Amplified two-photon absorption in trans-A2B2- porphyrins bearing nitrophenylethynyl substituents

Article abstract of DOI:10.1002/cphc.201200507

We show that peripheral nitro groups enhance the maximum two-photon absorption cross-section of trans-A₂B₂-porphyrins bearing two phenylethynyl substituents by more than one order of magnitude. Maximum values as high as 1000 GM result from realization of suitable conditions for effective resonance enhancement along with a lowering of the energy and intensification of the two-photon allowed transitions in the Soret region. Copyright

Full text of DOI:10.1002/cphc.201200507

DOI: 10.1002/cphc.201200507
Amplified Two-Photon Absorption in Trans-A2B2-
Porphyrins Bearing Nitrophenylethynyl Substituents
Agnieszka Nowak-Krꢀl,[a] Craig J. Wilson,[b] Mikhail Drobizhev,[c] Dmitry V. Kondratuk,[b]
Aleksander Rebane,*[c, d] Harry L. Anderson,*[b] and Daniel T. Gryko*[a, e]
We show that peripheral nitro groups enhance the maximum
two-photon absorption cross-section of trans-A2B2-porphyrins
bearing two phenylethynyl substituents by more than one
order of magnitude. Maximum values as high as 1000 GM
result from realization of suitable conditions for effective reso-
nance enhancement along with a lowering of the energy and
intensification of the two-photon allowed transitions in the
Soret region.
1. Introduction
Porphyrin derivatives exhibit intriguing nonlinear optical prop-
erties that are useful for all-optical switching and other optoe-
lectronic devices.[1] There is great interest in developing por-
phyrins with increased efficiency of instantaneous (intrinsic)
two-photon absorption (2PA) in the near-IR wavelength range,
especially because such compounds may be used as sensitizers
for deep-tissue photodynamic therapy.[2]
All these enhancement factors relate directly to the proper-
ties of the expanded p-conjugation system, and grow in pro-
portion to the number of the encompassed porphyrin units. In
the decorated single-core porphyrins, an additional 2PA en-
hancement effect arises from the lowering of the symmetry
and related emergence of new two-photon allowed transitions
below the Soret band.[7] Enhanced 2PA in symmetrical porphy-
rin monomers was also reported in peripherally substituted
tetraazaporphyrins, where the substituents with the strongest
electron-accepting ability led to the largest increase of the
2PA.[9]
Simple porphyrin monomers (both free-base and Zn metal-
lated versions) have small peak 2PA cross-sections, typically
not exceeding max(s2)~10 GM.[3] Conjugated porphyrin
dimers[4] and oligomers[5] are known to have large 2PA cross-
sections, reaching high peak values, max(s2)~103–104 GM
(1 GM=10À50 cm4 sÀ1 photonÀ1). Large 2PA cross-sections were
also reported for some other porphyrinoids.[6] However, the ex-
tensive p-conjugation in such systems may have drawbacks,
such as limited photostability. The efficiency of 2PA in porphy-
rin monomers may be enhanced by decorating the core with
strongly two-photon-absorbing chromophores,[7] but in this
case significant downsides include the complexity of the syn-
thesis and the high molecular weight. The challenge thus is to
find a simple way to increase the efficiency of 2PA in single-
core porphyrin structures.
Herein, we report the synthesis of a series of meso-arylethy-
nylporphyrins and study how the incorporation of two sym-
metrical ethynyl moieties decorated with different electron-do-
nating and electron-accepting end groups affects the 2PA in
a broad spectral range encompassing both Q-band and Soret
region. Meso-substituted arylethynyl porphyrins ever since the
first seminal contributions by Therien[10] and others[11] continue
to attract attention.[12] The ethynyl moieties elongate the p-
conjugation pathway, causing a characteristic bathochromati-
[a] A. Nowak-Krꢀl, Prof. D. T. Gryko
Institute of Organic Chemistry, Polish Academy of Sciences
01-224 Warsaw (Poland)
E-mail: dtgryko@icho.edu.pl
[b] Dr. C. J. Wilson, D. V. Kondratuk, Prof. H. L. Anderson
Department of Chemistry, Chemistry Research Laboratory
Oxford University, Oxford OX1 3TA (UK)
2. Results and Discussion
The high 2PA in conjugated porphyrin dimers and oligomers
results from at least three different effects: Firstly, enhance-
ment of the transition dipole moment from the ground state
to an effective intermediate state, which may be directly ob-
served as an increase of the extinction coefficient in the Q-
band region.[3–5] The second contributing factor is the increase
of the excited-state transition dipole moment connecting the
Q-band with the two-photon-allowed final state, which usually
lies in the Soret region. A third contribution originates from
the red-shift of the Q-band that brings the lowest one-photon-
allowed transition closer to the laser frequency, thus increasing
the resonance enhancement.[8]
E-mail: harry.anderson@chem.ox.ac.uk
[c] Dr. M. Drobizhev, Prof. A. Rebane
Department of Physics, Montana State University
Bozeman, MT 59717 (USA)
E-mail: rebane@physics.montana.edu
[d] Prof. A. Rebane
National Institute of Chemical Physics and Biophysics
Tallinn 12618 (Estonia)
[e] Prof. D. T. Gryko
Faculty of Chemistry, Warsaw University of Technology
00-664 Warsaw (Poland)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.201200507.
