Alkyl chain functionalised, cyclometalated platinum(II) complexes: Syntheses, luminescence properties and X-ray crystal structure

Article abstract of DOI:10.1016/j.jorganchem.2016.01.015

The synthesis and characterisation of nine new monometallic heteroleptic platinum complexes [PtCl(L^1-3)(DMSO)], [Pt(L^1-3)(acac)], [Pt(L^1-3)(8-Q)] (where L^1-3= N-octyl/dodecyl/hexadecyl-2-phenylquinoline-4-carbox

Full text of DOI:10.1016/j.jorganchem.2016.01.015

Accepted Manuscript
Alkyl chain functionalised, cyclometalated platinum(II) complexes: syntheses,
luminescence properties and X-ray crystal structure
Juliette A. Lowe, Oliver J. Stacey, Peter N. Horton, Simon J. Coles, Simon J.A. Pope
PII:
S0022-328X(16)30015-8
10.1016/j.jorganchem.2016.01.015
JOM 19366
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 29 October 2015
Revised Date: 11 January 2016
Accepted Date: 12 January 2016
Please cite this article as: J.A. Lowe, O.J. Stacey, P.N. Horton, S.J. Coles, S.J.A. Pope, Alkyl chain
functionalised, cyclometalated platinum(II) complexes: syntheses, luminescence properties and X-ray
crystal structure, Journal of Organometallic Chemistry (2016), doi: 10.1016/j.jorganchem.2016.01.015.
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Cyclometalated platinum complexes with visible luminescence
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Alkyl chain functionalised, cyclometalated platinum(II) complexes: syntheses,
luminescence properties and X-ray crystal structure
a
a
b
b
a
Juliette A. Lowe, Oliver J. Stacey, Peter N. Horton, Simon J. Coles and Simon J. A. Pope *
a
School of Chemistry, Main Building, Cardiff University, Museum Avenue, Cardiff, United Kingdom, CF10
3
AT. Tel: +44(0) 29 20879316, Fax: +44(0) 29 20874030, email: popesj@cardiff.ac.uk
b
UK National Crystallographic Service, Chemistry, Faculty of Natural and Environmental Sciences,
University of Southampton, Highfield, Southampton, SO17 1BJ, England
Abstract
The synthesis and characterisation of nine new monometallic heteroleptic platinum complexes
1
-3
1-3
1-3
1-3
[
PtCl(L )(DMSO)], [Pt(L )(acac)], [Pt(L )(8-Q)] (where L = N-octyl/dodecyl/hexadecyl-2-
phenylquinoline-4-carboxamides; acac = acetylacetonate; 8-Q = 8-quinolinato) are described.
1
Single crystal X-ray diffraction studies on [Pt(L )(acac)] revealed a square planar coordination
geometry with intermolecular Pt-Pt contacts at ca. 3.3 Å. The complexes were investigated using
1
95
1
Pt{ H} NMR spectroscopy, revealing varied chemical shifts around δPt -2800 ppm that were
strongly dependent upon the specific coordination environment of Pt(II). Luminescence studies
showed the complexes possess a phosphorescent character with tuneable emission wavelengths
between 605-641 nm, and luminescent lifetimes up to ca. 450 ns. Supporting TD-DFT studies
provided descriptions of the HOMO and LUMO energy levels of the key complex types, which
generally correlated well with the experimental spectra. The contribution of the Pt(5d) centre to the
calculated HOMOs was strongly ligand dependent, whilst the LUMOs were generally predicted to
be localized over the quinoline component of the cyclometalated ligand.
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Introduction
Cyclometelated platinum(II) complexes are highly attractive species to study due to their wide
1
ranging optoelectronic and biomedical applications. There is an ever-expanding range of suitable
ligands that can be coordinated to square planar Pt(II) in a cyclometalating manner. The relative
ease of design, and attempts at tuning the resultant physical properties of the complex, have led to
2
cyclometalated platinum complexes being studied in photocatalysis, photooxidation (via the
1
3
4
5
photogeneration of O ), electroluminescent cells, luminescent bioimaging agents and optical
2
6
sensors.
Planar cyclometalated Pt(II) complexes have also recently been investigated with respect to
7
the design of targeted agents for binding amyloid beta peptide, in the context of the inhibition of
Zn and Cu peptide complex formation (cf. Alzheimer’s disease). These studies follow on from the
8
detailed and lengthy history of the biomedical applications of square planar Pt(II) complexes,
9
particularly with respect to the treatment of cancer (cisplatin). Since cisplatin and its analogues are
regarded as non-luminescent, more recent approaches have looked at tethering fluorescent tags onto
closely related Pt(II) species, thus enabling ‘visualisation’ of the biologically active Pt(II) species in
1
0
a cellular environment. In this context cyclometalated Pt(II) species such as [Pt(C^N)(DMSO)Cl)]
where C^N = a cyclometalating unit) may have much to offer as we have shown that they can
(
1
1
possess luminescent properties; the relatively labile co-ligands enable their application to cell
imaging using confocal fluorescence microscopy and the development of prospective bimodal
1
2
imaging agents. Indeed the assessment of the cytotoxic nature of related Pt(II) complexes is an
1
3
area of intense study.
The focus of this paper is the development of 2-phenyl-4-quinolinecarboxamido alkyl-
derived ligands, which possess alkyl chain lengths of n = 8 (octyl), 12 (dodecyl) and 16 (hexadecyl)
1
-3
HL , respectively, leading to nine new cyclometalated Pt(II) complexes of the type
[
Pt(L)(DMSO)Cl)], [Pt(L)(acac)] (where acac = acetyacetonate) and [Pt(L)(8-Q)] (where 8-Q = 8-
quinolinato). These ligands can be synthesised from commercially available cinchophen (2-phenyl-
2

