Synthesis, characterization, and second-harmonic generation studies of rhenium(I) surfactant complexes in Langmuir-Blodgett films

Article abstract of DOI:10.1021/om990512q

A series of rhenium(I) surfactant complexes of general formula fac-[Re(CO)₃(bpy)(L)]PF₆ (bpy = 2,2′-bipyridine, L = 4-(4′-octadecyloxyphenylazo)pyridine (L1), 4-(4′-octadecyloxyphenylstilbazole)pyridine (L2), 4-(4′-octadecyloxyphenyl

Full text of DOI:10.1021/om990512q

5252
Organometallics 1999, 18, 5252-5258
Syn th esis, Ch a r a cter iza tion , a n d Secon d -Ha r m on ic
Gen er a tion Stu d ies of Rh en iu m (I) Su r fa cta n t Com p lexes
in La n gm u ir -Blod gett F ilm s
Vivian Wing-Wah Yam,* Yu Yang, He-Ping Yang, and Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, HKSAR, People’s Republic of China
Received J uly 2, 1999
A series of rhenium(I) surfactant complexes of general formula fac-[Re(CO)3(bpy)(L)]PF6
(bpy ) 2,2′-bipyridine, L ) 4-(4′-octadecyloxyphenylazo)pyridine (L1), 4-(4′-octadecyloxyphe-
nylstilbazole)pyridine (L2), 4-(4′-octadecyloxyphenylethynyl)pyridine (L3)) were synthesized
and characterized, and their photophysical and photochemical properties studied. The X-ray
crystal structure of the complex fac-[Re(CO)3(bpy)(L1)]PF6 has been determined. The
formation and optical properties of these complexes in Langmuir-Blodgett (LB) films were
studied by surface pressure-area (π-A) isotherms and UV-visible and luminescence
spectroscopy. Their second-harmonic generation (SHG) behavior has also been investigated.
These Re(I) surfactant complexes were shown to exhibit first-order hyperpolarizabilities
comparable to, and in some cases slightly higher than, those of their organic analogues.
In tr od u ction
centrosymmetric media for dipolar molecules. The Lang-
muir-Blodgett (LB) technique, which is one of the
powerful tools of making highly homogeneous, ordered
ultrathin films, has been exploited to build materials
with a non-centrosymmetric packing arrangement.6 A
number of π-conjugated organic compounds with electron-
donating and -accepting groups have been known to
show SHG behavior when incorporated into LB films.3
A number of organometallic compounds have also
been shown to exhibit second-order NLO properties
since their reports appeared in the late 1980s.7 Large
NLO responses are usually observed in organometallic
molecules that possess large charge-transfer character.8
Recent work by us has shown that the rhenium(I)
diimine tricarbonyl complexes, which are well-known
for the rich photophysical and photochemical properties
of their MLCT excited states,9,10 show, in addition to
their chemosensory11 and optical switching properties,10b
interesting NLO responses.10i,j,12
Nonlinear optical (NLO) materials are currently
under intensive investigation for their potential ap-
plication in optical signal processing and telecom-
munications.1 Much effort has been placed on the design
and syntheses of molecules with large nonlinearities and
on assembling and fabricating the molecules into mi-
croscopic structures such as crystals,2 Langmuir-
Blodgett (LB) films,3 self-assembly films,4 and poled
polymers.5 It is well-known that significant second-
harmonic generation (SHG) can only occur in non-
(1) (a) Molecular Nonlinear Optics; Zyss, J ., Ed.; Academic Press:
Boston, 1994. (b) Materials for Nonlinear Optics, Chemical Perspectives;
Marder, S. R., Sohn, J . E., Stucky, G. D., Eds.; ACS: Washington, DC,
1991. (c) Prasad, P. N.; Williams, D. J . Introduction to Nonlinear
Optical Effects in Molecules and Polymers; Wiley: New York, 1991.
(d) Munn, R. W.; Ironside, C. N. Principles and Applications of
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837. (b) Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98,
1375.
In this report, the synthesis and characterization of
a series of rhenium(I) surfactant complexes with ex-
tended donor-acceptor pyridine ligands, fac-[Re(CO)3-
(bpy)(L)]PF6 (bpy ) 2,2′-bipyridine, L ) 4-(4′-octadecyl-
oxyphenylazo)pyridine (L1), 4-(4′-octadecyloxyphenyl-
stilbazole)pyridine (L2), 4-(4′-octadecyloxyphenylethy-
nyl)pyridine (L3)), are described. The formation and
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10.1021/om990512q CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/11/1999

Rh(I) Surfactant Complexes in LB Films
Organometallics, Vol. 18, No. 25, 1999 5253
Sch em e 1
optical properties of these complexes in LB films have
been studied by surface pressure-area (π-A) isotherms
and UV-visible and luminescence spectroscopy. The
SHG capabilities of these complexes have also been
assessed.
