Synthesis and photophysical properties of donor-acceptor dithienophospholes

Article abstract of DOI:10.1002/ejoc.201000574

The synthesis and detailed photophysical studies of a series of 2,6-asymmetrically functionalized dithieno[3,2-b:2′,3′-d]phospholes are reported. One-photon spectroscopy revealed that the materials show similar significant Stokes shifts supporting very polar excited intramolecular chargetransfer (ICT) states. Investigation of their two-photon absorption (TPA) behavior indicated that the materials are also valuable TPA chromophores with reasonable cross-sections between 285-385 GM in the biologically relevant wavelength range 800-1100 nm. Moreover, the nonlinear optical features of the phosphole derivatives reported herein were found to remain almost unaltered after modification of the phosphorus center, either by oxidation and/or complexation.

Full text of DOI:10.1002/ejoc.201000574

FULL PAPER
DOI: 10.1002/ejoc.201000574
Synthesis and Photophysical Properties of Donor–Acceptor Dithienophospholes
Carlos Romero-Nieto,[a,b] Kenji Kamada,[c] David T. Cramb,[b] Sonia Merino,[a]
Julián Rodríguez-López,*[a] and Thomas Baumgartner*[b]
Keywords: Phosphorus heterocycles / Donor-acceptor systems / Conjugation / Solvatochromism / Two-photon absorption
The synthesis and detailed photophysical studies of a series
of 2,6-asymmetrically functionalized dithieno[3,2-b:2Ј,3Ј-
valuable TPA chromophores with reasonable cross-sections
between 285–385 GM in the biologically relevant wave-
d]phospholes are reported. One-photon spectroscopy re- length range 800–1100 nm. Moreover, the nonlinear optical
vealed that the materials show similar significant Stokes
shifts supporting very polar excited intramolecular charge-
transfer (ICT) states. Investigation of their two-photon ab-
sorption (TPA) behavior indicated that the materials are also
features of the phosphole derivatives reported herein were
found to remain almost unaltered after modification of the
phosphorus center, either by oxidation and/or complexation.
In general, it has been concluded that the conjugation
length, geometry, intramolecular charge transfer (ICT), po-
larizability, coplanarity, and the nature of the aromatic/π-
bridge have a significant impact on TPA cross-sections.[16,17]
Moreover, 3D branching was also found, in some cases, to
give rise to an enhancement in the TPA cross-section
through cooperative effects.[20] To date, a significant number
of heterocycles have been employed in corresponding mate-
rials used as either an aromatic/π-bridge or a donor–ac-
ceptor component.[17] The phosphole system, a five-mem-
bered heterocycle, however, has received little attention in
this context. This phosphorus-containing moiety presents
some particularly intriguing characteristics that make it sig-
nificantly different from other five-membered heterocycle
analogues. The pyramidal disposition of the phosphorus
center avoids efficient interaction between its lone pair or-
bital with the dienic, conjugated π system, reducing the aro-
maticity of the ring. Furthermore, this system also exhibits
some σ*–π* hyperconjugation through interaction of the
exocyclic P–R bond with the π-conjugated system that
lowers the LUMO energy level substantially. As a conse-
quence, the electronic structure of phospholes can be read-
ily controlled by simple chemical modifications at the phos-
phorus center and/or at the main scaffold.[21,22] In the late
1990s, theoretical studies already suggested that phospholes
could indeed be useful building blocks for the engineering
of dipolar chromophores with NLO properties.[23] In 2002,
Réau and co-workers determined the molecular first-hyper-
polarizability values of phosphole derivatives for the first
time. It was found that palladium-bridged dipolar phos-
phole dimers exhibit fairly high NLO activities assisted by
the metal atom, which also preclude the phosphorus atom
from further functionalization.[24] Later on, Matano and
co-workers[25] described a series of new donor–acceptor 2-
aryl-5-styrylphosphole derivatives. These noncoordinated
View this journal online at
Introduction
Two-photon absorption (TPA) is a third-order nonlinear
optical (NLO) process that has received a great deal of at-
tention in the last decades due to its potential for practical
application in two-photon fluorescence microscopy,[1–3] 3D
optical data storage and fabrication,[4–8] optical limit-
ing,[9–11] photodynamic therapy,[12–14] and multiphoton mi-
croscopy (MPM).[15,16] Significant progress has been made
with regard to the fine-tuning of fundamental photophysi-
cal parameters of organic TPA chromophores, such as non-
linear absorptivity range, TPA cross-section (σ2), and fluo-
rescence quantum yields (φPL), among other specific appli-
cation requirements.[17] In MPM applications, for example,
most of the common practical fluorescent dyes have two-
photon brightness values (σ2φPL) in the range 1–300 GM[18]
with TPA excitation wavelengths in the biologically trans-
parent range (800–1100 nm) that permit deeper penetration
of biological tissues. To improve the TPA cross-section val-
ues, a variety of structural motifs has been investigated,
both experimentally and theoretically, therefore allowing
comprehensive TPA structure–property relationships.[17,19]
2D molecules including dipolar (D-π-A) and quadrupolar
(A-π-A, D-π-D), as well as 3D ones (octupolar and dendri-
mers) have been reported to show excellent TPA results.[17]
[a] Facultad de Química, Universidad de Castilla-La Mancha,
13071 Ciudad Real, Spain
E-mail: julian.rodriguez@uclm.es
[b] Department of Chemistry, University of Calgary,
2500 University Drive NW, Calgary, AB T2N 1N4, Canada
E-mail: thomas.baumgartner@ucalgary.ca
[c] Photonics Research Institute, National Institute of Advanced
Industrial Science and Technology (AIST), AIST Kansai Cen-
ter,
1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201000574.
