Synthesis, characterization, electrochemistry, and photophysical studies of triarylamine-containing zinc(II) dIImine bis-thiolate complexes

Article abstract of DOI:10.1039/c5dt02920a

A series of triarylamine-containing Zn(ii) diimine bis-thiolate complexes, [Zn(N^N)(SC₆H₄Me-4)₂] (N^N = 5,5′-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-2,2′-bipyridine or 1,10-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-phenanthroline), were synthesized and characterized by ¹H NMR spectroscopy, FAB mass spectrometry and satisfactory elemental analysis. Some of the complexes exhibited intense emissions in dichloromethane solution with maxima at 611-685 nm, which originated from both ligand-to-ligand charge transfer [p_π(SR^-) → π(diimine)] and intraligand charge transfer [π(triarylamine) → π(diimine)] excited states. The emission maxima were tuned by variation of the donor or acceptor moieties. Thin film emission studies were also carried out on the complexes. All these complexes showed similar Gaussian-shaped emission bands with emission energies similar to those observed in dichloromethane solution at 298 K. In addition, the emission bands displayed concentration-dependent properties in thin-film emission studies.

Full text of DOI:10.1039/c5dt02920a

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Synthesis, characterization, electrochemistry, and
photophysical studies of triarylamine-containing
zinc(II) diimine bis-thiolate complexes
Cite this: DOI: 10.1039/c5dt02920a
Tao Yu, Vonika Ka-Man Au, Daniel Ping-Kuen Tsang, Mei-Yee Chan and
Vivian Wing-Wah Yam*
A series of triarylamine-containing Zn(II) diimine bis-thiolate complexes, [Zn(N^N)(SC6H4Me-4)2] (N^N =
5,5’-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-2,2’-bipyridine or 1,10-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-
phenanthroline), were synthesized and characterized by 1H NMR spectroscopy, FAB mass spectrometry
and satisfactory elemental analysis. Some of the complexes exhibited intense emissions in dichloro-
methane solution with maxima at 611–685 nm, which originated from both ligand-to-ligand charge
transfer [pπ(SR−) → π*(diimine)] and intraligand charge transfer [π(triarylamine) → π*(diimine)] excited
states. The emission maxima were tuned by variation of the donor or acceptor moieties. Thin film emis-
sion studies were also carried out on the complexes. All these complexes showed similar Gaussian-
shaped emission bands with emission energies similar to those observed in dichloromethane solution at
298 K. In addition, the emission bands displayed concentration-dependent properties in thin-film emis-
sion studies.
Received 29th July 2015,
Accepted 21st September 2015
DOI: 10.1039/c5dt02920a
www.rsc.org/dalton
center, zinc(II) complexes with a larger variety of excited states
would become accessible. Zinc(II) diimine bis-thiolate com-
Introduction
Emissive transition metal complexes have attracted immense plexes represent one of the typical classes of luminescent
attention over the past few decades in the area of functional zinc(II) complexes in which the emission is derived from
materials, especially for organic light-emitting device (OLED) excited states other than those of π–π* origin.8–12 The photo-
materials.1–5 Phosphorescent materials based on noble metal physical properties of zinc(II) diimine bis-thiolate complexes
centers, such as ruthenium(II),1 iridium(III),2 platinum(II),3 were first studied by Koester in 1975.8 They were then exten-
rhenium(I)4 and recently gold(III),5 have been widely studied sively studied by Crosby and coworkers who concluded that
and reported. On the other hand, the development of emissive the low-lying emissions were originated from the ligand-to-
metal complexes with other relatively less expensive and more ligand charge-transfer (LLCT) [pπ(SR−) → π*(diimine)] excited
earth-abundant transition metal centers is less explored. One state.9 Since then, zinc(II) diimine bis-thiolate complexes have
attractive candidate for luminescent transition metal com- become attractive and the photophysical properties based on
plexes is based on the use of a zinc(II) metal center owing to its the LLCT [pπ(SR−) → π*(diimine)] excited state were investi-
low cost and rich abundance.
gated by research groups including those of Crosby,10 Vogler11
Up to now, only a limited number of luminescent zinc(II) and Yam.12 Yam and coworkers further reported the supra-
complexes have been reported and most reported emissive molecular host–guest cation-binding studies of zinc(II) diimine
zinc(II) complexes were based on excited states of intraligand bis-thiolate complexes containing crown ether functional
(IL) π–π* origin, which were similar to those of conjugated groups.12a,b These zinc(II) complexes have also been explored
organic molecules.6 One of the early examples of luminescent as functional materials such as photochromic materials.12c,d
zinc(II) system is [Zn4O(acetate)6].7a Subsequently, a 7-azaindo-
Notably, the emission energies of these luminescent zinc(II)
late-containing tetrameric zinc(II) compound, [Zn4O- diimine bis-thiolate complexes with LLCT emissive states
(C7H5N2)6], was also reported.7b,c With the judicious choice could be readily tuned by varying both the diimine moieties
and introduction of appropriate organic ligands to the metal and the bis-thiolate moieties.12 These zinc(II) complexes can
potentially become one of the candidates in the limited library
of inexpensive triplet emitters with tunable emission pro-
perties. However, most of the zinc(II) diimine bis-thiolate com-
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong,
plexes reported were only emissive at low temperatures, and a
China. E-mail: wwyam@hku.hk; Fax: +(852) 2857-1586; Tel: +(852) 2859-2153
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very weak emission with low luminescence quantum yields or sions at room temperature. Different from the conventional
even non-emissive behavior was detected at ambient zinc(II) diimine bis-thiolate complexes, an additional emission
temperature.10,11
of ILCT [π(triarylamine) → π*(diimine)] excited state origin was
The donor–π-acceptor (D–π-A) type structure is considered observed. This ILCT excited state, together with the character-
to play an important role in designing light-emitting mole- istic LLCT [pπ(SR−)
π*(diimine)] excited state, would
→
cules as it represents an effective approach for attaining high enhance the luminescence observed at room temperature. The
luminescence quantum yield, lowering the energy band gap effects of the variation in the donor and acceptor moieties on
and producing a readily tunable band gap. Indeed, a number the photophysical properties of the zinc(II) complexes have
of emissive compounds with the D−π-A structure have been been investigated; in particular, their photophysical properties
reported.13 Introduction of a metal center into the D−π-A have been studied by UV-Vis absorption and emission spectro-
structure to achieve emissive transition metal complexes based scopy in solution and thin films. To provide insights into the
on the intraligand charge transfer (ILCT) excited states was energy levels of the frontier molecular orbitals of these com-
also reported.14
plexes, the electrochemical properties of all the complexes were
Herein we report the design and synthesis of a new class of also studied.