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A. Rebane, H. L. Anderson, D. T. Gryko et al.
cally shifted absorption.[13,14] Because simple tetraarylporphyr-
ins lack any considerable 2PA enhacement,[3] it would be of
most interest to study the effect of various end groups. Quan-
tum-chemical calculations on different meso-arylethynylpor-
phyrins performed about a decade ago by Zhou et al.[15] pre-
dict that the nitro end group, which is one of the strongest
electron-withdrawing substituents, should lead to the largest
2PA enhancement. By the same token, electron-donating end
groups are expected to have a smaller effect because the por-
phyrin core itself is relatively electron-rich. Specifically, Zhou
et al. calculated that the peak 2PA of the nitro end-capped
(NO2-p-NO2) structure is about 3500 GM compared to 400 GM
of the neutral (H-p-H) version. This prediction turns out to be
in good qualitative agreement with the experimental finding
presented here.
The aryl substituents directly connected to the other meso
positions are expected to have little effect on the electronic
structure because they are twisted at an angle of 60–908 with
respect to the plane of the porphyrin. The main role of these
substituents is to provide solubility and prevent aggregation.
Here, we also compare the properties of free-base porphyrins
with their zinc-metallated derivatives.
The meso-arylethynyl trans-A2B2-porphyrins 1–6 were pre-
pared according to a known procedure (Figure 1).[16] Porphyrin
2 was subjected to a typical zinc-insertion reaction to afford
porphyrin Zn-2 in 94% yield (see Scheme S1 of the Supporting
Information). A different strategy was utilized for the synthesis
of remaining porphyrins 9, Zn-9, Zn-13, and Zn-14. Porphyrin
Zn-7 was prepared as reported by Osuka and coworkers.[17]
Free-base porphyrin 9 was synthesized from Zn-7 via removal
of zinc followed by deprotection of silyl units and Sonogashira
coupling (Scheme 1). Deprotection of two silyl units followed
by Sonogashira coupling with a range of aryl iodides 8, 11–12
afforded final porphyrins Zn-9, Zn-13 and Zn-14 in good yields
(Scheme 2).
From the synthetic perspective, meso-substituted porphyrins
bearing two phenylethynyl substituents at the meso-positions
are one of the conceptually easiest ways to modify the por-
phyrin chromophore. The desire to achieve full comparison of
linear and nonlinear data inclined us to design a broad library
of trans-A2B2-porphyrins possessing two arylethynyl substitu-
ents in a 5,15-arrangement. One can envision that the two-
photon absorption cross-section of such porphyrins will
strongly depend on the electronic effect of the substituents.
As the porphyrin core is an electron-rich heterocyclic scaffold,
it should create an A-D-A system when combined with elec-
tron-withdrawing substituents. One may anticipate that s2
should be higher for this type of architecture than for an A-p-
A system.[1]
Figure 2 shows the 2PA spectra of free-base meso-arylethy-
nylporphyrins 1, 2 and 3. The spectra may be roughly divided
into the Q-band region (1050–1500 nm) and the Soret region
(<1000 nm). At the wavelengths shorter than 820–830 nm an
increasing contribution from the linear Q-band absorption
complicates accurate separation of the simultaneously occur-
ring 1PA and 2PA processes.[7] Comparison of the 2PA spectra
shows that end-capping with the cyano-group (1) as well as
the nitro-group (2) both amplify the 2PA with respect to the
Figure 1. Structures of porphyrins 1–6.
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Two-Photon Absorption in Porphyrins
Scheme 2. Synthesis of porphyrins Zn-9, Zn-13 and Zn-14.