wileyonlinelibrary.com
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J. Rodríguez-López, T. Baumgartner et al.
FULL PAPER
compounds showed higher first-hyperpolarizability values, throughout the whole reaction sequence. The expected
demonstrating an effective inductive effect between the do- 3JH,H coupling constants of 16.0 (Ϯ0.1) Hz for the vinylic
1
nor and acceptor moieties promoted by the vinylene bridge. protons in the H NMR spectrum clearly supported the se-
Despite the promising results obtained in second-order lective formation of E-configured double bonds. To deter-
nonlinear properties, some of us only very recently reported mine the influence of the phosphorus oxidation state on the
TPA cross-sections of dibenzophospholes, which turned out potential TPA properties of the system, compound 3 was
to be enhanced by spiro conjugation.[26] Yamaguchi and co- then oxidized in a standard procedure involving H2O2.[28]
workers reported earlier this year zwitterionic phospho- The 31P{1H} NMR signal at δ = 18.1 ppm supported the
nium-borate containing ladder-type acenes with very large successful oxidation of the phosphole moiety. Furthermore,
TPA cross-sections of up to 784 GM when excited at we were also interested in attaching a bulky group at the
1200 nm.[27]
phosphorus center to insert an out-of-plane moiety (apart
A few years ago, we introduced the dithieno[3,2-b:2Ј,3Ј-d]- from the intrinsic phenyl ring) to modify the third spatial
phosphole as a novel phosphorus-based building block,[28] dimension of the molecule. As mentioned above, it has been
which has successfully been employed in a variety of materi- demonstrated that 3D branched molecules can potentially
als, ranging from oligomers to polymers and dendrimers lead to synergistic effects by through-space interactions en-
with excellent optical properties.[28–30] The unique structural hancing the TPA features.[17] The intriguing optoelectronic
and photophysical properties of this distinct type of phos- properties demonstrated by dithienophosphole gold com-
phole, such as its versatile reactivity, tunability, and intense plexes in general,[30] encouraged us to use the gold(I) chlo-
fluorescence with high quantum yields, make it particularly ride fragment as an out-of-plane unit. Treatment of 3 with
attractive in the conception of new and improved materials. Au(THT)Cl (THT = tetrahydrothiophene) at room tem-
The ideal materials design for NLO applications requires perature provided the corresponding donor–acceptor phos-
the structure and, more importantly, the photophysical phole gold complex 5 in excellent yield (96%); the charac-
properties of TPA chromophores to be adaptable to a spe- teristic 31P{1H} NMR signal at δ = 8.9 ppm confirmed its
cific function. From this viewpoint, we decided to evaluate successful formation.[30] All new compounds were fully
the TPA capabilities of donor–acceptor dithienophosphole characterized by heteronuclear NMR spectroscopy (1H,
model compounds and to successively investigate the influ- 13C, 31P), mass spectrometry, and elemental analysis. Com-
ence of the oxidation state of the phosphorus atom and/or plete data are provided in the Experimental Section.
the variation of the third structural dimension on its TPA
properties. In this report we now describe the synthesis and
characterization of novel donor–acceptor vinylene-bridged
dithieno[3,2-b:2Ј,3Ј-d]phospholes, as well as a comprehen-
sive investigation of their one-photon and two-photon ab-
sorption features.