triarylamine-containing D−π-A type zinc(II) diimine bis-thiolate
complexes [ZnII{bipy(CHvCH-TPA)2}(SC6H4-Me-4)2] (1), [ZnII-
{bipy(CHvCH-TPA-carbazole)2}(SC6H4-Me-4)2] (2), [ZnII{bipy-
(CHvCH-TPA-C6Ph5)2}(SC6H4-Me-4)2]
(3),
[ZnII{phen-
Results and discussion
Synthesis and characterization
(CHvCH-TPE)2}(SC6H4-Me-4)2] (4), [ZnII{phen(CHvCH-TPA)2}-
(SC6H4-Me-4)2] (5) and [ZnII{phen(CHvCH-TPA-TPE)2}(SC6H4-
Me-4)2] (6) (TPA = triphenylamine, TPE = tetraphenylene
moiety), as shown in Fig. 1, to realize orange to deep-red emis-
The chemical structures of complexes 1–6 are described in
Fig. 1. All the intermediates were characterized by 1H NMR
spectroscopy. Complexes 1–6 were characterized by 1H NMR,
positive FAB mass spectroscopy and satisfactory elemental
analysis.
Electronic absorption spectroscopy
Dilute dichloromethane solutions of complexes 1–6 showed
yellow to red color at 298 K and the electronic spectral data of
these complexes are summarized in Table 1. The selected elec-
tronic absorption spectra are shown in Fig. 2 and 3.
In good agreement with the previous reports on zinc(II)
thiolate complexes and complexes with triarylamine groups,
complexes 1–3, 5 and 6 showed very intense absorption bands
ranging from 232 to 342 nm, with molar extinction coefficients
in the order of 104 dm3 mol−1 cm−1, which are tentatively
assigned as IL π–π* transitions of the ligands. The low-energy
bands at around 453–494 nm are assigned as LLCT transitions
from the thiolate moiety to the diimine moiety,9 mixed with
ILCT transitions from the triarylamine to the diimine moie-
ties.15,16 When compared to complex 1, the lower energy band
of complex 2 was similar in energy but the absorption band of
complex 3 was found to be red-shifted. Similar observations of
red shifts were found in the low-energy band upon introduc-
tion of the tetraphenylene groups when compared with com-
plexes
5 and 6. Attachment of pentaphenylbenzene or
tetraphenylene groups would result in the extension of the
π-conjugated system of the donor moiety, causing a decrease
in the energy gap between the donor moiety and the acceptor
moiety that would lead to a red shift in the ILCT transition
from the triarylamine to the diimine moiety. Moreover, the
π-conjugation of the diimine ligands would be increased upon
the attachment of pentaphenylbenzene or tetraphenylene,
which would further induce the red shift of the LLCT tran-
sition from the thiolate moiety to the lower-lying π* orbital of
Fig. 1 Structures of zinc(II) dithiolate diimine complexes containing
triarylamine or tetraphenylethene moieties.
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Table 1 Electronic absorption and emission data for complexes 1–6
Emission
Absorption λmax/nm
λmax/nm
(τ0/μs)
(ε/dm3 mol−1 cm−1
)
ϕem
a
Complex
Medium (T/K)
1
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
CH2Cl2 (298)
Glassb,c (77)
Solid (298)
Solid (77)
307 (42 890), 330 (42 080), 472 (66 715)
295 (81 310), 331 (77 930), 342 (74 830), 471 (48 720)
249 (214 600), 339 (68 300), 494 (62 645)
258 (71 360), 314 (50 350), 405 (67 000)
259 (46 030), 303 (44 770), 453 (62 250)
232 (108 300), 342 (86 730), 460 (73 330)
671 (<0.1)
488 (<0.1), 557 (0.14)
668 (<0.1)
674 (0.14)
685 (<0.1)
493 (0.11), 569 (0.22)
652 (<0.1)
654 (<0.1)
681 (<0.1)
508 (<0.1), 560 (0.14)
665 (<0.1)
661 (0.10)
590 (<0.1)
401 (0.14)
589 (<0.1)
538 (<0.1)
611 (<0.1)
470, 532, 562 (0.15)
621 (<0.1)
615 (0.14)
0.51
0.11
0.14
0.06
0.40
0.12
2
3
4
5
6
630 (<0.1)
476 (0.10), 557, 603 (0.15)
654 (0.11)
646 (0.15)
a The luminescence quantum yield, measured at room temperature using [Ru(bpy)3]Cl2 as a standard. b In 2-methyltetrahydrofuran glass.
c Vibronic-structured emission band.
