Electronic modulation of hyperpolarizable (porphinato)zinc(II) chromophores featuring ethynylphenyl-, ethynylthiophenyl-, ethynylthiazolyl-, and ethynylbenzothiazolyl-based electron-donating and -accepting moieties

Article abstract of DOI:10.1021/ic060898e

A series of conjugated (porphinato)zinc(II)-based chromophores structurally related to [5-(4-dimethylaminophenylethynyl)-15-(5-nitrothienyl-2-ethynyl)-10, 20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II) were synthesized using metal-catalyzed cross-coupling reactions involving [5-bromo-15-triisopropylsilylethynyl-10,20-diarylporphinato]zinc(II), [5-bromo-15-(4-dimethylaminophenylethynyl)-10,20-diarylporphinato]zinc(II), [5-(4-dimethylaminophenylethynyl)-15-ethynyl-10,20-diarylporphinato]zinc(II), and [5-(4-nitrophenylethynyl)-15-ethynyl-10,20-diarylporphinato]zinc(II), along with appropriately functionalized aryl, thienyl (or thiophenyl), thiazolyl, benzothiazolyl, and carbazolyl precursors. The linear and nonlinear optical properties of these asymmetrically 5,15-substitued-(10,20-diarylporphinato) zinc(II) chromophores that bear either 2-(9H-carbazol-9-yl)-thiophen-5-yl- ethynyl, 4-dimethylaminophenylethynyl, or 2-(N,N-diphenylamino)thiophen-5-yl- ethynyl electron-releasing groups and an electron-withdrawing group selected from 2-formyl-thiophen-5-yl-ethynyl, 2-(2,2-dicyanovinyl)-thiophen-5-yl-ethynyl, 4-nitrophenylethynyl, 6-nitrobenzothiazol-2-yl-ethynyl, or 5-nitrothiazol-2-yl- ethynyl are reported. The dynamic hyperpolarizabilities of these compounds were determined from hyper-Rayleigh light scattering measurements carried out at a fundamental incident irradiation wavelength (λ_inc) of 1300 nm; these measured β₁₃₀₀ values ranged from 690 → 1400 × 10^-30 esu. These data (i) show that these neutral dipolar molecules express substantial β₁₃₀₀ values, (ii) highlight that reductions in the magnitude of the aromatic stabilization energy of (porphinato)metal- pendant arylethynyl groups have a significant impact upon the magnitude of the molecular hyperpolarizability, and (iii) provide insights into advantageous design modifications for closely related structures having potential utility in long-wavelength electrooptic applications.

Full text of DOI:10.1021/ic060898e

Inorg. Chem. 2006, 45, 9703−9712
Electronic Modulation of Hyperpolarizable (Porphinato)zinc(II)
Chromophores Featuring Ethynylphenyl-, Ethynylthiophenyl-,
Ethynylthiazolyl-, and Ethynylbenzothiazolyl-Based Electron-Donating
and -Accepting Moieties
Tian-Gao Zhang,† Yuxia Zhao,§ Kai Song,‡ Inge Asselberghs,‡ Andre´ Persoons,‡ Koen Clays,*,‡ and
Michael J. Therien*,†
Center for Research on Molecular Electronics and Photonics, UniVersity of LeuVen,
B-3001 LeuVen, Belgium, Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences, Beijing 100080, China, and Department of Chemistry,
UniVersity of PennsylVania, Philadelphia, PennsylVania 19104-6323
Received May 23, 2006
A series of conjugated (porphinato)zinc(II)-based chromophores structurally related to [5-(4-dimethylaminophenyl-
ethynyl)-15-(5-nitrothienyl-2-ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II) were syn-
thesized using metal-catalyzed cross-coupling reactions involving [5-bromo-15-triisopropylsilylethynyl-10,20-
diarylporphinato]zinc(II), [5-bromo-15-(4-dimethylaminophenylethynyl)-10,20-diarylporphinato]zinc(II), [5-(4-dimethyl-
aminophenylethynyl)-15-ethynyl-10,20-diarylporphinato]zinc(II), and [5-(4-nitrophenylethynyl)-15-ethynyl-10,20-di-
arylporphinato]zinc(II), along with appropriately functionalized aryl, thienyl (or thiophenyl), thiazolyl, benzothiazolyl,
and carbazolyl precursors. The linear and nonlinear optical properties of these asymmetrically 5,15-substitued-
(10,20-diarylporphinato)zinc(II) chromophores that bear either 2-(9H-carbazol-9-yl)-thiophen-5-yl-ethynyl, 4-dimethyl-
aminophenylethynyl, or 2-(N,N-diphenylamino)thiophen-5-yl-ethynyl electron-releasing groups and an electron-
withdrawing group selected from 2-formyl-thiophen-5-yl-ethynyl, 2-(2,2-dicyanovinyl)-thiophen-5-yl-ethynyl, 4-nitro-
phenylethynyl, 6-nitrobenzothiazol-2-yl-ethynyl, or 5-nitrothiazol-2-yl-ethynyl are reported. The dynamic hyperpo-
larizabilities of these compounds were determined from hyper-Rayleigh light scattering measurements carried out
at a fundamental incident irradiation wavelength (
λ
inc) of 1300 nm; these measured â1300 values ranged from 690
30
f
1400
×
10- esu. These data (i) show that these neutral dipolar molecules express substantial â1300 values,
(ii) highlight that reductions in the magnitude of the aromatic stabilization energy of (porphinato)metal−pendant
arylethynyl groups have a significant impact upon the magnitude of the molecular hyperpolarizability, and (iii) provide
insights into advantageous design modifications for closely related structures having potential utility in long-wavelength
electrooptic applications.
Introduction
The low aromatic stabilization energy (ASE)1,19,20 coupled
with the electron-rich nature of these species relative to six-
membered aromatic carbocyclics21 drive the utility of
thiophene- and thiazole-containing structures in electrooptic
materials.
Thiophene and thiazole rings, among five-membered
heteroaromatics, have received appreciable attention as highly
polarizable π-bridges for nonlinear optical (NLO) materials,1-12
and media for electron- and energy-transfer reactions.13-18
Likewise, porphyrin-based building blocks have also
figured prominently in the range of unusually polarizable
* To whom correspondence should be addressed. E-mail: koen.clays@
fys.kuleuven.be (K.C.); therien@sas.upenn.edu (M.J.T.).
‡ University of Leuven.
(2) Raimundo, J.-M.; Blanchard, P.; Gallego-Planas, N.; Mercier, N.;
§ Chinese Academy of Sciences.
Ledoux-Rak, I.; Hierle, R.; Roncali, J. J. Org. Chem. 2002, 67, 205-
218.
† University of Pennsylvania.
(1) Breitung, E. M.; Shu, C.-F.; McMahon, R. J. J. Am. Chem. Soc. 2000,
122, 1154-1160.
(3) Miller, R. D.; Lee, V. Y.; Moylan, C. R. Chem. Mater. 1994, 6, 1023-
1032.