Exp er im en ta l Section
Ma ter ia ls. Re(CO)5Cl (98%, Strem), 2,2′-bipyridine (99%,
Lancaster), silver trifluoromethanesulfonate (99%, Aldrich),
and ammonium hexafluorophosphate (99.5%, Strem) were
used as received. 2-Methyl-3-butyn-2-ol (98%, Acros) was
distilled before use. Piperidine (99%, Acros) was distilled over
CaH2. All other solvents for synthesis were of analytical grade
and were used without further purification.
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W. W.; Wong, K. M. C.; Lee, V. W. M.; Lo, K. K. W.; Cheung, K. K.
Organometallics 1995, 14, 4043. (e) Yam, V. W. W.; Wong, K. M. C.;
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K. K. W.; Cheung, K. K.; Kong, R. Y. C. J . Chem. Soc., Chem. Commun.
1995, 1191. (g) Yam, V. W. W.; Lo, K. K. W.; Cheung, K. K.; Kong, R.
Y. C. J . Chem. Soc., Dalton Trans. 1997, 2067. (h) Yam, V. W. W.;
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Syn th esis. Synthetic schemes for the ligands and the
rhenium(I) complexes are summarized in Scheme 1.
Syn th esis of P yr id yl Liga n d s. trans-4-(4′-Hydroxyphenyl-
azo)pyridine,13 4-octadecyloxyphenylacetylene,14 and ligand
L215 were prepared according to literature procedures.
tr a n s-4-(4′-Octa d ecyloxyp h en yla zo)p yr id in e (L1). Un-
like the synthesis of trans-4(4′-methoxyphenylazo)pyridine
analogue,13 L1 was synthesized by stirring a mixture of trans-
4-(4′-hydroxyphenylazo)pyridine (0.5 g, 2.5 mmol), 1-bromo-
octadecane (0.8 g, 2.4 mmol), and potassium carbonate (0.69
g, 5 mmol) in dimethylformamide (DMF) (15 mL) at room
temperature for 3 days. Potassium bromide produced was
filtered off, and the DMF was removed by distillation under
reduced pressure. The residue was redissolved in chloroform
(15 mL) and washed with water (3 × 15 mL). The organic layer
was separated and dried over anhydrous magnesium sulfate.
Filtration and subsequent removal of the solvent by rotary
evaporation of the organic layer yielded the crude products,
which were purified by column chromatography on silica gel
using chloroform as eluent to afford 0.61 g of the pale yellow
desired product. Yield: 56%. 1H NMR (300 MHz, CDCl3,
relative to Me4Si): δ 8.77 (d, 2H, J ) 6.1 Hz, pyridyl), 7.95 (d,
2H, J ) 9.0 Hz, phenyl), 7.67 (d, 2H, J ) 6.2 Hz, pyridyl),
7.02 (d, 2H, J ) 9.0 Hz, phenyl), 4.06 (t, 2H, J ) 6.6 Hz,
-OCH2-), 1.83 (m, 2H, -CH2-), 1.48 (m, 2H, -CH2-), 1.26
(m, 28H, -CH2-), 0.88 (t, 3H, J ) 6.4 Hz, -CH3). Anal.
Found: C, 76.36; H, 10.04; N, 9.48. Calcd for C29H45N3O‚
1/4H2O: C, 76.35; H, 9.94; N, 9.21.
(13) Buncel, E.; Keum, S. R. Tetrahedron 1983, 39, 1091.
(14) (a) Melissaris, A. P.; Litt, M. H. J . Org. Chem. 1992, 57, 6998.
(b) Ames, D. E.; Bull, D.; Takundwa, C. Synthesis 1981, 364.
(15) Bruce, D. W.; Dunmur, D. A.; Lalinde, E.; Maitlis, P. M.;
Styring, P. Liq. Cryst. 1988, 3, 385.
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Sullivan, B. P.; Noe, L. J . J . Phys. Chem., B 1997, 101, 3174.

5254 Organometallics, Vol. 18, No. 25, 1999
Yam et al.
4-(4′-Octadecyloxyph en yleth yn yl)pyr idin e (L3). L3 was
synthesized by modification of a literature method for 5,5′-
[(4-hexadecyloxyphenyl)ethynyl]-2,2′-bipyridine.16 A mixture
of 4-bromopyridine hydrochloride (0.21 g, 1.1 mmol) and
4-octadecyloxyphenylacetylene (0.37 g, 1 mmol) was dissolved
in freshly distilled piperidine (10 mL). Copper(I) iodide (10 mg),
dichlorobis(triphenylphosphine)palladium(II) (10 mg), and
triphenylphosphine (40 mg) were added as the catalysts. The
mixture was heated to reflux under nitrogen for 24 h. The
purification was the same as that of L1 except that n-hexanes-
ethyl acetate (3:1, v/v) was used as eluent instead of chloro-
form. Recrystallization from ethyl acetate yielded 0.34 g of the
pure product. Yield: 75%. 1H NMR (300 MHz, CDCl3, ppm
relative to Me4Si): δ 8.58 (dd, 2H, J 1 ) 4.5 Hz, J 2 ) 1.6 Hz,
1929 (s) ν(CO), 1919 (s) ν(CO). Positive FAB-MS m/z: 877
{M}+, 427 {M - L2}+. Anal. Found: C, 51.50; H, 5.35; N, 3.83.