Fig. 2 Electronic absorption spectra of complexes 1–3 in dichloro-
Fig. 3 Electronic absorption spectra of complexes 4–6 in dichloro-
methane solution at 298 K.
methane solution at 298 K.
Luminescence spectroscopy
the diimine moiety. For complex 4 that does not contain any
All the zinc(II) diimine bis-thiolate complexes showed intense
orange to deep red luminescence upon excitation in both
dilute degassed dichloromethane solution and the solid
state at λ > 350 nm. Upon excitation, complexes 1–6 showed
triarylamine moieties, the high-energy bands at 258 nm and
317 nm and the low-energy band at 405 nm are assigned as IL
π–π* transitions mixed with LLCT characters from the thiolate
moiety to the diimine moiety.9
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intense luminescence in degassed dichloromethane solu- emission bands of the free ligands and the zinc(II) complexes.
tion at room temperature, in the solid state at room temp- The emission bands of complexes 1–3, 5 and 6 are tentatively
erature and at 77 K and in the 2-methyltetrahydrofuran glass assigned as the ILCT [π(triarylamine) → π*(bipyridine)] emis-
state at 77 K. Fig. 4 and 5 show the selected emission spectra sion with mixing of a LLCT [pπ(SR−) → π*(diimine)] excited
of complexes 1–6 in degassed dichloromethane solution at state. Upon increasing the π-conjugation of the triarylamine
room temperature and the emission data are summarized in derivatives, the emission bands of complexes 2 and 3 were
Table 1.
found to be slightly red-shifted compared to those of complex
The emission spectra of complexes 1–3, 5 and 6 in degassed 1. A larger π-conjugation would increase the electron-donating
dichloromethane solution at room temperature displayed abilities of the modified triphenylamine groups, leading to a
intense broad structureless emission bands at 611–685 nm. smaller ILCT [π(triarylamine) → π*(bipyridine)] energy. More-
Compared to free ligands which displayed IL π–π* emission over, an increase in the π-conjugation of the diimine ligands
with maxima of 538–557 nm in dichloromethane solution at would reduce the energy of the LLCT [pπ(SR−) → π*(diimine)]
298 K, the emission bands of these complexes showed obvious emission. On the other hand, the presence of pentaphenyl-
red shifts. The red shifts indicated the different origins of the benzene16b and carbazole substituents16c with multi-ring struc-
tures in complexes
2 and 3 would result in a lower
luminescence quantum yield of the complexes due to the
facile molecular rotation of the aromatic rings in the solution
state. For complex 4, which does not contain triarylamine
moieties, the emission band with a peak maximum at ca.
590 nm in degassed dichloromethane solution at room temp-
erature is tentatively assigned as the LLCT [pπ(SR−) → π*
(diimine)] emission since the emission band showed a red
shift of 269 cm−1 in emission energy when compared to that
of the IL π–π* emission of the free ligand.
In 2-methyltetrahydrofuran glass at 77 K, complexes 1–3, 5
and 6 showed two emission bands. The high-energy bands at
around 470–508 nm are assigned as the IL π–π* emission;
while the low-energy bands may originate from the ILCT
[π(triarylamine) → π*(bipyridine)] excited states, mixed with
the LLCT [π(SR−) → π*(bipyridine)] character, as reported pre-
viously in the literature.9,16 For these complexes, increased
emission energies were observed in the glass states compared
to those in solutions. This can be explained by the lack of
solvent reorganization following the excitations due to the
increased rigidity in the glass medium. The solid state emis-
sions of complexes 1–6 at 298 K and 77 K showed emission
bands similar in energies and shapes as those in dichloro-
methane solutions at 298 K, indicating their similar emission
origin.