10.1021/ic060898e CCC: $33.50
Published on Web 10/26/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 24, 2006 9703

Zhang et al.
and hyperpolarizable structures.22-32 The coupling of thiophene
rings with porphyrinic units has been exploited in the
development of NLO chromophores that possess substantial
molecular hyperpolarizabilities at a fundamental incident
irradiation wavelength (λinc) of 1300 nm;29,33 interestingly,
the linear and nonlinear optical properties of this series of
electronically asymmetric porphyrin-(oligo)thiophene chro-
mophores challenge the classic concept of the nonlinearity/
transparency tradeoff in charge-transfer chromophores.29
We report herein a complimentary set of conjugated
(porphinato)zinc(II)-based chromophores structurally related
to [5-(4-dimethylaminophenylethynyl)-15-(5-nitrothienyl-2-
ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)-
porphinato]zinc(II)29 that features ethynylphenyl-, ethynyl-
thiophenyl-, ethynylthiazolyl-, and ethynylbenzothiazolyl-
based electron-donating and -accepting moieties. These
species were synthesized via metal-catalyzed cross-coupling
reactions involving [5-bromo-15-triisopropylsilylethynyl-
10,20-diarylporphinato]zinc(II), [5-bromo-15-(4-dimethyl-
aminophenylethynyl)-10,20-diarylporphinato]zinc(II), [5-(4-
dimethylaminophenylethynyl)-15-ethynyl-10,20-diarylpor-
phinato]zinc(II), and [5-(4-nitrophenylethynyl)-15-ethynyl-
10,20-diarylporphinato]zinc(II), along with appropriately
functionalized aryl, thienyl, thiazolyl, benzothiazolyl, and
carbazolyl precursors. We describe the linear spectroscopic
properties and determine the dynamic hyperpolarizabilities
(âλ values) measured via hyper-Rayleigh light scattering
(HRS) for 1300 nm incident irradiation. These data show
that these neutral dipolar molecules express substantial â1300
values and provide insights into design modifications for
closely related structures with potential utility in long-
wavelength electrooptic applications.
(4) Davey, M. H.; Lee, V. Y.; Wu, L.-M.; Moylan, C. R.; Volksen, W.;
Knoesen, A.; Miller, R. D.; Marks, T. J. Chem. Mater. 2000, 12, 1679-
1693.
(5) Cai, C.; Liakatas, I.; Wong, M.-S.; Bosch, M.; Bosshard, C.; Gunter,
P.; Concilio, S.; Tirelli, N.; Suter, U. W. Org. Lett. 1999, 1, 1847-
1849.
(6) Wang, Y.-K.; Shu, C.-F.; Breitung, E. M.; McMahon, R. J. J. Mater.
Chem. 1999, 9, 1449-1452.
(7) Dirk, C. W.; Katz, H. E.; Schilling, M. L.; King, L. A. Chem. Mater.
1990, 2, 700-705.
(8) Casado, J.; Pappenfus, T. M.; Miller, L. L.; Mann, K. R.; Orti, E.;
Viruela, P. M.; Pou-Amerigo, R.; Hernandez, V.; Lopez Navarrete, J.
T. J. Am. Chem. Soc. 2003, 125, 2524-2534.
Experimental Section
(9) Kim, O.-K.; Fort, A.; Barzoukas, M.; Blanchard-Descec, M.; Lehn,
J.-M. J. Mater. Chem. 1999, 9, 2227-2232.
Materials. Inert atmosphere manipulations were carried out under
nitrogen prepurified by passage through an O2 scrubbing tower
(Schweizerhall R3-11 catalyst) and a drying tower (Linde 3-Å
molecular sieves). Air-sensitive solids were handled in a Braun
150-M glovebox. Standard Schlenk techniques were employed to
manipulate oxygen- and moisture-sensitive chemicals. Tetrahydro-
furan (Fisher Scientific, HPLC grade) was distilled from potassium/
benzophenone, while diethylamine and triethylamine were distilled
from CaH2; DMF (anhydrous), toluene (anhydrous), 1,2-dichloro-
ethane (anhydrous), o-xylene (anhydrous), diisopropylamine (re-
distilled, 99.5%), and N,N-diisopropylethylamine (redistilled, 99.5%)
were used as received from Aldrich. Pd2(dba)3, Pd(PPh3)4, CuI,
AsPh3, P(t-Bu)3, n-BuLi, and NaO(t-Bu) were obtained from either
Aldrich or Strem. n-Tetrabutylammonium fluoride (TBAF) (1.0 M
in THF) was obtained from Aldrich, while trimethylsilylacetylene
was obtained from GFS Chemicals. Alumina (neutral, grade I) and
iodine were obtained from Fisher. Diphenylamine, 9H-carbazole,
2-iodothiophene, 2-bromothiazole, 2-amino-6-nitrobenzothiazole,
isoamylnitrite, diiodomethane, 5-(trimethylsilylethynyl)-thiophene-
2-carbaldehyde, and malononitrile were purchased from Aldrich.
2-Ethynyl-5-nitrothiophene was synthesized via established
methods.34-36 5-(Trimethylsilylethynyl)-thiophene-2-carbaldehyde
was synthesized following a literature method.37 The syntheses of
5,15-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)porphyrin, [5-bromo-
10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc-
(II), [5,15-dibromo-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)-
phenyl)porphinato]zinc(II), [5-bromo-15-triisopropylsilylethynyl-
10,20-diarylporphinato]zinc(II) (porphyrin 1), [5-(4-dimethyl-
aminophenylethynyl)-15-bromo-10,20-bis(3,5-bis(3,3-dimethyl-1-
butyloxy)phenyl)porphinato]zinc(II) (porphyrin 2), [5-(4-dimethyl-
aminophenylethynyl)-15-ethynyl-10,20-diarylporphinato]zinc(II) (por-
(10) Rao, V. P.; Jen, A. K. Y.; Wong, K. Y.; Drost, K. J. Tetrahedron
Lett. 1993, 34, 1747-1750.
(11) Bedworth, P. V.; Cai, Y.; Jen, A.; Marder, S. R. J. Org. Chem. 1996,
61, 2242-2246.
(12) Steybe, F.; Effenberger, F.; Gubler, U.; Bosshard, C.; Gunter, P.
Tetrahedron 1998, 54, 8469-8480.
(13) Odobel, F.; Suresh, S.; Blart, E.; Nicolas, Y.; Quintard, J.-P.; Janvier,
P.; Le Questel, J.-Y.; Illien, B.; Rondeau, D.; Richomme, P.; Haupl,
T.; Wallin, S.; Hammarstrom, L. Chem.sEur. J. 2002, 8, 3027-3046.
(14) Effenberger, F.; Wuerthner, F.; Steybe, F. J. Org. Chem. 1995, 60,
2082-2091.
(15) Wuerthner, F.; Vollmer, M. S.; Effenberger, F.; Emele, P.; Meyer, D.
U.; Port, H.; Wolf, H. C. J. Am. Chem. Soc. 1995, 117, 8090-8099.
(16) Vollmer, M. S.; Wurthner, F.; Effenberger, F.; Emele, P.; Meyer, D.
U.; Stumpfig, T.; Port, H.; Wolf, H. C. Chem.sEur. J. 1998, 4, 260-
269.
(17) Vollmer, M. S.; Effenberger, F.; Stumpfig, T.; Hartschuh, A.; Port,
H.; Wolf, H. C. J. Org. Chem. 1998, 63, 5080-5087.
(18) Ikemoto, J.; Takimiya, K.; Aso, Y.; Otsubo, T.; Fujitsuka, M.; Ito, O.
Org. Lett. 2002, 4, 309-311.