Calcd for fac-[Re(CO)3(bpy)L2]PF6: C, 51.76; H, 5.39; N, 4.12.
fa c-[Re(CO)3(bpy)(L3)]P F6: yellow-orange crystalline solid,
yield 75%. Mp: 136.5 °C. 1H NMR (300 MHz, CDCl3, ppm
relative to Me4Si): δ 9.07 (d, 2H, J ) 5.0 Hz, 6,6′-H of bpy),
8.56 (d, 2H, J ) 8.2 Hz, 3,3′-H of bpy), 8.29 (m, 2H, 4,4′-H of
bpy), 8.05 (d, 2H, J ) 6.1 Hz, pyridyl H ortho to N), 7.75 (m,
2H, 5,5′-H of bpy), 7.41 (d, 2H, J ) 8.8 Hz, phenyl H of L3),
7.32 (d, 2H, J ) 6.1 Hz, pyridyl H meta to N), 6.85 (d, 2H, J
) 8.8 Hz, phenyl H of L3), 3.95 (t, 2H, J ) 6.5 Hz, -OCH2-),
1.77 (m, 2H, -CH2-), 1.43 (m, 2H, -CH2-), 1.25 (m, 28H,
-(CH2)14-), 0.87 (t, 3H, J ) 6.3 Hz, -CH3). UV-vis (CH2Cl2,
λ/nm (ꢀ × 10-4/dm3mol-1cm-1)): 366 (3.47). UV-vis (LB film,
λ/nm): 350. IR (Nujol, ν/cm-1): 2035 (s) ν(CO), 1942 (s) ν(CO),
1908 (s) ν(CO), 2185(v), 2219 (m) ν(CtC). Positive FAB-MS
m/z: 874 {M}+, 427 {M - L3}+. Anal. Found: C, 51.77; H,
5.12; N, 3.78. Calcd for fac-[Re(CO)3(bpy)L3]PF6: C, 51.87; H,
5.21; N, 4.13.
P h ysica l Mea su r em en ts a n d In str u m en ta tion . The
UV-vis spectra were obtained on a Hewlett-Packard 8452A
diode array spectrophotometer, IR spectra as Nujol mulls on
a Bio-Rad FTS-7 spectrophotometer, and steady-state excita-
tion and emission spectra on a Spex Fluorolog-2 111 spectro-
fluorometer with or without Corning filters. Low-temperature
(77 K) spectra were recorded using an optical Dewar sample
holder. Proton NMR spectra were recorded on a Bruker DPX-
300 NMR spectrometer with chemical shifts reported relative
to tetramethylsilane (Me4Si). Positive ion fast-atom bombard-
ment (FAB) and electron impact (EI) mass spectra were
recorded on a Finnigan MAT95 mass spectrometer. Elemental
analyses were performed on a Carlo Erba 1106 elemental
analyzer at the Institute of Chemistry in Beijing, Chinese
Academy of Sciences.
Emission lifetime measurements were made using a con-
ventional laser system. The excitation source was the 355 nm
output (third harmonic) of a Quanta-Ray Q-switched GCR-
150-10 pulsed Nd:YAG laser. Luminescence decay signals were
recorded on a Tektronix TDS 620A digital oscilloscope and
analyzed using a program for exponential fits according to the
equation I(t) ) I0 exp(-t/τ), where I(t) stands for emission
intensity at time t after the laser pulse and I0 is the initial
intensity at t ) 0. All solutions for photophysical studies were
prepared under vacuum in a 10 cm3 round-bottom flask
equipped with a sidearm 1 cm fluorescence cuvette sealed from
the atmosphere by a Kontes quick-release Teflon stopper.
Solutions were rigorously degassed with no fewer than four
freeze-pump-thaw cycles.
pyridyl), 7.48 (d, 2H, J ) 8.8 Hz, phenyl), 7.35 (dd, 2H, J 1
)
4.5 Hz, J 2 ) 1.6 Hz, pyridyl), 6.89 (d, 2H, J ) 8.8 Hz, phenyl),
3.98 (t, 2H, J ) 6.6 Hz, -OCH2-), 1.79 (m, 2H, -CH2-), 1.46
(m, 2H, -CH2-), 1.26 (m, 28H, -(CH2)14-), 0.88 (t, 3H, J )
6.3 Hz, -CH3). 13C NMR (75.5 MHz, CDCl3, ppm relative to
Me4Si): 159.96, 149.68, 133.43, 131.86, 125.36, 114.64, 113.81
(pyridyl and phenyl C), 94.45, 85.57 (-CtC-), 68.11, (-OCH2-
), 31.94, 29.72, 29.61, 29.39, 29.16, 26.01, 22.71, 14.13 (alkyl
C). EI-MS m/z: 447 (M+). Anal. Found: C, 83.33; H, 10.37; N,
3.10. Calcd for C31H45N3O: C, 83.17; H, 10.13; N, 3.13.
Syn th esis of Rh en iu m (I) Com p lexes. The rhenium(I)
complexes fac-[Re(CO)3(bpy)Cl]9d,j,10 and fac-[Re(CO)3(bpy)-
(MeCN)]OTf 10,17 were prepared according to literature meth-
ods.