Results and Discussion
Synthesis and Characterization
For the purpose of this study, three donor–acceptor di-
thienophosphole derivatives were synthesized according to
Scheme 1. The general synthetic strategy towards these sys-
tems involved a stepwise Wittig–Horner coupling protocol
between aldehyde 1[29e] and para-substituted donor or ac-
ceptor benzylphosphonates. In a recent study on symmetri-
cally substituted dithienophospholes, we could verify that
this coupling leads to selective formation of E-configured
vinylene bridges.[29e] In variation to our published pro-
Scheme 1. Synthesis of donor–acceptor dithieno[3,2-b:2Ј,3Ј-d]phos-
phole derivatives.
cedure, building block 1 was treated with diethyl 4-(di-
phenylamino)benzylphosphonate (1.3 equiv.), yielding
monofunctionalized compound 2 in 74% yield. Access to
this monosubstituted compound benefits from our observa-
tions that the Wittig–Horner coupling only proceeds very
slowly when electron-donating benzyl moieties are used.
Linear (One-Photon) Absorption and Emission Spectroscopy
To gain detailed information on the excited states of the
From this asymmetric compound, a second Wittig–Horner new donor–acceptor dithienophospholes and to acquire
reaction with diethyl 4-(trifluoromethyl)benzylphosphonate deeper insight into important structure–property relation-
gave rise to 3 in 93% yield, which showed a 31P{1H} NMR ships, we first studied the one-photon absorption (OPA)
signal at δ = –19.9 ppm. Importantly, this synthetic proto- features of the different derivatives. Importantly, all com-
col allowed us to preserve the trivalent phosphorus pounds are transparent to linear absorption between 800
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Synthesis and Photophysical Properties of Dithienophospholes
and 1100 nm, preventing possible residual absorptions dur- very slight changes in the absorption spectra reveal that the
ing the TPA measurements. The single-photon photophysi- oxidation and complexation of the phosphorus atom lo-
cal properties of compounds 2–5 in dichloromethane cated at the center of the π-conjugated molecules have al-
(DCM) and 2-methoxyethanol (ME) are listed in Table 1 most no effect on the linear absorption properties of the
(see also Figure 1).
system. The absorption maxima of compounds 3–5 were,
however, found to be redshifted with the solvent polarity
upon moving from DCM to ME. This positive solvatochro-
mism effect indicates that the electronic state reached after
excitation is more polar than the ground state.[31] With re-
spect to the fluorescence features, similar deep-red emission
maxima were observed for compounds 3–5 in solution
(DCM: λem = 627–631 nm, ME: λem = 638–645 nm). Again,
the emission properties remained almost unaltered after
either oxidation or complexation of the central phosphole
moiety. Notably, these emissions represent the most red-
shifted values in term of wavelengths by using phosphole
oligomers to date, and illustrate the high value of the do-
nor–acceptor approach to lowering optical band gaps.
Moreover, the observed Stokes shifts of ∆ν = 4526–
5249 cm–1 (DCM) and ∆ν = 4814–4987 cm–1 (ME) are
rather large for dithienophospholes,[28] which is a clear indi-
cation of the high polarizability of the π-conjugated system.
Furthermore, it is well established that donor–acceptor-
functionalized molecules can lead to intramolecular charge
transfer (ICT) processes, which would explain the large
Stokes shifts observed. Typical ICT consists of the charge
redistribution from the donor to acceptor unit upon exci-
tation. As a result, the global charge of the molecule un-
dergoes a rearrangement that gives rise to charge-separated
excited states. Fluorescence lifetime decay measurements
also pointed to such a process. Experimental values are
summarized in Table 1. In line with the observed Stokes
shifts, the multiexponential fit of the fluorescence decay is
a further indication that complex relaxation mechanisms of
the locally excited state toward the ground state are taking
place.[32] In addition, to support a possible ICT, DFT calcu-
lations were performed for compounds 3 and 4 at the
B3LYP/6-31G* level of theory. The optimized structures
possess a high degree of coplanarity, which is a beneficial
factor for the communication between the donor and ac-
ceptor end groups, hence favoring NLO phenomena in ge-
neral. The calculated frontier orbitals for compound 3 are
shown in Figure 2 (see Supporting Information for 4). The
HOMO is largely located at the donor end of the materials,
whereas the LUMO is located at the acceptor end, demon-
strating an efficient conjugation along the extended conju-
gated backbone.
Table 1. One-photon photophysical properties.
