Syntheses, and optical, fluorescence, and nonlinear optical characterization of phosphine-substituted terthiophenes

Article abstract of DOI:10.1021/ic101624y

Earlier studies of phosphine-substituted terthiophenes have demonstrated that some of these materials exhibit nonlinear absorption at 532 nm. However, this wavelength is significantly removed from the linear absorption maxima of the complexes, suggesting that better nonlinear absorption might be observed at wavelengths closer to the linear absorption maxima. To investigate this possibility, a library of compounds has been prepared either by varying the group attached to the nonbonding pair of electrons on the phosphorus atoms of 5,5″-bis(diphenylphosphino)-2,2′:5′,2″-terthiophene (PT₃P), or by introducing additional substituents on the 5″-position of 5-(diphenylphosphino)-2,2′:5′,2″- terthiophene (PT₃). All these compounds have been characterized using multinuclear NMR, UV-vis, and fluorescence spectroscopy. The compounds are strongly fluorescent, and both the fluorescence wavelength and the intensity depend upon the thiophene substituents. The nonlinear optical properties have also been evaluated at various wavelengths in the blue region. Each compound exhibits reverse saturable absorption, and the intensity of the reverse saturable absorption at a particular wavelength depends on the chemical structure of the compound.

Full text of DOI:10.1021/ic101624y

Inorg. Chem. 2011, 50, 2015–2027 2015
DOI: 10.1021/ic101624y
Syntheses, and Optical, Fluorescence, and Nonlinear Optical Characterization
of Phosphine-Substituted Terthiophenes
Qun Zhao,† Jianwei Wang,‡ Jason L. Freeman,† Makeba Murphy-Jolly,† Ashley M. Wright,§ Debra J. Scardino,§
Nathan I. Hammer,§ Christopher M. Lawson,‡ and Gary M. Gray*,†
†Department of Chemistry, and ‡Department of Physics, The University of Alabama at Birmingham, 1530 Third
Avenue S., Birmingham, Alabama 35294, United States, and §Department of Chemistry and Biochemistry,
Coulter Hall 113, The University of Mississippi, Oxford, Mississippi 38677, United States
Received August 10, 2010
Earlier studies of phosphine-substituted terthiophenes have demonstrated that some of these materials exhibit
nonlinear absorption at 532 nm. However, this wavelength is significantly removed from the linear absorption maxima
of the complexes, suggesting that better nonlinear absorption might be observed at wavelengths closer to the linear
absorption maxima. To investigate this possibility, a library of compounds has been prepared either by varying the
group attached to the nonbonding pair of electrons on the phosphorus atoms of 5,500-bis(diphenylphosphino)-
2,20:50,200-terthiophene (PT3P), or by introducing additional substituents on the 500-position of 5-(diphenylphosphino)-
2,20:50,200-terthiophene (PT3). All these compounds have been characterized using multinuclear NMR, UV-vis, and
fluorescence spectroscopy. The compounds are strongly fluorescent, and both the fluorescence wavelength and the
intensity depend upon the thiophene substituents. The nonlinear optical properties have also been evaluated at
various wavelengths in the blue region. Each compound exhibits reverse saturable absorption, and the intensity of the
reverse saturable absorption at a particular wavelength depends on the chemical structure of the compound.
Introduction
computing.5 A large number of conjugated metal-organic
macrocycles, including various metalloporphyrins6-9 and
metallophthalocyanines,10-15 display reverse saturable ab-
sorption in the green region of the visible spectrum. Numer-
ous materials are also known to exhibit two-photon absorp-
tion in the red and near-infrared regions.16-22 However, only
one material showing nonlinear absorption (NLA) in the
blue region of the visible spectrum has been reported.23
Materials exhibiting third-order nonlinear optical proper-
ties have been investigated for important applications such as
optical switching,1,2 optical power limiting,3,4 and optical
*To whom correspondence should be addressed. Phone: (205) 934-8294.
Fax: (205) 934-2543. E-mail: gmgray@uab.edu.
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r
2011 American Chemical Society
Published on Web 02/28/2011
pubs.acs.org/IC

2016 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
Chart 1. Chemical Structures of Phosphine-Substituted Terthiophenes
Polythiophene-derived compounds possessing extended π-
conjugated networks and large concentrations of easily polar-
izable electrons are one class of materials that exhibit promising
third-order nonlinear optical behavior.24,25 Functionalization
of short conjugated oligothiophenes can change the third-order
nonlinear optical properties of the compounds and may also
increase their solubilities, allowing solutions with high concen-
trations to be prepared to maximize the macroscopic nonli-
nearity of the bulk solution.26-28 In our first paper in this area,
we demonstrated that some transition metal complexes with
diphenylphosphino-2,20-terthiophene ligands exhibited non-
linear optical absorption at 532 nm and that the nature of the
metal center affects the strength of the NLA.29 However, the
fact that this wavelength is significantly removed from the
linear absorption maxima of the complexes suggests that better
NLA might be observed at wavelengths closer to the linear
absorption maxima, especially if excited state absorption is a
major contributor to the NLA.
In this paper, we report the syntheses of two families of
phosphine-substituted terthiophenes shown in Chart 1. The
first family consists of disubstituted terthiophenes derived from
5,500-bis(diphenylphosphino)-2,20:50,200-terthiophene (PT3P),
and the second family consists of monosubstituted terthio-
phenes derived from 5-(diphenylphosphino)-2,20:50,200-terthio-
phene (PT3). The linear optical properties of the compounds
have been evaluated using both UV-vis and fluorescence
spectroscopy, and the nonlinear optical properties have been
evaluated using NLA measurements with picosecond laser
pulses in the blue region near the absorption maxima of the
compounds.
liquids over CaH2 for several hours followed by distillation. Com-
pounds 1 and 5 were prepared using literature procedures.30
Spectroscopic Characterization. One-dimensional multinuc-
lear 1H, 31P{1H}, and 13C{1H} NMR spectra were recorded on a
Bruker DRX-400 NMR spectrometer. The 31P{1H} NMR spectra
were referenced to external 85% phosphoric acid (H3PO4) in a
coaxial tube that also contained chloroform-d. The 1H NMR and
13C{1H} NMR spectra were referenced to internal tetramethylsi-
lane (TMS). Two-dimensional COSY (Correlated Spectroscopy),
HSQC (Heteronuclear Single Quantum Coherence Spectroscopy),
and HMBC (Heteronuclear Multiple Bond Correlation) were
recorded on a Bruker DPX-300 NMR spectrometer. Electrospray
ionization mass spectrometry (ESI MS) was performed on a
MicroMass Platform LCZ instrument. Linear absorption spectra
were recorded on a Varian Cary-100 UV-visible spectrophot-
ometer. Microanalyses for % C and H were performed by Atlantic
Microlab, Inc.