(19) Cook, M. J.; Katritzky, A. R.; Linda, P. In AdV. Heterocycl. Chem.;
Katritzky, A. R., Boulton, A. J., Eds.; Academic Press: New York,
1974; Vol. 17, pp 255-356.
(20) Wheland, G. W. Resonance in Organic Chemistry; Wiley: New York,
1955.
(21) Smith, M. B.; March, J. March’s AdVanced Organic Chemistry: Reac-
tions, Mechanisms, and Structure, 5th ed.; Wiley: New York, 2001.
(22) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J. Science 1994, 264,
1105-1111.
(23) LeCours, S. M.; Guan, H.-W.; DiMagno, S. G.; Wang, C. H.; Therien,
M. J. J. Am. Chem. Soc. 1996, 118, 1497-1503.
(24) LeCours, S. M.; DiMagno, S. G.; Therien, M. J. J. Am. Chem. Soc.
1996, 118, 11854-11864.
(25) Susumu, K.; Therien, M. J. J. Am. Chem. Soc. 2002, 124, 8550-
8552.
(26) Uyeda, H. T.; Zhao, Y.; Wostyn, K.; Asselberghs, I.; Clays, K.;
Persoons, A.; Therien, M. J. J. Am. Chem. Soc. 2002, 124, 13806-
13813.
(27) Angiolillo, P. J.; Uyeda, H. T.; Duncan, T. V.; Therien, M. J. J. Phys.
Chem. B. 2004, 108, 11893-11903.
(28) Duncan, T. V.; Rubtsov, I. V.; Uyeda, H. T.; Therien, M. J. J. Am.
Chem. Soc. 2004, 126, 9474-9475.
(29) Zhang, T.-G.; Zhao, Y.; Asselberghs, I.; Persoons, A.; Clays, K.;
Therien, M. J. J. Am. Chem. Soc. 2005, 127, 9710-9720.
(30) Susumu, K.; Duncan, T. V.; Therien, M. J. J. Am. Chem. Soc. 2005,
127, 5186-5195.
(31) Yeung, M.; Ng, A. C. H.; Drew, M. G. B.; Vorpagel, E.; Breitung, E.
M.; McMahon, R. J.; Ng, D. K. P. J. Org. Chem. 1998, 63, 7143-
7150.
(32) Anderson, H. L. Chem. Commun. 1999, 2323-2330.
(33) Zhang, T.-G. Ph.D. Thesis, University of Pennsylvania, 2003.
(34) Mueller, T. J. J.; Robert, J. P.; Schmaelzlin, E.; Braeuchle, C.;
Meerholz, K. Org. Lett. 2000, 2, 2419-2422.
(35) Xia, A.; Selegue, J. P. Inorg. Chim. Acta 2002, 334, 219-224.
(36) Vegh, D.; Kovac, J.; Dandarova, M. Tetrahedron Lett. 1980, 21, 969-
970.
(37) Wu, I.-Y.; Lin, J. T.; Luo, J.; Li, C.-S.; Tsai, C.; Wen, Y. S.; Hsu,
C.-C.; Yeh, F.-F.; Liou, S. Organometallics 1998, 17, 2188-2198.
9704 Inorganic Chemistry, Vol. 45, No. 24, 2006

Electronic Modulation of Hyperpolarizable Chromophores
phyrin 3), and [5-ethynyl-15-(4-nitrophenylethynyl)-10,20-di-
arylporphinato]zinc(II) (porphyrin 4) have been reported pre-
viously.23,25,26,29,38 The synthesis and electrooptic properties of the
nonlinear optical chromophore [5-(4-dimethylaminophenylethynyl)-
15-(5-nitrothienyl-2-ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-bu-
tyloxy)phenyl)porphinato]zinc(II) (compound 1) have been de-
scribed recently.29
Synthesis of Nonlinear Optical Chromophores. Synthetic
details and analytical data for all precursor compounds are described
in the Supporting Information.
[5-(4-Dimethylaminophenylethynyl)-15-(2-formylthiophen-5-
yl-ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)-
porphinato]zinc(II) (Compound 2). Porphyrin 2 (12.8 mg, 11.1
µmol), 5-ethynyl-thiophene-2-carbaldehyde (12.2 mg, 89.9 µmol),
Pd(PPh3)4 (38 mg, 32.8 µmol), CuI (12 mg, 63.0 µmol), THF (20
mL), and triethylamine (5 mL) were placed into a Schlenk tube,
and the reaction mixture was stirred at 55 °C for 18 h. The reaction
mixture was monitored via electron absorption spectroscopy. After
the reaction mixture was filtered and evaporated, the green residue
was chromatographed sequentially over silica gel (3:1 hexanes/
THF), size-exclusion media (BioBeads S-X1, BioRad, THF), and
silica gel (CHCl3). A green solid was obtained after evaporation
of solvent. Yield: 12 mg (92%, based on 12.8 mg of the porphyrinic
1H NMR spectra were recorded on either 250 MHz Bru¨ker AC-
250 or 360 MHz Bru¨ker AM-360 spectrometers. All chemical shifts
1
for H NMR spectra are relative to that of TMS. All J values are
reported in Hertz; the number of attached protons is found in
parentheses following the chemical shift value. Chromatographic
purification (silica gel 60, 230-400 mesh, EM Scientific; Bio-Beads
S-X1, Bio-Rad Laboratories) of all newly synthesized compounds
was accomplished on the benchtop. MALDI-TOF mass spectro-
scopic data were obtained with either an Applied Biosystems
Perceptive Voyager-DE instrument in the Laboratories of Dr. Virgil
Percec (Department of Chemistry, University of Pennsylvania) or
a PerSpective BioSystems Voyager-DE instrument in the Labora-
tories of Dr. William DeGrado (Department of Biochemistry and
Biophysics, University of Pennsylvania School of Medicine).
Samples were prepared as micromolar solutions in THF, and either
dithranol (Aldrich) or R-cyano-4-hydroxy cinnamic acid (R-CHCA)
was utilized as the matrix. FAB data was obtained at the Drexel
Mass Spectrometry facility. Electrospray ionization (ESI-MS) and
chemical ionization (CI-MS) data were obtained in the University
of Pennsylvania Chemistry Mass Spectrometry Facility.
Instrumentation. Electronic spectra were recorded on an OLIS
UV/vis/near-IR spectrophotometry system that is based on the optics
of a Cary 14 spectrophotometer. Emission spectra were recorded
on a SPEX Fluorolog luminescence spectrophotometer that utilized
a T-channel configuration with a red-sensitive R2658 Hamamatsu
PMT and liquid-nitrogen-cooled InGaAs detector; these spectra
were corrected using the spectral output of a calibrated light source
supplied by the National Bureau of Standards. Time-correlated
single photon counting (TCSPC) spectroscopic measurements were
performed at the Regional Laser and Biotechnology Laboratory
(RLBL) at the University of Pennsylvania using an instrument
described previously;39 these data were analyzed using Lifetime
(RLBL) and Globals Unlimited (LFD, University of Illinois)
Programs.