Solvent[a]
λabs
[nm] [nm]
λem logε[c] ∆ν[d]
η[e]
[ns]
φPL
[f]
[cm–1]
nd
[%]
2
3
DCM
DCM
453,
503[b]
474
633
631
nd
nd
nd
24
5249 1.08Ϯ0.005
(52.1%)
25
2.48Ϯ0.004
(47.9%)
ME
DCM
491
489
643 5.15 4814
nd
15
24
4
5
628
nd
4526 0.94Ϯ0.007
(33.2%)
2.43Ϯ0.003
(66.8%)
ME
DCM
492
479
645 5.14 4821
nd
12
14
627
nd
4928 0.55Ϯ0.003
(76.4%)
1.32Ϯ0.016
(21.8%)
4.01Ϯ0.035
(1.8%)
ME
484
638 5.29 4987
nd
10
[a] DCM = CH2Cl2; ME = 2-methoxyethanol. [b] λmax excitation.
[c] Molar extinction coefficient. [d] Stokes shift (∆ν = 1/λabs
1/λem). [e] Fluorescence lifetime; decay curves were analyzed with
two or three exponential components. The number in brackets is
the amplitude ratio in %. [f] Fluorescence quantum yield relative to
fluorescein (in 0.01  KOH/ethanol); Ϯ15%. nd = not determined.
–
Figure 1. Normalized absorption and emission of compounds 3, 4,
and 5 in DCM.
Despite the differences between the absorption and emis-
sion values, the quantum yields (φPL) for compounds 3, 4,
The absorption maxima of all compounds are in the and 5 in DCM are relatively high at φPL = 25, 24, and 14%,
range λmax = 484–492 nm in ME and λmax = 474–489 nm respectively. The oxidation of the phosphorus atom does
in DCM. These results are quite remarkable since it has not seem to affect the fluorescence quantum yields. How-
commonly been observed that oxidation of the phosphorus ever, the φPL value of the gold complex is slightly lower,
atom is accompanied by a redshift (Ͻ40 nm) in the absorp- probably due to the heavy atom effect. Donor–acceptor
tion and emission spectra.[28] The same is true for transi- structural motifs, in general, lead to a decrease in the φPL
tion-metal-complexed phospholes, which undergo a less values.[33] Intriguingly, the donor–acceptor phosphole de-
pronounced bathochromic shift (Ͻ20 nm)[28,30] compared rivatives only show a minor decrease when compared with
to noncoordinated dithienophospholes. In this case, the their quadrupolar homologues,[29e] which makes these de-
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Table 2. Photophysical properties of compound 4 in different sol-
vents.
Solvent Polarity Et(30) λabs [nm] λem [nm] ∆ν [cm–1][a] φPL [%][b]
Toluene
Ether
THF
AcOEt
CHCl3
DCM
DMF
EtOH
ME
33.9
34.5
37.4
38.1
39.1
40.7
43.2
51.9
52.0
486
481
485
483
492
489
489
489
492
591
592
607
608
619
628
640
641
645
3656
3870
4144
4257
4170
4526
4825
4849
4821
20
20
22
21
24
24
14
12
12
[a] Stokes shift (∆ν = 1/λabs – 1/λem). [b] Fluorescence quantum
yield relative to fluorescein (in 0.01  KOH/ethanol); Ϯ15%.
increasing the polarity of the medium (see Table 2). Such
characteristic behavior, as well as the large Stokes shifts,
even in non-polar solvents, reveal that a significant degree
of electronic reorganization takes place upon excitation and
this gives rise to a polar charge-separated emitting state, as
anticipated previously. This feature is also supported by the
large excited state dipole moment of µe = 34.2 D for 4 that
was estimated by the Lippert–Mataga model[35] on the basis
of the solvatochromism and the DFT-computed ground-
state dipole moment of µg = 8.6 D. As a consequence of the
interaction between the dipole moments of the compound
and the solvent molecules, the fluorescence quantum yields
are significantly influenced by the solvent polarity, from φPL
= 20% (toluene) to φPL = 12% (EtOH, ME). Finally, it is
important to note that compounds 3–5 exhibit high photo-
stability during the performed experiments; no decomposi-
tion or cis/trans isomerization processes were detected.