5,500-Bis(diphenyloxophosphino)-2,20:50,200-terthiophene, Ph2(O)-
P(C4H2S)3P(O)Ph2, 2. Compound 2 was prepared by a modifica-
tion of a previous procedure.31 Excess H2O2-urea pellets (4.0 g)
were added to a solution of 1 (1.00 g, 1.62 mmol) in CH3OH (200
mL). The reaction mixture was stirred at room temperature over-
night and then was evaporated to dryness under reduced pressure to
yield a solid residue. The residue was purified by column chroma-
tography (hexanes-ethyl acetate, 1:3 v/v) to yield the analytically
pure product as a yellow crystalline solid (0.70 g, 66%). ESI-MS:
648.7 [Mþ]. 31P{1H} NMR (CDCl3): 23.42 (s). 13C{1H} NMR
(CDCl3): δ 145.13 (d, |3JCP| 5.4 Hz, CTh-2), 137.70 (d, |2JCP| 8.9 Hz,
1
C
C
C
Th-4), 136.07 (d, |4JCP| 1.6 Hz, CTh-2 ), 132.73 (d, | JCP| 110.6 Hz,
Th-5), 132.44 (d, |1JCP| 110.3 Hz, CPh-i), 132.37 (d, |4JCP| 2.8 Hz,
Ph-p), 131.58 (d, |2JCP| 10.4 Hz, CPh-o), 128.62 (d, |3JCP| 12.7 Hz,
0
CPh-m), 125.97 (s, CTh-3 ), 124.80 (d, | JCP| 12.8Hz, CTh-3). 1H NMR
(CDCl3): 7.73-7.67 (m, 8H, HPh-o), 7.47-7.43 (m, 4H, HPh-p),
7.39-7.35 (m, 8H, HPh-m), 7.29 (dd, 2H, |3JPH| 7.5 Hz, |3JHH| 3.7
Hz, HTh-4), 7.15 (dd, 2H, |3JHH|3.7Hz,|4JPH|1.9Hz, HTh-3),7.03(s,
3
0
Experimental Section
2H, HTh-3 ). UV-vis (CH2Cl2): λmax/nm (ε/dm3 mol-1 cm-1) =
Materials. All reagents were reagent grade quality, purchased
commercially, and used as such unless otherwise indicated. Urea
hydrogen peroxide (1 g tablets) was purchased from Acros Organ-
ics. Tetrahydrofuran (THF) was dried over MgSO4, refluxed over
sodium/benzophenone and then distilled prior to use. Dry 1,2-
dichloroethane and chloroform were prepared by refluxing the
0
3
3
373 (20300). Anal. Calcd for [C36H26O2P2S3 H2O]: C, 64.85; H,
4.20. Found: C, 64.50; H, 4.09.
5,500-Bis(diphenylsulfidophosphino)-2,20:50,200-terthiophene, Ph2-
(S)P(C4H2S)3P(S)Ph2, 3. Excess elemental sulfur (0.30 g) was
added to a solution of 1 (0.40 g, 0.65 mmol) in CH2Cl2 (50 mL).
The reaction mixture was stirred at room temperature overnight, and
then was evaporated under reduced pressure to give a solid residue.
The residue was purified by column chromatography. First elution
with hexanes removed the excess sulfur and then elution with Et2O
yielded the analytically pure product as a yellow crystalline solid
(24) Roncali, J. Chem. Rev. 1992, 92, 711–738.
(25) Dodabalapur, A.; Bao, Z.; Makhija, A.; Laquindanum, J. G.; Raju,
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Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 2017
3
(0.25 g, 60%). ESI-MS: 681.3. 31P{1H} NMR (CDCl3): 34.64 (s).
(CDCl3): δ 182.40 (s, CCHO), 146.14 (s, CTh-5 ), 144.80 (d, | JCP
|
00
13C{1H} NMR (CDCl3): δ 145.47 (d, |3JCP| 5.1 Hz, CTh-2), 137.66
2
5.3 Hz, CTh-2), 142.04 (s, CTh-2 or 5 or 2 ), 137.67 (d, | JCP| 8.9 Hz,
0
0
00
(d, |2JCP| 8.7 Hz, CTh-4), 136.13 (d, |4JCP| 1.6 Hz, CTh-2 ), 134.32 (d,
0
00
CTh-4), 137.31 (s, CTh-3 ), 137.27 (s, CTh-2
0
or 50 or 200
), 136.10 (s,
|
|1JCP| 92.1 Hz, CTh-5), 133.22 (d, |1JCP| 89.6 Hz, CPh-i), 131.92 (d,
CTh-2 or 5 or 2 ), 133.34 (d, | JCP| 110.0 Hz, CTh-5), 132.49 (d, |1JCP
1
0
0
00
|4JCP| 3.0 Hz, CPh-p), 131.78 (d, |2JCP| 11.3 Hz, CPh-o), 128.62 (d,
110.2 Hz, CPh-i), 132.40 (d, |4JCP| 2.7 Hz, CPh-p), 131.80 (d, |2JCP
|
3
|3JCP| 13.1 Hz, CPh-m), 125.92 (s, CTh-3 ), 124.77 (d, | JCP| 12.9 Hz,
10.4 Hz, CPh-o), 128.63 (d, |3JCP| 12.7 Hz, CPh-m), 126.95(s, CTh-3 or
0
0
CTh-3). 1H NMR (CDCl3): 7.82-7.76 (m, 8H, HPh-o), 7.54-7.45 (m,
0
00
3
4 ), 126.14 (s, CTh-4 ), 125.12 (d, | JCP| 12.7 Hz, CTh-3), 124.51 (s,
12H, HPh-p and m), 7.32-7.26 (dd, 2H, |3JPH| 8.2 Hz, |3JHH| 3.8 Hz,
0
0
1
C
Th-3 or 4 ). HNMR(CDCl3):9.87(1H, s, HCHO), 7.81-7.74 (4H,
H
Th-4), 7.18-7.16 (dd, 2H, |3JHH| 3.8 Hz, |4JPH| 1.8 Hz, HTh-3),
00
m, CPh-o), 7.68 (1H, d, |3JHH| 3.8 Hz, HTh-3 ), 7.61-7.59 (2H, m,
CPh-p), 7.53-7.50 (4H, m, CPh-m), 7.35 (1H, dd, |3JPH| 7.5 Hz,
7.10 (s, 2H, HTh-3 ). UV-vis (CH2Cl2): λmax/nm (ε/dm3 mol-1
0
3
3
cm-1) = 377 (19300). Anal. Calcd for [C36H26P2S5]: C, 63.51; H,
3.85. Found: C, 63.06; H, 4.19.
|3JHH| 3.8 Hz, HTh-4), 7.28-7.17 (3H, m, HTh-3 and HTh-3 and
0
3
0
00
H
Th-4 ), 7.17 (1H, d, | JHH| 3.8 Hz, HTh-4 ). UV-vis (CH2Cl2):
5,500-Bis(diphenylmethylphosphino)-2,20:50,200-terthiophene Io-
dide, [Ph2(Me)P(C4H2S)3P(Me)Ph2]I2, 4. Excess CH3I (1.0 mL)
was added to a solution of 1 (0.30 g, 0.49 mmol) in CH2Cl2 (30 mL).
The reaction mixture was stirred at room temperature overnight
and then was evaporated under reduced pressure to give a yellow
solid residue. Recrystallization from CH3CN/Et2O yielded the ana-
lytically pure product as a yellow crystalline solid (0.35 g, 80%).
31P{1H} NMR (CD3CN): 16.97 (s). 13C{1H} NMR (CD3CN): δ
λ
max/nm (ε/dm3 mol-1 cm-1) = 401 (37000). Anal. Calcd for
3
3
[C25H17O2PS3]: C, 63.01; H, 3.60. Found: C, 62.79; H, 3.67.
500-Hydroxymethyl-5-(diphenyloxophosphino)-2,20:50,200-terthio-
phene, Ph2(O)P(C4H2S)3CH2OH, 8. Sodium borohydride (0.010 g,
0.26 mmol) was added to a stirred solution of 7(0.050 g, 0.10 mmol)
in 10 mL of dry THF under nitrogen at ambient temperature. The
reaction mixture was stirred overnight and then the THF was
evaporated, water was added, and the mixture was stirred for 1 h.