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4
-quinolinecarboxylic acid), and we have previously shown that derivatives of this ligand class can
1
4
be used to develop related cyclometalated Ir(III) complexes with tuneable luminescent properties.
The reasons for the incorporation of alkyl chains are two fold: firstly, to improve the organic
solubility of the resultant Pt(II) species isolated as intermediates and thus facilitate further
reactivity, and secondly, to allow for future consideration of these complexes as cellular bioimaging
agents. Previous studies on luminescent rhenium(I) complexes functionalised with alkyl chains have
shown that enhanced lipophilicity of organometallic complexes can dramatically improve transport
1
5
across the cell membrane and aid intracellular distribution.
It is also noteworthy that cinchophen-based species also have a long history of biomedical
application. Cinchophen itself was used as an analgesic to treat gout in the early twentieth century,
whilst 2-phenyl-4-quinolinecarboxamides have been investigated as therapeutics for neurological
1
6
diseases, including schizophrenia.
Results and Discussion
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Scheme 1. Synthesis of the complexes: i) DMSO, rt; ii) 2,4-pentanedione, 3-pentanone; iii) 8-
hydroxyquinoline, 2-methoxyethanol.
Synthesis of the ligands and complexes
The ligands were prepared following previous reports for related amide-functionalised ligands
1
3
based on the cinchophen structure. Thus, 2-phenyl-4-quinolinecarbonyl chloride was reacted with
1
a series of n-alkyl amines with octyl, dodecyl and hexadecyl length chains to give the ligands HL ,
2
3
HL and HL respectively.
The complexes (Scheme 1) were synthesised according to our previous reports on related
1
1,12
Pt(II) systems
which involves the generation of a precursor Pt(II) dimer species [Pt(L)(ꢀ-Cl)]2
which is then split by DMSO to give monometallic [Pt(L)(DMSO)Cl] allowing further reactivity
3
and addition of co-ligands. The solubility characteristics of HL (hexadecyl) were incompatible
with the aqueous reaction mixtures typically used for the synthesis of the ꢀ-dichloro-bridged Pt(II)
dimers. Therefore, in this case, additional 2-ethoxyethanol was added in an attempt to improve the
solubility of the ligand in the reaction medium. Despite this, the reaction yield for the dimer
3
1
2
[
Pt(L )(ꢀ-Cl)] was still lower than for HL and HL , which is attributed to the highly hydrophobic
2
3
character of the hexadecyl chain in HL . In all three cases unreacted ligand was removed from the
dimer material by washing the crude solid product with dichloromethane. The subsequent splitting
of the dimers in DMSO yielded the monometallic [Pt(L)(DMSO)Cl] species which were isolated
and spectroscopically characterised. The DMSO adducts were then reacted further with either 2,4-
pentanediketone to give [Pt(L)(acac)], or 8-hydroxyquinoline to give [Pt(L)(8-Q)].
Characterisation of the ligands and complexes
1
-3
The ligands HL were characterised using the traditional array of spectroscopic and analytical
1
techniques. H NMR spectroscopy revealed that the amide NH proton of the ligands appears as a
1
3
1
broadened triplet between 6.37 – 6.93 ppm, depending upon the alkyl chain length. C{ H} NMR
4

