared excita-
tion.
Luminescence of metalloporphyrins 1 and 2 is significantly
red-shifted and could be accurately measured only using
specialized infrared enhanced detection systems, such as
Hamamatsu R2685 PMT. The results of the measurements
are summarized in Table 1, and the emission spectra are
shown in Figure 3. In all cases, the origins of the emission
bands were confirmed by comparing the absorption and
excitation spectra.
The obvious difference between compounds 1 and 2 is
that the major emission from the former is fluorescence,
while the latter mainly exhibits phosphorescence from the
T1 state. This difference is due to the enhanced intersystem
crossing, which is known to be amplified in porphyrins by
heavy metals such as Pd and Pt.11
In summary, Zn and Pd meso-tetraphenyl[2,3]tetranaph-
thaloporphyrins exhibit strong near infrared absorption bands
and luminesce in solutions at room temperature. These
compounds present an interest as chromophores for biomedi-
cal applications, such as in vivo oxygen imaging and PDT.
Acknowledgment. Support from Grant NS-31465 from
the NIH and from Contract 02-5403-21-2 with Anteon Inc.
is acknowledged. The authors thank Prof. David F. Wilson
for many useful discussions.
Supporting Information Available: Synthesis and character-
ization of porphyrins, details of optical measurements, description
of the calculations, and NSD analyses. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC034257K
Fluorescence of 1 (λmax ) 732 nm) has a Stokes shift of
12 nm and presents almost an ideal mirror image of the
absorption Q-band. Such a small Stokes shift (227 cm-1) is
rather surprising in a view of the highly distorted molecular
structure of 1. It has been observed that other nonplanar Zn
porphyrins, such as Zn dodecaphenylporphyrin (ZnDPP) and
Zn octaethyltetraphenylporphyrin (ZnOETPP), exhibit sig-
(15) Lash, T. D.; Chandrasekar, P. J. Am. Chem. Soc. 1996, 118, 8767-
8768.
(16) Gentemann, S.; Nelson, N. Y.; Jaquinod, L.; Nurco, D. J.; Leung, S.
H.; Medforth, C. J.; Smith, K. M.; Fajer, J.; Holten, D. J. Phys. Chem.
B 1997, 101, 1247-1254.
(17) Callis, J. B.; Gouterman, M.; Jones, Y. M.; Henderson, B. H. J. Mol.
Spectrosc. 1971, 39, 410-420.
Inorganic Chemistry, Vol. 42, No. 14, 2003 4255