Structure-property relationships in PtII diimine-dithiolate nonlinear optical chromophores based on arylethylene-1,2-dithiolate and 2-thioxothiazoline-4,5-dithiolate

Article abstract of DOI:10.1002/ejic.201200346

Eighteen new [Pt^II(NN)(SS)] complexes [23-40; NN = diimine: 2,2'-bipyridine, 1,10-phenanthroline and alkyl/aryl-substituted derivatives; SS = arylethylene-1,2-dithiolate (R-edt^2-: R = phenyl, 2-naphthyl, 1-pyrenyl), N-substituted 2-thioxothiazoline-4,5-dithiolate (R-dmet ^2-: R = methyl, ethyl, phenyl)] have been synthesized and characterized by spectroscopic (UV/Vis/NIR, fluorescence) and electrochemical (CV) measurements. Single-crystal X-ray diffraction analysis allowed structural characterization of five of the complexes (27-29, 31, and 37). Structural modifications capable of affecting the nature and energies of the frontier molecular orbitals in these systems were assessed and hybrid DFT and time-dependent (TD) DFT calculations, carried out both in the gas phase and in the presence of several solvents (CH₂Cl₂, CHCl ₃, CH₃CN, acetone, thf, dmf, dmso, and toluene), allowed the trends observed in the voltammetric data and in the energies of the peculiar solvatochromic visible absorption bands to be rationalized. In addition, to evaluate the second-order nonlinear optical properties of 23-40, first static hyperpolarizability values β_tot were calculated both in the gas phase and in CH₂Cl₂, the highest values being obtained for [Pt(NN)(Me-dmet)] complexes (NN = 4,4'-diphenyl-2,2'-bipyridine and 4,7-diphenyl-1,10-phenanthroline; β_tot = 691 × 10 ^-30 and 604 × 10^-30 esu, respectively). Eighteen [Pt(NN)(SS)] complexes (NN = diimine; SS = arylethylene-1,2-dithiolate, N-substituted 2-thioxothiazoline-4,5-dithiolate) have been prepared. All complexes feature a notable negative solvatochromism and potential SONLO properties on the basis of their GS electronic structures. Copyright

Full text of DOI:10.1002/ejic.201200346

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FULL PAPER
DOI: 10.1002/ejic.201200346
Structure–Property Relationships in PtII Diimine-Dithiolate Nonlinear Optical
Chromophores Based on Arylethylene-1,2-dithiolate and 2-Thioxothiazoline-
4,5-dithiolate
Anna Pintus,[a] M. Carla Aragoni,[a] Nathalie Bellec,[b] Francesco A. Devillanova,[a]
Dominique Lorcy,[b] Francesco Isaia,[a] Vito Lippolis,[a] Rebecca A. M. Randall,[c]
Thierry Roisnel,[b] Alexandra M. Z. Slawin,[c] J. Derek Woollins,[c] and
Massimiliano Arca*[a]
Keywords: Solvatochromism / Platinum / Nonlinear optics / Density functional calculations / N ligands / S ligands
∧
∧
∧
Eighteen new [PtII(N N)(S S)] complexes [23–40; N N = di-
time-dependent (TD) DFT calculations, carried out both in
the gas phase and in the presence of several solvents
(CH2Cl2, CHCl3, CH3CN, acetone, thf, dmf, dmso, and tolu-
ene), allowed the trends observed in the voltammetric data
and in the energies of the peculiar solvatochromic visible ab-
sorption bands to be rationalized. In addition, to evaluate the
second-order nonlinear optical properties of 23–40, first static
hyperpolarizability values βtot were calculated both in the gas
phase and in CH2Cl2, the highest values being obtained for
imine: 2,2Ј-bipyridine, 1,10-phenanthroline and alkyl/aryl-
substituted derivatives; S S = arylethylene-1,2-dithiolate (R-
∧
edt2–: R = phenyl, 2-naphthyl, 1-pyrenyl), N-substituted 2-
thioxothiazoline-4,5-dithiolate (R-dmet2–: R = methyl, ethyl,
phenyl)] have been synthesized and characterized by spec-
troscopic (UV/Vis/NIR, fluorescence) and electrochemical
(CV) measurements. Single-crystal X-ray diffraction analysis
allowed structural characterization of five of the complexes
(27–29, 31, and 37). Structural modifications capable of af-
fecting the nature and energies of the frontier molecular or-
bitals in these systems were assessed and hybrid DFT and
∧
∧
[Pt(N N)(Me-dmet)] complexes (N N = 4,4Ј-diphenyl-2,2Ј-
bipyridine and 4,7-diphenyl-1,10-phenanthroline; βtot
691ϫ10–30 and 604ϫ10–30 esu, respectively).