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spectroscopy showed overlapping resonances in the aliphatic regions associated with the alkyl
chains of the ligands and thus fewer signals than theoretically predicted.
1
Typically, for the H NMR spectra of [Pt(L)(DMSO)Cl] the methyl resonance of the
1
95
coordinated DMSO appeared around δH 3.6 ppm with satellites attributed to coupling to the Pt
nucleus. The [Pt(L)(acac)] complexes revealed the singlet resonance at δH 5.6 ppm associated with
1
95
1
the coordinated acac ligand. Pt{ H} NMR spectra obtained for the three [Pt(L)(acac)] complexes
each appeared around δPt -2775 ppm suggesting that alteration of the alkyl chain length had very
little effect upon the Pt(II) centre. This value for δPt is consistent with our previous reports on
1
1,12
related cinchophen-derived complexes of Pt(II)
and very close to the reported chemical shift for
1
7
195
the benchmark analogue [Pt(ppy)(acac)] (where ppy = 2-phenylquinoline) at -2868 ppm. The Pt
resonances for the remaining complexes were all consistent with our previous studies on related Pt
1
1
complexes of this type. Mass spectrometry studies on the [Pt(L)(acac)] complexes generally
-
showed a [M – H] cluster of peaks matching the predicted isotopic distribution; [Pt(L)(8-Q)]
+
complexes revealed a [M + Na] cluster of peaks, again with the appropriate isotopic distribution
for Pt. The [Pt(L)(DMSO)Cl] species were, unsurprisingly, prone to fragmentation and loss of
ligand; typical m/z values revealed the expected isotopic pattern for Pt, but with a loss of both
chloride and DMSO ligands upon ionisation.
1
X-ray crystal structure of [Pt(L )(acac)]
1
X-ray crystallographic studies were undertaken on suitable crystals of [Pt(L )(acac)] which were
obtained by the slow evaporation of a concentrated chloroform solution of the complex. The
structure (Figure 1) revealed the expected coordination sphere with a weakly distorted square planar
geometry at Pt(II). The bond lengths around the Pt centre were found to be 1.952(6) and 2.041(5) Å
for the Pt-C and Pt-N bonds, respectively, and 2.006(4) and 2.089(4) Å for the Pt-O bond lengths
(where the shorter bond is trans to the coordinated N atom). These are very comparable to the bond
lengths reported for the structure of the related complex [Pt(ppy)(acac)], as well as being in line
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11,12
with our previous observations on related cinchophen derived Pt(II) complexes.
There is a head-
to-tail packing arrangement of the complexes within the crystal form, driven by the formation of
dimers through a Pt-Pt interaction of 3.327(1) Å (and therefore below the sum of the van der Waal’s
1
8
radii).
1
Figure 1. X-ray crystal structure of [Pt(L )(acac)]. Ellipsoids are drawn at 50% probability and H
atoms and solvent molecules are omitted. Crystal data for [Pt(L1)(acac)]: C H Cl N O Pt, M =
30
35
3
2
3
7
73.04, red plate, a = 14.0542(10), b = 8.3288(5), c = 25.6474(18) Å,
α
= 90,
β
= 93.606(2),
γ
= 90,
3
-1
V = 2996.2(3) Å , monoclinic, space group P2 /n, Z = 4,
µ
= 4.985 mm , reflections collected =
1
2
2
30031, independent reflections = 6837, R = 0.1338, R1 = 0.0448, wR2 [F > 2σ(F )] = 0.0784, R1
int
=
0.0713, wR2 = 0.0825.
UV-vis. absorption and luminescence studies
The electronic absorption spectra of the free ligands (in chloroform) were dominated by the
1
expected
π-π* transitions typical of a phenylquinoline chromophore; each ligand possesses two
peaks at around 332 and 264 nm. The UV-vis absorption data for all complexes is collected in Table
1. For the [Pt(L)(DMSO)Cl] complexes the UV-vis spectra (in chloroform) displayed
1
bathochromically shifted features with a peak at ca. 285 nm attributed to ligand-centred
π-π*
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transitions and a broad, lower intensity band ca. 365 nm with a weak shoulder at 420 nm.
Conversion to the [Pt(L)(acac)] revealed spectra (in chloroform) which retain the ligand-centred
features, but modulate the appearance of the broad visible absorption band at 400-500 nm (for
example, Figure 2). Notably for the [Pt(L)(8-Q)] species an additional absorption feature was
displayed in the visible part of the spectrum at 450-575 nm. The results show that the length of the
alkyl chain (octyl, dodecyl, hexadecyl) imparts little influence on the energies of the absorption
bands, which is consistent with the expected similarities in electronic structure for these complexes.
Supporting theoretical TD-DFT calculations on closely related cyclometalated Pt(II) model
complexes (based on cyclometalating L = ethyl-2-phenylquinoline-4-carboxylate) show that the
nature of the HOMO-LUMO transitions are likely to vary according to the ancillary ligands at Pt(II)
(
see Table 1). In particular, the studies show that the calculated percentage of Pt 5d orbital
contribution to the HOMO varies significantly across the series [Pt(L)(DMSO)Cl] versus
Pt(L)(acac)] versus [Pt(L)(8-Q)]. Thus, for [Pt(L)(8-Q)] complexes, where the percentage of Pt 5d
[
character contributing to the HOMO is calculated to be < 5%, ligand(quinolinato)-to-
ligand(quinoline) charge transfer (LLCT) transitions are predicted to contribute to the HOMO-
LUMO transition. This predicted transition probably corresponds to the experimentally observed
lowest energy absorption at 450-575 nm for the [Pt(L)(8-Q)] complexes. In comparison, for the
[
Pt(L)(acac)] species, the percentage of Pt 5d character contributing to the HOMO is calculated to
be ca. 40%, suggesting a greater metal(platinum)-to-ligand(quinoline) charge transfer (MLCT)
contribution to the visible absorption band of [Pt(L)(acac)].
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Compound
HOMO-1
HOMO
LUMO
[
Pt(L)(acac)]
[
[
Pt(L)(DMSO)Cl]
Pt(L)(8-Q)]
Table 1. Calculated frontier orbitals for [Pt(L)(acac)], [Pt(L)(DMSO)Cl] and [Pt(L)(8-Q)]
complexes (where L = ethyl-2-phenylquinoline-4-carboxylate).
All of the complexes were shown to be luminescent in chloroform solution following excitation in
the visible region at 420 nm (Table 1). The broad featureless emission profiles occur between 590 –
640 nm and were clearly dependent upon the nature of the ancillary ligands coordinated to Pt(II)
(Figure 3). In the case of [Pt(L)(acac)] species the alkyl chain length does not impart any shift in
emission energy. A comparison of the [Pt(L)(acac)] and [Pt(L)(8-Q)] species show that the former
possess a longer emission wavelength and thus larger Stokes’ shift compared to the latter. The
luminescence lifetimes of the [Pt(L)(acac)] and [Pt(L)(8-Q)] complexes were in the range 211-439
8

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ns and thus consistent with a phosphorescent emitting state that is likely to comprise admixtures of
3
3
MLCT/ LLCT. The [Pt(L)(acac)] complexes clearly displayed significantly longer lifetimes than
the 8-quinolinato analogues. The corresponding lifetimes of the precursor [PtCl(L)(DMSO)]
species are notably shorter (24-54 ns) suggesting a more pronounced quenching of the excited state,
due to the coordinated DMSO and chloride ligands, the latter known to contribute to quenching in
1
9
certain metal complexes. Quantum yields in aerated solvent were modest (≤1%) but in line with
11
previous studies on this class of complex.
Table 2. UV-vis and luminescence spectroscopic data for the complexes (in aerated chloroform).
Complex
Absorption
λmax / nm)
Emission
λem / nm)
Lifetime Quantum
a
b
c
(
(
(τ
/ ns)
Yield
1
[
[
[
[
[
[
[
[
[
Pt(L )(DMSO)Cl]
272, 281, 341, 368, 422sh
300, 349, 368, 417
609
618
606
615
617
606
592
617
593
24
380
211
54
-
1
Pt(L )(acac)]
0.006
0.004
-
1
Pt(L )(8-Q)]
263, 370, 505
2
Pt(L )(DMSO)Cl]
281, 363, 430sh
2
Pt(L )(acac)]
284, 345, 368, 415
406
238
28
0.01
0.005
-
2
Pt(L )(8-Q)]
265, 269, 368, 502
3
Pt(L )(DMSO)Cl]
265, 284, 365, 426sh
259, 286, 295, 344, 361, 414
283, 346, 362, 429, 496
3
Pt(L )(acac)]
439
227
0.01
0.004
3
Pt(L )(8-Q)]
a
b
using 420 nm excitation; using 295 or 372 nm excitation; c using [Ru(bipy) ](PF ) in aerated
3
6 2
2
0
MeCN as standard (Φ = 0.016).
9