Figure 2. Frontier orbitals of compound 3. Top: LUMO; bottom:
HOMO; (B3LYP/6-31G* level of theory).
rivatives particularly interesting for the study of TPA-in-
duced fluorescent applications. Because of the magnitude
of the observed Stokes shifts, we wanted to discern other
possible phenomena besides ICT that could interfere with
the TPA measurements. Particularly, undesired aggrega-
tions in the excited state could also contribute to the cross-
section values[34] and thus to inaccurate structure–property
relationships. To eliminate this possibility, concentration ex-
periments were carried out for compounds 3–5 and a sim-
ilar trend was observed for all of them. We recorded their
absorption and emission spectra with increasing the con-
centration from 10–7 to 10–5  in ME (see Supporting Infor-
mation). However, even after these two orders of magnitude
Nonlinear (Two-Photon) Absorption Spectroscopy
TPA spectra of compounds 3–5 in DCM and ME are
increments, no changes either in the absorption or in the shown in Figure 3. All three compounds show a very broad
emission maxima could be detected. Therefore, concentra- absorption along the whole range employed in biological
tion dependent aggregation could be discarded from these applications (∆λ2max = 800–1100 nm). Almost no differ-
experiments.
ences were found between the spectra recorded in DCM
Due to the very similar photophysical features of com- and ME, suggesting that the two-photon excited states are
pounds 3–5, we representatively chose compound 4 to carry hardly affected by the polarity of the medium. The maxi-
out more detailed one-photon investigations. To examine mum cross-section values are listed in Table 3. All com-
the solvatochromism of compound 4, the absorption and pounds present moderately high cross-sections around σ2 =
emission spectra were recorded in a variety of different sol- 335–385 GM in DCM and σ2 = 285–345 GM in ME that
vents (see Table 2).
are larger than those of somewhat related donor–acceptor
Although some minor deviation from the trend was de- and donor–donor dithienothiophene analogues.[36] Accord-
tected in the absorption features when increasing the sol- ing to the double level model,[17] donor–acceptor molecules
vent polarity [according to the Et(30) scale], a strong solva- usually present TPA maxima in around double the wave-
tochromism effect can be observed for the emission features. length of the single-photon absorption peak. However, no
The shortest emission wavelength maximum at λem
591 nm in the least polar solvent (toluene) is redshifted by maxima for all compounds, although a very small peak is
about ∆λem = 54 nm upon using ME as solvent (λem located there. Despite a triple level model being potentially
=
clear TPA maxima were detected around twice the OPA
=
645 nm). Thus, the solvent polarity allows significant tun- applicable, the explanation for this deviation is currently
ing of the luminescence properties of the material. It is unclear, but, however, is under detailed investigation. Sim-
noteworthy that the range of the emission maxima (591– ilar to the single-photon absorption studies, TPA properties
645 nm, ∆λem = 54 nm) is five times larger than the range of the materials remained almost unchanged when varying
of the absorption maxima (481–492 nm, ∆λabs = 11 nm) on the oxidation state of the phosphorus center from +3 to +5.
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Synthesis and Photophysical Properties of Dithienophospholes
Recently, it has been demonstrated in pure metal complex tile reactivity of the phosphorus atom to be structurally/
TPA chromophores that a change in the oxidation state of chemically adapted to precise applications while keeping the
the metal center can lead to dramatic changes in their non- TPA features intact.
linear responses.[37] Interestingly however, the third-order
response of the donor–acceptor dithienophosphole deriva-
Table 3. TPA properties of compounds 3–5.
[a]
[b]
tives appears to be preserved after chemical/structural
modifications at the phosphorus center. By complexation of
the phosphorus atom, we evaluated whether the TPA prop-
erties could also be impacted through interactions between
the out-of-plane orbitals of the Au–Cl fragment and the
phosphole main scaffold. However, although the cross-sec-
tion was indeed slightly increased, the interactions were not
significant enough to claim major changes in the TPA prop-
erties. Compared to the notable enhancement in second-
order NLO properties by complexation of related phos-
pholes,[24] it can be concluded that the TPA properties of
donor–acceptor dithienophospholes are relatively silent to-
ward complexation of the phosphole center. This fact, to-
gether with the preservation of the TPA features in the dif-
ferent oxidation states of the phosphorus center (+3, +5),
are particularly interesting since they offer the possibility of
(1) obtaining dithienophospholes with specific cross-sec-
tions and, consecutively, (2) taking advantage of the versa-
Compound
Solvent
λmax [nm]
σ2 [GM]
3
DCM
ME
DCM
ME
DCM
ME
817
819
817
819
817
819
335
285
385
320
375
345
4
5
[a] TPA wavelength maxima. [b] TPA cross-section: GM
10–50 cm4 sphoton–1.