=
center can be found in heteroleptic complexes of the type
Introduction
∧
[M(S S)(L)], in which L is a second bidentate ligand, which
[15]
∧
During the past decade the interest shown by the scien-
tific community in homoleptic and heteroleptic metal com-
plexes of ene-1,2-dithiolato (1,2-dithiolene) ligands (S S)
in turn can be a different (S S)Ј ligand
or a ligand of
different nature. Although numerous L ligands have been
used so far, a primary role has been played by diimines
∧
∧
has continuously increased, as attested by the number of
papers and reviews published each year on the topic.[1–5]
The reason for such interest lies in the ample range of appli-
cations that result from the optical,[6,7] magnetic,[8,9] con-
ducting,[8] and photoconducting[10] properties of 1,2-di-
thiolene complexes as well as their role in biological sys-
tems.[11–13] Square-planar 1,2-dithiolene complexes of d8
N N, for example, 2,2Ј-bipyridine, 1,10-phenanthroline,
8
∧
∧
and a few others. [M(N N)(S S)] complexes (M = d metal
ion), first described by Miller and Dance[16] and largely
studied as SONLO materials[17–19] and solar-cell sensitiz-
ers,[20–25] show peculiar electronic features, including the
ability to undergo reversible electrochemical processes[25,26]
and intense absorptions (ε ≈ 103–104 m–1 cm–1) in the Vis/
NIR region.[23,26–29] This absorption has been the subject
of theoretical and experimental investigations by many re-
search groups,[27,30–37] who have demonstrated its charge-
metal ions M, such as NiII, PdII, PtII, and AuIII [2]
have been
,
largely exploited as second-order nonlinear optical
(SONLO) materials.[6,7,14] The required lack of inversion
transfer (CT) character due to monoelectronic excitation
∧
[a] Dipartimento di Scienze Chimiche e Geologiche, Università from the HOMO, localized on the S S ligand, which as-
sumes the ene-1,2-dithiolate limiting form (–S–C=C–S–)
degli Studi di Cagliari,
S. S. 554 Bivio per Sestu, 09042 Monserrato, CA, Italy
with a non-negligible participation of the central metal ion,
to the LUMO, localized on the N N diimine. Therefore
Fax: +39-070-675-4456
∧
E-mail: marca@unica.it
[b] Sciences Chimiques de Rennes, UMR 6226 CNRS-Université
de Rennes 1,
Campus de Beaulieu, 35042 Rennes Cedex, France
[c] EaStCHEM School of Chemistry, University of St. Andrews,
North Haugh, St. Andrews, Fife, KY16 9ST, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200346.
this transition, described as a mixed-metal/ligand-to-ligand
CT process (MMLLЈCT), leads to an excited state, which
is less polar or even polarized in the opposite direction with
respect to the ground state.[38,39] This is in agreement with
the remarkable negative solvatochromism observed for the
Eur. J. Inorg. Chem. 0000, 0–0
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M. Arca et al.