The resultant yellow precipitate was collected by filtration, and
dried. Recrystallization from hexanes-ethyl acetate afforded the
analytically pure product as yellow crystals (0.045 g, 90%). ESI-
MS: 478.9. 31P{1H} NMR (CDCl3): 23.04 (s). 13C{1H} NMR
148.66 (d, |3JCP| 5.7 Hz, CTh-2), 142.73 (d, |2JCP| 9.6 Hz, CTh-4),
4
135.33 (d, |4JCP| 1.9 Hz, CTh-2 ), 135.09 (d, | JCP| 3.1 Hz, CPh-p),
0
132.67 (d, |2JCP| 11.5 Hz, CPh-o or m), 129.84 (d, |3JCP| 13.4 Hz,
3
Ph-m or o), 127.97 (s, CTh-3 ), 126.86 (d, | JCP|13.9Hz, CTh-3), 119.39
0
C
(d, |1JCP| 92.0 Hz, CTh-5), 116.13 (d, |1JCP| 103.8 Hz, CPh-i), 9.88 (d,
|1JCP| 59.1 Hz, CCH3). 1H NMR (CD3CN): 7.95-7.90 (m, 4H, HPh
(CDCl3): δ 145.80 (d, |3JCP| 5.5 Hz, CTh-2), 144.50 (s, CTh-5 ),
00
2
138.01 (s, CTh-2 or 5 or 2 ), 137.78 (d, | JCP| 9.1 Hz, CTh-4), 136.50 (s,
0
0
00
and HTh-4), 7.87-7.74 (m, 18H, HPh), 7.67-7.65 (dd, 2H, |3JHH|4.0
1
0
0
00
0
0
00
CTh-2 or 5 or 2 ), 134.28 (s, CTh-2 or 5 or 2 ), 132.44 (d, | JCP| 110.0
Hz, CPh-i), 132.35 (d, |4JCP| 2.7 Hz, CPh-p), 131.70 (d, |1JCP| 110.7
Hz, CTh-5), 131.81 (d, |2JCP| 10.4 Hz, CPh-o), 128.61 (d, |3JCP| 12.7
Hz, |4JPH| 2.2 Hz, HTh-3), 7.47 (s, 2H, HTh-3 ), 2.96 (d, 6H, | JPH| 14
2
0
Hz, HCH3). UV-vis (CH3CN): λmax/nm (ε/dm3 mol-1 cm-1) =
3
3
387 (35500). Anal. Calcd for [C38H32P2S3I2 H2O]: C, 49.68; H, 3.73.
Found: C, 49.60; H, 3.60.
00
0
00
0
or 30
or 4 ),
), 123.70 (s,
or 30
Hz, CPh-m), 125.89 (s, CTh-4
or 4 ), 125.87 (s, CTh-4
124.28 (d, |3JCP| 12.8 Hz, CTh-3), 124.25 (s, CTh-4
0
or 300
5-(Diphenyloxophosphino)-2,20:50,200-terthiophene, Ph2(O)P-
(C4H2S)3H, 6. Excess H2O2-urea pellets (4.0 g) were added to
a solution of 5 (1.32 g, 3.05 mmol) in CH3OH (300 mL). The reac-
tion mixture was stirred at room temperature overnight and then
was evaporated to dryness under reduced pressure to give a solid
residue. This residue was purified by column chromatography
(Et2O eluent) to yield the analytically pure product as a yellow
crystalline solid (1.15 g, 85.1%). ESI-MS: 449.0 [Mþ]. 31P{1H}
CTh-4 or 3 ), 60.02 (s, CCH2). 1H NMR(CDCl3):7.78-7.73 (4 H, m,
HPh-o), 7.62-7.56 (2H, m, HPh-p), 7.51-7.48 (4H, m, HPh-m), 7.26
(1H, dd, |3JPH|7.8Hz, |3JHH|3.8Hz, HTh-4), 7.15 (1H, dd, |4JPH|1.9
0
00
Hz, |3JHH| 3.8 Hz, HTh-3), 7.05 (1H, d, |3JHH| 3.9 Hz, HTh-3 or 4 ),
0
0
6.98 (2H, d, |3JHH| 3.8 Hz, HTh-3
0
00
and HTh-3 ), 6.86 (1H, d,
or 40
|3JHH| 3.5 Hz, HTh-4 ), 4.80 (2H, s, HCH2). UV-vis (CH2Cl2):
00
λ
max/nm (ε/dm3 mol-1 cm-1) = 377 (21300). Anal. Calcd for
3
3
[C25H19O2PS3]: C, 62.74; H, 4.00. Found: C, 62.28; H, 3.91.
5-(Diphenyloxophosphino)-2,20:50,200-terthiophene-500-carboxy-
lic Acid,Ph2(O)P(C4H2S)3COOH, 9. A mixture of Ag2O (2.0 g,
8.6 mmol) in water (10 mL) was added to a solution of NaOH
(1.0 g, 25 mmol) in water (10 mL) at room temperature. After this
mixture was stirred for 15 min, a solution of 7 (0.20 g, 0.42 mmol) in
THF (50 mL) was slowly added. The reaction mixture was stirred at
room temperature for 0.5 h, and then was refluxed for 2 days. Next,
the reaction mixture was acidified to pH = 4 with 10% aqueous
HCl solution. The resulting brown precipitate was collected by
filtration and washed with methanol. The filtrate and washings were
combined and evaporated under reduced pressure to give a solid
residue. The residue was purified by column chromatography with
ethyl acetate as the eluent to yield the analytically pure product as an
orange powder (0.12 g, 58%). ESI-MS: 492.9. 31P{1H} NMR
(CD3OD): 24.11 (s). 1H NMR (CD3OD): 7.09-7.03 (m. 4H, HPh),
6.99-6.97 (m, 3H, HPh and HTh), 6.92-6.88 (m, 4H, HPh),
6.72-6.71 (m, 1H, HTh), 6.68-6.66 (m, 1H, HTh), 6.61-6.61(m,
2H, HTh), 6.58-6.57 (m, 1H, HTh).
NMR (CDCl3): 22.65 (s). 13C{1H} NMR (CDCl3): δ 145.73 (d,
2
|3JCP| 5.3 Hz, CTh-2), 137.93 (s, CTh-5 or 2 ), 137.73 (d, | JCP| 8.9 Hz,
0
00
4
0
00
0
CTh-4), 136.64 (s, CTh-5 or 2 ), 134.39 (d, | JCP| 1 Hz, CTh-2 ), 132.62
(d, |1JCP| 110.2 Hz, CPh-i), 132.01 (d, |1JCP| 111.6 Hz, CTh-5), 132.31
(d, |4JCP| 2.8 Hz, CPh-p), 131.83 (d, |2JCP| 10.4 Hz, CPh-o), 128.59 (d,
|3JCP| 12.7 Hz, CPh-m), 127.98 (s, CTh-4 ), 125.86 (s, CTh-3 or 4 ),
00
0
0
3
), 124.45 (s, CTh-3 or 4 ), 124.33 (d, | JCP| 12.8
00
0
0
or 500
125.01 (s, CTh-3
Hz, CTh-3), 124.15 (s, CTh-3
). 1H NMR (CDCl3): 7.80-
00
or 500
7.75 (m, 4H, HPh-o), 7.58-7.56 (m, 2H, HPh-p), 7.52-7.47 (m, 4H,
HPh-m), 7.36 (dd, 1H, |3JPH| 7.5 Hz, |3JHH| 3.8 Hz, HTh-4), 7.25 (dd,
1H, |3JHH| 5.1 Hz, |4JHH| 1.1 Hz, HTh-3
), 7.21 (dd, 1H, |4JPH
|
00
or 500
1.9 Hz, |3JHH| 3.8 Hz, HTh-3), 7.19 (m, 1H, HTh-3
), 7.13 (d, 1H,
0
00
or 500
|3JHH| 3.8 Hz, HTh-3 or 4 ), 7.08 (d, 1H, | JHH| 3.8 Hz, HTh-3 or 4 ),
3
0
0
0
7.03 (dd, 1H, |3JHH| 5.1 Hz, |3JHH| 3.6 Hz, HTh-4 ). UV-vis (CH2-
00
Cl2):λmax/nm (ε/dm3 mol-1 cm-1) = 368 (20500). Anal. Calcd for
3
3
[C24H17OPS3]: C, 64.26; H, 3.82. Found: C, 64.50; H, 4.01.