=
Conclusions
In summary, a new series of 2,6-donor–acceptor-func-
tionalized dithienophosphole derivatives has been synthe-
sized that can structurally be modified by simple and ef-
ficient reactions at the phosphorus center. Their linear and
nonlinear optical properties have been studied. Investiga-
tion of their photophysical properties revealed large Stokes
shifts with significant fluorescence quantum yields and high
photostability. For the first time, two-photon absorption
properties of asymmetric donor–acceptor dithieno[3,2-
b:2Ј,3Ј-d]phosphole derivatives have been reported. All
compounds show moderately high TPA cross-sections in
the wavelength range suitable for biological/biomedical ap-
plications. Furthermore, the third-order nonlinear optical
properties were found to remain unaltered after structural/
chemical modifications at the phosphole center, which op-
ens the possibility to develop TPA chromophores that can
easily and efficiently be modified a posteriori for specific
applications. Currently, we aim to explore suitable donor–
acceptor dithienophosphole derivatives as selective molecu-
lar biomarkers for imaging applications.
Experimental Section
General Procedures and Spectroscopic Measurements: All manipula-
tions were carried out under a dry nitrogen atmosphere by em-
ploying standard Schlenk techniques. Column chromatography was
carried out by using silica gel (70–230 mesh, 60 Å) and aluminum
oxide (activated, neutral, Brockmann I, standard grade, ≈150 mesh,
58 Å). Solvents were dried by using standard procedures. H2O2 and
tBuOK were purchased from Aldrich and used as received. 2,6-
Diformyldithieno[3,2-b:2Ј,3Ј-d]phosphole (1),[29e] diethyl 4-(trifluo-
romethyl)benzylphosphonate,[38a] diethyl 4-(diphenylamino)benzyl-
phosphonate,[38b] and Au[THT]Cl[38c] were prepared according to
literature procedures. 31P{1H} NMR, 1H NMR, and 13C{H} NMR
spectra were recorded with a Bruker DMX-300 or Bruker DRX-
400 spectrometer. Chemical shifts were referenced to external 85%
H3PO4 (31P) and external TMS (13C, 1H). Electron ionization
(70 eV) mass spectra were obtained with a Finnigan SSQ 7000
spectrometer, and electrospray ionization mass spectra were ob-
tained with a Bruker Daltonic Esquire 3000 spectrometer. All fluo-
rescence experiments were recorded by using HPLC-grade solvents
Figure 3. TPA spectra of compounds 3 (top), 4 (middle), and 5
(bottom) in DCM and in ME.
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J. Rodríguez-López, T. Baumgartner et al.
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with a Jasco FP-6600 spectrofluorometer and UV/Vis/NIR Cary
5000 spectrophotometer. The fluorescence decay was measured by
the time-correlated single-photon counting (TCSPC) method under
air-saturated conditions.
25 °C): δ = –19.9 ppm. MS (EI, 70 eV): m/z (%) = 711 (100) [M]+.
C43H29F3NPS2 (711.80): calcd. C 72.56, H 4.11, N 1.97; found C
72.65, H 3.89, N 1.96.
Compound 4: Asymmetric compound 3 (80 mg, 0.1 mmol) was
treated with hydrogen peroxide (0.5 mL, 33% w/v) in CH2Cl2
(25 mL) at room temperature overnight. After removing all vola-
tiles under vacuum, the residue was taken up in CH2Cl2 again and
then filtered over alumina. Evaporation of the solvent afforded a
TPA Measurements: TPA spectra were measured by an open-aper-
ture Z-scan method with an optical parametric amplifier (pulse
width typ. 140 fs, 1.0 kHz repetition rate, incident power = 0.05–
0.4 mW varying at least four different powers for each measure-
ment point). The incident power approximately corresponds to the
on-axis peak intensity I0 of 200 GW/cm2 or less at the focal point.
The Rayleigh range of the setup was typically 4–6 mm depending
on the wavelength. The sample solution (1.3–2.7 m) was held in
a 1-mm quartz cuvette. The details of the setup were reported else-
where.[39] The recorded open-aperture Z-scan traces (see Support-
ing Information for typical traces) were analyzed by curve fitting
with a model function assuming the energy transmittance of a tem-
poral and spatial Gaussian pulse through a two-photon absorptive
media.[20b] The TPA coefficient β was obtained from the linear plot
of the two-photon absorbance, q0. The latter was obtained from
the curve fitting against the incident power because q0 is linear to
I0 (therefore, to the incident power) for TPA. TPA cross-section σ2
was obtained from the convention σ2 = βλ/(hcN), where N is the
number density of the molecule, λ is the incident wavelength, c is
the speed of light, and h is the Planck’s constant.