1
starting material). H NMR (CDCl3/TMS/pyridine-d5): δ 9.93 (s,
1H, CHO), 9.69 (d, 2H, â, J ) 4.58), 9.54 (d, 2H, â, J ) 4.49),
8.97 (d, 2H, â, J ) 4.44), 8.92 (d, 2H, â, J ) 4.44), 7.88 (d, 2H,
Ar, J ) 8.71), 7.77 (d, 1H, thienyl, J ) 3.96), 7.62 (d, 1H, thienyl,
J ) 3.91), 7.32 (d, 4H, Ar, J ) 2.25), 6.87 (m, 4 H, Ar), 4.21 (t,
8 H, OCH2CH2), 3.10 (s, 6H, NMe2), 1.85 (t, 8H, OCH2CH2), 1.01
(s, 36 H, tert-butyl). Vis (λmax(log ꢀ); THF): 461 (5.26), 676 (4.74).
Fluorescence emission (THF): 696 nm. MALDI-TOF: 1202.5,
calcd for C73H79N5O5SZn: 1201.5.
[5-(4-Dimethylaminophenylethynyl)-15-(2-(2,2-dicyanovinyl)-
thiophen-5-yl-ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyl-
oxy)phenyl)porphinato]zinc(II) (Compound 3). Compound 2
(147 mg, 122 µmol), and malononitrile (180 mg, 2.72 mmol) were
placed in a 100 mL Schlenk tube and dried under vacuum. Alumina
(neutral activity I, 1.04 g) and THF (30 mL) were added; after
three freeze-pump-thaw cycles, the mixture was stirred at room
temperature (RT) for 9.5 h. The mixture was then filtered and
evaporated to give a brownish-green residue which was sequentially
flash-chromatographed over silica gel (CHCl3), Bio-Beads SX-1
(THF), and silica gel (CHCl3), to give the product, isolated as a
brown-green solid. Yield: 105 mg (69%, based on 147 mg of the
porphyrinic starting material). 1H NMR (pyridine-d5): δ 10.14 (d,
2 H, â, J ) 4.25), 9.87 (d, 2 H, â, J ) 4.44), 9.35 (d, 4 H, â, J )
4.54), 8.45 (s, 1 H, vinylic), 8.18 (d, 2 H, phenyl, J ) 8.57), 7.82
(d, 1 H, thienyl, J ) 4.16), 7.80 (d, 4 H, phenyl, J ) 1.72), 7.76
(d, 1 H, thienyl, J ) 3.78), 7.39 (m, 2 H, Ar), 6.94 (d, 2 H, phenyl,
J ) 8.86), 4.36 (t, 8 H, OCH2CH2, J ) 7.07, 7.01), 2.90 (s, 6 H,
NMe2), 1.91 (t, 8 H, OCH2 CH2, J ) 6.95, 7.14), 0.98 (s, 36 H,
tert-butyl). Vis (λmax(log ꢀ); THF): 469 (4.69), 698 (4.41).
Fluorescence emission (THF): 759 nm. MALDI-TOF: 1250.0
(M+); ESI-MS: 1249.5; calcd for C76H79N7O4SZn: 1249.5.
[5-(4-Dimethylaminophenylethynyl)-15-(6-nitrobenzothiazol-
2-yl-ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)-
porphinato]zinc(II) (Compound 4). Porphyrin 3 (113 mg, 0.103
mmol), 2-iodo-6-nitrobenzothiazole (331 mg, 1.08 mmol), Pd-
(PPh3)4 (122 mg, 0.105 mmol), CuI (31 mg, 0.163 mmol), THF
(20 mL), and (i-Pr)2NEt (1.6 mL) were placed in a 100 mL Schlenk
tube and heated at 60 °C for 19 h. After cooling to RT, the mixture
was poured into deionized water, extracted with methylene chloride,
HRS Measurements. Femtosecond HRS experiments were
performed at 1300 nm.40 Disperse red 1 (DR1, â1300 ) 54 × 10-30
esu in CHCl3) was utilized as a reference dipolar chromophore.
2
Standard local field correction factors were applied [(nD
+
2)/3)]3, where n is the refractive index of the solvent at the sodium
D line], to correct for the solvent dependence of the hyperpolar-
izability of the external reference. Note that these experiments were
performed at low chromophore concentrations (<4 × 10-5 M-1);
the linearity of the HRS signal as a function of chromophore
concentration confirmed that no significant self-absorption of the
second harmonic generation (SHG) signal occurred in these
experiments. HRS signals measured for the dipolar 5,15-disubsti-
tuted-(10,20-diarylporphinato)zinc(II) chromophores were analyzed
as resulting from a single major hyperpolarizability tensor com-
41
ponent, i.e., the diagonal component âzzz along the molecular z
(41) Note: In the NLO community, âzzz denotes a first hyperpolarizability
tensor component along the dipolar molecular z axis for charge transfer,
while âxxx refers to one of the four nonzero hyperpolarizability tensor
components for a D3h-symmetric octopolar molecule in the xy plane,
the z axis again being the unique molecular axis perpendicular to this
plane. With respect to the previous body of literature describing the
electronic transitions of electronically asymmetric [5,15-bis(aryl-
ethynyl)porphinato]metal compounds, the axis of longest conjugation
is denoted as x.
axis, which corresponds in the molecular reference frame to the
axis of highest conjugation.
(38) DiMagno, S. G.; Lin, V. S.-Y.; Therien, M. J. J. Org. Chem. 1993,
58, 5983-5993.
(39) Holtom, G. R. SPIE 1990, 1204, 2-12.
(40) Olbrechts, G.; Wostyn, K.; Clays, K.; Persoons, A. Opt. Lett. 1999,
24, 403-405.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9705

Zhang et al.
dried over Na2SO4, filtered, and evaporated. The green residue was
chromatographed sequentially over silica gel, Bio-Beads SX-1
(THF), and silica gel (19:1 CHCl3/THF). Yield: 101 mg (77% based
on 113 mg of the porphyrinic starting material). 1H NMR (CDCl3/
TMS/1-drop-pyridine-d5): δ 9.68 (d, 2 H, â, J ) 4.43), 9.59 (d, 2
H, â, J ) 4.77), 9.00 (d, 2 H, â, J ) 4.49), 8.91 (d, 2 H, â, J )
4.60), 8.65 (d, 1 H, H7 of 6-nitrobenzothiazolyl acceptor, J ) 2.11),
8.25 (dd, 1 H, H5 of 6-nitrobenzothiazolyl acceptor, J ) 2.19, 6.83,
2.14), 7.98 (d, 1 H, H4 of 6-nitrobenzothiazolyl acceptor, J ) 8.97),
7.86 (d, 2 H, Ar, J ) 8.82), 7.35 (d, 4 H, Ar, J ) 2.10), 6.90 (t, 2
H, Ar, J ) 2.25, 2.24), 6.82 (d, 2 H, Ar, J ) 8.86), 4.23 (t, 8 H,
OCH2 CH2), 3.08 (s, 6 H, NMe2), 1.85 (t, 8 H, OCH2 CH2), 1.02
(s, 36 H, tert-butyl). Vis (λmax(log ꢀ); THF): 465 (5.25), 686 (4.87).
Fluorescence emission (THF): 716 nm. ESI-MS: 1269.56 (M+),
calcd for C75H79N7O6SZn: 1269.51.
porphinato]zinc(II) (Compound 7). 9-(5-Iodothiophen-2-yl)-9H-
carbazole (179 mg, 477 µmol), porphyrin 4 (52.5 mg, 47.9 µmol),
Pd2(dba)3 (36.3 mg, 39.3 µmol), AsPh3 (87 mg, 284 µmol), THF
(20 mL), and (i-Pr)2NH (2 mL) were placed in a 100 mL Schlenk
tube under N2. The reaction mixture was stirred at 60 °C for 6 h.