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3
3
Figure 2. UV-vis absorption spectra comparing [Pt(L )(acac)] (black line) and [Pt(L )(8-Q)] (grey
line) (in chloroform).
6
5
000000
000000
7
6
5
4
3
2
1
00000
00000
00000
00000
00000
00000
00000
0
4000000
3
2
1
000000
000000
000000
0
2
50
350
450
550
650
250
350
450
550
650
wavelength / nm
wavelength / nm
3
Figure 3. Normalised excitation (grey) and emission (black) spectra for [Pt(L )(8-Q)] (left) and
3
[
Pt(L )(acac)] (right) (aerated chloroform, λex = 420 nm).
Conclusions
The work has shown that highly lipophilic cyclometalated Pt(II) complexes can be synthesised from
carboxamide derivatives of 2-phenylquinoline. Supporting spectroscopic and X-ray structural data
show that the complexes possess the anticipated formulations. The stepwise synthesis of the
complexes allow a range of ancillary ligands to be coordinated to Pt(II) enabling tuning of the
absorption and emission properties of the complexes. The addition of an 8-quinolinato chelate
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[
Pt(L)(8-Q)] results in a bathochromically shifted absorption whilst the emission is at a higher
energy relative to the [Pt(L)(acac)] species. The acac complexes also display the longest
phosphorescent lifetimes in this series of complexes, with values up to 439 ns. Generally, the
electronic effect of the alkyl chain is neglible with chain length differences imparting only minor
variations in the photophysical parameters. Given the promising nature of the luminescence
properties, future studies will explore the cell imaging potential of this series of complexes with
particular attention on the cellular uptake characteristics of these highly lipophilic complexes.
Experimental
All reactions were performed with the use of vacuum line and Schlenk techniques. Reagents were
1
13
1
commercial grade and were used without further purification. H and C{ H} NMR spectra were
1
95
1
run on NMR-FT Bruker 250 or 400 spectrometers, Pt{ H} on NMR-FT 500 spectrometer all
1
13
1
recorded in CDCl . H and C{ H} NMR chemical shifts (δ) were determined relative to internal
3
TMS and are given in ppm. Low-resolution mass spectra were obtained by the staff at Cardiff
University. High-resolution mass spectra were carried out by at the EPSRC National Mass
Spectrometry Service at Swansea University. UV-Vis studies were performed on a Jasco V-570
spectrophotometer as chloroform solutions. Photophysical data were obtained on a JobinYvon-
Horiba Fluorolog spectrometer fitted with a JY TBX picosecond photodetection module as
chloroform solutions. Emission spectra were uncorrected and excitation spectra were instrument
corrected. The pulsed source was a Nano-LED configured for 372 nm output operating at 1 MHz.
Luminescence lifetime profiles were obtained using the JobinYvon-Horiba FluoroHub single
photon counting module and the data fits yielded the lifetime values using the provided DAS6
deconvolution software.
X-ray data collection and processing
2
1
Suitable crystals were selected and data collected following a standard method, on a Rigaku R-
AXIS Spider molybdenum sealed tube diffractometer at 120K equipped with a RAPID image plate
1
1

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2
2
detector. Cell determination and data collection were carried out using CrystalClear. Structure
2
3
solution and refinement using SHELX programs. CCDC 1432127 contains supplementary X-ray
1
crystallographic data for [Pt(L )(acac)]. This data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, Union Road, Cambridge, CB2 1EZ; fax(+44) 1223-336-033 or email:
deposit@ccdc.cam.ac.uk.
DFT studies
2
4
Non-relativistic calculations were performed on the Gaussian 09 program.
Geometry
2
5
optimisations were carried out without constraints using the B3LYP functional. The Stuttgart-
2
6
Dresden basis set was used for the Pt atoms, and was invoked with pseudo-potentials for the core
2
7
electrons, with a 6-31G(d) basis set for all remaining atoms. TD-DFT studies were performed
using the same functional, but with 6-31+G(d,p) on all non-metal atoms, and also included a
2
8
simulated MeCN environment using the polarized continuum model (PCM) approach. For
prediction of absorption spectra, the geometry used to calculate orbital and other properties was
used without modification. For the prediction of emission energies, however, the triplet state was
allowed to relax to its optimal geometry using unrestricted B3LYP in the gas phase, prior to
solvated TD-DFT.
Materials
2-phenyl-4-quinolinecarboxylic acid and potassium tetrachloroplatinate were used as purchased
from Alfa Aesar.
Synthesis
1
Synthesis of HL : Thionyl chloride (excess) was added, dropwise, to a stirring suspension of 2-
phenyl-4-quinolinecarboxylic acid (0.465 g, 1.869 mmol) in chloroform (10 mL). The reaction was
1
2