FULL PAPER
visible absorption, which is responsible for its large nonline- electrochemical, and spectroscopic features of PtII com-
arity,[27,30,31,40] especially in the case of M = Pt.[33]
plexes obtained from derivatives of two classes of diimines,
A large number of diimine-dithiolate complexes have 2,2Ј-bipyridine (bipy) and 1,10-phenanthroline (phen), and
been investigated so far, the majority of which contain the two classes of 1,2-dithiolates, 2-thioxothiazoline-2,4-di-
well-known maleonitrile-1,2-dithiolate (mnt2–),[23,26,33,40] thiolate (R-dmet2–) and arylethylene-1,2-dithiolate (R-
benzene-1,2-dithiolate (bdt2–)[25,32,38] and its derivatives, edt2–). Starting from eight different diimines [bipy (1), 5,5Ј-
and 2-thioxo-1,3-dithiole-4,5-dithiolate (dmit2–)[29,41,42] as Me2bipy (2), 4,4Ј-Me2bipy (3), 4,4Ј-tBu2bipy (4), 4,4Ј-
∧
S S ligands. Oddly, notwithstanding the large number of Ph2bipy (5), phen (6), 4,7-Ph2phen (7), and 3,4,7,8-
SONLO theoretical investigations, mostly by density func- Me4phen (8), Table 1] and six different dithiolates [Ph-,
tional theory (DFT),[43] first-principle calculations of the Naph-, and Pyr-edt2– (Naph = 2-naphthyl, Pyr = 1-pyrenyl)
first hyperpolarizability β have rarely been reported.[35,36,44] and Me-, Et-, and Ph-dmet2–], 18 new complexes (23–40)
In recent years we have reported on bis(1,2-dithiolene) were obtained (Scheme 1, Table 2). The complexes were de-
complexes of d8 metal ions featuring intrinsically asymmet- signed with the aim of separating the contributions of the
rically substituted “non-innocent”[45–48] 1,2-dithiolato li- diimines from those of the dithiolates in the final complexes
gands ranging from simple monosubstituted ethylene-1,2- to ascertain the effect of peripheral alkyl or aryl substitu-
dithiolates (R-edt2–)[49,50] to heterocycles such as N,NЈ-di- ents on their properties. We therefore prepared complexes
substituted
2-thioxoimidazoline-4,5-dithiolate
(R,RЈ- that could be grouped into three series (Table 2) that feature
timdt2–)[51–54] and N-substituted 2-thioxo-1,3-thiazoline- a single diimine (bipy or phen) coupled to different 1,2-
4,5-dithiolate (R-dmet2–),[55–60] structurally intermediate be- dithiolates (N N = bipy in Series 1, 23–28; N N = phen in
∧
∧
tween R,RЈ-timdt2– and dmit2–.
Series 2, 33–38, respectively) or a single 1,2-dithiolate (Me-
dmet2–) with variously substituted diimines (Series 3, 26,
29–32, 36, 39, and 40).
Table 1. Substituents R1–R4 in the complexes of the type
∧
[Pt(N N)Cl2] (9–16).[a]
∧
∧
N N [Pt(N N)Cl2]
R1
R2
R3
R4
1
2
3
4
5
6
7
8
9
H
Me
H
H
H
–
H
H
Me
tBu
Ph
–
–
–
–
–
–
H
H
Me
–
–
–
–
–
H
Ph
Me
10
11
12
13
14
15
16
–
–
–
–
[a] See Scheme 1.
In this paper we report on the preparation of novel di-
imine-dithiolate PtII complexes featuring R-edt2– and R-
dmet2– ligands coupled to variously substituted 2,2Ј-bipyr-
idine and 1,10-phenanthroline derivatives to give an unprec-
edented set of 18 mixed-ligand complexes, the structural,
electrochemical, and spectroscopic features of which, inter-
preted on the basis of DFT calculations, allow sound struc-
ture–property relationships to be established that will be
useful for the design of potential candidates for SONLO
applications.
Results and Discussion
Previous attempts[18,20,27,38] to ascertain structure–prop-
erty relationships for [M(N N)(S S)] diimine-dithiolate
complexes compared complexes in which the S S ligands ing the corresponding protected species, monosubstituted
generally belonged to very inhomogeneous classes, so that 1,3-dithiol-2-ones[49–50] or 4,5-bis(2-cyanoethylthio)-2-thi-
although general rules on the effect of changing the metal oxothiazolines,[57–60] respectively, with strong bases in the
and the classes of both types of ligands were established, presence of the desired metal ion to give the corresponding
Synthesis
R-edt2– and R-dmet2– ligands can be generated by treat-
∧
∧
∧
no investigations on the fine-tuning of the observed proper- bis(1,2-dithiolene)
complexes.[49–60]
Therefore
the
2–
∧
∧
∧
ties, such as redox potentials and UV/Vis absorption, have [Pt(N N)(S S)] complexes featuring S S = R-edt (23–25
been reported. In this context, the work presented herein and 33–35, Table 2) and S S = R-dmet2– (26–32 and 36–40)
∧
focused on the systematic investigation of the structural, were synthesized by treating the appropriate R-edt2– and
2
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
∧
∧
∧
Scheme 1. Pathways for the synthesis of diimine-dithiolate complexes [Pt(N N)(S S)] (23–40) starting from the [Pt(N N)Cl2] complexes
∧
∧
(9–16) of diimines N N (1–8) and 1,2-dithiolates S S (17–22). Substituents R1–R6 for each compound are summarized in Tables 1 and
2.