Fig. 4 Normalized emission spectra of complexes 1–3 in CH2Cl2 at
298 K.
Electrochemical studies
In order to gain insights into the energy levels of the frontier
molecular orbitals of the complexes, the electrochemical pro-
perties of complexes 1–6 were studied. Cyclic voltammetry was
performed for all the complexes in CH2Cl2 with 0.1 M
nBu4NPF6 as a supporting electrolyte. The electrochemical data
are summarized in Table 2. A quasi-reversible wave at ca. +0.86
to +0.96 V was observed for complexes 1–3 and 5–6, and it is
assigned as the oxidation of the triarylamine moieties.15,16
Except for complex 4, irreversible oxidation waves at +1.10 to
+1.36 V and +1.55 to +1.67 V were observed and are attributed
to the oxidation of the thiolate ligands, similar to those
reported previously.12b The oxidation wave at ca. +1.45 V was
observed for complex 4 which is considered as the oxidation of
the tetraphenylethylene moieties.17
Fig. 5 Normalized emission spectra of complexes 4–6 in CH2Cl2 at
298 K.
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Table 2 Electrochemical data for complexes 1–6a
Oxidation E1/2 b/V Reduction E1/2 b/V
vs. S.C.E. (ΔEp/mV) vs. S.C.E. (ΔEp/mV)
Complex
[ZnII{bipy(CHvCH-PA)2}-
(SC6H4–Me–4)2] (1)
+0.88b (89)
+1.18c
−1.32b (86)
−1.64b (104)
−1.89d
+1.60c
[ZnII{bipy(CHvCH-TPA-
+0.91b (79)
−1.25b (72)
−1.56b (56)
−1.81d
carbazole)2}(SC6H4-Me-4)2] (2) +1.26c
+1.66c
[ZnII{bipy(CHvCH-TPA-
C6Ph5)2}(SC6H4-Me-4)2] (3)
+0.86b (70)
−1.29b (85)
−1.60b (95)
−1.87d
+1.30c
+1.59c
[ZnII{phen(CHvCH-TPE)2}-
(SC6H-Me-4)2] (4)
+1.19c
−1.37b (77)
−1.68b (99)
−1.96d
+1.45c
+1.67c
[ZnII{phen(CHvCH-TPA)2}-
(SC6H-Me-4)2] (5)
+0.95b (89)
+1.10c
−1.46b (87)
−1.76b (92)
+1.58c
[ZnII{phen(CHvCH-TPA-
TPE)2}(SC6H4-Me-4)2] (6)
+0.96b (148)
+1.36b (131)
+1.55b (117)
−1.43b (72)
−1.74b (91)
Fig. 6 Normalized photoluminescence (PL) spectra of complex
doped into MCP at different concentrations.
1
a In dichloromethane (0.1 M nBu4NPF6) as the supporting electrolyte at
room temperature; scan rate 100 mV s−1 b E1/2 = (Epa + Epc)/2; Epa and
.
Epc are peak anodic and peak cathodic potentials, respectively and ΔEp
= |Epa − Epc|. c Irreversible oxidation wave. The potential refers to Epa
which is the anodic peak potential. d Irreversible reduction wave. The
potential refers to Epc which is the cathodic peak potential.
Two or three reduction waves were observed in the reductive
scan of complexes 1–6. The first quasi-reversible reduction
couple at ca. −1.25 to −1.46 V is associated with the first
reduction of bipyridine or phenanthroline ligand-centered
reduction.18 In addition, all the complexes showed a second
reduction wave at ca. −1.56 V to −1.76 V, which can be
assigned as the second reduction of the N^N diimine
ligands.18a,19 By comparing the first reduction couples of com-
plexes 1–3, it was found that the attachment of carbazole and
pentaphenylbenzene substituents on the triarylamine moieties
would give rise to less negative potentials for the first
reduction wave. These could be attributed to the increase in
the π-conjugation of the ligands upon introduction of the
carbazole and the pentaphenylbenzene substituents on the
triarylamine moieties. An increase in the π-conjugation of the
ligands would lead to a lower-lying π* orbital of the ligands,
rendering the bipyridine ligands much more ready to be
reduced. Similarly, complex 6 showed a less negative first
reduction potential when compared to complex 5. The third
reduction waves of complexes 1–4, which were irreversible,
could be tentatively assigned as the further reduction of the
diimine ligands as described in the previous reports.18c
Fig. 7 Absolute photoluminescence (PL) quantum yields at different
excitation wavelengths of complex
concentrations.
1 doped into MCP at different
films of complexes 1, 3 and 5 doped into MCP at different con-
centrations, respectively.
All these complexes showed similar emission bands with
emission energies similar to those observed in dichloro-
methane solution at 298 K. The emission maxima and lumine-
scence quantum yields in thin films were found to be strongly
dependent on the concentrations of zinc(II) compounds. As
shown in Fig. 6, complex 1 exhibited orangish-red emissions
with a peak maximum at 619 nm for 5 wt% which progress-
Thin-film emission studies
The photoluminescence (PL) properties of luminescent zinc(II) ively red-shifted to 664 nm as the dopant concentration was
compounds in solid thin films were studied by doping com- increased to 50 wt%. It was observed that the luminescence
plexes 1, 3 and 5 into N,N′-dicarbazolyl-3,5-benzene (MCP) pre- quantum yields in the thin film decreased from 0.339 for 5 wt
pared by spin-coating. Fig. 6–11 display the normalized % to 0.084 in 50 wt%, as shown in Fig. 7. This concentration
emission spectra and luminescence quantum yields in thin quenching phenomenon was widely reported for luminescent
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Fig. 8 Normalized photoluminescence (PL) spectra of complex
doped into MCP at different concentrations.
3
Fig. 10 Normalized photoluminescence (PL) spectra of complex
doped into MCP at different concentrations.
5
Fig. 9 Absolute photoluminescence (PL) quantum yields at different
excitation wavelengths of complex 3 doped into MCP at different
concentrations.
Fig. 11 Absolute photoluminescence (PL) quantum yields at different
excitation wavelengths of complex 5 doped into MCP at different
concentrations.
organic compounds and metal complexes.20 For complexes
3 and 5, a red shift in the emission and a decrease in the
Conclusion
luminescence quantum yields were also observed when the In summary, a series of D-π–A type zinc(II) diimine bis-thiolate
dopant concentrations were increased. The highest lumine- complexes with triarylamine- or tetraphenylethylene-substi-
tuted phenanthroline and bipyridine ligands, have been
scence quantum yield reached as high as 0.491 for a 5 wt%
thin film sample. It should be highlighted that, unlike the designed and synthesized and their photophysical properties
case in solution, the luminescence quantum yield of complex have been studied. Electrochemical studies have also been per-
formed to provide insights into their frontier orbital energy
3 was found to be higher than that of complex 1 in the thin
film at the same dopant concentration. This could be attri- levels. It is shown that intense orange to deep red lumine-
buted to the presence of the more bulky pentaphenylbenzene scence derived from LLCT [pπ(SR−) → π*(diimine)] excited
states mixed with a ILCT [π(triphenylamine derivatives) → π*
substituents on the triarylamine moiety, which can rigidify
complex 3 and reduce the rate of non-radiative decay via the (diimine)] or LLCT [pπ(SR−) → π*(diimine)] character can be
slowing down of vibrational or rotational motions in the solid realized by forming the D-π–A structures and the emission
energies can be fine-tuned and red-shifted upon the introduc-
state, yielding a higher luminescence quantum yield.