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heated at reflux for 16 h under dinitrogen. The solvent was then removed in vacuo and the yellow
solid redissolved in chloroform (10 mL) before the selected 1-octylamine (0.219 g, 1.699 mmol)
i
was added dropwise to the stirring solution. EtN Pr (excess) was added dropwise and the mixture
2
was stirred for 16 h at room temperature under dinitrogen. The solvent was removed in vacuo
before being redissolved in dichloromethane (20 mL). The crude mixture was washed with aqueous
NaHCO (sat. 2 × 20 mL), water (1 × 20 mL) and brine (1 × 20 mL). The organic phase was
3
collected, dried over MgSO and filtered before the solvent was removed in vacuo. Yield = 0.434 g
4
1
3
(
71%). H NMR (400 MHz, CDCl ): δ 7.98 (1H, d, J = 8.4 Hz), 7.94 - 7.91 (2H, m), 7.84 (1H,
3 H HH
3
d, J = 8.0 Hz), 7.60 – 7.56 (1H, m), 7.51 (1H, s), 7.42 - 7.40 (3H, m), 7.33 – 7.29 (1H, m), 6.93
HH
3
(
1H, br. t, J = 4.4 Hz), 3.35 - 3.30 (2H, m), 1.59 – 1.52 (2H, m), 1.34 – 1.19 (10H, m), 0.90 (3H,
HH
3
13
1
t, J = 6.4 Hz) ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 167.6, 156.7, 148.5, 143.4, 138.7,
HH
3
C
130.3, 129.9, 129.0, 127.5, 127.3, 125.1, 123.4, 116.4, 40.3, 31.9, 29.7, 29.4, 27.1, 22.8, 14.2 ppm.
+
3
-1
-1
MS(ES) found m/z = 361.22 for [M + H] . UV-vis (CHCl ): λ (ε / dm mol cm ) 263 (29100),
3
max
-1
3
27 (6600) nm. IR (thin film): νmax 3306 (N-H), 1636 (C=O) cm .
2
1
Synthesis of HL : as for HL , but using 2-phenyl-4-quinolinecarboxylic acid (0.370 g, 1.486
1
mmol) and 1-dodecylamine (0.250 g, 1.351 mmol). Yield = 0.416 g (74%). H NMR (400 MHz,
3
CDCl ): δ 8.13 (1H, d, J = 8.0 Hz), 8.09 – 8.06 (3H, m), 7.77 (1H, s), 7.73 – 7.69 (1H, m), 7.52
3
H
HH
3
–
1
1
2
=
7.46 (4H, m), 6.37 (1H, br. t, JHH = 4.4 Hz), 3.54 – 3.49 (2H, m), 1.71 – 1.63 (2H, m), 1.42 –
3
13
1
.22 (18H, m), 0.88 (3H, t, J = 6.4 Hz) ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 167.6,
HH
3
C
56.7, 148.4, 143.5, 138.6, 130.3, 129.9, 129.0, 127.6, 127.4, 125.1, 123.5, 116.5, 68.2, 40.3, 32.0,
+
9.7, 29.4, 29.3, 27.1, 22.8, 14.2 ppm. MS(ES) found m/z = 417.32 for [M + H] . HR MS found m/z
3
-1
-1
417.2898; C H N O requires 417.2900. UV-vis (CHCl ): λ (ε / dm mol cm ) 268 (27500),
28
37
2
3
max
-1
3
22 (6000) nm. IR (thin film): νmax 3306 (N-H), 1636 (C=O) cm .
1
3

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3
1
Synthesis of HL : as for HL , using 2-phenyl-4-quinolinecarboxylic acid (0.454 g, 1.826 mmol)
1
and 1-hexadecylamine (0.4 g, 1.660 mmol). Yield = 0.572 g (73%). H NMR (400 MHz, CDCl ):
3
3
δ 8.12 – 8.04 (4H, m), 7.75 (1H, s), 7.72 – 7.68 (1H, m), 7.51 – 7.45 (4H, m), 6.50 (1H, br. t, J
H
HH
3
=
4.4 Hz), 3.52 – 3.46 (2H, m), 1.69 – 1.61 (2H, m), 1.41 – 1.19 (24H, m), 0.87 (3H, t, J = 6.8
HH
1
3
1
Hz) ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 167.6, 156.6, 148.5, 143.3, 138.7, 130.1, 129.9,
3
C
129.8, 128.9, 127.6, 127.5, 127.2, 125.1, 123.4, 116.3, 53.5, 40.3, 32.0, 29.8, 29.7, 29.5, 29.1, 27.1,
+
3
-1
-
2
2.8, 14.2 ppm. MS(ES) found m/z = 473.34 for [M + H] . UV-vis (CHCl ): λ (ε / dm mol cm
3
max
1
-1
)
257 (76000), 324 (28500) nm. IR (thin film): νmax 3306 (N-H), 1633 (C=O) cm .
1
Synthesis of [Pt(L )(µ-Cl)] : using potassium tetrachloroplatinate (0.057 g, 0.137 mmol) and HL1
2
(0.050 g, 0.139 mmol). A solution of potassium tetrachloroplatinate(II) (1.0 eq.) in water (2 mL)
was added to a stirring solution of HL (1.0 eq.) in 2-ethoxyethanol (6 mL) under dinitrogen and
heated to 80 °C for 16 h in a foil-wrapped flask. Brine (10 mL) was added to the cooled solution
and the resultant precipitate was collected on a sinter and washed with water (2 × 10 mL) and dried.
The precipitate was washed with dichloromethane to remove any unreacted ligand. Yield = 0.070 g
(87%).
2
1
Synthesis of [Pt(L )(µ-Cl)] : as for [Pt(L )(ꢀ-Cl)] , but using potassium tetrachloroplatinate (0.050
2
2
2
g, 0.120 mmol) and HL (0.050 g, 0.120 mmol). The solvent ratio was adjusted to 4:1 by using 8
mL of 2-ethoxyethanol. The precipitate was washed with dichloromethane to remove any unreacted
ligand. Yield = 0.068 g (87%).
3
1
Synthesis of [Pt(L )(µ-Cl)] : as for [Pt(L )(ꢀ-Cl)] , but using potassium tetrachloroplatinate (0.097
2
2
3
g, 0.233 mmol) and HL (0100 g, 0.212 mmol). The solvent ratio was adjusted to 4:1 by using 8
mL of 2-ethoxyethanol. The precipitate was washed with dichloromethane to remove any unreacted
ligand. Yield = 0.095 g (64%).
1
4