After cooling to RT, the reaction mixture was evaporated to dryness,
and the isolated green residue was chromatographed over silica gel
using 5:1 hexanes/THF as the eluant. A green solid was isolated
and chromatographed on Bio-Beads SX-1 (THF) followed by silica
gel (CHCl3) to give a green solid. Yield: 52 mg (81%, based on
1
52.5 mg of the porphyrinic starting material). H NMR (CDCl3/
TMS/pyridine-d5): δ 9.66 (t, 4 H, â, J ) 4.38, 4.46), 9.01 (t, 4 H,
â, J ) 4.53, 4.86), 8.41 (d, 2 H, Ar, J ) 9.04), 8.16 (d, 2 H, Ar,
J ) 7.84), 8.12 (d, 2 H, Ar, J ) 8.89), 7.77 (d, 1 H, thienyl, J )
3.86), 7.71 (d, 2 H, Ar, J ) 8.11), 7.53 (m, 2 H, Ar), 7.41-7.32
(m, 7 H, 6 Ar + 1 thienyl), 6.89 (t, 2 H, J ) 2.17, 2.18), 4.21 (t,
8 H, average J ) 7.33), 1.83 (t, 8 H, average J ) 7.30), 1.01 (s, 36
H, tert-butyl). Vis (λmax(log ꢀ); THF): 459 nm (5.08) and 665 nm
(4.69). Fluorescence emission (THF): 682 nm. MALDI-TOF
(M+): 1340.73, calcd for C82H80N6O6SZn: 1340.52.
[5-(4-Dimethylaminophenylethynyl)-15-(5-nitrothiazol-2-yl-
ethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)por-
phinato]zinc(II) (Compound 5). Porphyrin 3 (144 mg, 132 µmol),
2-bromo-5-nitrothiazole (273 mg, 1306 µmol), Pd(PPh3)4 (97 mg,
83.9 µmol), CuI (27 mg, 142 µmol), THF (25 mL), and (i-Pr)2NEt
(2 mL) were placed in a 100 mL Schlenk tube, and the mixture
was heated at 54 °C for 23 h. After cooling to RT, the reaction
mixture was poured into a saturated NaCl solution, extracted with
CHCl3, dried over Na2SO4, filtered, and evaporated. The brownish-
green residue was chromatographed sequentially over silica gel (3:1
hexanes/THF), Bio-Beads SX-1 (THF), and silica gel (19:11 CHCl3/
THF). Yield: 85 mg (53%, based on 144 mg of the porphyrinic
Results and Discussion
Design and Synthesis. The syntheses of a series of
conjugated (porphinato)zinc(II) (PZn)-based chromophores
(Figure 1) structurally related to compound 129 are outlined
in Schemes 1 and 2. These porphyrinic compounds exploit
arylethynyl-, thienylethynyl-, thiazolylethynyl-, benzothia-
zolylethynyl-, and carbazolylethynyl-based donor (D) and
acceptor (A) moieties. Note that two structures (compounds
6 and 7) feature 4-nitrophenylethynyl electron-withdrawing
moieties, while compounds 1-5 define a set of chro-
mophores having a fixed 4-dimethylaminophenylethynyl
electron-releasing group.
All of these chromophores derive from a common syn-
thon26,29 (porphyrin 1, see Experimental Section) and a
succession of metal-catalyzed cross-coupling reactions.38
Fabrication of compounds 1-7 proceeds through the
intermediacy of either brominated porphyrin 223 (see
Experimental Section) or ethynylated porphyrin 426,29 (see
Experimental Section) intermediates and appropriately func-
tionalized aryl, thienyl, thiazolyl, benzothiazolyl, and car-
bazolyl reagents. Compounds 1-7 all feature a 5,15-
diethynyl(porphinato)zinc(II) core, a structural motif well
established as a key component of a wide range of potent
NLO chromophores.23,26,28,29,31,42,43
1
starting material). H NMR (CDCl3/TMS/1-drop-pyridine-d5): δ
9.67 (d, 2 H, â, J ) 4.51), 9.48 (d, 2 H, â, J ) 4.53), 8.98 (d, 2 H,
â, J ) 4.56), 8.90 (d, 2 H, â, J ) 4.58), 8.59 (br. s, 1 H, thiazolic
C-H), 7.84 (d, 2 H, Ar, J ) 8.65), 7.33 (d, 4 H, Ar, J ) 2.08),
6.90 (t, 2 H, Ar, J ) 2.08, 2.12), 6.80 (d, 2 H, Ar, J ) 8.66), 4.22
(t, 8 H, OCH2CH2, J ) 7.32, 7.35), 3.06 (s, 6 H, NMe2), 1.86 (t,
8 H, OCH2 CH2, J ) 7.33, 7.32), 1.01 (s, 36 H, tert-butyl). Vis
(λmax(log ꢀ); THF): 458 nm (5.07) and 694 nm (4.75). Fluorescence
emission (THF): 712 nm. ESI MS: 1219.54 (M+), calcd for
C71H77N7O6SZn: 1219.49; FAB: 1220.6 (MH+), calcd for
C71H78N7O6SZn: 1220.5.
[5-(2-(N,N-Diphenylamino)thiophen-5-yl-ethynyl)-15-(4-nitro-
phenylethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)-
porphinato]zinc(II) (Compound 6). N-(5-Iodothiophen-2-yl)-
diphenylamine (92 mg, 244 µmol), porphyrin 4 (64 mg, 55.3
µmol), Pd(PPh3)4 (64 mg, 55.3 µmol), CuI (19 mg, 99.7 µmol),
THF (20 mL), and (i-Pr)2NH (2 mL) were placed in a 100 mL
Schlenk tube under nitrogen. The reaction vessel was shielded from
light and stirred at 44 °C for 24 h. After cooling to RT, the dark
green reaction mixture was poured into deionized water, extracted
with CH2Cl2, dried over Na2SO4, filtered, and evaporated. The green
residue was chromatographed sequentially over silica gel (4:1
hexanes/THF), Bio-Beads SX-1 (THF), and silica gel (CHCl3) to
give a green solid. Yield: 22 mg (44%, based on 64 mg of the
porphyrinic starting material). 1H NMR (CDCl3/TMS/pyridine-
d5): δ 9.61 (d, 2 H, â, J ) 4.68), 9.58 (d, 2 H, â, J ) 4.67), 8.99
(d, 2 H, â, J ) 4.68), 8.93 (d, 2 H, â, J ) 4.68), 8.36 (d, 2 H, Ar,
J ) 8.77), 8.06 (d, 2 H, J ) 8.83), 7.47 (d, 1 H, J ) 3.95), 7.40-
7.29 (m, 12 H, Ar), 7.14 (m, 2 H, para-Ar), 6.89 (t, 2 H, J ) 2.16,
2.05), 6.70 (d, 1 H, thienyl, J ) 3.94), 4.20 (t, 8 H, J ) 7.30,
7.36), 1.85 (t, 8 H, J ) 7.31, 7.28), 1.01 (s, 36 H, tert-butyl). Vis
(λmax(log ꢀ); THF): 458 nm (5.02), 674 nm (4.63). Fluorescence
emission (THF): 713 nm. MALDI-TOF (MH+): 1343.8, calcd for
C82H82N6O6SZn + H: 1343.5.