Gen er a l Syn th esis of fa c-[Re(CO)3(bp y)(L)]P F 6. This
was synthesized by modification of a reported procedure.17
A
mixture of fac-[Re(CO)3(bpy)(MeCN)]OTf (1 equiv) and ligand
L (1.5 equiv) in tetrahydrofuran (THF) was heated to reflux
under nitrogen for 12 h. The resulting solution was allowed
to cool and evaporated to dryness under vacuum. The residue
-
was then dissolved in methanol and metathesized to its PF6
salt upon addition of a saturated methanolic solution of NH4-
PF6. The solid obtained was recrystallized by vapor diffusion
of diethyl ether into a dichloromethane solution of the product.
fa c-[Re(CO)3(bp y)(L1)]P F 6: red crystalline solid, yield
85%. Mp: 120.5 °C. 1H NMR (300 MHz, acetone-d6, ppm
relative to Me4Si): δ 9.53 (d, 2H, J ) 5.6 Hz, 6,6′-H of bpy),
8.75 (m, 4H, 3,3′-H of bpy and pyridyl H ortho to N), 8.50 (m,
2H, 4,4′-H of bpy), 8.04 (m, 2H, 5,5′-H of bpy), 7.94 (d, 2H, J
) 9.0 Hz, phenyl H of L1), 7.72 (d, 2H, J ) 6.8 Hz, pyridyl H
meta to N), 7.15 (d, 2H, J ) 9.1 Hz, phenyl H of L1), 4.15 (t,
2H, J ) 6.5 Hz, -OCH2-), 1.82 (m, 2H, -CH2-), 1.49 (m, 2H,
-CH2-), 1.28 (m, 28H,-(CH2)14-), 0.87 (t, 3H, J ) 6.4 Hz,
-CH3). UV-vis (CH2Cl2, λ/nm (ꢀ × 10-4/dm3mol-1cm-1)): 396
(3.36). UV-vis (LB film, λ/nm): 388. IR (Nujol, ν/cm-1): 2031
(s) ν(CO), 1936 (s) ν(CO), 1915 (s) ν(CO). Positive FAB-MS
m/z: 879 {M}+, 427 {M - L1}+. Anal. Found: C, 49.26; H,
5.13; N, 6.91. Calcd for fac-[Re(CO)3(bpy)L1]PF6: C, 49.27; H,
5.18; N, 6.84.
La n gm u ir -Blod gett (LB) F ilm P r ep a r a tion . Ultrapure
water (resistivity >18 MΩ cm) was obtained from an Elga
UHQ PS apparatus and was immediately used for the Z-type
LB film preparation. The quartz substrates were made hy-
drophilic by consecutive sonication in detergent for 30 min and
acetone for 15 min and soaking in both chromic acid and
piranha solution (30% H2O2-H2SO4, 3:7 v/v) for 8 h each before
they were finally washed repeatedly with copious amounts of
distilled and ultrapure water. The complexes in dichlo-
romethane (1.02 mg cm-3 for fac-[ReCO)3(bpy)(L1)]PF6, 1.04
mg cm-3 for fac-[Re(CO)3(bpy)(L2)]PF6, and 1.00 mg cm-3 for
fac-[Re(CO)3(bpy)(L3)]PF6) were spread onto a pure water
phase (pH 5.4, 18 °C) in a Nima model-622 computer-controlled
trough. After a 15 min period to allow for the evaporation of
the solvent, surface pressure-area (π-A) isotherms were
recorded at a barrier compression speed of 150 cm2 min-1. The
monolayers formed under a constant surface pressure (30 mN
m-1 for fac-[Re(L1)(CO)3(bpy)]PF6, 25 mN m-1 for both fac-
[Re(L2)(CO)3(bpy)]PF6, and fac-[Re(L3)(CO)3(bpy)]PF6) were
transferred onto hydrophilically treated quartz substrates after
maintaining the pressure constant at the transfer pressure
fa c-[Re(CO)3(bp y)(L2)]P F 6: yellow crystalline solid, yield
1
84%. Mp: 142 °C. H NMR (300 MHz, CDCl3, ppm relative to
Me4Si): δ 9.07 (d, 2H, J ) 5.4 Hz, 6,6′-H of bpy), 8.54 (d, 2H,
J ) 8.2 Hz, 3,3′-H of bpy), 8.27 (d, 2H, J ) 7.9 Hz, 4,4′-H of
bpy), 7.95 (d, 2H, J ) 6.7 Hz, pyridyl H ortho to N), 7.73 (m,
2H, 5,5′-H of bpy), 7.41 (d, 2H, J ) 8.8 Hz, phenyl H of L2),
7.31 (d, 2H, J ) 6.7 Hz, pyridyl H meta to N), 7.25 (d, 1H, J
) 16 Hz, vinyl H of L2), 6.85 (d, 2H, J ) 8.8 Hz, phenyl H of
L2), 6.70 (d, 1H, J ) 16 Hz, vinyl H of L2), 3.95 (t, 2H, J ) 6.5
Hz, -OCH2-), 1.77 (m, 2H, -CH2-), 1.43 (m, 2H, -CH2-),
1.25 (m, 28H, -(CH2)14-), 0.87 (t, 3H, J ) 6.4 Hz, -CH3). UV-
vis (CH2Cl2, λ/nm (ꢀ × 10-4/dm3mol-1cm-1)): 370 (2.92). UV-
vis (LB film, λ/nm): 366. IR (Nujol, ν/cm-1): 2028 (s) ν(CO),
(16) El-Ghayoury, A.; Douce, L.; Ziessel, R. Liq. Cryst. 1996, 21, 143.