1
red solid (70 mg, 98%). H NMR (400 MHz, CD2Cl2, 25 °C): δ =
3
7.75 (dd, JP,H = 13.6 Hz, J = 7.6 Hz, 2 H, o-Ph), 7.63–7.55 (m, 5
4
H), 6.90–6.95 (m, 1 H), 7.46 (td, J = 7.6 Hz, JP,H = 3.2 Hz, 2 H,
m-Ph), 7.35–7.26 (m, 7 H), 7.17 (d, J = 2.8 Hz, 1 H), 7.11–7.05 (m,
8 H), 7.02–6.99 (m, 3 H) ppm. 13C NMR (75 MHz, CD2Cl2,
25 °C): δ = 149.1 (s, thiophene), 148.9 (s, thiophene), 148.5 (s, Ar),
147.9 (s, Ar), 146.6 (s, Ar), 140.6 (s, Ar), 140.4 (s, Ar), 139.7 (d,
1JC,P = 112.3 Hz, ipso-thiophene), 133.1 (d, JC,F = 2.8 Hz, Ar),
2
131.3 132.9 (d, JC,P = 11.3 Hz, thiophene), 130.5 (s, ArH), 130.1
2
(s, ArH), 129.9 (s, ArH), 129.5 (d, JC,P = 12.9 Hz, o-Ph), 128.1 (s,
ArH), 127.9 (s, ArH), 127.1 (s, ArH), 126.1 (q, JC,F = 3.6 Hz, Ar),
125.4 (s, ArH), 124.3 (q, JC,F = 270.75 Hz, Ar), 124.1 (s, ArH),
124.1 (s, ArH), 123.4 (s, ArH), 119.5 (s, ArH) ppm. 31P{1H} NMR
(162 MHz, CDCl3, 25 °C): δ = 18.1 ppm. MS (EI, 70 eV): m/z (%)
= 727 (98) [M]+, 364 (100). C43H29F3NOPS2 (727.80): calcd. C
70.96, H 4.02, N 1.92; found C 70.63, H 4.37, N 1.73.
Compound 5: Asymmetric compound 3 (100 mg, 0.14 mmol) was
treated with Au[THT]Cl (45 mg, 0.14 mmol) in CH2Cl2 (10 mL) at
room temperature for 1 h. After removing all volatiles under vac-
uum, the residue was purified by washing with diethyl ether and
pentane and then crystallized from DCM/pentane to afford a red
solid (127 mg, 96%). 1H NMR (400 MHz, CD2Cl2, 25 °C): δ = 7.75
Compound 2: tBuOK (147 mg, 1.3 mmol, 1.2 equiv.) was added in
small portions to a solution of 1 (360 mg, 1.1 mmol, 1 equiv.) and
diethyl 4-(diphenylamino)benzylphosphonate (563 mg, 1.4 mmol)
in THF (50 mL) at –78 °C. After 1 h, the reaction mixture was
allowed to reach room temperature and stirred for an additional
4 h. H2O was added, and the crude was neutralized with HCl (2 ).
The product was extracted with CH2Cl2, and the organic layer was
dried with MgSO4. After evaporation of the solvent, the crude was
purified by column chromatography (SiO2, DCM as eluent) to ob-
tain a red solid (463 mg, 74%). 1H NMR (300 MHz, CDCl3,
25 °C): δ = 9.85 (s, 1 H, CHO), 7.79 (s, 1 H, thiophene), 7.37–7.25
3
(dd, JP,H = 14.8 Hz, J = 7.2 Hz, 2 H, o-Ph), 7.59–7.52 (m, 5 H),
4
7.46 (td, J = 8.0 Hz, JP,H = 2.8 Hz, 2 H, m-Ph), 7.32–7.22 (m, 7
H), 7.09–6.89 (m, 13 H) ppm. 13C NMR (101 MHz, CDCl3, 25 °C):
δ = 148.6 (d, JC,P = 13.8 Hz, thiophene), 148.3 (d, JC,P = 13.9 Hz,
thiophene), 147.5 (s, Ar), 147.4 (s, Ar), 146.2 (s, Ar), 140.0 (s, Ar),
1
149.8 (s, Ar), 138.0 (d, JC,P = 67.67 Hz, ipso-thiophene), 133.7 (d,
3
(m, 10 H), 7.13–7.01 (m, 11 H), 6.92 (d, JH,H = 15.9 Hz, 1 H,
JC,P = 15.9 Hz, Ar), 133.1 (br. s, Ar), 131.1 (s, Ar), 130.1 (s, ArH),
-CH=CH-) ppm. 13C NMR (101 MHz, CDCl3, 25 °C): δ = 182.7
2
129.8 (d, JC,P = 13.0 Hz, thiophene), 129.8 (s, ArH), 129.6 (s,
(s, CHO), 148.2 (s, Ar), 147.5 (s, Ar), 147.4 (d, JC,P = 5.4 Hz, thio-
ArH), 127.7 (s, ArH), 127.7 (s, ArH), 126.8 (s, ArH), 126.0 (br. s,
Ar), 126.0 (d, JC,P = 62.216 Hz, ipso-Ph), 125.1 (s, ArH), 125.0 (s,
ArH), 124.5 (q, JC,F = 271.0 Hz, Ar), 118.9 (s, ArH) ppm. 31P{1H}
NMR (162 MHz, CDCl3, 25 °C): δ = 8.9 ppm. MS (ESI+): m/z =
943 [M]+, 605 [M – PhPAuCl]+. C43H29AuClF3NPS2 (944.22):
calcd. C 54.70, H 3.10, N 1.48; found C 55.01, H 2.89, N 1.36.