5-(Diphenyloxophosphino)-2,20:50,200-terthiophene-500-carbalde-
hyde, Ph2(O)P(C4H2S)3CHO, 7. Compound 6 (0.55 g, 1.2 mmol)
was dissolved in 50 mL of dry 1,2-dichloroethane under nitrogen
atmosphere. Excess DMF (2.0 mL) was first added to this
solution and then POCl3 (0.60 mL, 6.6 mmol) was added drop-
wise with stirring. The reactionmixture was heated at 60 °C under
nitrogen for 36 h and then was poured slowly into 100 mL of
saturated aqueous sodium acetate solution. This mixture was
stirred for 2 h, and then the organic layer was diluted with
CH2Cl2, separated, and washed with water. After evaporation
of the solvents, the solid residue was purified with silica gel flash
chromatography (hexanes-ethyl acetate 1:1) to yield the analy-
tically pure product as a yellow product (0.50 g, 86%). ESI-MS:
476.9. 31P{1H} NMR (CDCl3): 22.29 (s). 13C{1H} NMR
Methyl 5-(diphenyloxophosphino)-2,20:50,200-terthiophene-500-car-
boxylate, Ph2(O)P(C4H2S)3COOCH3, 10. Concentrated H2SO4
(1.0 mL) was added to a solution of 9 (0.10 g, 0.20 mmol) in
methanol (100 mL). The reaction mixture was stirred under reflux
overnight and then was evaporated under reduced pressure to give a
solid residue. The residue was washed with water and then was
purified by column chromatography (hexane-ethyl acetate, 1:1, v/v)
to yield the analytically pure product as a yellow solid (0.095 g,
90%). ESI-MS: 506.9. 31P{1H} NMR (CDCl3): 22.81 (s). 13C{1H}
NMR (CDCl3): δ 162.35 (s, CCdO), 145.08 (d, |3JCP| 5.5 Hz, CTh-2),
2
143.24 (s, CTh-5 ), 137.69 (d, | JCP| 8.8 Hz, CTh-4), 136.52 (s, CTh-5 ),
00
0
1
136.22 (d, |4JCP| 1 Hz, CTh-2 ), 134.30 (s, CTh-3 ), 132.93 (d, | JCP
|
0
00

2018 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
110.6 Hz, CTh-5), 132.52 (d, |1JCP| 110.1 Hz, CPh-i), 132.36 (d, |4JCP
|
Table 1. Data Collection Parameters for X-ray Structure Determination
2.7 Hz, CPh-p), 131.80 (d, |2JCP|10.4Hz, CPh-o), 128.62 (d, |3JCP| 12.7
identification code
empirical formula
formula weight
temperature
2
3
Hz, CPh-m), 126.00 (s, CTh-3 and 4 ), 124.86 (d, | JCP| 12.7 Hz, CTh-3),
0
0
C36 H28 O3 P2 S3
666.70
293(2) K
0.71073 A
monoclinic
C2/c
a = 18.327(4) A
˚
b = 9.6335(19) A
˚
c = 18.711(4) A
124.22 (s, CTh-4 ), 52.30 (s, CCH3). 1H NMR (CDCl3): 7.80-
00
7.78 (m, 4H, HPh-o), 7.77 (d, 1H, |3JHH| 3.9 Hz, HTh-3 ),
00
˚
wavelength
7.71-7.70 (m, 2H, HPh-p), 7.52-7.50 (m, 4H, HPh-m), 7.35 (dd,
1H, |3JPH| 7.5 Hz, |3JHH| 3.8 Hz, HTh-4), 7.26 (dd, 1H, |4JPH| 1.9 Hz,
crystal system
space group
unit cell dimensions
|3JHH| 3.8 Hz, HTh-3), 7.18 (d, 1H, |3JHH| 3.8 Hz, HTh-4 ), 7.15 (d,
0
˚
1H, |3JHH| 3.8 Hz, HTh-3 ), 7.13 (d, 1H, | JPH| 3.8 Hz, HTh-4 ),
3
0
00
3.89 (s, 3H, HCH3). UV-vis (CH2Cl2): λmax/nm (ε/dm3 mol-1
3
3
cm-1) = 387 (12800). Anal. Calcd for [C26H19O3PS3]: C, 61.64; H,
3.78. Found: C, 61.66; H, 3.99.
β = 103.74 (3)°
3208.9(11) A
3
˚
volume
Z
density (calculated)
absorption coefficient
F(000)
500-Phenyliminomethyl-5-(diphenyloxophosphino)-2,20:50,200-ter-
hiophene, Ph2(O)P(C4H2S)3CHNPh, 11. A solution of 7 (0.050 g,
0.10 mmol) and aniline (40 μL, 4.38 mmol) in 10 mL of dry CHCl3
was refluxed under nitrogen for 36 h. After evaporation of the sol-
vents, the residue was purified with flash chromatography (CH2Cl2-
ethyl acetate, 3:1, neutral aluminum oxide) to yield the analytically
pure product as a yellow powder (0.050 g, 86%). ESI-MS: 551.9.
31P{1H} NMR (CDCl3): 22.57 (s). 13C{1H} NMR (CDCl3): δ
0
4
1.380 Mg/m3
0.367 mm-1
1384
crystal size
θ range for data collection
index ranges
0.5 ꢀ 0.7 ꢀ 0.3 mm3
2.24° to 22.48°
-10 e h e 19
-10 e k e 9
-20 e l e 19
4840
152.32 (s, CC=N), 151.12 (s, CTh-5 or 2
or NPh-i), 145.28 (d, |3JCP
|
00 or 500
reflections collected
0
or 200 or 500
5.3 Hz, CTh-2), 141.85 (s, CTh-5
0
or NPh-i), 141.04 (s,
independent reflections
absorption correction
refinement method
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
2093 [R(int) = 0.0511]
None
or 200 or 500
CTh-5
or NPh-i), 137.68 (d, |3JCP| 8.6 Hz, CTh-3 or 4),
full-matrix least-squares on F2
2093/0/230
1.132
or NPh-i), 135.80 (d, |4JCP| 1.6 Hz, CTh-2 ),
0
00
0
or 500
137.24 (s, CTh-5 or 2
132.98 (d, |5JCP| 2.1 Hz, CTh-3 or 4 ), 132.71 (d, | JCP| 113 Hz, CTh-5),
132.57 (d, |1JCP| 108 Hz, CPPh-i), 132.34 (d, |4JCP| 2.5 Hz, CPPh-p),
131.81 (d, |2JCP| 10.4 Hz, CPPh-o), 129.18 (s, CNPh-o or NPh-m), 128.61
1
0
0
R1 = 0.0875
wR2 = 0.2150
R1 = 0.1091
wR2 = 0.2365
(d,|3JCP|12.6Hz,CPPh-m), 126.22 (s, CTh-3 or 4 ), 126.09 (s, CTh-3
0
0
00
00 or 4
),
R indices (all data)
), 124.73 (d, |2JCP| 12.8 Hz, CTh-3 or 4), 124.29
00
or 400
125.74 (s, CTh-3
(s, CNPh-p), 121.05 (s, CNPh-o or NPh-m). H NMR (CDCl3): 8.44
1
-3
˚
largest diff. peak and hole
1.034 and -0.456 e A
(1H, s, HC=N), 7.73-7.67 (4 H, m, HPPh), 7.55-7.42 (6H, m,
length quartz cell, and the concentrations used were 4.0 ꢀ 10-6 mol/
L. All the fluorescence spectra were recorded with constant slit
widths of 5 nm. All solutions were prepared using optima grade di-
chloromethane at room temperature, and the solutions were deoxy-
genated by bubbling N2 through them for approximately 5 min.
The fluorescence intensity was approximately corrected ac-
cording to the equation34
H
PPh), 7.35-7.28 (4H, m, HTh), 7.28-7.07 (7H, m, HNPh and HTh).
UV-vis (CH2Cl2): λmax/nm (ε/dm3 mol-1 cm-1) = 411 (47800).
3
3
Anal. Calcd for [C31H22NOPS3]: C, 67.49; H, 4.02. Found: C, 67.08;
H, 4.10.
X-ray Data Collection and Solution. A suitable single crystal
of 2 was glued on a glass fiber with epoxy and aligned upon an
Enraf-Nonius CAD4 single-crystal diffractometer under aero-
bic conditions. Standard peak search and automatic indexing
routines followed by least-squares fits of 25 accurately centered
reflections resulted in accurate unit cell parameters. The space
group of the crystal was assigned on the basis of systematic
absences and intensity statistics. All data collections were
carried out using the CAD4-PC software,32 and details of the
data collections are given in Table 1. The analytical scattering
factors of the complex were corrected for both Δf0 and iΔf00
components of anomalous dispersion. All data were corrected
for Lorentz and polarization effects.