(17) (a) Sullivan, B. P.; Meyer, T. J . J . Chem. Soc., Chem. Commum.
1984, 1244. (b) Tapolsky, G.; Duesing, R.; Meyer, T. J . J . Phys. Chem.
1989, 93, 3885.
for 15 min for stabilization, at a dipping speed of 5 mm min-1
The transfer ratios were close to unity.
.

Rh(I) Surfactant Complexes in LB Films
Organometallics, Vol. 18, No. 25, 1999 5255
Ta ble 1. Cr ysta l a n d Str u ctu r e Deter m in a tion
Da ta for fa c-[Re(CO)3(bp y)(L1)]P F 6
-
formula
fw
[C42H53N5O4Re]+PF6
1023.08
T, K
301
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
cryst syst
space group
Z
9.275(2)
20.345(3)
24.350(3)
83.52(2)
87.61(2)
80.49(2)
4501(1)
triclinic
P1h (No. 2)
4
F(000)
D
2064
1.509
calcd, g cm-3
cryst dimens, mm
λ, Å (graphite monochromated,
Mo KR)
0.40 × 0.25 × 0.05
0.71073
µ(Mo KR), cm-1
28.06
collection range
2θmax ) 51.2° (h, 0 to 11;
k, -23 to 24; l, -29 to 29)
oscillation, deg
no. of images collected
distance, mm
3
70
120
exposure time, s
no. of data collected
no. of unique data
Rint
400
35946
14530
0.037
no. of data used in refinement, m 10251 (I > 3σ(I))
no. of params refined, p
1011
0.038
0.054
1.77
0.04 (for atoms of the
complex cations)
+1.04, -1.03
R(Fo)a
F igu r e 1. Perspective drawing of one of the complex
cations of fac-[Re(CO)3(bpy)(L1)]PF6 with atomic number-
ing scheme. Hydrogen atoms have been omitted for clarity.
Thermal ellipsoids were shown at the 50% probability level.
Rw(Fo)a
goodness-of-fit, S
maximum shift, (shift/error)max
residual extrema in
final diff map, e Å-3
refinement of the structure was solved by direct methods
(SIR9220b) and expanded by the Fourier method, and refine-
ment was by full-matrix least-squares using the software
package TeXsan20c on a Silicon Graphics Indy computer. One
crystallographic asymmetric unit consists of two independent
w ) 4Fo2/σ2(Fo)2, where σ2(Fo)2 ) [σ2(I) + (0.035Fo2)2] with I >
a
3σ(I).
-
formula units. Two of the F atoms of one of the PF6 were
Secon d -Ha r m on ic Gen er a tion (SHG) Mea su r em en ts.
The setup for SHG measurements was similar to that reported
in the literature.18 The source was the fundamental 1064 nm
output of a Quanta-Ray Q-switched GCR-150-10 pulsed Nd:
YAG laser. The 532 nm signals generated were recorded on a
Tektronix TDS-620A digital oscilloscope. SHG measurements
were performed in the transmission mode with the fundamen-
tal beam at 45° to the monolayer film. Prior to each measure-
ment, the monolayer film at the backside of the substrate was
wiped off carefully with lens tissue soaked with chloroform in
order to prevent interference between signals arising from the
monolayers at the front and backside of the substrate. In the
treatment of data, it was assumed that all the molecules on
the quartz substrate have a common tilt angle φ with a random
azimuthal distribution. The SHG data were analyzed by the
general procedure described by Ashwell et al.19
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of fac-[Re-
(CO)3(bpy)(L1)]PF6 were obtained by slow diffusion of diethyl
ether vapor into their dichloromethane solution. A brown
crystal of dimensions 0.40 × 0.25 × 0.05 mm mounted on a
glass fiber was used for data collection at 28 °C on a MAR
diffractometer with a 300 mm image plate detector using
graphite-monochromatized Mo KR radiation. The images were
interpreted and intensities integrated using the program
DENZO.20a The space group was determined on the basis of a
statistical analysis of intensity distribution, the successful
disordered with F(3) and F(3′) each having an occupation
number of 0.5 and F(6) and F(6′) having occupation numbers
of 0.7 and 0.3, respectively. In the least-squares refinement,
106 non-H atoms were refined anisotropically, the 14 F atoms
were refined isotropically, and 106 H atoms at calculated
positions with thermal parameters equal to 1.3 times that of
the attached C atoms were not refined. Crystal and structure
determination data are summarized in Table 1.