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tion of the pentaphenylbenzene substituents on the triaryl- four successive freeze–pump–thaw cycles. Luminescence
amine groups. The properties of the luminescent zinc(II) com- quantum yields were measured by the optical dilute method
pounds in the solid-state thin films were studied by doping reported by Demas and Crosby.23 Degassed aqueous [Ru(bpy)3]
complexes 1, 3 and 5 into N,N′-dicarbazolyl-3,5-benzene (MCP) Cl2 solution (ϕ = 0.042, excitation wavelength at 418 nm) was
at different concentrations. Intense orange to red emissions used as the reference.24 The absolute luminescence quantum
with high luminescence quantum yields were observed yields of the thin films were measured on a Hamamatsu
suggesting that this class of zinc(II) complexes may serve as C9920-03 absolute photoluminescence quantum yield
promising candidates for the fabrication of OLEDs.
measurement system. Cyclic voltammograms were obtained by
a CH Instruments model CHI 600A electrochemical analyzer.
The electrolytic cell used was a conventional two-compartment
cell. Electrochemical measurements were performed in
dichloromethane solution with tetrabutylammonium hexa-
fluorophosphate (0.1 M) as the supporting electrolyte at
ambient temperature. An Ag/AgNO3 (0.1 M in acetonitrile) elec-
trode was used as the reference electrode, and a glassy carbon
electrode (CH Instruments) was used as the working electrode.
The counter electrode was a platinum wire. The working elec-
trode surface was first polished with a 1 μm alumina slurry
(Linde), followed by a 0.3 μm alumina slurry, on a microcloth
(Buehler Co.). Treatment of the electrode surfaces was as
reported previously.25 The ferrocenium/ferrocene couple
(FeCp2+/0) was used as the internal reference.26 All solutions
for electrochemical studies were deaerated with a prepurified
argon gas just before measurements.
Experimental section
Materials and reagents
4-Bromo-N,N-diphenylaniline and 4-methylbenzenethiol were
purchased from Sigma-Aldrich Chemical Co., while triethyl-
t
phosphate, zinc acetate dehydrate and BuOK were purchased
from Aldrich. Tetra-n-butylammonium hexafluorophosphate
was purchased from Aldrich and recrystallized from absolute
ethanol three times before use. All chemicals were of analytical
grade and used as received. 4-(1,2,2-Triphenylvinyl)benz-
aldehyde, 4-(1,2,2-triphenylvinyl)phenyl)boronic acid and
4-(diphenylamino)benzaldehyde were synthesized according to
the literature.21 The synthesis of ligands including bipy-
(CHvCH-TPA)2, bipy(CHvCH-TPA-carbazole)2 and bipy-
(CHvCH-TPA-C6Ph5)2 was performed according to a reported
procedure.16 9-Bis(bromomethyl)-1,10-phenanthroline was syn-
thesized by a modified literature procedure.22 All solvents were
purified and distilled according to the standard procedures
before use.
Synthesis
N,N-Diphenyl-4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-amine.
To
a mixture of 4-bromo-N,N-diphenylaniline (3.242 g,
10 mmol) and (4-(1,2,2-triphenylvinyl)-phenyl)boronic acid
(5.640 g, 15 mmol) in degassed THF (30 ml) was added
aqueous K2CO3 solution (2 M, 10 ml). After degassing for
Physical measurements and instrumentations
1H NMR spectra were recorded on
a Bruker DPX-300 20 minutes, [Pd(PPh3)4] (100 mg, 0.10 mmol) was added to the
(300 MHz) or a Bruker DPX-400 (400 MHz) Fourier transform mixture. The resulting mixture was stirred at reflux for
NMR spectrometer with chemical shifts recorded relative to 40 hours under an argon atmosphere. After cooling to room
tetramethylsilane (Me4Si). Positive ion FAB mass spectra were temperature, the mixture was filtered and the filtrate was puri-
recorded on a Finnigan MAT95 mass spectrometer or a fied by column chromatography on silica gel (60–230 mesh)
Thermo Scientific DFS high-resolution magnetic sector mass with CH2Cl2–hexane (1 : 5, v/v) as the eluent. A pale green solid
spectrometer. Elemental analyses of the complexes were per- was obtained. Yield: 4.087 g (71%). 1H NMR (400 MHz,
formed on the Carlo Erba 1106 elemental analyzer at the Insti- CD3COCD3, 298 K, relative to Me4Si): δ = 7.04–7.14 (m, 24H,
tute of Chemistry, Chinese Academy of Sciences (Beijing, –C6H5, –C6H4– and –NC6H5), 7.23 (d, 8.4 Hz, 2H, –NC6H4–),
China).
UV-Vis spectra were recorded on a Varian Cary 50 UV/Vis
7.55 (d, 8.4 Hz, 2H, –NC6H4–); positive EI-MS: m/z 575.2 [M]+.