Scheme 1. Preparation of porphyrin 9.
Table 1. Linear and nonlinear optical properties of porphyrins 1–6, 9, Zn-
9, Zn-13 and Zn-14 in CCl4.
max
Compd.
EWG/EDG
l1PA [nm]
l2PA[nm] [s2 [GM]]
neutral (3) arylethynylporphyrin. The electron-withdrawing
cyano group increases the cross section more or less uniformly
in the entire range of the wavelengths 820–1500 nm by about
a factor of 2. The nitro end groups increase the cross section
relative to 3 by approximately an order of magnitude, in the
Soret region of the spectrum. Both 1 and 3 show a pair of 2PA
transitions at 840–960 nm, and the corresponding spectral
shapes are very similar to both compounds.
1
2
Zn-2
3
4
5
6
9
Zn-9
Zn-13
Zn-14
H2TPP
CN
446, 691[a]
453, 694[a]
464, 666[b]
443,689[a]
445, 692[a]
450, 700[a]
457, 671[c]
456, 697[d]
466, 679[d]
475, 685[d]
455, 663[d]
421, 654[b]
870 [150], 960 [10], 1260 [20]
870 [1600], 900 [1000], 1260 [40]
870 [540], 900 [360], 1210 [23]
840 [200], 1250 [10]
840 [100]
840 [30]
840 [10]
870 [750], 1240 [70]
870 [650], 1250 [40]
850 [650]
NO2
NO2
H
CN
OMe
CN
NO2
NO2
NBu2
Bu
The 2PA spectrum of the nitro-porphyrin 2 shows a signifi-
cant shoulder at 900 nm, which dominates this part of the
spectrum. The fact that none of these 2PA transitions could be
attributed to features in the 1PA spectrum, including the peak
of the Soret band, confirms that the corresponding two-
photon allowed transitions are to states with gerade parity. The
corresponding 2PA cross section values are collected in
Table 1. In the Soret region all studied spectra show a steep in-
crease due to the resonance enhancement effect,[7] which con-
tributes to ultimate maximum 2PA cross section value. As was
mentioned above, this value depends not only on the two-
photon allowed transitions in the Soret region, but also on the
properties of 1PA transitions in Q-band.
850 [30]
800 [7], 1180 [4]13
H
[a] in CH2Cl2. [b] in CCl4/0.08% THF. [c] in TFA. [d] in CCl4/1% pyridine.
While the peak extinction of the lowest Q-band is compara-
ble for all compounds studied here, differences of the 1PA
peak wavelengths and widths probably contribute to the
cross-sections listed in Table 1. For example, the fact that at
840 and 900 nm 2 has an about three-times-larger 2PA cross-
section than Zn-2 may be due to a ~30 nm difference in the
peak wavelengths of the corresponding Q-bands. In the case
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A. Rebane, H. L. Anderson, D. T. Gryko et al.
sorptive processes.[19] However, direct comparison of these re-
sults is not justified in this case, because these authors used
very different experimental conditions from ours. Their laser
has high repetition rate (100 MHz) and low peak power (~1 nJ
per laser pulse) whereas we used low-repetition-rate
(1 kHz)/high-peak-power (>5 mJ) pulses. As a result, in quanti-
tative terms, our peak intensity is about 1000–10000 times
higher, which explains why Therien and co-workers see much
more linear absorption contribution.
It is interesting to compare our experimental 2PA values for
2 with the reported quantum-chemical calculations.[15] The pre-
dicted 1PA peak wavelength in the region 370–400 nm (Soret
peak) is very close to the observed values. At the same time,
the calculations predicted the 2PA maxima at 640–650 nm,
that is, above the 1PA Soret band, whereas the experimentally
observed 2PA transition is at a considerably lower energy
(900 nm). Nevertheless, the experimental data appear to con-
firm the main theoretical prediction that the maximum 2PA
cross-section occurs in the Soret region and is amplified by
electron-accepting nitro groups, rather than electron-donating
groups. Also, our measured maximum 2PA values, 1000 and
110 GM, are in qualitative agreement with the theoretical pre-
dictions of 3500 and 450 GM for the nitro- and neutral end
groups, correspondingly. In the Q-region, all three compounds
have similar peaks that may be attributed to the peaks in the
corresponding 1PA spectra.