Figure 2 emphasizes the various conjugated, π aromatic
components of compounds 1-7. Previous studies establish
that enhanced hyperpolarizabilities in classic NLO push-
pull chromophore structures based on aryl donor, bridge, and
acceptor components are often observed upon heteroaromatic
replacement of these units, as such species possess typically
a lower aromatic stabilization (delocalization) energy (Sup-
porting Information);1,2,7,10,19-21,29,44,45 PZn-based structures
(42) Priyadarshy, S.; Therien, M. J.; Beratan, D. N. J. Am. Chem. Soc.
1996, 118, 1504-1510.
(43) Karki, L.; Vance, F. W.; Hupp, J. T.; LeCours, S. M.; Therien, M. J.
J. Am. Chem. Soc. 1998, 120, 2606-2611.
(44) Waite, J.; Papadopoulos, M. G. J. Phys. Chem. 1990, 94, 6244-6249.
(45) Hsu, C.-C.; Shu, C.-F.; Huang, T.-H.; Wang, C. H.; Lin, J.-L.; Wang,
Y.-K.; Zang, Y.-L. Chem. Phys. Lett. 1997, 274, 466-472.
[5-(2-(9H-Carbazol-9-yl)-thiophen-5-yl-ethynyl)-15-(4-nitro-
phenylethynyl)-10,20-bis(3,5-bis(3,3-dimethyl-1-butyloxy)phenyl)-
9706 Inorganic Chemistry, Vol. 45, No. 24, 2006

Electronic Modulation of Hyperpolarizable Chromophores
Figure 1. Structures of the push-pull (hetero)arylethynyl porphyrins investigated.
Scheme 1. Syntheses of Compounds 2 and 3
1-7 thus differ from the archetypal push-pull [bis(aryl-
ethynyl)porphinato]zinc(II) NLO chromophore23,42 and ex-
ploit ethynylthiophene, ethynylthiazole, and ethynylben-
zothiazole components. Motivating factors for selection of
diphenylamino-N-thiophen-2-yl-5-ethynyl,11,46-50 5-(carbazol-
9-yl-thiophen-2-yl-5-ethynyl,51-55 2-formyl-thiophen-5-yl-
ethynyl, 2-(2,2-dicyanovinyl)-thiophen-5-yl-ethynyl,2,9,10,56-58
and 6-nitro-benzothiazol-2-yl-ethynyl3,4 electron-releasing
and electron-withdrawing components in 1-7 are congruent
with established literature precedent; the Supporting Infor-
mation correlates the lower aromatic stabilization energy of
these heteroaromatic electron-releasing and -withdrawing
units with a substantial body of spectroscopic data.
(51) Zhang, Y.-D.; Wang, L.; Wada, T.; Sasabe, H. Chem. Commun. 1996,
559-561.
(52) Zhang, Y.-D.; Wang, L.; Wada, T.; Sasabe, H. Macromolecules 1996,
29, 1569-1573.
(46) Moylan, C. R.; Twieg, R. J.; Lee, V. Y.; Swanson, S. A.; Betterton,
K. M.; Miller, R. D. J. Am. Chem. Soc. 1993, 115, 12599-12600.
(47) Verbiest, T.; Burland, D. M.; Jurich, M. C.; Lee, V. Y.; Miller, R. D.;
Volksen, M. Science 1995, 268, 1604-1606.
(53) Zhang, Y.; Wada, T.; Sasabe, H. J. Mater. Chem. 1998, 8, 809-828.
(54) Meshulam, G.; Berkovic, G.; Kotler, Z.; Ben-Asuly, A.; Mazor, R.;
Shapiro, L.; Khodorkovsky, V. Synth. Met. 2000, 115, 219-223.
(55) Meshulam, G.; Berkovic, G.; Kotler, Z. Opt. Lett. 2001, 26, 30-32.
(56) Katz, H. E.; Singer, K. D.; Sohn, J. E.; Dirk, C. W.; King, L. A.;
Gordon, H. M. J. Am. Chem. Soc. 1987, 109, 6561-6563.
(57) Kuder, J. E.; Limburg, W. W.; Pochan, J. M.; Wychick, D. J. Chem.
Soc., Perkin 2 1977, 1643-1651.
(48) Whitaker, C. M.; Patterson, E. V.; Kott, K. L.; McMahon, R. J. J.
Am. Chem. Soc. 1996, 118, 9966-9973.
(49) Thayumanavan, S.; Barlow, S.; Marder, S. R. Chem. Mater. 1997, 9,
3231-3235.
(50) Yang, J.-S.; Chiou, S.-Y.; Liau, K.-L. J. Am. Chem. Soc. 2002, 124,
2518-2527.
(58) Wu, X. M.; Wu, J.; Liu, Y.; Jen, A. K. Y. Chem. Commun. 1999,
2391-2392.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9707

Zhang et al.
Scheme 2. Syntheses of Compounds 4, 5, 6, and 7
Linear and Nonlinear Optical Properties. For these
dipolar molecules, the diagonal component âzzz of the molec-
ular first hyperpolarizability (or second-order nonlinear
polarizability) tensor has been evaluated (see Experimental
Section). The molecular first hyperpolarizability, â, was
determined by HRS measurements for compounds 1-7 in
THF solution.59,60 As these compounds fluoresce, it is essen-
tial to use a femtosecond (fs) pulsed laser in these experi-
ments in order to discriminate between scattering (immediate
and hyper-Rayleigh) and time-delayed, multiphoton fluores-
cence. Our approach for eliminating a multiphoton contribu-
tion to the HRS signal involves a Fourier transform of the
frequency domain data to the time domain: as the fluores-
cence is to a large extent delayed in time, it is advantageous
to measure the HRS signal at early times following the
incident fundamental laser pulse.61 In the frequency domain,
this results in any fluorescence signals being phase-shifted
and diminished in amplitude with increasing amplitude
modulation (AM) frequencies.62,63 Such fs HRS measure-
ments of fluorescent molecules that discriminate between
scattering and multiphoton fluorescence are performed at
successively higher AM frequencies. The analysis of the
frequency-dependent apparent hyperpolarizability data pro-
vides a true (fluorescence-free) hyperpolarizability value at
infinitely high frequency, the magnitude of the multiphoton
fluorescence contribution at zero frequency, and a fluores-
cence lifetime; this latter quantity can be compared with the
corresponding fluorescence lifetime obtained from time-
correlated single-photon counting (TCSPC) experiments.
To verify temporal, thermal, and photochemical stability
of chromophores 1-7 under these HRS nonlinear optical
(59) Clays, K.; Persoons, A. Phys. ReV. Lett. 1991, 66, 2980-2983.
(60) Clays, K.; Persoons, A. ReV. Sci. Instrum. 1992, 63, 3285-3289.
(61) Noordman, O. F. J.; van Hulst, N. F. Chem. Phys. Lett. 1996, 253,
145-150.
(62) Olbrechts, G.; Strobbe, R.; Clays, K.; Persoons, A. ReV. Sci. Instrum.
1998, 69, 2233-2241.
(63) Wostyn, K.; Binnemans, K.; Clays, K.; Persoons, A. ReV. Sci. Instrum.
2001, 72, 3215-3220.