4-(Phenyl(4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-yl)amino)-
spectrophotometer. A steady state fluorescence spectrofluoro- benzaldehyde. To
a mixture of N,N-diphenyl-4′-(1,2,2-tri-
meter was equipped with a R2658P PMT detector. For the life- phenyl-vinyl)-[1,1′-biphenyl]-4-amine (2.879 g, 5 mmol) and
time measurements, the excitation source was the 355 nm DMF (439 mg, 6 mmol) in degassed 1,2-dichloroethane
output (third harmonic) of a Spectra-Physics Quanta-Ray (30 ml) at 0 °C under an argon atmosphere was added POCl3
Q-switch GCR-150-10 pulsed Nd:YAG laser. The luminescence (920 mg, 6 mmol) in a dropwise manner. The resulting
decay signals were detected by a Hamamatsu R928 photomulti- mixture was stirred at ambient temperature for 1 hour and
plier tube, recorded on
a
Tektronix Model TDS-620
A
heated to reflux for 24 hours. After cooling to 0 °C, aqueous
(500 MHz, 2 GS s−1) digital oscilloscope, and analyzed by K2CO3 solution (2 M, 10 ml) was added slowly to the mixture.
using a program for exponential fit. All the solutions for the The mixture was poured into water and extracted with CH2Cl2.
photophysical studies were degassed on a high-vacuum line in Further purification was performed by column chromato-
a two-compartment cell consisting of a 10 mL Pyrex bulb and a graphy on silica gel (60–230 mesh) with CH2Cl2–hexane (1 : 2,
1 cm path length quartz cuvette that was sealed from the v/v) as the eluent. Solvent removal yielded a light yellow solid.
atmosphere by a Bibby Rotaflo HP6/6 quick-release Teflon Yield: 2.023 g (67%). 1H NMR (400 MHz, CDCl3, 298 K, relative
stopper. The solutions were rigorously degassed with at least to Me4Si): δ = 7.04–7.20 (m, 23H, –C6H5, –C6H4–, –NC6H4– and
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–NC6H5), 7.33–7.35 (m, 4H, –NC6H4– and –NC6H5), 7.52 (m, –CHvCH–), 7.71–7.75 (m, 4H, phenanthroline and
2H, –NC6H4–), 7.69 (m, 2H, –NC6H4–), 9.82 (s, 1H, –CHO); –CHvCH–), 7.90 (d, 8.4 Hz, 2H, phenanthroline), 8.18 (d, 8.4
positive FAB-MS: m/z 603.2 [M]+.
Tetraethyl((1,10-phenanthroline-2,9-diyl)bis(methylene))bis-
Hz, 2H, phenanthroline); positive FAB-MS: m/z 1379.0 [M]+.
[ZnII{bipy(CHvCH-TPA)2}(SC6H4-Me-4)2] (1). This was pre-
(phosphonate). To a 50 ml round-bottomed flask containing pared by a method similar to that described for other related
2,9-bis(bromomethyl)-1,10-phenanthroline (0.732 g, 2 mmol) zinc(II) diimine bis-thiolate complexes.12 To a solution of zinc
was added triethylphosphate (10 ml, 58.8 mmol). The mixture acetate dihydrate (22.0 mg, 0.10 mmol) in degassed methanol–
was heated to reflux for 12 hours. After cooling to room temp- THF (1 : 1, v/v, 10 ml) was added dropwise 4-methyl-
erature, hexane (30 ml) was added and the mixture was stirred benzenethiol (27.3 mg, 0.22 mmol) in degassed methanol–
for 1 hour. The light yellow precipitate formed was collected by THF (1 : 1, v/v, 10 ml). After stirring for 30 minutes, bipy
filtration. The solid was washed several times with hexane. (CHvCH-TPA)2 (69.5 mg, 0.10 mmol), which had been dis-
Yield: 7.872 g (82%). 1H NMR (400 MHz, CDCl3, 298 K, relative solved in degassed THF (10 ml), was added slowly into the
to Me4Si): δ = 1.26–1.30 (m, 12H, –OC2H5), 3.01 (s, 4H, –CH2–), mixture. The resulting mixture was stirred for 24 hours under
4.11–4.18 (m, 8H, –OC2H5), 7.76–7.78 (m, 4H, phenanthroline), an argon atmosphere. After adding methanol (20 ml), the deep
8.21 (d, 8.20 Hz, 2H, phenanthroline); positive EI-MS: m/z red precipitate formed was collected by filtration. The precipi-
480.1 [M]+.
phen(CHvCH-TPA)2. To
tate was washed three times with methanol. A red powder was
a
two-necked round-bottomed obtained. Yield: 73.1 mg (71%). 1H NMR (400 MHz, CDCl3,
flask containing tetraethyl-((1,10-phenanthroline-2,9-diyl)bis 298 K): δ = 2.12 (s, 6H, –CH3), 6.68 (d, 8.0 Hz, 4H, –SC6H4–),
(methylene))bis(phosphonate) (0.240 g, 0.5 mmol) and 6.84 (d, 16.2 Hz, 2H, –CHvCH–); 7.05–7.20 (m, 22H, –NC6H5,
4-(diphenylamino)benzaldehyde (0.300 g, 1.1 mmol) was added –SC6H4– and –CHvCH–), 7.28–7.32 (m, 8H, –NC6H4–), 7.40 (d,
degassed THF (30 ml) under an argon atmosphere. After 8.7 Hz, 4H, –NC6H4–), 7.81 (d, 8.2 Hz, 2H, bipyridine), 7.94 (d,
cooling to 0 °C, tBuOK (0.224 g, 2 mmol) was added. Upon stir- 8.0 Hz, 2H, bipyridine), 8.56 (s, 2H, bipyridine); positive
ring for 12 hours under an argon atmosphere, the mixture was FAB-MS: m/z 911.3 [M − S − C6H4 − Me − p]+; elemental ana-
poured into 95% ethanol (150 ml), and stirred for another lyses calcd for C66H58N4S2Zn·H2O (found): C 75.02 (75.22),
hour. The yellow precipitate formed was collected by filtration. H 5.31 (5.18), N 5.47 (5.49).