All crystallographic calculations were performed with the
Siemens SHELXTL-PC program package.33 All heavy atom
positions were located using Direct Methods. Full-matrix re-
finements of the positional and anisotropic thermal parameters
for all non-hydrogen atoms versus F2 were carried out.
All hydrogen atoms were placed in calculated positions with
ꢀ
ꢁ
ODex þ ODem
FcorrðλÞ ¼ FobsðλÞ antilog
ð1Þ
2
where Fobs(λ) and Fcorr(λ) are the measured and corrected fluor-
escence intensities, respectively, ODex and ODem are the optical
densities at the excitation and the emission wavelength, respec-
tively, assuming ODem = 0. The integrated fluorescence intensity I
(that is, the area of the fluorescence spectrum) was calculated using
the equation
Z
b
I ¼
FcorrðλÞ dλ
ð2Þ
a
where Fcorr(λ) is the corrected fluorescence spectrum on the
wavelength scale, [a, b] is the finite range of wavelength, and Δλ
is the integration step (which is the band-pass). All the fluorescence
spectra were recorded at the constant band-passes of 1.0 nm. It is
straightforward to evaluate such integrals numerically. Among
many numerical integration schemes, the trapezoidal rule to
approximate the integral was adopted because of its simplicity
and sufficient accuracy.35
˚
the appropriate molecular geometry and δ (C-H) = 0.96 A.
The isotropic thermal parameter of each hydrogen atom
was fixed equal to 1.2 times the Ueq value of the atom to which
it was bound. Crystallographic data has been deposited with
the Cambridge Crystallographic Database Centre (CCDC
773042).
The relative quantum yield for comparison with different
samples was calculated using the equation34
Solution Phase Fluorescence Measurements. Emission spectra
in solution were obtained on a Cary Eclipse Fluorometer. Each of
the compounds was freshly purified by chromatography before
being used for the fluorescence measurements. Each solution was
excited at the absorption wavelength maximum using a 10 mm path
Q
I ODR n
¼
ð3Þ
QR
IR OD nR
(34) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.;
Springer Science þ Business Media Inc.: New York, 2004; Chapter 2.
(35) Atkinson, K.E. An Introduction to Numerical Analysis, 2nd ed., John
Wiley & Sons: New York, 1989; Chapter 5.
(32) CAD4-PC, Version 1.2; Enraf-Nonius: Delft, The Netherlands, 1988.
(33) Sheldrick, G. M. SHELXTL NT, Version 6.12; Bruker AXS, Inc.:
Madison, WI, 2001.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 2019
Scheme 1. Synthesis of Compounds 2, 3, and 4 from Ph2P(C4H2S)3PPh2 (1)
where Q is the quantum yield, I is the integrated intensity, OD is
the optical density, and n is the refractive index of the solvent.
The subscript R refers to the reference solution, which was a
CH2Cl2 solution of terthiophene (T3).
Results and Discussion
Syntheses of Derivatives of 5,500-Bis(diphenylphos-
phino)-2,20:50,200-terthiophene. Bis(diphenenylphosphino)-
and (diphenylphosphino)-substituted terthiophenes, 1
and 6, were synthesized by lithiation of terthiophene
followed by quenching with chlorodiphenylphosphine.
Pure 6 was obtained in reasonably good yield (70%) by
this synthetic approach, although Field et al. had pre-
viously reported that the selective monolithiation of
terthiophene proved impossible using a wide range of
stoichiometries and reaction conditions.30 Compounds 2,
3, and 4 were synthesized by treating the free ligand 1 with
hydrogen peroxide, elemental sulfur, and methyl iodide,
respectively, as shown in Scheme 1. Compounds 2-4 were
obtained in good yields and in high purities after workup
by either column chromatography or recrystallization.
Functionalization of 5-(Diphenyloxophosphino)-2,20:50,200-
terthiophene at the 500-Position. Oligothiophenes have been
functionalized with a wide variety of organic functional
groups to prepare molecular materials with a range of
electrical and optical properties. Functional groups that
have been incorporated into terthiophenes include alde-
hyde, carboxylic acid, methyl carboxylate, and hydroxy-
methyl groups.36-41 However, no terthiophenes with both a
phosphine substituent and one of these organic substituents
have been reported. We have used modifications of the
standard synthetic procedures to prepare terthiophenes with
Thin Film and Single Molecule Fluorescence Measurements.
Emissions from thin films composed of the disubstituted
terthiophenes 2, 3, and 4 and from single disubstituted terthio-
phene molecules of 4 were measured using a Nikon TE-2000U
inverted microscope. Molecules were deposited from dilute
solutions (10-6 mol/L for thin films and 10-8 mol/L for single
molecule measurements) in THF onto plasma-cleaned co-
verslips using the drop cast method. The 457 nm line from a
Coherent Innova 200 Ar ion laser was employed to excite the
samples as a function of laser power and fluorescence emission
was detected using a Princeton Instruments Photonmax EM-
CCD camera. Typical CCD camera exposure times were 0.2 s.
Solid state fluorescence spectra were obtained by dispersing
the emitted light using a Princeton Instruments 2150 Spectro-
graph before detection.
Linear and Nonlinear Optical Transmission Measurements.
Linear transmission measurements of dichloromethane solu-
tions of the compounds (3.65 ꢀ 10-3 mol/L for 2, 3, and 10;
3.5 ꢀ 10-3 mol/L for all other compounds) in a 1 mm cuvette
were performed on a Shimadzu UV-3101PC Spectrophot-
ometer. Nonlinear transmission measurements were performed
at 450 nm, 480 and 532 nm on the same solutions in the same
cuvette. A wavelength tunable laser system, consisting of an
EKSPLA PG401 optical parametric generator (OPG) pumped
by a PL2143A/ss model-locked Nd:YAG laser with a pulse
width of 27 ps and a repetition rate of 10 Hz, was used as the light
source. Laser radiation energy was gradually changed by using a
motorized attenuator based on a combination of a half-wave
plate and a Glan-Taylor prism. Part of the laser beam was then
reflected by a beam splitter to a reference detector to monitor the
incident energy. The remaining beam was focused by a 300 mm
lens to the center of a 1 mm sample cell (Spectrosil 21-Q-1,
Starna Cells, Inc.). The diameters of focused beam were 73, 80,
and 97 μm at 450, 480, and 532 nm, respectively. The transmitted
signal energy and the reference energy were monitored by two
Molectron J4-09 pyroelectric joule meters.
(36) Wei, Y.; Wang, B.; Wang, W.; Tian, J. Tetrahedron Lett. 1995, 36,
665–668.
(37) Parakka, J. P.; Cava, M. P. Tetrahedron 1995, 51, 2229–2242.
(38) Skene, W. G.; Dufresne, S. Org. Lett. 2004, 6, 2949–2952.
(39) Kiriy, N.; Bocharova, V.; Kiriy, A.; Stamm, M.; Krebs, F. C.; Adler,
H. Chem. Mater. 2004, 16, 4765–4771.
(40) Nakagawa, H.; Gomi, K.; Yamada, K. Chem. Pharm. Bull. 2001, 49,
49–53.
(41) Noguchi, T.; Hasegawa, M.; Tomisawa, K.; Mitsukuchi, M. Bioorg.
Med. Chem. 2003, 11, 4729–4742.

2020 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
Scheme 2. Functionalization of Ph2(O)P(C4H2S)3H (6)
a diphenylphosphine oxide on the 5-position and an organic
functional group at the 500-position as shown in Scheme 2. As
discussed below, the incorporation of an organic functional
group has significant effects on the linear and nonlinear
optical properties of the molecules. In addition, the functional
groups may change inherent solubilities of chromophores or
allow the chromophores to be attached to polymers.