R-dmet2– ligands generated in situ with the corresponding all featuring R-dmet2– 1,2-dithiolates. Selected bond lengths
∧
[Pt(N N)Cl2] complexes 9–16, in turn obtained by reaction and angles are presented in Table 3 and crystallographic
of the diimines 1–8 with K2PtCl4 according to literature data are provided in Table S5 in the Supporting Infor-
methods (Scheme 1 and Table 1).[61,62]
mation. As an example, the molecular structure of 37 is
illustrated in Figure 1 (the structures of 27 in 27·1/2thf, 28,
29, and 31 are given in Figures S1–S4 in the Supporting
Information). Note that 37 is an unusual example of a di-
Crystallographic Studies
Single crystals suitable for X-ray diffraction analysis were imine-dithiolate complex bearing a 1,10-phenanthroline li-
collected for 27 (isolated as 27·1/2thf), 28, 29, 31, and 37, gand because, to the best of our knowledge, only [Pt(Ph2-
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Table 2. Substituents R1–R6 in the complexes 23–40 belonging to
∧
∧
the general classes [Pt(bipy)(S S)] (Series 1), [Pt(phen)(S S)]
∧
(Series 2), and [Pt(N N)(Me-dmet)] (Series 3).[a]
∧
∧
Series 1
Series 2 Series 3 N N S S R1 R2 R3 R4 R5
R6
23
24
25
26
27
28
1
1
1
1
1
1
2
3
4
5
6
6
6
6
6
6
7
8
17
18
19
20
21
22
H
H
H
H
H
H
H
H
H
H
H
H
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Ph
–
–
–
Naph[b]
Pyr[c]
–
–
–
–
–
–
–
26
Me
Et
Ph
Me
Me
Me
Me
–
29
30
31
32
20 Me H
20
20
20
17
18
19
20
21
22
20
20
H
H
H
–
–
–
–
–
–
–
Me
tBu –
Ph
–
–
–
–
–
–
–
–
33
34
35
36
37
38
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph
Ph
Figure 1. ORTEP drawing of 37 showing the atom-labeling scheme.
Thermal ellipsoids are drawn at the 60% probability level. Hydro-
gen atoms have been omitted for clarity.
Naph[b]
–
–
Pyr[c]
36
–
–
–
–
–
Me
Et
Ph
Me
Me
the 2-thioxo-1,3-thiazoline or diimine moieties (in the case
of 29 and 31) with dihedral angles C(4)–N(1)–Pt–S(1) rang-
ing between 169.39 and 177.81° (Table 3). In all cases, the
platinum atom is coordinated by the two diimine N atoms
and the two S atoms of the 1,2-dithiolato ligand[65] in a
39
40
–
–
–
Me Me
[a] See Scheme 1. [b] Naph = 2-naphthyl. [c] Pyr = 1-pyrenyl.
phen)(dtbdt)] (Ph2-phen: 4,7-diphenyl-1,10-phenanthroline; slightly distorted square-planar geometry.
dtbdt2–: 3,5-di-tert-butyl-1,2-benzenedithiolate)[63] and
A comparison of the bond lengths and angles in 27 and
[Pt(phen)(tdt)], embedded in the heterotrinuclear complex 37 (differing just by the identity of the diimine ligand)
[PtAg2(phen)(tdt)(dppm)2](SbF6)2 [tdt2– = 3,4-toluenedi- shows that the introduction of a 1,10-phenanthroline in
thiolate; dppm = bis(diphenylphosphanyl)methane],[64] have place of a 2,2Ј-bipyridine causes small but significant differ-
∧
been structurally characterized so far.