Resu lts a n d Discu ssion
Syn th eses a n d Ch a r a cter iza tion . All the Re(I)
complexes were synthesized by modification of a litera-
1
ture procedure10,17 and characterized by H NMR, IR,
positive-ion FAB-MS, and elemental analyses. The
structure of fac-[Re(CO)3(bpy)(L1)]PF6 was determined
by X-ray crystallography, in which the trans configu-
ration of the azopyridyl group in the ligand was estab-
lished. The trans configuration of the stilbazole unit in
fac-[Re(CO)3(bpy)(L2)]PF6 has also been confirmed by
1H NMR spectroscopy, in which the coupling constant
of the two olefinic hydrogens of 16 Hz is typical of that
for trans-alkenes. All the complexes show three intense
(20) (a) DENZO: The HKL Manual-A description of programs
DENZO, XDISPLAYF, and SCALEPACK written by Gewirth, D. with
the cooperation of the program authors Otwinowski, Z., and Minor,
W., Yale University: New Haven, 1995. (b) SIR92: Altomare, A.;
Cascarano, M.; Giacovazzo, C.; Guagliardi, A.; Burla, M. C.; Polidori,
G.; Camalli, M. J . Appl. Cryst. 1994, 27, 435. (c) TeXsan: Crystal
Structure Analysis Package; Molecular Structure Corporation, The
Woodlands, TX, 1985 and 1992.
(18) (a) Dougherty, J . P.; Kurtz, S. K. J . Appl. Crystallogr. 1976, 9,
145. (b) Girling, I. R.; Cade, N. A.; Kolinsky, P. V.; Peterson, I. R.;
Ahmad, M. M.; Neal, D. B.; Petty, M. C.; Roberts, G. G.; Feast, W. J .
J . Opt. Soc. Am. 1987, B4, 950.
(19) Ashwell, G. J .; Hargreaves, R. C.; Baldwin, C. E.; Bahra, G. S.;
Brown, C. R. Nature 1992, 357, 393.

5256 Organometallics, Vol. 18, No. 25, 1999
Yam et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for fa c-[Re(CO)3(bp y)(L1)]P F 6
Re(1)-N(1)
Re(1)-N(3)
Re(1)-C(2)
O(1)-C(1)
O(3)-C(3)
2.183(5)
2.222(6)
1.932(8)
1.144(9)
1.153(10)
Re(1)-N(2)
Re(1)-C(1)
Re(1)-C(3)
O(2)-C(2)
N(4)-N(5)
2.179(6)
1.934(10)
1.926(10)
1.120(8)
1.261(8)
N(1)-Re(1)-N(2)
N(1)-Re(1)-C(1)
N(1)-Re(1)-N(3)
N(2)-Re(1)-C(1)
N(2)-Re(1)-C(3)
N(3)-Re(1)-C(2)
C(1)-Re(1)-C(2)
C(2)-Re(1)-C(3)
N(4)-N(5)-C(19)
75.4(2)
92.9(3)
98.7(3)
95.3(3)
173.2(3)
95.6(3)
85.3(3)
87.0(3)
114.8(6)
N(1)-Re(1)-N(3)
N(1)-Re(1)-C(2)
N(2)-Re(1)-N(3)
N(2)-Re(1)-C(2)
N(3)-Re(1)-C(1)
N(3)-Re(1)-C(3)
C(1)-Re(1)-C(3)
N(5)-N(4)-C(16)
86.0(2)
173.9(3)
82.2(2)
99.0(3)
177.5(3)
94.0(3)
88.4(3)
111.1(6)
F igu r e 3. Surface pressure-area (π-A) isotherms of fac-
[Re(CO)3(bpy)(L)]PF6 (L ) L1, L2, L3) and BI.
The coordination geometry at the Re atom is distorted
octahedral with the three carbonyl ligands arranged in
a facial fashion, which is similar to that found in other
related rhenium(I) systems.21 The hydrophobic aliphatic
chain is running along an axis that is almost perpen-
dicular to the plane containing the Re atom and the
bipyridine unit. The complex fac-[Re(CO)3(bpy)(L1)]PF6
crystallizes in the centrosymmetric space group P1h. As
seen in Figure 2, the long hydrocarbon chains of the two
adjacent neighboring complex cations are arranged in
a head-to-tail fashion, which leads to centrosymmetry
and therefore the lack of SHG capability of the complex
in the crystal form.