3. Conclusions
In conclusion, we have demonstrated free-base and Zn-metal-
lated porphyrin monomers with symmetrical peripheral nitro
groups achieve large intrinsic 2PA in the near-IR range of
wavelengths, with maximum values of s2 >1000 GM. Due to
their good photostability and simple design, these compounds
may have practical applications in optoelectronics and photo-
medicine.
Figure 2. Dependence of the 2PA cross-section spectrum on the end group
in the free-base meso-arylethynylporphyrins in CCl4 solution in 3, 1 and 2
(symbols). The thin solid line shows the extinction (right vertical scale) as
a function of the 1PA transition wavelength (upper horizontal scale). The
shaded interval indicates a gap in the wavelength tuning of the OPA; verti-
cal arrows indicate the distinct bands in the Soret region.
Experimental Section
All chemicals were used as received unless otherwise noted. Re-
agent grade solvents (CH2Cl2, hexane) were distilled prior to use.
1
All reported H NMR and 13C NMR spectra were collected using 500
or 400 MHz spectrometers. Chemical shifts (d ppm) were deter-
mined with TMS as the internal reference; J values are given in Hz.
The UV/Vis absorption spectra were recorded in CH2Cl2, CH2Cl2-pyr-
idine or CCl4-THF. The absorption wavelengths are reported in nm
with the extinction coefficient in MÀ1 cmÀ1 in brackets. Chromatog-
raphy was performed on silica (230–400 mesh). The mass spectra
were obtained via field desorption MS (FD-MS), electrospray ioniza-
tion (ESI-MS), and matrix-assisted laser desorption/ionization
(MALDI). Porphyrins 1–6 and Zn-7 were prepared according to the
literature procedures.[16,17]
of Zn-13 bearing electron-donating NBu2 groups, the larger
2PA cross-section value in the Soret region may be attributed
in part to the substituents, and in part to the resonance en-
hancement, which is increased because Zn-substitution causes
the 1PA spectrum to shift to the red. The dependences ob-
served here are similar to that reported for a series of electron-
donating and electron-withdrawing end caps on fluorenyl-type
chromophores.[18] Otherwise, Zn-substitution appears to have
minimal influence on the 2PA properties.
Two-photon absorption measurements were carried out using
a wavelength-tunable femtosecond laser system that comprises
a Ti:Sapphire femtosecond oscillator (Mira 900, Coherent Inc.)
pumped by a CW frequency-doubled Nd:YAG laser (Verdi, Coherent
Inc.) and a 1 kHz repetition rate Ti:sapphire femtosecond regenera-
tive amplifier (Legend H, Coherent Inc.). The pulses from the Ti:sap-
Therien and co-workers studied two-photon absorption of
very similar p-extended porphyrins claiming that 2PA cross-sec-
tions are on the order of 10 GM, and that a significant portion
of the detected fluorescence is the result of other, linear ab-
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Two-Photon Absorption in Porphyrins
phire amplifier were down-converted with an optical parametric
amplifier, OPA (TOPAS-C, Quantronix), whose output signal (idler)
was continuously tunable from 1100 to 1600 (1600 to 2200) nm.
The second harmonic of idler was used for two-photon excitation
in the lex =800–1100 nm region and the fundamental of the signal
in the 1100–1400 nm region. The OPA output signal pulse energy
was 100–250 mJ (5–10 mJ after frequency doubling), and the pulse
duration was 70–120 fs. A detailed description of the experimental
procedure has been described earlier.[20] Briefly, the linearly polar-
ized excitation laser beam was slightly focused with an f=25 cm
lens onto the sample solution contained in a 1ꢂ1 cm2 spectro-
scopic cell and placed 15 cm behind the lens. A small fraction of
the beam was split off by a thin glass plate placed just before the
sample and directed to the reference detector (Molectron). The
sample fluorescence was collected with a spherical mirror (f=
50 cm, diameter d=10 cm) and focused with magnification ratio
~1 on the entrance slit of an imaging grating spectrometer (Jobin
Yvon Triax 550). The 2PA spectrum (in relative units) was obtained
by tuning the wavelength of OPA, and measuring the correspond-
ing intensity of two-photon excited fluorescence. The wavelength
tuning of OPA and data collection were computer-controlled with
a LabView routine. At each wavelength, the fluorescence intensity
was normalized to the square of the excitation photon flux, mea-
sured in the reference channel. The correction to the spectral varia-
tions of the OPA output (pulse duration and beam spatial profile)
was done by using Rhodamine B in methanol as a standard, whose
2PA spectrum is well characterized.[20] To exclude possible artifacts,
for example, due to absorption at wavelengths close to the linear
absorption, we checked that at each wavelength the fluorescence
signal increased as a square of the excitation intensity. Absolute
2PA cross sections were measured using relative fluorescence tech-
nique as described[20] with rhodamine B as a standard.[20] To obtain
absolute 2PA spectra in GM units, all relative 2PA spectra were cali-
brated to the known (at one wavelength in each spectral region)
absolute cross section value. The 2PA properties were measured in
CCl4 solutions.