NMR Spectroscopic Characterization. All the new com-
pounds have been characterized by 31P{1H}, 13C{1H}, and
1H NMR spectroscopy and mass spectroscopy. The mass
spectra exhibited parent ions for the desired compounds in
all cases. The 13C{1H} and 1H NMR spectra are quite com-
plicated and were assigned using a combination of two-
dimensional COSY, HSQC, and HMBC techniques. In
some cases it was not possible to uniquely assign all the
resonances, and all possible assignments are indicated in the
Experimental Section of this article.
considerably downfield compared to that of 1 (23.42, 34.64,
and 16.97 ppm, respectively) indicating that coordination of
the lone pair causes a significant downfield shift in the
31P{1H} NMR resonance. The 31P{1H} NMR resonance
of 2, in which an oxygen is coordinated to the phosphorus, is
upfield of that of 3, in which a sulfur is coordinated to the
phosphorus. This indicates that the shifts in the 31P{1H}
NMR resonances are not entirely due to the electron with-
drawing abilities of the groups coordinated to the lone pair
of the phosphorus. The chemical shifts of the 31P NMR
resonances of 2, 3, and 4 are quite similar to those of their
bithiophene analogues, Ph2(X)P(C4H2S)2P(X)Ph2 (X = O,
22.54 ppm; S, 34.64 ppm; CH3þ I-, 17.73 ppm)42 indicating
that replacing a bithiophene with a terthiophene has no
significant effect on the local magnetic field at the phos-
phorus atom.
The 31P{1H} NMR resonances of 6-8, 10, and 11 in
CDCl3 are singlets with chemical shifts between 22.09 and
23.04 ppm. Their chemical shifts are similar to one another
and to that of 2 (23.42 ppm) even if the substituent extends
the conjugation of the molecule. The similarities suggest that
the substituent at the opposite end of the terthiophene has
little effect on 31P{1H} NMR chemical shift, and hence on
the electron density at the diphenylphosphine oxide group.
Single-Crystal X-ray Diffraction Analysis. We have pre-
viously reported the crystal structures for three bithiophene
derivatives, Ph2(X)P(C4H2S)2P(X)Ph2 in which X is O, S,
The 31P{1H} NMR spectra are of particular interest be-
cause they provide insight into the factors that affect the elec-
tron density at the phosphorus. The resonances of 1 and 5 in
CDCl3 are singlets with very similar chemical shifts (-18.75
and -18.71 ppm, respectively) that are typical for diphenyl-
phosphines with 2-thienyl substituents.42 The 31P{1H} NMR
resonances of compounds 2, 3, and 4 are also singlets but are
(42) Zhao, Q.; Owens, S. B., Jr.; Gray, G. M.; Wang, J.; Lawson, C. M.
Main Group Chem. 2007, 6, 215–229.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 2021
˚
Table 2. Selected Bond Lengths (A), Bond Angles (deg), and torsion angles (deg)
for 2
C1-P1
C9-P1
O1-P1
C15-P1
1.857(7)
1.793(6)
1.467(5)
1.796(6)
O1-P1-C1
O1-P1-C9
O1-P1-C15
112.8(3)
113.0(3)
112.8(3)
S1-C4-C5-S2
S1-C1-P1-O1
C14-C9-P1-O1
-34.2(15)
59.3(4)
53.2(6)
Table 3. Intermolecular Edge to Face π-π Interactions in the Crystal
Structure of 2
centroid of ringa
˚
distance (A)
atom (ring)
C11 (phenyl a)
C12 (phenyl a)
C13 (phenyl a)
C18 (phenyl b)
C20 (phenyl b)
C2 (thiophene a)
phenyl b
3.938
4.012
3.676
3.701
3.941
3.627
thiophene b
phenyl b
phenyl a
thiophene a
phenyl a
a Phenyl a is the phenyl comprised of C9-C14, phenyl b is the phenyl
comprised of C15-C20, thiophene a is the thiophene comprised of S1
and C1-C4 and thiophene b is the thiophene comprised of S2 and
C5-C8. Thiophene 2 is disordered about the inversion center, and the
centroid for the two disordered rings is the inversion center.
cell in Figure 2a, but the molecules occupying the centers
of the edges are rotated by (-53.8°) from those occupying
the centers of the faces, as shown by the drawing of the ab
face of the unit cell in Figure 2b.
Figure 1. Molecular structure of 2 showing one orientation of the
disordered central thiophene ring. Hydrogen atoms are omitted, and
the atomic displacement ellipsoids are drawn at 25% probability.
A second feature of interest in the solid state structure of 2
is the planarity of the terthiophene group. Because of the
location of the center of symmetry of 2, this is measured only
by the S(1)-C(4)-C(6)-S(2A) torsion angle. The signifi-
cant deviation of this angle from 180° (157.5(6)°) may be a
result of the π-π stacking involving the thiophene rings.
The final feature of interest in the solid state structure
of 2 is the orientation of the aromatic phosphorus sub-
stituents relative to the phosphorus-oxygen bond. The
conformation about the phosphorus is a distorted tetrahe-
dron with all of the O-P-C angles equal to one another and
greater than the ideal angle of 109.5°. Orientations of the
three aromatic substituents can be determined by comparing
the S1-C1-P1-O1, C14-C9-P1-O1, and C16-C15-
P1-O1 torsion angles (S1, O1, and C16 are the ortho ring
atoms that are on the same side of the least-squares plane
through C1, C9, and C14 as is the oxygen). The fact that all
three torsion angles have positive signs means that the rings
have a propeller orientation; however, the much larger
C14-C9-P1-O1 torsion angle means that propeller or-
ientation is distorted. It is of interest that the phosphor-
us-oxygen bond is nearly in the plane of one of the phenyl
rings in 2 while in the structure of Ph2(O)P(C4H2S)2P-
(O)Ph2, the phosphorus-oxygen bonds are nearly in the
planes of the thienyl rings.42
and CH3 I-.42 The most interesting feature of these
þ
structures was the extensive π-π stacking that resulted in
quite different orientations of the molecules in the crystals.
The different orientations appeared to depend both on the
crystallization conditions and on the X group. Thus, it is of
interest to determine how replacing a bithiophene with a
terthiophene affects the ability of the molecule to engage in
π-π stacking.
Crystals of compound 2 suitable for X-ray diffraction
were obtained by slow diffusion of hexanes into a concen-
trated CH2Cl2 solution of the compound. Compound 2crys-
tallizes in the C2/c space group with the molecule occupying
an inversion center. The center thiophene ring is thus disor-
dered about this inversion center. The molecular structure of
2 is shown in Figure 1, and the selected bond lengths, bond
angles, and torsion angles are given in Table 2.
The most interesting aspect of the crystal structure of 2
is the extensive π-π stacking that is observed. Edge-to-
face interactions are observed with all of the phenyl and
thiophene rings as shown by the data in Table 3. Interac-
tions are observed between phenyl a and two adjacent
molecules of 2 and between phenyl b and one of the same
adjacent molecules of 2 as well as another adjacent
molecule of 2. These interactions result in a tightly packed
array in which molecules of 2 are located on the centers of
each edge of the unit cell as well as on the centers of two
opposite faces. The dihedral angles between the least-
squares planes through the central, disordered thiophenes
are zero, as shown in the drawing of the ac face of the unit
Linear Absorption Spectra. Dichloromethane solutions
of 2-8, 10, and11 have an absorption band between 350 and
450 nm. The parent compounds 1 and 5 exhibit similar
bands, and these bands have been assigned to π f π*
transitions on the basis of density functional calculations.43
(43) Stott, T. L.; Wolf, M. O. J. Phys. Chem. B 2004, 108, 188815–188819.

2022 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
Figure 2. Left: ac face of the unit cell of 2. Right: ab face of the unit cell of 2.
Figure 3. Linear absorption spectra in a 1-mm cell. Upper left: T3, 2 and 6; upper right: T3, 2, 3, and 4; bottom: 6, 7, 8, 10, and 11. All solution
concentrations are 2.9 ꢀ 10-4 mol/L in CH2Cl2. The solvent has negligible linear absorption in this spectral region.