ACCEPTED MANUSCRIPT
1
29
Synthesis of [Pt(L )(DMSO)Cl]: Based on a modified literature methodology. Crude [Pt(L1)(ꢀ-
Cl)] (0.070 g, 0.059 mmol) was dissolved in a minimum volume of DMSO before being
2
precipitated with brine (10 mL), filtered on a sinter, washed with water (2 × 20 mL) and then dried.
1
3
Yield = 0.044 g (55 %). H NMR (400 MHz, CDCl ): δ 8.95 (1H, d, J = 8.8 Hz), 8.29 – 8.27
3
H
HH
3
(
1H, m (with satellites)), 7.94 (1H, d, JHH = 8.0 Hz), 7.75 (1H, s), 7.71 – 7.47 (1H, m), 7.58 – 7.56
3
(
1H, m), 7.51 – 7.47 (1H, d), 7.21 – 7.19 (2H, m), 6.51 (1H, br. t, JHH = 5.6 Hz), 3.60 (6H, s (with
3
satellites), 3.55 – 3.50 (2H, m), 1.72-1.65 (2H, m), 1.43 – 1.25 (10H, m), 0.89 (3H, t, J = 7.2 Hz)
HH
13
1
ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 166.7, 166.2, 147.1, 146.7, 145.6, 142.8, 133.7, 130.8,
3
C
130.0, 128.6, 127.9, 126.1, 125.5, 124.8, 124.5, 114.3, 46.2, 41.0, 40.4, 31.9, 29.6, 29.3, 27.1, 22.7,
1
95
1
4.2 ppm. Pt NMR (107.51 MHz, CDCl ): δ -2672 ppm. MS(ES) found m/z = 618.9 for [M -
3
Pt
+
3
-1
-1
Cl – DMSO + 2MeOH] . UV-vis (CHCl ): λ (ε / dm mol cm ) 272 (18440), 281 (16980), 368
3
max
-1
(
4190), nm. IR (thin film): νmax 1647 cm .
2
1
2
Synthesis of [Pt(L )(DMSO)Cl]: as for [Pt(L )(DMSO)Cl], but using [Pt(L )(µ-Cl)] (0.068 g,
2
1
3
0
.026 mmol). Yield = 0.035 g (93%). H NMR (400 MHz, CDCl ): δ 8.92 (1H, d, J = 8.8 Hz),
3 H HH
3
8
.28 – 8.25 (1H, m), 7.91 (1H, d, J = 8.0 Hz), 7.70 (1H, s), 7.68 – 7.64 (1H, m), 7.55 – 7.53 (1H,
HH
3
m), 7.47 – 7.43 (1H, m), 7.19 – 7.17 (2H, m), 6.66 (1H, br. t, J = 5.6 Hz), 3.59 (6H, s (with
HH
satellites)), 3.52 – 3.47 (2H, m), 1.71 – 1.64 (2H, m), 1.43 – 1.22 (18H, m), 0.87 (3H, t, 6.8 Hz)
13
1
ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 207.1, 166.6, 166.1, 147.0, 146.6, 145.6, 142.5, 129.9,
3
C
1
1
28.5, 127.8, 126.1, 125.4, 124.8, 114.2, 53.5, 46.2, 41.0, 40.3, 31.0, 29.7, 29.6, 29.6, 29.4, 29.3,
1
95
4.2 ppm. Pt NMR (107.51 MHz, CDCl ): δ -2681 ppm. MS(ES) found m/z = 683.3 for [M –
3
Pt
+
3
-1
-1
DMSO – Cl + MeCN + MeOH] . UV-vis (CHCl ): λ
(ε / dm mol cm ) 281 (20000), 363
3
max
-1
(
5480) nm. IR (thin film): νmax 1645, 1543 cm .
1
5