phy on silica gel (40–608C petroleum ether:EtOAc 100:1) gave
a dark purple solid (39 mg, 78%): UV/vis (CH2Cl2) lmax (e)=436 (331
000), 584 (41 700), 679 (16 600), 544 nm (12 300); 1H NMR
(400 MHz, CDCl3) d=À2.20 (br s, 2H, NH), 0.86–1.04 (m, 40H, CH2,
CH3), 1.26–1.58 (m, 78H, CH2), 1.72–1.92 (m, 20H, CH2), 4.14 (t, J=
6.4 Hz, 8H, OCH2), 6.90 (t, J=2.2 Hz, 2H, ArHpara), 7.34 (d, J=2.2 Hz,
4H, ArHortho), 8.94 (d, J=4.8 Hz, 4H, bH), 9.60 ppm (d, J=4.8 Hz,
4H, bH); MS LR (MALDI ToF MS+) calcd for C104H162N4O4Si2 ([M+
H]·+) 1588.6, found 1589.2.
5,15-Bis(3,5-dioctyloxyphenyl)-10,20-bis(4-nitrophenylethynyl)-
porphyrin (9): Tetra-n-butylammonium flouride (1.0m solution in
THF, 0.82 mL, 0.82 mmol) was added to a solution of 5,15-bis(3,5-
dioctyloxyphenyl)-10,20-bis(trihexylsilanylethynyl)porphyrin
(7)
(65 mg, 40.9 mmol) in CH2Cl2 (10 mL) and stirred for 30 min. The re-
action mixture was passed through a short silica gel column
(CH2Cl2) and the solvent was removed. The residue was mixed with
tris(dibenzylideneacetone)dipalladium(0) (35 mg, 38 mmol), PPh3
(40 mg, 0.152 mmol), and 1-iodo-4-nitrobenzene (8) (80 equiv,
1.26 g, 5.09 mmol) and dried under high vacuum before dry tolu-
ene (20 mL) and diisopropylamine (20 mL) were added. The mix-
ture was degassed and the reaction stirred at 608C overnight. The
volume was reduced and the mixture passed through a short silica
gel column (CH2Cl2). Recrystallization by layer addition (CH2Cl2/ace-
tone) gave a dark green solid (34 mg, 66%): UV/vis (CH2Cl2) lmax
(e)=455 (407 000), 609 (75 900), 694 nm (51 300); 1H NMR
(400 MHz, CDCl3) d=À2.03 (br s, 2H, NH), 0.88 (t, J=7.0 Hz, 12H,
CH3), 1.26–1.43 (m, 32H, CH2), 1.50–1.60 (m, 8H, CH2), 1.87–1.94 (m,
8H, CH2), 4.17 (t, J=6.7 Hz, 8H, OCH2), 6.95 (t, J=2.2 Hz, 2H,
ArHpara), 7.38 (d, J=2.2 Hz, 4H, ArHortho), 8.07 (d, J=8.9 Hz, 4H,
ArH), 8.40 (d, J=8.9 Hz, 4H, ArH), 9.02 (d, J=4.5 Hz, 4H, bH),
9.61 ppm (d, J=4.5 Hz, 4H, bH); MS LR (MALDI ToF MS+) calcd for
C80H92N6O8 ([M+H] +) 1265.62, found 1266.44.