As expected, the absorption maximum depends on the
nature of the substituents on the terthiophene. Substitution
of terthiophene with diphenyl(oxo)phosphino groups causes
a red shift of 14 nm for each group (terthiophene: λmax = 354
nm; 6: λmax = 368 nm; and 2: λmax = 382 nm) as shown in
Figure 3a. This is consistent with the results of studies of
related phosphine-substituted oligothiophenes and their
amino analogues and has been rationalized as being due to
stabilization of the lowest unoccupied molecular orbital via
a bonding interaction with the phosphorus.44,45
Changing the group attached to the lone pair of electrons
on the phosphorus has little effect on the absorption maxi-
mum (2(X=O):λmax=382 nm; 3(X=S):λmax=382 nm; 4
(X=Meþ): λmax=387 nm). This is in contrast with previous
results for the bithiophene compounds Ph2(X)P(C4H2S)2P-
(X)Ph2 (X = O: λmax=326 nm; X=S: λmax=342 nm; X=
Meþ: λmax = 332 nm) but is consistent with results from
density functional theory (DFT) calculations indicating that
terthiophenes have little P character in their highest occupied
and lowest unoccupied molecular orbitals.43 It is of interest
(44) Tabet, A.; Schroder, A.; Hartmann, H.; Rohde, D.; Dunsch, L. Org.
Lett. 2003, 5, 1817–1820.
(45) Changenet, P.; Plaza, P.; Martin, M. M.; Meyer, Y. H.; Rettig, W.
Chem. Phys. 1997, 221, 311–322.

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Inorganic Chemistry, Vol. 50, No. 5, 2011 2023
that although the substituent on the lone pair of electrons on
the phosphorus does not affect the absorption maximum, it
does affect the molar absorptivity with 2(O) and3(S) having
lower molar absorptivities than terthiophene and 4 (Meþ)
having a higher molar absorptivity than terthiophene.
The linear absorption characteristics are very sensitive
to the nature of the substituent at the 500-position for the
derivatives of the monophosphine 6. A red shift is observed
as more highly conjugated groups are introduced at the
500-position (6 (H): λmax = 367 nm; 8 (CH2OH): λmax = 376
nm; 10 (CO2Me): λmax = 386 nm; 7 (CHO): λmax = 398 nm;
11 (CH=NPh): λmax = 411 nm) consistent with Wood-
ward’s Rules for conjugated carbonyl compounds.46 The
substituent at the 500-position also affects the molar absorp-
tivity with the most conjugated compounds exhibiting the
highest molar absorptivities.
Solution Phase Fluorescence Spectra. The emission
spectra were studied to gain additional insight into the
nature of the first singlet excited state of the compounds in
this photophysical study. For most fluorescent compounds,
emission is produced by either a π* f π or a π* f n
transition, depending on which of these is the less energetic.
Empirically, π f π* transitions are characterized by higher
molar absorptivities and relatively higher fluorescence quan-
tum yields than those of n f π* transitions.47 As previously
reported by Wolf for the parent compounds 1 and 5, the
emission is attributed to a π* f π transition.43 DFT
calculations, also reported by Wolf, supported this assign-
ment by demonstrating that planarization does not occur
at the phosphorus. In this case, the emission of the disubsti-
tuted terthiophene (λem = 465 nm) was red-shifted by 20 nm
relative to that of the monosubstituted terthiophene (λem
=
446 nm).43
The solution phase emission spectra for compounds
2-4, 6-8, and 10-11 (summarized in Table 4) show
maximum emission bands in the blue region (between 430
and 480 nm), and are red-shifted relative to that of terthio-
phene (T3: λem = 410, 430 nm).48 Figure 4a shows the repre-
sentative excitation and emission spectra for compound 2
with two emission bands at 430 and 454 nm, respectively,
similar to those seen in other oligothiophenes.49 The corre-
sponding excitation spectra for these two emission bands
were identical to their absorption spectra, which indicates
the presence of a single species in the ground state. Figure 4b
shows the comparison of the intensity of the emission spectra
for compounds 2, 3, 6, and 8 under the condition that the
optical densities of the solutions are identical at the excita-
tion wavelengths. For better comparison, the relative quan-
tum yields (Q/QR) for all the compounds were calculated
Table 4. Emission Data for 1-8, and 10-11 in Dichloromethane Solution
λ
abs/nm (ε/dm3
3
mol-1 cm-1 a
)
λ
em /nmb
ODe
If
Q/QR
g
cpd
T3
3
354 (28200)
410, 430c
407, 426 c
465 d
0.110
1.00
1.00
1
383 d
2
3
4
5
373 (20300)
377 (19300)
387 (35500)
374 d
430, 454
435, 462
475
0.0809
0.0769
0.141
1.96
0.629
0.857
2.67
0.900
0.669
446 d
6
7
8
10
11
368 (20500)
401 (37000)
377 (21300)
387 (12800)
411 (47800)
450
477
456
439, 462
475
0.0812
0.143
0.0845
0.0510
0.190
0.697
1.50
1.16
0.606
0.565
0.944
1.15
1.51
1.31
0.327
a Linear absorption band maximum in CH2Cl2 solution. b Emission
band maximum in CH2Cl2 solution. c First (upper) values were mea-
sured for CH2Cl2 solutions. Second (lower) values are from reference 48
and are for dioxane solutions. d Data are from reference 43 and are for
hexanes solutions. e Optical density or absorbance at the excitation
wavelength. f Integrated fluorescence intensity from the corrected fluores-
cence spectrum. The values reported are the ratio based on T3. g The
ratio of the quantum yields using T3 as the internal reference. See eq 3.
Figure 5. Thin film fluorescence emission spectra for 2, 3, and 4, using
the 457 nm Ar ion laser line for excitation.
Figure 4. Left (a): excitation and emission spectra for 2; excitation spectrum 1 (dashed line): λEm = 454 nm; excitation spectrum 2 (dotted line):
λEm = 430 nm. Right (b): emission spectra of the 4 ꢀ 10-6 mol/L solutions of 2, 3, 6, and 8 with identical optical density of 0.080 at their excitation
wavelengths in a 10 mm cell.

2024 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
Figure 6. Singlemolecule fluorescencetimetracesfor4showingstable emission(top), blinking(centerleft), and photobleaching(centerright)and thinfilm
fluorescence emission for 4 as a function of laser power for 4 using the 457 nm Arþ laser line for excitation (bottom).
using the CH2Cl2 solution of T3 as the reference solution
(summarized in Table 4).
quantum yield with 3 (S) and 4 (Meþ) having much lower
quantum yields than does 2 (O).
A comparison of the emission spectra for the mono- and
disubstituted terthiophenes shows the effect of adding diphe-
A comparison of the emission spectra for the mono-
substituted terthiophenes shows the effect of changing the
functional R-group at the 500-position. Compounds 7 (R =
CHO), 8(R =CH2OH), and 10 (R =CO2Me) show higher
quantum yields than does 6 (R = H). However, compound
11 (R = CHNPh) shows relatively lower quantum yield
than does 6.
Thin Film and Single Molecule Fluorescence Spectra. Some
of the most important applications for fluorescent materials
involve emission from the solid state.50,51 Thin film fluores-
cence spectra from the disubstituted terthiophenes 2, 3, and 4
were recorded so that the solid state emission characteristics
could be compared to those of the compounds in solution. A
comparison of the thin film emission spectra for disubstitut-
ed terthiophenes 2, 3, and 4 is shown in Figure 5. All three
exhibit intense solid state and single molecule emission using
457 nm cw laser excitation with 4 exhibiting the longest
wavelength emission of the three compounds. Emissions
nyl(oxo)phosphino groups to the terthiophene (T3: λem
=
410, 430 nm; 6: λem = 450 nm; 2: λem = 430, 454 nm).
Adding the first group (T3 versus 6) causes a significant red
shift but no significant change is observed when the second
group is added (2 versus 6) at the 500-position of the
terthiophene moiety. To our surprise, the introduction of
the second diphenyl(oxo)phosphino group significantly af-
fects the fluorescence quantum yield with 2 exhibiting much
higher quantum yield than 6.
A comparison of the emission spectra for the disubstitut-
ed terthiophenes 2, 3, and 4 shows the effect of the group on
the phosphorus lone pair on the emission spectra. Although
the substituent on the phosphorus does not significantly
affect the emission maximum, it does affect the fluorescence
(46) Woodward, R. B. J. Am. Chem. Soc. 1941, 63, 1123–1126.