Su r fa ce P r essu r e-Ar ea (π-A) Isoth er m s. π-A
isotherms for the complexes are shown in Figure 3. All
curves show one well-defined condensed region with
surface pressure > 30 mN m-1 and a collapse pressure
of ca. 50 mN m-1, indicative of the stable air-water
interface behavior of the complexes. The molecular areas
obtained by the extrapolation of the condensed region
to zero surface pressure (61 Å2/molecule for fac-[Re-
(CO)3(bpy)(L2)]PF6, 63 Å2/molecule for both fac-[Re-
(CO)3(bpy)(L1)]PF6 and fac-[Re(CO)3(bpy)(L3)]PF6) are
found to be very close to the calculated values (55 Å2)
based on the crystal structure of fac-[Re(CO)3(bpy)(L1)]-
PF6, suggesting that the complex molecules are packed
closely in the film.
Electr on ic Absor p tion Sp ectr oscop y. Figure 4
depicts the UV-vis spectra of the complexes in dichlo-
romethane and in LB films. The electronic absorption
spectra of all the complexes show an intense absorption
at ca. 350-450 nm in dichloromethane at 298 K. With
reference to previous spectroscopic work on related
rhenium(I) diimine systems,9,10,17,22 this absorption band
is most likely assigned as the dπ(Re) f π*(bpy) metal-
to-ligand charge-transfer (MLCT) transition. The ob-
servation of an extinction coefficient on the order of 104
dm3 mol-1 cm-1 for this band, which is much larger than
an order of 103 dm3 mol-1 cm-1 commonly observed for
rhenium(I) diimine MLCT transition, is suggestive of a
spectral assignment of the band as consisting of an
admixture of intraligand (IL) π f π* and MLCT
F igu r e 2. Packing diagram of fac-[Re(CO)3(bpy)(L1)]PF6
in the unit cell, showing the head-to-tail arrangement of
the long aliphatic hydrocarbons of two pairs of complex
cations. The disordered PF6 ions have been omitted for
clarity.
-
IR absorption bands at ca. 1900-2100 cm-1, typical of
the tricarbonyl Re(I) moiety in the facial arrangement.21
Cr ysta l Str u ctu r e. The perspective drawing of the
complex cation of fac-[Re(CO)3(bpy)(L1)]PF6 is shown
in Figure 1. Selected bond distances and angles are
given in Table 2. The perspective drawing of fac-[Re-
(CO)3(bpy)(L1)]PF6 in the unit cell is shown in Figure
2.
(21) Giordano, P. J .; Wrighton, M. S. J . Am. Chem. Soc. 1979, 101,
2888.

Rh(I) Surfactant Complexes in LB Films
Organometallics, Vol. 18, No. 25, 1999 5257
Ta ble 3. P h otop h ysica l Da ta of Re(I) Diim in e Com p lexes
absorption λmax/nm
emission λem/nm
(τ0/µs)
compound
medium (T/K)
(ꢀ × 10-4/dm3 mol-1 cm-1
)
[Re(CO)3(bpy)(L1)]PF6
CH2Cl2 (298)
LB film
396 (3.36)
388
b
370 (2.92)
366
b
366 (3.47)
350
b
554
c
492
540
530
492
549 (1.63)
551
495, 527, 560
glass (77)a
CH2Cl2 (298)
LB film
[Re(CO)3(bpy)(L2)]PF6
[Re(CO)3(bpy)(L3)]PF6
glass (77)a
CH2Cl2 (298)
LB film
glass (77)a
a
b
All glasses are 4:1 (v/v) ethanol-methanol mixture. Not measured. c Too weak to be measured.
F igu r e 5. UV-vis spectral traces of fac-[Re(CO)3(bpy)-
(L1)]PF6 deposited on a quartz substrate as a function of
layer number. The inset shows the absorbance at 388 nm
as a function of layer number.
LB film relative to that in fluid solution and is at-
tributed to rigidochromic effects,23 which are commonly
reported in the Re(I) diimine systems.
Em ission Sp ectr oscop y. Emission data for the
complexes in various media are summarized in Table
3. The emission spectra exhibit a broad band centered
at ca. 490-560 nm, attributed to the triplet MLCT
emission, typical of Re(I) diimine complexes.9,10,17,22 The
emission energies of the complexes at 77 K glass state
and in LB films were found to be blue-shifted with
respect to that in fluid solution, attributed to the
phenomenon of luminescence rigidochromism.23 Figure
6 shows the emission spectra of fac-[Re(CO)3(bpy)(L2)]-
PF6 in various media. The emission spectrum of fac-
[Re(CO)3(bpy)(L3)]PF6 at 77 K glass state shows vibron-
ic structures with progressional spacing of ca. 1220
cm-1, typical of the ring C-H deformation vibrations
in the ground state. This is suggestive of the involve-
ment of both the bipyridine and ligand L3 in the excited
state, supporting the assignment of an emission origin
of mixed MLCT/IL character.