C
[5,15-Bis(3,5-dioctyloxyphenyl)-10,20-bis[4-(N,N-dibutylamino)-
phenylethynyl]porphyrinato]zinc(II) (Zn-13): [5,15-Bis(3,5-diocty-
loxyphenyl)-10,20-bisethynylporphyrinato]zinc(II) (Zn-10) (40 mg,
37 mmol),
tris(dibenzylideneacetone)dipalladium(0)
(4.4 mg,
[5,15-Bis[tris((tert-butoxycarbonyl)methyloxy)phenyl]-10,20-bis-
(4-nitrophenylethynyl)porphyrinato]zinc(II) (Zn-2): To the solution
of porphyrin 2 (32 mg, 21 mmol) in CHCl3 (2 mL), MeOH (0.18 mL),
and Et3N (0.4 mL, 2.9 mmol) zinc(II) acetate dihydrate (24 mg,
0.11 mmol) was added and the reaction mixture was stirred in
reflux for 19 h. Then, the reaction mixture was evaporated to dry-
ness and the residue was chromatographed (silica, toluene:CH-
Cl3:acetone 30:20:2 to 35:15:2). A solid was crystallized (CH2Cl2/
hexane) to afford Zn-2 (31 mg, 94%) in form of green crystals: Rf =
0.38 (CHCl3/toluene/acetone 6:4:1); UV/vis (CCl4/0.08% THF) lmax
(e)=464 (294000), 666 (53700), 281 (25600); 1H NMR (500 MHz,
[D8]THF) d=1.40 (s, 36H, CH3), 1.62 (s, 18H, CH3), 4.83 (s, 8H,
OCH2), 4.97 (s, 4H, OCH2), 7.46 (s, 4H, ArH), 8.29 (AA’BB’, J=8.8 Hz,
4H, ArH), 8.48 (AA’BB’, J=8.8 Hz, 4H, ArH), 9.02 (d, J=4.5 Hz, 4H,
bH), 9.74 ppm (d, J=4.6 Hz, 4H, bH); 13C NMR (125 MHz, [D8]THF)
d=28.3, 28.5, 67.9, 71.1, 81.3, 81.9, 95.7, 99.2, 100.6, 117.1, 123.9,
124.8, 131.3, 131.7, 133.0, 133.8, 138.0, 139.2, 148.2, 150.8, 151.3,
152.9, 168.6, 168.9 ppm; HR MS (ESI) calcd for C84H86N6O22Zn
1596.9886, found 1596.9897; isotope profiles match.
4.7 mmol), PPh3 (9.2 mg, 35 mmol) and CuI (3.3 mg, 18 mmol) were
dried under vacuum before dry NEt3 (3 mL) was added and the
mixture degassed. N,N-dibutyl-4-iodoaniline (4 equiv, 98 mg,
296 mmol) was added and the mixture was stirred at 508C for 2 h
when TLC (40–608C petroleum ether:EtOAc:pyridine 10:1:1, Rf =
0.80) showed the reaction to be complete. The volume was re-
duced and the mixture passed through a short silica gel column
(CH2Cl2). Column chromatography (40–608C petroleum ether:E-
tOAc:pyridine 100:1:1 to 100:8:1) followed by recrystallization by
layer addition (CH2Cl2/MeOH) gave a dark green solid (34 mg,
62%): UV/vis (CH2Cl2/1% pyridine) lmax (e)=476 (25 7000), 692 (79
1
400), 297 (39 800), 329 nm (34 700); H NMR (400 MHz, CDCl3/5%
[D5]pyridine) d=0.88–1.63 (m, 80H, CH2CH3), 1.91 (m, 8H, CH2),
3.16 (s, 8H, NCH2), 4.16 (t, J=6.4 Hz, 8H, OCH2), 6.42 (d, J=7.8 Hz,
4H, ArH), 6.90 (s, 2H, ArHpara), 7.42 (s, 4H, ArHortho), 7.46 (d, J=
7.8 Hz, 4H, ArH), 9.00 (d, J=4.4 Hz, 4H, bH), 9.62 ppm (d, 4H, J=
4.4 Hz, bH); 13C NMR (100 MHz, CDCl3/5% [D5]pyridine) d=14.04,
14.12, 20.35, 22.68, 26.15, 29.29, 29.35, 29.46, 31.84, 50.60, 68.43,
90.64, 98.41, 101.04, 103.20, 109.18, 110.96, 114.19, 122.18, 130.74,
132.23, 132.51, 144.26, 147.63, 149.30, 152.04, 158.26 ppm; LR MS
(MALDI ToF MS+) calcd for C96H127N6O4Zn ([M+H] +) 1491.92,
found 1492.79.
5,15-Bis(3,5-dioctyloxyphenyl)-10,20-bis(trihexylsilylethynyl)por-
phyrin (7): [5,15-Bis(3,5-dioctyloxyphenyl)-10,20-bis(trihexylsilanyle-
thynyl)porphyrinato]zinc(II) (Zn-7) (50 mg, 0.03 mmol) was dis-
solved in CHCl3 (10 mL), TFA (1.32 mmol, 1.0 mL of 10% (v/v) solu-
tion in CHCl3) was added and the mixture was stirred for 30 min.