(47) Valeur, B. Molecular Fluorescence: Principles and Applications;
Wiley-VCH: Weinheim, Germany, 2002.
(50) Noda, T.; Ogawa, H.; Noma, N.; Shirota, Y. Appl. Phys. Lett. 1997,
70, 699–701.
(51) Kim, D.; Salman, S.; Coropceanu, V.; Salomon, E.; Padmaperuma,
A. B.; Sapochak, L. S.; Kahn, A.; Bredas, J.-L. Chem. Mater. 2010, 22, 247–
254, and references therein.
(48) Becker, R. S.; Seixas de Melo, J.; Macuanita, A. L.; Elisei, F. J. Phys.
Chem. 1996, 100, 18683–18695.
ꢁ
^
(49) DiCesare, N.; Belletete, M.; Marrano, C.; Leclerc, M.; Durocher, G.
J. Phys. Chem. A 1998, 102, 5142–5149.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 2025
Figure 7. Comparison of the nonlinear transmittances of dichloromethane solutions of 2 and 3 (upper left), 2 and 6 (lower left) and 6, 8, and 10 (upper
right) in a 1 mm cell as a function of incident energy with a 27 ps laser pulses at 450 nm.
from all three are truncated because of the dichroic and
emission filters employed with the 457 nm laser excitation.
The emission from 2 and 3 continually decreases above
500 nm and is consistent with the solution phase measure-
ments. An emission maximum in 4, however, is observed
at 520 nm in the thin film spectrum, suggesting a red-shift in
the solid state emission spectrum compared to solution
measurements.
Thin film and single molecule fluorescence emissions
from the disubstituted terthiophenes 2, 3, and 4 were
obtained as function of laser power to investigate the
possibility of NLA manifested in the fluorescence emis-
sion. Representative fluorescence time traces from single
4 molecules are shown in Figure 6a. The single disubsti-
tuted terthiophene molecules exhibit both blinking and
photobleaching in the solid state,52 and for this reason
fluorescence measurements as a function of laser power
were inconclusive. Thin film fluorescence requirements as
a function of laser power for 4, which exhibits the largest
absorption and most intense emission of the three disub-
stituted terthiophenes with 457 nm excitation, are shown
in Figure 6b. These results are representative of those of 2
and 3 in that thin film emission for all three compounds
was observed to increase linearly with laser power. This
suggests that higher peak laser power (such as that
employed for the NLA results discussed below) is prob-
ably required to observe nonlinear effects in the fluores-
cence emission. This could not be done using cw excita-
tion because laser powers above 300 μW result in rapid
irreversible photobleaching of the thin films.
Nonlinear Optical Characterization. Because NLA is
very dependent on wavelength, we have characterized the
NLA of the compounds described in this manuscript over a
range of wavelengths in the blue and green spectral regions
near their linear absorption peaks. NLA measurements were
performed on dichloromethane solutions of 2-8, and10-11
whose concentrations were between 3.50 ꢀ 10-3 and 3.65 ꢀ
10-3 mol/L in a 1 mm cuvette. To observe non-resonant
NLA, linear transmittance must be large (greater than 70%
for our system). On the basis of the linear absorption data
discussed previously, 2, 3, 6, 8, and 10 have linear transmis-
sions above 70% at 450 nm, all compounds except 11 have
linear transmissions above 70% at 480 nm and all com-
pounds have linear transmissions above 90% at 532 nm.
Figures 7, 8 and 9 show the nonlinear transmittance of
compounds at 450 nm, 480 and 532 nm, respectively.
At 450 and 480 nm, all compounds with linear transmit-
tances >70% exhibit significant NLA as the input energy is
increased. The threshold of the NLA, defined as the incident
(52) Odoi, M. Y.; Hammer, N. I.; Rathnayake, H. P.; Lahti, P. M.;
Barnes, M. D. ChemPhysChem 2007, 8, 1481–1486.

2026 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhao et al.
Figure 8. Comparison ofthe nonlineartransmittances ofdichloromethanesolutionsof2, 3, and 4 (upper left), 2 and 6 (lower left) and 6, 7, 8, and 10(upper
right) in a 1 mm cell as a function of incident energy with 27 ps laser pulses at 480 nm.
Figure 9. Comparison of the nonlinear transmittances of dichloromethane solutions of 2, 3, and 4 (left) and 6, 7, 8, 10, and 11 (right) a 1-mm cell as a
function of incident energy with 27 ps laser pulses at 532 nm.
fluence at which the transmittance starts to deviate from the
linear transmittance, is about 0.3 J/cm2. At 450nm, all of the
NLA curves have approximately the same shape, and the
major factor determining the NLA appears to be the linear
absorption. Slight changes in the curve shape because of the
terthiophene substituents are observed as shown by the plot
of the NLA curves of 2 and 6. It is interesting that the
addition of a second diphenyl(oxo)phosphine group to the
terthiophene shifts the linear absorption maximum closer to
450 nm but slightly weakens the NLA at that wavelength.
The NLA at 480 nm is somewhat weaker than is the
NLA at 450 nm for all the compounds (transmittance at

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 2027
1.7 J/cm2: 2, 59% versus 63%; 3, 50% versus 59%, 6, 58%
versus 68%; 8, 44% versus 55%; 10, 66% versus 69%). In
the case of 3, this decrease appears to be primarily due to
the decrease in linear absorption, but in the cases of 6, 8,
and 10, which have approximately the same linear ab-
sorption at 480 nm, the NLA curve of 8 is significantly
steeper than are those of 6 and 10. The NLA curve for 7,
whose NLA could not be measured at 450 nm because of
its low linear transmittance at that wavelength, is even
steeper (transmittance at 1.7 J/cm2: 50%) than is that of 8
demonstrating that the 200-substitutent can have a signifi-
cant effect on the NLA at a given wavelength.
At 532 nm, 11 exhibits the strongest NLA although its
linear transmittance is 88% at this wavelength. Perhaps
this is because 532 nm is considerably closer to the linear
absorption peak of 11 than to those of any of the other
compounds. It is also interesting that 10 still exhibits
some NLA absorption at 532 nm. This makes it the
broadest band nonlinear absorber of all of the terthio-
phene derivatives in this paper.
can be varied by the appropriate choice of the 500-substituent
and the group attached to the nonbonding pair of electrons
on the diphenylphosphino substituent. The introduction
of functional groups at the 500-position of the terthiophene
also means that it should be possible to attach these nonli-
near absorbers to polymers for use in oriented thin films
or nanoparticles to generate hybrid nonlinear absorbing
materials.
The emission spectra for all of these terthiophene deriva-
tives show maximum emission bands in the blue region. Both
the emission maxima and fluorescence quantum yields can be
tuned by varying the500-substituent, the group attachedto the
phosphorus atoms, and the number of the phosphorus-donor
groups with compound 2 exhibiting the strongest fluores-
cence emission intensity. These results suggest that materials
with even higher quantum efficiencies could be prepared by
increasing the number of thiophene units. Thin film fluores-
cence measurements also indicate that these materials might
serve as good blue emitters in the solid state.
Acknowledgment. The authors gratefully acknowledge
an Army Research Laboratories Cooperative Agreement
(W011NF-06-2-0033) and NSF Cooperative Agreements
(EPS-0814103 and EPS-0903787) for support of this
research.
Conclusions
Terthiophenes with at least one diphenylphosphino-de-
rived substituent exhibit NLA in the blue spectra region. For
each of the terthiophene derivatives, the NLA is strongest at
wavelengths near the linear absorption maximum of the
compound. In addition, the group at the 500-position of the
terthiophene has a significant effect on the NLA as well as on
both the linear absorption maximum and the emission
maximum of the compound. This means that the strength
of the NLA and the wavelength at whichtheNLA is observed
Supporting Information Available: Crystal structure data for 2
including tables of atomic coordinates, anisotropic thermal
parameters, all bond lengths and angles, and hydrogen isotropic
displacement parameters using the crystallographic information
file (CIF) format. This material is available free of charge via the
Internet at http://pubs.acs.org.