Figure 2. Conjugated, π aromatic frameworks to which antipodal electron-
releasing and electron-withdrawing groups are attached in compounds 1-7.
9708 Inorganic Chemistry, Vol. 45, No. 24, 2006

Electronic Modulation of Hyperpolarizable Chromophores
Figure 5. Comparative ground-state electronic absorption spectra for
compounds 6 and 7 in THF solvent.
Figure 3. Comparative ground-state electronic absorption spectra for
compounds 1, 2, and 3 in THF solvent.
Figure 6. Comparative fluorescence emission spectra for compounds 6
and 7 in THF solvent.
high-frequency limit; simultaneous fitting of the amplitude
and the phase data determines the fluorescence-free first
hyperpolarizability value (Figure 9). Table 1 provides an
overview of the linear and nonlinear optical properties of
this series of chromophores.
Figure 4. Comparative fluorescence emission spectra for compounds 1,
2, and 3 in THF solvent.
measurement conditions (high peak power pulsed illumina-
tion over multiple measurement cycles), electronic absorption
and emission spectra (Figures 3-8) were compared before
and after acquisition of NLO data; these studies indicated
that all these species were robust. The apparent dynamic
hyperpolarizability as a function of modulation frequency
for 1-7 did show an appreciable frequency dependence and
phase accumulation for increasing modulation frequencies
at 1300 nm. Therefore, the dynamic apparent hyperpolariz-
ability values at this wavelength were extrapolated to the
The compound 1 benchmark,29 which features dimethyl-
aminophenylethynyl-donor and nitrothienylethynyl-acceptor
moieties, shows a sizable dynamic hyperpolarizability at 1300
nm (690 × 10-30 esu). An important factor governing the
magnitude of the dynamic hyperpolarizability value in
oligothiophenyl and oligothiophenylethynyl elaborated por-
phyrin-based chromophores has been shown to be the degree
of Q-state derived resonance enhancement factor. For these
compounds, this value is largely determined by the proximity
of the x-polarized41 Q-band λmax value to the second harmonic
Inorganic Chemistry, Vol. 45, No. 24, 2006 9709

Zhang et al.
Compounds 2 and 3, which possess, respectively, formyl
and dicyanovinyl acceptor groups,31,56 confirm these earlier
conclusions. Previous studies examining hyperpolarizable
porphyrin-based donor-acceptor chromophores that feature
thiophenyl, [2,2′]bithiophenyl, and [2,2′;5′,2′′]terthiophenyl
units terminated with a 5-nitro group and points of con-
nectivity that vary between the macrocycle meso-carbon
position and meso-appended-ethynyl moiety show that the
spectral position of the x-polarized Q-state derived absorption
maximum and, hence, the first hyperpolarizability value are
dependent upon the number of intervening thiophene units.
The Table 1 data show that modulation of the thienyl
acceptor strength (Supporting Information) at constant
conjugation length controls similarly the Q-band λmax value.
Because the Soret (B band) absorption λmax value lies far
from the λinc second-harmonic wavelength (650 nm) and
varies little in compounds 1-7, the resonance enhancement
originating from the B-state manifold centered near 450 nm
can be considered near constant. As the Q-band absorption
λmax is sensitive to the nature of the acceptor in 1-3,
electronic modulation at the thienyl 2-position has a pro-
nounced effect on measured dynamic first hyperpolarizabili-
ties. Because compound 2’s formyl group drives a blue-
shift of the Q-band λmax toward the second-harmonic
wavelength relative to that observed for compound 1, while
the stronger dicyanovinyl acceptor in compound 3 effects a
corresponding x-polarized Q-state red-shift, compound 2
possesses the largest â1300 value of these three chromophores.
Note that the impact of decreasing the Eop - 2Einc energy
separation in this spectral region (compound 2) has a much
greater impact on the magnitude of âλ than does the
augmentation of Pge and ∆µge (eq 1) that derives from the
superior dicyanovinyl acceptor (compound 3; see Figure 3,
Table 1).
Figure 7. Comparative ground-state electronic absorption spectra for
compounds 4 and 5 in THF solvent.
With respect to the linear spectroscopy of these com-
pounds, it is clear that the relative acceptor strength is also
reflected in the fluorescence Stokes shift. The Stokes shifts
for compounds 1-7 vary from 364 to 1150 cm-1, indicating
that these PZn-based chromophores undergo modest-to-
substantial excited-state electronic structural redistributions.
These Stokes shift data are consistent with expectations based
on (i) previous studies of closely related D-A derivatized
PZn chromophores,9,38,42,67,68 (ii) electronic structural effects
arising from the integration of heteroaromatics possessing
modest aromatic stabilization energies along molecular axis
of highest conjugation,13,30,68-71 and (iii) the energetic
proximity of the D, PZn-based bridge, and A frontier orbital
energy levels,9,30,38,42,67,68 which suggest that the excited states
of these species should possess an appreciable quinoidal
Figure 8. Comparative fluorescence emission spectra for compounds 4
and 5 in THF solvent.
wavelength of 650 nm, when performing HRS experiments
at 1300 nm.29 The impact of 2-photon resonance enhance-
ment can be appreciated within the context of a simple
2-level formulation of â (eq 1).64-66
6(Pge)2n(∆µge)n(Eop)2n
[(Eop)2n - (2Einc)2][(Eop)2n - Einc
â′ )
(1)
n
2
]
(67) Garcia, P.; Pernaut, J. M.; Hapiot, P.; Wintgens, V.; Valat, P.; Garnier,
F.; Delabouglise, D. J. Phys. Chem. 1993, 97, 513-516.
(68) Rao, V. P.; Cai, Y. M.; Jen, A. K. Y. Chem. Commun. 1994, 1689-
1690.
In the above equation, Eop is the energy of the optical
transition of interest, and Pge and ∆µge are, respectively, the
transition strength and ground-to-excited-state dipole moment
change associated with the charge-transfer absorption.
(69) Chosrovian, H.; Rentsch, S.; Grebner, D.; Dahm, D. U.; Birckner, E.;
Naarmann, H. Synth. Met. 1993, 60, 23-26.
(70) Becker, R. S.; de Melo, J. S.; Macanita, A. L.; Elisei, F. J. Phys. Chem.
1996, 100, 18683-18695.
(64) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664-2668.
(65) Oudar, J. L. J. Chem. Phys. 1977, 67, 446-457.
(66) Willetts, A.; Rice, J. E.; Burland, D. M.; Shelton, D. P. J. Chem. Phys.
1992, 97, 7590-7599.
(71) Pappenfus, T. M.; Raff, J. D.; Hukkanen, E. J.; Burney, J. R.; Casado,
J.; Drew, S. M.; Miller, L. L.; Mann, K. R. J. Org. Chem. 2002, 67,
6015-6024.
9710 Inorganic Chemistry, Vol. 45, No. 24, 2006

Electronic Modulation of Hyperpolarizable Chromophores
Figure 9. Typical dependence of measured values, and the phase angle between the HRS signal and fluorescence reference signal, determined as a function
of modulation frequency. Data displayed are for compound 7.