ences in the structural features of the [Pt(S S)] moiety. In
The quality of the structures, testified by the R indices particular, the Pt–S and C–S distances are shorter than
(see Table S5), is in some cases not excellent as a result of those determined in the diimine-dithiolate complexes con-
either disordered atoms unsuitable for splitting in the com- taining 2,2Ј-bipyridine derivatives, resulting in a widening
plex molecules (29, 37) or solvent molecules encapsulated of the S–Pt–S angle.
in the cavities (27). The unit cell of 27·1/2thf contains two
A comparison of the parameters determined for 27, 28,
units of 27 lying in parallel planes and slipping over each 29, and 31 shows that the addition of alkyl substituents to
other and a solvent molecule. Moreover, it is worth underli- the 2,2Ј-bipyridine ligand does not induce significant
ning that the structure of 29 features the simultaneous pres- changes. Notably, the C(1)–C(2), C(1,2)–S(1,2), Pt–S(1,2),
ence of two kinds of complex units (occupancies 65 and and Pt–N(1,2) distances determined for complexes 27–29,
35%) that differ in the parameters of the Me-dmet2– ligand 31, and 37 are very close to the average distances deter-
and are flipped by 180° with respect to each other. Since mined for all the platinum diimine-dithiolate complexes
the bond angles and distances in each complex unit do not characterized by single-crystal X-ray diffraction and avail-
show significant differences, the average values are reported able in the Cambridge Structural Database [1.374(40),
in Table 3. An inspection of all the crystal structures shows 1.747(27), 2.255(13), and 2.048(18) Å, respectively][66,67] and
that the complexes are planar but for the substituents on testify the π-electron-accepting ability of the diimines.[68]
Table 3. Selected bond lengths [Å] and angles [°] in the crystal structures of 27·1/2thf,[a] 28, 29,[b] 31, and 37.
27·1/2thf[a]
28
29[b]
31
37
Pt–S(1)
Pt–S(2)
Pt–N(1)
Pt–N(2)
S(1)–Pt–S(2)
N(1)–Pt–N(2)
C(1)–S(1)
C(2)–S(2)
C(1)–C(2)
C(4)–N(1)–Pt–S(1)
2.266(3)
2.276(3)
2.053(9)
2.038(10)
91.03(11)
79.77(4)
1.758(12)
1.735(11)
1.324(15)
177.48(5)
2.267(3)
2.266(4)
2.037(12)
2.050(8)
90.99(12)
78.78(4)
1.746(14)
1.730(10)
1.350(18)
169.39(7)
2.132(5)
2.361(4)
2.045(4)
2.049(5)
92.8(15)
80.2(18)
1.764(19)
1.739(18)
1.320(3)
175.47(8)
2.267(8)
2.274(9)
2.044(3)
2.045(3)
90.86(3)
79.42(11)
1.737(4)
1.734(3)
1.340(5)
173.82(2)
2.233(4)
2.235(4)
2.009(11)
1.960(10)
97.09(12)
86.00(4)
1.735(14)
1.723(15)
1.342(2)
177.81(5)
[a] Average values of the two independent complex units in the unit cell of 27·1/2thf. [b] Bond lengths and angles taken from the conformer
with the highest occupancy (65%) in the structure of 29 (see Discussion).
4
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
An examination of the crystal packing in these com-
plexes shows that the π-electron systems of the diimine and
1,2-dithiolate are involved in the formation of intermo-
lecular interactions for all the compounds characterized
structurally. In the case of 27·1/2thf, the crystal packing
originates from face-to-face π–π interactions between the
2,2Ј-bipyridine ligands of symmetry-related complex units
in a head-to-tail disposition (1 – x, 1 – y, 1 – z; intercentroid
distance 3.70 Å) and between the 2,2Ј-bipyridine ligands
and the C2S2Pt metallacycle (intercentroid distance 3.57 Å)
and results in the formation of tetrameric aggregates (Fig-
ure S5 in the Supporting Information). Slightly weaker in-
teractions of the same type generate a complex network,
leaving cavities that host the thf solvent molecules.