The precipitate was dissolved in CH2Cl2 and washed 3 times
[ZnII{bipy(CHvCH-TPA-carbazole)2}(SC6H4-Me-4)2] (2). The
with water. The solution was dried over anhydrous MgSO4. complex was prepared according to the preparation of complex
After evaporation of most of the solvent, recrystallization by 1, except that bipy(CHvCH-TPA)2 was replaced by bipy
vapor diffusion of acetone into a concentrated solution of the (CHvCH-TPA-carbazole)2 (135.6 mg, 0.1 mmol). A red powder
compound gave the product as a yellow solid. Yield: 0.151 g was obtained. Yield: 78.4 mg (47%). 1H NMR (400 MHz,
1
(42%). H NMR (400 MHz, (CD3)2SO, 298 K, relative to Me4Si): CDCl3, 298 K): δ = 2.15 (s, 6H, –CH3), 6.70 (d, 8.0 Hz, 4H,
δ = 7.01 (d, 8.6 Hz, 4H, –NC6H4–), 7.09–7.14 (m, 12H, –NC6H4– –SC6H4–), 7.00 (d, 16.7 Hz, 2H, –CHvCH–), 7.16 (d, 8.0 Hz,
and –NC6H5), 7.35–7.38 (m, 8H, –NC6H4– and –NC6H5), 7.51 4H, –SC6H4–), 7.31–7.35 (m, 12H, carbazole and –NC6H4–),
(d, 16.3 Hz, 2H, –CHvCH–), 7.71 (d, 8.6 Hz, 2H, –NC6H4–), 7.44–7.59 (m, 38H, carbazole, –NC6H4– and –CHvCH–), 7.87
7.90–7.94 (m, 4H, phenanthroline and –CHvCH–), 8.06 (d, 8.3 Hz, 2H, bipyridine), 8.01 (d, 8.5 Hz, 2H, bipyridine),
(d, 8.4 Hz, 2H, phenanthroline), 8.43 (d, 8.4 Hz, 2H, phenan- 8.17 (d, 7.7 Hz, 2H, carbazole), 8.67 (s, 2H, bipyridine); positive
throline); positive FAB-MS: m/z 718.2 [M]+.
phen(CHvCH-TPE)2. Following the procedure for the
FAB-MS: m/z 1664.5 [M]+; elemental analyses calcd for
112H80N8S2Zn·2.5H2O·1.5CH2Cl2 (found): C 74.09 (74.07),
C
preparation of phen(CHvCH-TPA)2, phen(CHvCH-TPE)2 was H 4.82 (5.01), N 6.09 (6.20).
prepared by replacing 4-(diphenylamino)benzaldehyde with
[ZnII{bipy(CHvCH-TPA-C6Ph5)2}(SC6H4-Me-4)2]
(3). The
4-(1,2,2-triphenylvinyl)benzaldehyde (0.396 g, 1.1 mmol). complex was prepared according to the preparation of complex
Yield: 0.143 g (32%). 1H NMR (400 MHz, CDCl3, 298 K, relative 1, except that bipy(CHvCH-TPA)2 dissolved in degassed THF
to Me4Si): δ = 7.03–7.13 (m, 34H, –C6H5 and –C6H4–), 7.41 (d, (10 ml) was replaced by bipy(CHvCH-TPA-C6Ph5)2 (252 mg,
8.3 Hz, 4H, –C6H4–), 7.60 (d, 16.4 Hz, 2H, –CHvCH–), 7.68 (d, 0.1 mmol) dissolved in degassed dichloromethane (20 ml). A
16.4 Hz, 2H, –CHvCH–), 7.71 (s, 2H, phenanthroline), 7.88 (d, red powder was obtained. Yield: 161.5 mg (57%). 1H NMR
8.4 Hz, 2H, phenanthroline), 8.18 (d, 8.4 Hz, 2H, phenanthro- (400 MHz, CDCl3, 298 K, relative to Me4Si): δ = 2.12 (s, 6H, –CH3),
line); positive FAB-MS: m/z 892.3 [M]+.
6.40 (d, 8.4 Hz, 4H, –SC6H4–), 6.54 (d, 8.4 Hz, 4H, –SC6H4–),
phen(CHvCH-TPA-TPE)2. Following the procedure for the 6.64–6.68 (m, 12H, –NC6H4–), 6.77 (d, 16.3 Hz, 2H, –CHvCH–),
preparation of phen(CHvCH-TPA)2, phen(CHvCH-TPA-TPE)2 6.84–6.91 (m, 104H, –NC6H4– and –C6H5), 7.09–7.15 (m, 6H,
was prepared by replacing 4-(diphenylamino)benzaldehyde –NC6H4– and –CHvCH–), 7.22 (d, 8.5 Hz, 4H, –NC6H4–), 7.78 (d,
with
4-(phenyl(4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-yl)- 8.3 Hz, 2H, bipyridine), 7.90 (d, 8.2 Hz, 2H, bipyridine), 8.55 (s,
amino)benzaldehyde (0.664 g, 1.1 mmol). Yield: 0.339 g (49%). 2H, bipyridine); positive FAB-MS: m/z 2708.1 [M − S − C6H4 −
1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si): δ = Me − p]+; elemental analyses calcd for C208H148N4S2Zn·CH2Cl2
7.04–7.18 (m, 48H, –C6H5, –C6H4–, –NC6H5 and –NC6H4–), (found): C 86.03 (85.99), H 5.28 (5.41), N 1.92 (1.88).