2
phene), 141.1 (s, thiophene), 136.4 (s, thiophene), 132.9 (d, JC,P
=
21.21 Hz, o-Ph), 130.2 (s, ArH), 129.9 (s, ArH), 129.6 (s, p-Ph),
3
129.6 (s, ArH), 129.2 (d, JC,P = 8.1 Hz, m-Ph), 127.9 (s, ArH),
127.7 (s, ArH), 125.0 (s, ArH), 125.0 (s, ArH), 123.6 (s, ArH), 122.9
(s, ArH), 119.8 (s, ArH) ppm. 31P{1H} NMR (162 MHz, CDCl3,
25 °C): δ = –20.0 ppm. C35H24NOPS2 (569.68): calcd. C 73.79, H
4.25, N 2.46; found C 73.58, H 4.58, N 2.42.
Supporting Information (see footnote on the first page of this arti-
cle): Photophysical details on the concentration studies for 3–5;
solvatochromism for 4; DFT calculations for 4; fluorescence decay
measured by the time-correlated single-photon counting (TCSPC)
method for compounds 3–5; details on TPA measurements for 3–
5.
Compound 3: To a mixture of compound 2 (180 mg, 0.3 mmol) and
4-(trifluoromethyl)benzylphosphonate
(121 mg,
0.41 mmol,
1.3 equiv.) was added tBuOK (43 mg, 0.4 mmol, 1.2 equiv.) at
–78 °C. The reaction mixture was stirred for 1 h at low temperature
and allowed to reach room temperature. After 4 h, H2O was added,
and the crude was neutralized with 2  HCl. The product was ex-
tracted with CH2Cl2, and the organic layer was dried with MgSO4.
After evaporation of the solvent, the crude was washed with hep-
Acknowledgments
tane to obtain an orange solid (198 mg, 93%). 1H NMR (300 MHz, Financial support by the Natural Sciences and Engineering Re-
[D6]acetone, 25 °C): δ = 7.80–7.68 (m, 6 H), 7.62–7.58 (m, 1 H),
7.50–7.19 (m, 13 H), 7.15–6.96 (m, 9 H) ppm. 13C NMR (75 MHz,
CD2Cl2, 25 °C): δ = 148.5 (s, thiophene), 148.3 (s, thiophene), 148.2
(s, Ar), 148.0 (s, Ar), 146.1 (s, Ar), 141.1 (s, Ar), 140.9 (s, Ar), 132.9
search Council (NSERC) of Canada, Ministerio de Educación y
Ciencia of Spain (project CTQ2006-08871) co-funded by Fondo
Europeo de Desarrollo Regional, European Union, and Junta de
Comunidades de Castilla-La Mancha (project PCI08-0033) is
gratefully acknowledged. C.R. thanks Junta de Comunidades de
Castilla-La Mancha for a scholarship. T.B. thanks Alberta Ingenu-
ity (now part of Alberta Innovated Technology Futures) for a New
2
(d, JC,P = 20.3 Hz, m-Ph), 128.4 (s, Ar), 127.7 (s, ArH), 126.9 (s,
Ar), 126.1 (q, JC,F = 2.7 Hz, Ar), 125.2 (s, ArH), 125.0 (s, ArH),
124.4 (s, ArH), 124.7 (q, JC,F = 274.2 Hz, Ar), 123.8 (s, ArH), 123.6
(s, ArH), 120.6 (s, ArH) ppm. 31P{1H} NMR (162 MHz, CDCl3, Faculty Award.
5230
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 5225–5231

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Received: April 23, 2010
Published Online: August 3, 2010
Eur. J. Org. Chem. 2010, 5225–5231
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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