Secon d -Ha r m on ic Gen er a tion (SHG). The SHG
results of the Re(I) complexes are summarized in Table
4. The first-order hyperpolarizability (â) of fac-[Re(CO)3-
(bpy)(L2)]PF6 is found to be 1.4-1.5 times that of its
structurally related organic counterpart, (E)-N-methyl-
4-(2-(4-octadecyloxyphenyl)ethenyl)pyridinium iodide (BI),
which has a â value of 1.5 × 10-28 esu.24 The SHG
F igu r e 4. UV-vis spectra of fac-[Re(CO)3(bpy)(L)]PF6
where L ) L1 (s), L2 (‚‚‚) and L3 (- - -) (a) in CH2Cl2, (b)
in LB films.
character. The electronic absorption spectra of fac-[Re-
(CO)3(bpy)(L1)]PF6 in LB films as a function of layer
number are shown in Figure 5. A linear relationship
between the absorbance at 388 nm and the number of
layers deposited on the quartz substrate is observed,
indicative of the good deposition behavior of the com-
plex. A blue shift of the low-energy absorption band is
observed in the UV-vis spectra of the complexes in the
(22) (a) Leasure, R. M.; Sacksteder, L.; Nesselrodt, D.; Reitz, G. A.;
Demas, J . N.; DeGraff, B. A. Inorg. Chem. 1991, 31, 3722. (b) Zipp, A.
P.; Sacksteder, L.; Streich, J .; Cook, A.; Demas, J . N.; DeGraff, B. A.
Inorg. Chem. 1993, 32, 5629. (c) Sacksteder, L.; Zipp, A. P.; Brown, E.
A.; Streich, J .; Demas, J . N.; DeGraff, B. A. Inorg. Chem. 1990, 29,
4335. (d) Sacksteder, L.; Demas, J . N.; DeGraff, B. A. Anal. Chem.
1993, 65, 3480. (e) Bacon, J . R.; Demas, J . N. Anal. Chem. 1987, 59,
2780. (f) Carraway, E. R.; Demas, J . N.; DeGraff, B. A. Anal. Chem.
1991, 63, 337. (g) Boyde, S.; Strouse, G. F.; J ones, W. E., J r.; Meyer,
T. J . J . Am. Chem. Soc. 1989, 111, 7448. (h) Chen, P.; Curry, M.; Meyer,
T. J . Inorg. Chem. 1989, 28, 2271. (i) Tapolsky, G.; Duesing, R.; Meyer,
T. J . Inorg. Chem. 1990, 29, 2285.
(23) (a) Dominey, R. N.; Hauser, B.; Hubbard, J .; Dunham, J . Inorg.
Chem. 1991, 30, 4754. (b) Sullivan, B. P. J . Phys. Chem. 1989, 93, 24.
(c) Lees, A. J . Comments Inorg. Chem. 1995, 17, 319.
(24) Lupo, D.; Prass, W.; Scheunemann, U.; Laschewsky, A.; Rings-
dorf, H.; Ledoux, I. J . Opt. Soc. Am. 1988, B5, 300.

5258 Organometallics, Vol. 18, No. 25, 1999
Yam et al.
F igu r e 6. Normalized emission spectra of fac-[Re(CO)3-
(bpy)(L2)]PF6: (s) at glass state (77 K); (- - -) in LB film;
(‚‚‚) in CH2Cl2.
Ta ble 4. F ir st-Or d er Molecu la r
Hyp er p ola r iza bility a n d Absor ba n ce Ma xim u m of
Re(I) Diim in e Com p lexes in La n gm u ir -Blod gett
F ilm s
UV-vis spectra
λ
max/nm abs per layer â(complex)/â(BI)a
relative SHG
F igu r e 7. Schematic drawing of the proposed model of fac-
[Re(CO)3(bpy)(L2)]PF6 on a quartz substrate and the il-
lustration of the charge-transfer contribututions to the
resultant dipole moment.
compound
[Re(CO)3(bpy)(L1)]PF6
[Re(CO)3(bpy)(L2)]PF6
[Re(CO)3(bpy)(L3)]PF6
388
366
350
0.012
0.017
0.021
1.7-2.3
1.4-1.5
0.7
a
BI ) (E)-N-methyl-4-(2-(4-octadecyloxyphenyl)ethenyl)pyri-
in the resultant is enhanced, leading to an increase in
the first-order hyperpolarizability relative to that of BI.
dinium iodide.
capability of BI has been ascribed to the donor-acceptor
charge transfer resulting from the electron donation of
the alkoxy group to the pyridinium unit. It is likely that
in the present system two types of charge transfer exist
and occur along different directions, the resultant of
which contributes to the observed hyperpolarizability
(Figure 7). One is the Re(I) f bpy metal-to-ligand
charge transfer (MLCT), which occurs in the plane of
the Re(I) atom and the bipyridine unit. The other is the
ligand-centered charge transfer similar to BI, which
occurs along the backbone of the ligand L and perpen-
dicular to the Re-bpy plane. Although they act in
different directions, it is likely that the dipole moment
Ack n ow led gm en t. V.W.W.Y. acknowledges finan-
cial support from the Research Grants Council and The
University of Hong Kong. Y.Y. acknowledges the receipt
of a part-time Demonstratorship administered by The
University of Hong Kong.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and a full list of bond
distances and angles for fac-[Re(CO)3(bpy)(L1)]PF6 are depos-
ited as Supporting Information. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM990512Q