The reaction mixture was passed through a short silica gel column
(CHCl3/1% pyridine) and the solvent was removed. Chromatogra-
C
[5,15-Bis-(3,5-dioctyloxyphenyl)-10,20-bis(4-butylphenylethynyl)-
porphyrinato]zinc(II) (Zn-14): [5,15-Bis(3,5-dioctyloxyphenyl)-10,20-
bisethynylporphyrinato]zinc(II) (Zn-10) (30 mg, 28 mmol), tris(diben-
zylideneacetone)dipalladium(0) (3.3 mg, 3.5 mmol), PPh3 (6.9 mg,
ChemPhysChem 0000, 00, 1 – 8
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A. Rebane, H. L. Anderson, D. T. Gryko et al.
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M. Balaz, M. K. Kuimova, D. Phillips, M. Drobizhev, A. Rebane, B. C.
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26 mmol) and CuI (2.5 mg, 13 mmol) were dried under vacuum
before dry NEt3 (6 mL) was added and the mixture degassed. 1-
Butyl-4-iodobenzene (4 equiv, 57 mg, 222 mmol) was added and
the reaction was stirred at 508C for 0.5 h when TLC (40–608C pe-
troleum ether:EtOAc:pyridine 10:1:1, Rf =0.80) showed the reaction
to be complete. The volume was reduced and the mixture passed
through a short silica gel column (CH2Cl2). Column chromatogra-
phy (40–608C petroleum ether:EtOAc:pyridine 100:1:1 to 100:3:1)
followed by recrystallization by layer addition (CH2Cl2/MeOH) gave
a dark green solid (35 mg, 93%): UV/vis (CH2Cl2/1% pyridine) lmax
(e)=453 (245 000), 661 (75 900), 310 (38 000), 606 nm (17 000);
1H NMR (400 MHz, CDCl3/5% [D5]pyridine) d=0.88 (t, J=6.7 Hz,
12H, CH3), 1.01 (t, J=7.4 Hz, 6H, CH3), 1.25–1.57 (m, 40H, CH2),
1.69–1.76 (m, 8H, CH2), 1.84–1.93 (m, 8H, CH2), 2.76 (t, J=7.7 Hz,
8H, ArCH2), 4.16 (t, J=6.6 Hz, 8H, OCH2), 6.91 (t, J=2.1 Hz, 2H,
ArHpara), 7.36 (d, J=2.1 Hz, 4H, ArHortho), 7.38 (d, J=8.0 Hz, 4H, ArH),
7.94 (d, J=8.0 Hz, 4H, ArH), 8.98 (d, J=4.6 Hz, 4H, bH), 9.70 ppm
(d, J=4.6 Hz, 4H, bH); 13C NMR (100 MHz, CDCl3/5% [D5]pyridine)
d=14.01, 14.10, 22.66, 26.14, 28.26, 29.42, 31.81, 68.35, 101.57,
114.49, 121.54, 122.29, 128.80, 130.55, 131.46, 132.40, 143.46,
144.58, 149.69, 151.98, 158.14 ppm; LR MS (MALDI ToF MS+) calcd
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1700–1704; g) J. E. Raymond, A. Bhaskar, T. Goodson III, N. Makiuchi, K.
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355, 175.
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Am. Chem. Soc. 1996, 118, 1497–1503; b) S. M. LeCours, S. G. DiMagno,
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9061–9064.
for C88H108N4O4Zn (M +) 1348.76, found 1349.59.