ACCEPTED MANUSCRIPT
3
1
3
Synthesis of [Pt(L )(DMSO)Cl]: as for [Pt(L )(DMSO)Cl], but using [Pt(L )(µ-Cl)] (0.095 g,
2
1
3
0
8
.068 mmol). Yield = 0.071 g (67%). H NMR (400 MHz, CDCl ): δ 8.91 (1H, d, J = 8.8 Hz),
3 H HH
3
.27 – 8.25 (1H, m ), 7.91 (1H, d, J = 8.4 Hz), 7.71 (1H, s), 7.68 – 7.64 (1H, m), 7.55 – 7.53
HH
3
(
1H, m), 7.47 – 7.43 (1H, m), 7.19 – 7.17 (2H, m), 6.90 (1H, br. t, JHH = 6.0 Hz), 3.58 (6H, s (with
3
satellites)), 3.51 – 3.46 (2H, m), 1.70 – 1.63 (2H, m), 1.42 – 1.18 (26H, m), 0.86 (3H, t, J = 6.8
HH
195
Hz) ppm. Pt NMR (107.51 MHz, CDCl ): δ -2678 ppm. MS(ES) found m/z = 739.4 for [M –
3
Pt
+
194
DMSO – Cl + MeCN + MeOH] . HR MS found m/z = 813.2514; C H N SO Cl Pt [M + Cl]
3
4
49
2
2
2
3
-1
-1
requires 813.2513. UV-vis (CHCl ): λmax (ε / dm mol cm ) 265 (10130), 284 (9640), 365 (4460)
3
-1
nm. IR (thin film): νmax 1639, 1543 cm .
1
1
Synthesis of [Pt(L )(acac)]: [Pt(L )(DMSO)Cl] (0.044 g, 0.066 mmol) and sodium acetylacetonate
monohydrate (0.080 g, 0.660 mmol) was dissolved in 3-pentanone (5 mL). The reaction was stirred
at room temperature for 16 h under dinitrogen. The solvent was removed in vacuo and the crude
product dissolved in dichloromethane (10 mL) and filtered to remove any insoluble salts. The crude
product was purified by column chromatography (silica, dichloromethane) where elution of the first
yellow band with dichloromethane gave the desired product obtained as a dark yellow solid. Yield
1
3
3
=
0.038 g (89%). H NMR (400 MHz, CDCl ): δ 9.43 (1H, d, J = 8.8 Hz), 8.00 (1H, dd, J
HH
=
=
3
H
HH
4
3
8
8
5
.4 Hz, J = 1.2 Hz), 7.70 – 7.64 (2H, m), 7.57 (1H, s), 7.51 – 7.47 (1H, m), 7.33 (1H, dd, JHH
HH
4
3
.0 Hz, J = 1.2 Hz), 7.17 – 7.13 (1H, m), 7.02 – 6.98 (1H, m), 6.66 (1H, br. t, J = 6.0 Hz),
HH
HH
.57 (1H, s), 3.55 – 3.50 (2H, m), 2.04 (3H, s), 2.03 (3H, s), 1.75 – 1.67 (2H, m), 1.45 – 1.28 (10H,
3
13
1
m), 0.91 (3H, t, J = 6.8 Hz) ppm. C{ H} NMR (75.6 MHz, CDCl ): δ 185.7, 184.0, 169.3,
HH
3
C
1
1
66.8, 149.4, 145.7, 144.7, 139.8, 131.0, 129.7, 129.6, 127.1, 126.5, 125.2, 125.1, 124.5, 124.0,
1
95
14.2, 101.9, 40.3, 31.9, 29.8, 29.4, 28.5, 27.3, 27.2, 22.8, 14.2 ppm. Pt NMR (107.51 MHz,
-
3
-1
CDCl ): -2776 ppm. MS(ES) found m/z = 652.2 for [M - H] . UV-vis (CHCl ): λ (ε / dm mol
3
3
max
-1
-
cm ) 300 (9920), 349 (2810), 368 (3126), 423 (2420) nm. IR (thin film): ν 1738, 1643, 1582 cm
max
1
.
1
6

ACCEPTED MANUSCRIPT
2
1
2
Synthesis of [Pt(L )(acac)]: as [Pt(L )(acac)], but using [Pt(L )(DMSO)Cl] (0.035 g, 0.048 mmol)
1
and sodium acetylacetonate monohydrate (0.059 g, 0.484 mmol). Yield = 0.031 g (90%). H NMR
3
3
(
500 MHz, CDCl ): δ 9.48 (1H, d, J = 9.0 Hz), 8.03 (1H, d, J = 8.0 Hz), 7.72 – 7.67 (2H,
3 H HH HH
3
m), 7.63 (1H, s), 7.53 – 7.50 (1H, m), 7.40 – 7.38 (1H, d, J = 7.5 Hz), 7.19 – 7.16 (1H, m), 7.05
HH
3
–
7.02 (1H, m), 6.48 (1H, br. t, JHH = 6.0 Hz), 5.57 (1H, s), 3.56 – 3.52 (2H, m), 2.04 (3H, s), 2.03
3
13
1
(
3H, s), 1.73 – 1.67 (2H, m), 1.35 – 1.22 (18H, m), 0.83 – 0.89 (3H, t, JHH = 7.5 Hz) ppm. C{ H}
NMR (75.6 MHz, CDCl ): δ 185.7, 184.1, 169.5, 166.8, 149.5, 145.7, 144.7, 139.9, 131.1, 129.8,
3
C
129.6, 127.2, 126.6, 125.2, 125.1, 124.5, 124.0, 114.2, 101.9, 40.4, 32.0, 29.7, 29.4, 28.5, 27.3,
1
95
2
7.2, 22.8, 14.2 ppm. Pt NMR (107.51 MHz, CDCl ): -2779 ppm. MS(ES) found m/z = 708.5 for
3
-
194
[
(
M – H] . HR MS found m/z = 725.2841; C H N O Pt [M + OH] requires 725.2844. UV-vis
33 43 2 4
3
-1
-1
-1
CHCl ): λ (ε / dm mol cm ) 284 (4180), 368 (2910) nm. IR (thin film): ν 1668, 1523 cm .
3
max
max
3
1
3
Synthesis of [Pt(L )(acac)]: as [Pt(L )(acac)], but using [Pt(L )(DMSO)Cl] (0.071 g, 0.091 mmol)
1
and sodium acetylacetonate monohydrate (0.111 g, 0.911 mmol). Yield = 0.034 g (49%). H NMR
3
3
(
400 MHz, CDCl ): δ 9.53 (1H, d, J = 8.8 Hz), 8.07 (1H, d, J = 8.4 Hz), 7.77 – 7.70 (3H,
3
H
HH
HH
3
4
m), 7.57 – 7.53 (1H, m), 7.47 (1H, dd, J = 7.2 Hz, J = 1.2 Hz), 7.24 – 7.20 (1H, m), 7.12 –
HH
HH
3
7
.08 (1H, m), 6.29 (1H, br. t, J = 5.6 Hz), 5.58 (1H, s), 3.59 – 3.54 (2H, m), 2.05 (3H, s), 2.04
HH
3
195
(
(
(
3H, s), 1.74 – 1.67 (2H, m), 1.46 – 1.24 (26H, m), 0.88 (3H, t, JHH = 7.2 Hz) ppm. Pt NMR
-
107.51 MHz, CDCl ): -2791 ppm. MS(ES) found m/z = 764.4 for [M - H] . UV-vis (CHCl ): λ
3
3
max
3
-1
-1
ε / dm mol cm ) 263 (7950), 293 (7580), 348 (2410), 357 (2720), 421 (1560) nm. IR (thin film):
-1
νmax 1669, 1548 cm .
1
30
Synthesis of [Pt(L )(8-Q)]: Based on
a
modified literature methodology,
using
[
(
Pt(L1)(DMSO)Cl] (0.033 g, 0.049 mmol), Na CO (0.010 g, 0.099 mmol) and 8-hydroxyquinoline
2
3
0.008 g, 0.054 mmol). The red solution was concentrated in vacuo and diethyl ether (5 mL) was
1
7