7.27–7.35 (m, 8H, –NC6H5 and –NC6H4–), 7.46–7.48 (m, 4H,
–NC6H5 and –NC6H4–), 7.55–7.61 (m, 6H, –NC6H4– and was prepared according to the preparation of complex 1,
[ZnII{phen(CHvCH-TPE)2}(SC6H4-Me-4)2] (4). The complex
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except that bipy(CHvCH-TPA)2 was replaced by phen of a postgraduate studentship and V. K.-M. A. acknowledges
(CHvCH-TPE)2 (89.3 mg, 0.10 mmol). The precipitate was the receipt of a postdoctoral fellowship, both administered by
further purified by recrystallization by vapor diffusion of The University of Hong Kong.
diethyl ether into a concentrated solution of the crude product
in CH2Cl2. Green needle-shaped crystals were obtained. Yield:
89.2 mg (72%). 1H NMR (400 MHz, CDCl3, 298 K, relative to
Me4Si): δ = 1.88 (s, 6H, –CH3), 6.31 (d, 7.8 Hz, 4H, –SC6H4–),
6.92 (d, 7.8 Hz, 4H, –SC6H4–), 7.01–7.17 (m, 30H, –C6H4– and
References
–C6H5), 7.25–7.31 (m, 8H, –C6H5), 7.48 (d, 16.0 Hz, 2H,
–CHvCH–), 7.69 (s, 2H, phenanthroline), 8.09 (d, 8.7 Hz, 2H,
phenanthroline), 8.16 (d, 16.0 Hz, 2H, –CHvCH–), 8.26 (d,
8.7 Hz, 2H, phenanthroline); positive FAB-MS: m/z 959.4
[M − C6H4 − Me − p]+; elemental analyses calcd for
C70H54N2S2Zn·CH2Cl2·H2O (found): C 80.15 (79.98), H 5.35
(5.28), N 2.38 (2.25).
1 (a) Y.-L. Tung, S.-W. Lee, Y. Chi, L.-S. Chen, C.-F. Shu,
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[ZnII{phen(CHvCH-TPA)2}(SC6H4-Me-4)2] (5). The complex
was prepared according to the preparation of complex 1,
except that bipy(CHvCH-TPA)2 was replaced by phen
(CHvCH-TPA)2 (71.8 mg, 0.10 mmol). The precipitate was
further purified by recrystallization by vapor diffusion of
diethyl ether into a concentrated solution of the crude product
in CH2Cl2. Orange needle-shaped crystals were obtained. Yield:
84.5 mg (82%). 1H NMR (400 MHz, CDCl3, 298 K, relative to
Me4Si): δ = 1.83 (s, 6H, –CH3), 6.37 (d, 7.7 Hz, 4H, –SC6H4–),
6.97 (d, 8.4 Hz, 4H, –NC6H4–), 7.02 (d, 7.7 Hz, 4H, –SC6H4–),
7.08–7.11 (m, 4H, –NC6H5), 7.16 (d, 8.0 Hz, 8H, –NC6H5),
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–NC6H4–), 7.52 (d, 16.0 Hz, 2H, –CHvCH–), 7.67 (s, 2H, phenan-
throline), 8.10–8.14 (m, 4H, phenanthroline and –CHvCH–),
8.23 (d, 8.6 Hz, 2H, phenanthroline); positive FAB-MS: m/z 1027.3
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C 75.59 (75.66), H 5.19 (5.28), N 5.34 (5.58).
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[ZnII{phen(CHvCH-TPA-TPE)2}(SC6H4-Me-4)2]
(6). The
complex was prepared according to the preparation of complex
1, except that bipy(CHvCH-TPA)2 was replaced by phen
(CHvCH-TPA-TPE)2 (137.9 mg, 0.10 mmol). Yield: 108.3 mg
(64%). 1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si): δ =
1.82 (s, 6H, –CH3), 6.38 (d, 7.3 Hz, 4H, –SC6H4–), 7.00–7.19 (m,
52H, –NC6H4–, –NC6H5, –C6H4–, –C6H5 and –SC6H4–),
7.31–7.41 (m, 12H, –NC6H4– and –NC6H5), 7.49–7.51 (m, 6H,
–NC6H4– and –CHvCH–), 7.63 (s, 2H, phenanthroline),
8.07–8.13 (m, 4H, phenanthroline and –CHvCH–), 8.21 (d,
8.5 Hz, 2H, phenanthroline); positive FAB-MS: m/z 1567.9
[M − S − C6H4 − Me − p]+; elemental analyses calcd for
C118H88N4S2Zn·1.5H2O (found): C 82.47 (82.41), H 5.34 (5.34),
N 3.26 (3.33).
Acknowledgements
V. W.-W. Y. acknowledges support from The University of Hong
Kong under the URC Strategic Research Theme on New
Materials. This work was fully supported by a grant from the
Theme–Based Research Scheme of the Research Grants
Council of the Hong Kong Special Administrative Region,
China (Project No. T23-713/11). T. Y. acknowledges the receipt
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