C
[5,15-Bis(3,5-dioctyloxyphenyl)-10,20-bis(4-nitrophenylethynyl)-
porphyrinato]zinc(II) (Zn-9): [5,15-Bis(3,5-dioctyloxyphenyl)-10,20-
bisethynylporphyrinato]zinc(II) (Zn-10) (40 mg, 37 mmol), tris(diben-
zylideneacetone)dipalladium(0) (4.4 mg, 4.7 mmol), PPh3 (9.2 mg,
35 mmol) and CuI (3.3 mg, 18 mmol) were dried under vacuum
before dry NEt3 (3 mL) was added and the mixture degassed. 1-
Iodo-4-nitrobenzene (8) (4 equiv, 74 mg, 296 mmol) was added and
the reaction stirred at 508C for 2 h when TLC (40–608C petroleum
ether:EtOAc:pyridine 10:1:1, Rf =0.60) showed the reaction to be
complete. The volume was reduced and the mixture passed
through a short silica gel column (CH2Cl2). Column chromatogra-
phy (40–608C petroleum ether:EtOAc:pyridine 100:5:5 to 100:10:5)
followed by recrystallization by layer addition (CH2Cl2/MeOH) gave
a dark green solid (37 mg, 75%): UV/vis (CH2Cl2/1% pyridine) lmax
(e)=466 (302 000), 678 (83 200), 343 (25 700), 598 nm (8 500);
1H NMR (400 MHz, CDCl3/5% [D5]pyridine) d=0.88 (t, J=6.7 Hz,
12H, CH3), 1.44–1.26 (m, 32H, CH2), 1.60–1.51 (m, 8H, CH2), 1.95–
1.88 (m, 8H, CH2), 4.19 (t, J=6.6 Hz, 8H, OCH2), 6.92 (s, 2H, ArHpara),
7.39 (d, J=1.8 Hz, 4H, ArHortho), 7.88 (d, J=8.4 Hz, 4H, ArH), 8.22 (d,
J=8.4 Hz, 4H, ArH), 9.09 (d, J=4.4 Hz, 4H, bH), 9.57 ppm (d, J=
4.4 Hz, 4H, bH); 13C NMR (100 MHz, CDCl3/5% [D5]pyridine) d=
14.09, 22.65, 29.15, 29.25, 29.43, 31.81, 68.42, 94.58, 99.17, 99.60,
100.58, 114.61, 123.76, 130.44, 130.94, 131.60, 132.95, 144.12,
146.48, 150.15, 151.97, 158.29 ppm; MS LR (MALDI ToF MS+) calcd
for C80H91N6O8Zn ([M+H] +) 1327.62, found 1328.56).
C
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Beratan, J. Phys. Chem. C 2012, 116, 9724–9733; b) A. Ryan, A. Gehrold,
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D. T. Gryko, Chem. Asian J. 2012, 7, 1887–1894.
Acknowledgements
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Splan, J. Phys. Chem. A 2011, 115, 10452.
D.T.G. and A.N.-K. thank the Polish Ministry of Science and Higher
Education (Contract N204 123837). This work was partially sup-
ported by the European Commission (TOPBIO ITN), and by an
Oxford University Clarendon Fund Scholarship (to DVK). We
thank the EPSRC mass spectrometry service (Swansea) for mass
spectra.
Keywords: chromophores · nonlinear optics · porphyrinoids ·
two-photon absorption · p-expansion
[15] X. Zhou, A.-M. Ren, J.-K. Feng, X.-J. Liu, J. Mol. Struct. THEOCHEM 2004,
679, 157.
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Two-Photon Absorption in Porphyrins
´
[16] A. Nowak-Krꢀl, B. Koszarna, S. Y. Yoo, J. Chrominski, M. K. We˛cławski, C.-
[19] J. A. N. Fisher, K. Susumo, M. J. Therien, A. G. Yodh, J. Chem. Phys. 2009,
130, 134506.
H. Lee, D. T. Gryko, J. Org. Chem. 2011, 76, 2627.
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Kim, A. Osuka, Chem. Eur. J. 2005, 11, 3389–3404.
[20] N. S. Makarov, M. Drobizhev, A. Rebane, Opt. Express 2008, 16, 4029.
[18] A. Rebane, M. Drobizhev, N. S. Makarov, E. Beuerman, J. E. Haley, D. M.
Krein, A. R. Burke, J. L. Flikkema, T. M. Cooper, J. Phys. Chem. A 2011,
115, 4255–4262.
Received: June 22, 2012
Published online on && &&, 0000
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ARTICLES
A. Nowak-Krꢀl, C. J. Wilson, M. Drobizhev,
D. V. Kondratuk, A. Rebane,*
Enhanced absorption: As a result of
suitable conditions for effective reso-
nance enhancement along with a lower-
ing of the energy and intensification of
the two-photon allowed transitions in
the Soret region, peripheral nitro
groups enhance the maximum two-
photon absorption cross-section of
trans-A2B2-porphyrins bearing two phe-
nylethynyl substituents by more than
one order of magnitude.
H. L. Anderson,* D. T. Gryko*
&& – &&
Amplified Two-Photon Absorption in
Trans-A2B2-Porphyrins Bearing
Nitrophenylethynyl Substituents
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ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 8
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These are not the final page numbers!