Table 1. Linear and Nonlinear Optical Properties for Porphyrin Chromophores 1-7 in THF Solvent
B band
max/(nm)
Q-band
fluorescence
E0,0
(eV)
Stokes
â1300
chromophore
λ
λ
max/(nm)
λ
em/(nm)
shift (cm-1
)
(10-30 esu)
1
2
3
4
5
6
7
465
461
469
465
458
458
459
685
676
698
686
694
674
665
714
696
759
716
712
713
682
2.16
2.18
2.12
2.15
2.15
2.19
2.20
593
425
1151
611
364
812
375
690
1020
785
1140
1000
810
1400
resonance contribution. The quinoidal resonance form en-
hances the extent to which electron density is redistributed
between the electron-releasing and electron-accepting com-
ponents of these chromophores in the excited state. Consis-
tent with the large dicyanovinyl acceptor strength, compound
3 possesses the largest magnitude Stokes shift and the lowest
energy fluorescence emission λmax. Note that, while the
Stokes shift reflects the extent of ground-to-excited-state
electronic charge redistribution (∆µge) and has been often
taken as a qualitative measure of chromophoric static
hyperpolarizability, the fact that theses values do not track
with the experimentally determined dynamic hyperpolariz-
abilities (Table 1), points to the over-riding importance of
Q-state derived resonance enhancement factor in determining
the â1300 value for compounds 1-7.
Compounds 6 and 7 are compound 1 analogues in which
the charge-transfer direction is inverted; note that in 6 and 7
that it is the aryl ring that bears the 4′-nitro group while the
thienyl unit features a 2′-electron-releasing moiety. This
electronic structural modification has only a modest impact
upon the electronic absorption spectra of these species
relative to that of the compound 1 benchmark (Figures 3
and 5, Table 1); in contrast, the emission spectra of these
species (Figures 4 and 6) reflect that diminished excited-
state structural heterogeneity is manifest in compound 7
relative to compounds 1 and 6, which derives from the fact
that the compound 7 electron-releasing group is a planar,
conjugated carbazolyl unit. Note that the x-polarized Q-state
absorption of 6 and 7 are blue-shifted relative to compound
1; hence, the measured dynamic hyperpolarizability values
at λinc ) 1300 nm are affected by resonance enhancement
in much the same way as discussed above for compounds
1-3 (Table 1). While compound 6 and 7 â1300 values exceed
that measured for compound 1, note that the observed
enhancement in nonlinear response determined in 7 exceeds
that of compounds 1 and 6 by approximately 2-fold.
For compound 1-7, it is noteworthy that oscillator
strengths of the low energy Q-state electronic manifolds are
virtually identical (Figures 3, 5, and 7). Considering com-
pounds 6 and 7 as a case in point (Figure 5), it is clear that
a diminished S0 f S1 transition energy is not correlated with
an increase in the first hyperpolarizability. Reductions in the
magnitude of the optical band gap, however, are commonly
correlated with augmented first hyperpolarizabilities; this
effect is commonly referred to as the nonlinearity/transpar-
ency tradeoff.72,73 That this correlation is not observed in 6
and 7 and throughout the range of chromophores described
herein derives likely from the transfer of oscillator strength
between overlapping π-π* and CT transitions within the
low-energy transition manifold as a function of the nature
of electron-releasing and electron-withdrawing components
in these structures. This effect has been noted in closely
related chromophores.29 Hence, as highlighted in Figure 5
(see also Figures 3 and 7), Pge remains relatively constant
while ∆µge varies with nature of donor and acceptor; small
reductions in the Eop - 2Einc energy gap thus enable large
modulations in the â1300 value in compounds 1-7 at
approximately constant chromophoric transparency.
(72) Ledoux, I.; Zyss, J.; Jutand, A.; Amatore, C. Chem. Phys. 1991, 150,
117-123.
(73) Cheng, L.-T.; Tam, W.; Stevenson, S. H.; Meredith, G. R.; Rikken,
G.; Marder, S. R. J. Phys. Chem. 1991, 95, 10631-10643.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9711

Zhang et al.
Compounds 4 and 5 probe the effect of diminishing the
acceptor aromatic stabilization energy (Supporting Informa-
tion) relative to the compound 1 benchmark. Compounds
4 and 5 utilize, respectively, nitrobenzothiazolylethynyl and
nitrothiazolylethynyl acceptor groups and a dimethylami-
nophenylethynyl donor unit in common with compound 1.
As seen in the linear absorption spectra (Figure 7), the
reduced acceptor aromatic stabilization energies in 6 and 7
effect a similar spectroscopic perturbation relative to the
compound 1 spectrum, as was observed when the dicy-
anovinyl unit was introduced to the thienyl 2-position
(compound 3, Figure 3). Consistent with the above discus-
sion, differences in the measured dynamic hyperpolarizabili-
ties of compounds 3, 4, and 5 track qualitatively with the
extent of Q-state derived resonance enhancement (Table 1).
which reductions in the magnitude of the aromatic stabiliza-
tion energy of these groups impact the molecular hyperpo-
larizability.
Recent studies examining hyperpolarizable porphyrin-
based donor-acceptor chromophores that feature thiophenyl,
[2,2′]bithiophenyl, and [2,2′;5′,2′′]terthiophenyl units termi-
nated with a 5-nitro group, and points of connectivity that
vary between the macrocycle meso-carbon position and
meso-appended-ethynyl moiety, show that â1300 values as
large as 4350 × 10-30 esu can be engineered.29 The fact that
this work demonstrates that classic donor-acceptor electronic
modulation of the compound 1 benchmark (â1300 ) 690 ×
10-30 esu) leads to significantly enhanced hyperpolarizabili-
ties, suggests that further improvements in the already large
magnitude â1300 values expressed within this broader family
of prophyrin-oligo(aromatic heterocycle)-based neutral di-
polar chromophores should be possible.
Conclusion
A series of conjugated (porphinato)zinc(II)-based chro-
mophores structurally related to compound 129 were syn-
thesized using metal-catalyzed cross-coupling reactions
involving [5-bromo-15-triisopropylsilylethynyl-10,20-di-
arylporphinato]zinc(II), [5-bromo-15-(4-dimethylaminophe-
nylethynyl)-10,20-diarylporphinato]zinc(II), [5-(4-dimethyl-
aminophenylethynyl)-15-ethynyl-10,20-diarylporphinato]-
zinc(II), and [5-(4-nitrophenylethynyl)-15-ethynyl-10,20-
diarylporphinato]zinc(II), with appropriately functionalized
aryl, thienyl, thiazolyl, benzothiazolyl, and carbazolyl precur-
sors. The measured â1300 values for these hyperpolarizable
(porphinato)zinc(II) chromophores that feature ethynyl-
thiophenyl-, ethynylthiazolyl-, and ethynylbenzothiazolyl-
based electron-releasing and -withdrawing groups ranged
from 690 f 1400 × 10-30 esu and highlight the extent to
Acknowledgment. This work was funded through grants
from the Office of Naval Research N00014-01-1-0725, the
U. S. Department of Energy (DE-FG02-04ER46156), the
Belgian government (IUAP/5/3), the Flemish Fund for
Scientific Research (G.0261.04), and the University of
Leuven (G0A/2000/03). M.J.T. thanks the MRSEC Program
of the National Science Foundation (DMR00-79909) for
infrastructural support.
Supporting Information Available: Syntheses and character-
ization data for key precursor structures and chromophoric bench-
marks; Hammett correlation analysis, NMR, absorption, and
emission data for porphyrin-based compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC060898E
9712 Inorganic Chemistry, Vol. 45, No. 24, 2006