ACCEPTED MANUSCRIPT
added. The precipitate was filtered, washed with diethyl ether (2 × 10 mL) to remove excess 8-
hydroxyquinoline, and methanol (1 × 5 mL). The solid was dissolved in dichloromethane and dried
1
in vacuo to afford a red solid. Yield = 0.026 g, (76%). H NMR (400 MHz, CDCl ): δ 9.64 (1H, d,
3
H
3
3
3
JHH = 8.4 Hz), 8.95 (1H, m), 8.32 (1H, d, J = 8.4 Hz), 7.90 (1H, d, J = 8.0 Hz), 7.75 – 7.71
HH
HH
(1H, m), 7.57 – 7.52 (2H, m), 7.43 – 7.38 (2H, m), 7.30 – 7.25 (2H, m), 7.18 – 7.12 (2H, m), 7.07 –
3
7
.04 (1H, m), 6.97 (H, d, J = 7.6 Hz), 6.88 – 6.85 (1H, m), 3.58 – 3.48 (2H, m), 1.81 – 1.72 (2H,
HH
3
195
m), 1.49 – 1.25 (10H, m), 0.92 (3H, t, J = 6.8 Hz) ppm. Pt NMR (107.51 MHz, CDCl ): δ -
HH
3
Pt
+
3
-1
2
998 ppm. MS(ES) found m/z = 753.3 for [M + MeOH + Na] . UV-vis (CHCl ): λ (ε / dm mol
3 max
-1
-1
cm ) 280 (10230), 370 (2530), 505 (750) nm. IR (thin film): ν 1645, 1539 cm .
max
2
Synthesis of [Pt(L )(8-Q)]: as [Pt(L1)(8-Q)], but using [Pt(L2)(DMSO)Cl] (0.052 g, 0.072 mmol),
Na CO (0.038 g, 0.360 mmol) and 8-hydroxyquinoline (0.021 g, 0.145 mmol). Yield = 0.033 g
2
3
1
3
(
61%). H NMR (400 MHz, CDCl ): δ 9.61 (1H, d, J = 8.4 Hz), 8.94 – 8.88 (1H, m with
3 H HH
3
3
satellites), 8.31 (1H, d, J = 8.0 Hz), 7.86 (1H, d, J = 8.0 Hz), 7.71 – 7.67 (1H, m), 7.56 – 7.50
HH
HH
(3H, m), 7.39 – 7.35 (2H, m), 7.27 – 7.24 (1H, m) 7.14 – 6.97 (4H, m), 6.82 – 6.79 (1H, m), 3.57 -
3
195
3
.49 (2H, m), 1.81 – 1.75 (2H, m), 1.48 – 1.25 (18H, m), 0.89 (3H, t, JHH = 6.8 Hz) ppm. Pt
+
NMR (107.51 MHz, CDCl ): δ -2972 ppm. MS(ES) found m/z = 777.8 for [M + Na] . UV-vis
3
Pt
3
-1
-1
(
CHCl ): λ (ε / dm mol cm ) 265 (8640), 368 (2640), 506 (750) nm. IR (thin film): ν 1646,
3
max
max
-1
1
539 cm .
3
1
3
Synthesis of [Pt(L )(8-Q)]: as [Pt(L )(8-Q)], but using [Pt(L )(DMSO)Cl] (0.029 g, 0.037 mmol),
Na CO (0.020 g, 0.186 mmol) and 8-hydroxyquinoline (0.011 g, 0.074 mmol). Yield = 0.021 g
2
3
1
3
(
68%). H NMR (400 MHz, CDCl ): δ 9.64 (1H, d, J = 8.8 Hz), 8.93 (1H, d (with satellites),
3
H
HH
3
3
3
JHH = 3.2 Hz), 8.31 (1H, d, J = 8.0 Hz), 7.88 (1H, d, J = 8.0 Hz), 7.74 – 7.70 (1H, m), 7.56 –
HH
HH
7
6
.52 (2H, m), 7.41 – 7.36 (3H, m), 7.29 – 7.24 (1H, m) 7.14 – 7.13 (2H, m), 7.06 – 7.03 (1H, m),
3
.97 (1H, d, J = 7.6 Hz), 6.85 – 6.82 (1H, m), 3.56 - 3.45 (2H, m), 1.80 – 1.71 (2H, m), 1.45 –
HH
1
8

ACCEPTED MANUSCRIPT
3
195
1
.19 (26H, m), 0.88 (3H, t, J = 7.2 Hz) ppm. Pt NMR (107.51 MHz, CDCl ): δ -2977 ppm.
HH
3
Pt
+
3
-1
-1
MS(ES) found m/z = 833.5 for [M + Na] . UV-vis (CHCl ): λ (ε / dm mol cm ) 352 (2750),
3
max
-1
3
69 (2590), 438 (1080), 504 (1190) nm. IR (thin film): νmax 1670, 1597 cm .
Acknowledgements
Dr James A. Platts is thanked for supporting TD-DFT calculations. We thank Cardiff University for
financial support and the staff of the EPSRC UK National Mass Spectrometry Facility at Swansea
University. We also thank the EPSRC for the use of the National Crystallographic Service at the
University of Southampton.
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Highlights
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Synthesis of alkyl chain adorned 2-phenylquinoline ligands
Synthesis of lipophilic cyclometalated Pt(II) complexes
Long-lived luminescence from Pt(II) complexes in solution