Figure 2. Perspective drawing of the interacting symmetry-related
molecular units in the crystal structure of 28. Hydrogen atoms have
been omitted for clarity. Symmetry operation Ј: 1 – x, 1 – y, 1 – z.
Also in the case of 28, weak π–π interactions lead to
the formation of discrete aggregates. In fact, although the
rotation of the phenyl substituent on the 1,3-thiazoline ring
(65.73° between the average planes defined by the thiazoline
and phenyl rings) prevents stacking interactions similar to
those described for 27, pairs of interactions between the π
system of the heterocyclic ring of the Ph-dmet2– ligand and
the Pt atom of a symmetry-related molecule lead to the for-
mation of “diads” (Pt–centroid distances: 3.644 and
3.678 Å, Figure 2). Two types of π–π supramolecular con-
tacts extend the interactions between the units of 28: 1) a
slipped edge-to-edge interaction between the bipyridine mo-
lecules results in the formation of ribbons running along
the a vector (see Figure S6 in the Supporting Information)
and 2) face-to-face π–π interactions between eclipsed cou-
ples of the phenyl substituents (distance between the planes
of the phenyl rings: 3.26 Å) keep together the ribbons to
form stacks oriented along the a vector determining the
overall three-dimensional structure. Although the crystal
structure of 29 shows the disorder described above, it is
clear that monomeric units stack along the a vector with
a zig-zag motif through slipped π–π stacking interactions
between the 5,5Ј-dimethyl-2,2Ј-bipyridine ligands (inter-
centroid distance between pyridine units: 3.62 Å) and face-
to-face interactions with the C3NS heterocycle of the Me-
dmet2– moiety (intercentroid distance: 3.52 Å). Weak con-
tacts involving the methyl substituents of the 1,2-dithiolates
and the 2,2Ј-bipyridine units lead to packing of the stacks
along the b and c axes. In the crystal packing of 31, parallel
molecular units can be envisaged with π–π face-to-face in-
teractions between C2N2Pt metallacycles of couples of com-
plex units in a head-to-tail disposition (intercentroid dis-
tance: 3.76 Å). Weak intermolecular contacts involving the
coordinating sulfur atoms and the endocyclic chalcogen
respectively] are involved in weak contacts with hydrogen
atoms of the 1,10-phenanthroline ligands of different pairs
of molecules disposed almost orthogonally [86.01°; S(3)···
H(7)ЈЈ 2.97 Å, S(3)···H(8)ЈЈ 2.86 Å, S(4)···H(10)ЈЈЈ 2.97 Å;
symmetry operations, ЈЈ: 1/2 + x, y, 1/2 – z, ЈЈЈ: 5/2 – x, –y,
1/2 + z].
Figure 3. Perspective drawing of the interacting symmetry-related
molecular units in the crystal structure of 37. Hydrogen atoms have
been omitted for clarity. Symmetry operation Ј: 2 – x, –y, –z.
Electrochemistry
Cyclic voltammetry (CV) measurements performed on
species of each Me-dmet2– ligand [S(2)···S(4)Ј 3.50 Å; sym- 23–40 in dmso show that with the exception of 40, all the
metry operation Ј: –1 – x, –y, –z], which are slightly shorter complexes exhibit two one-electron redox waves that fall in
than the sum of the van der Waals radii (3.60 Å), generate the ranges from –1.79 to –1.56 and from –0.16 to 0.05 V vs.
II
ribbons through weak minor hydrophobic contacts.
the Fc+/Fc couple (E1/2 and E1/2III, respectively, Table 4,
Finally, the crystal structure of 37 shows that π–π inter- Figure 4 for 24), which corresponds to the reduction of the
actions between the benzenoid ring of the 1,10-phen- neutral species to a monoanionic species and to the oxi-
anthroline and the Et-dmet2– ligands result in the formation dation of the neutral species to a monocationic species,
of weakly bonded pairs of molecules with intermetallic Pt– respectively. Four of the complexes (26–28 and 32) show a
PtЈ distances of 3.80 Å (Figure 3). The endocyclic and ter- further reduction process below –2.0 V (E1/2I, Table 4; Fig-
minal sulfur atoms of the Et-dmet2– ligand [S(3) and S(4), ure S7 in the Supporting Information for 26).
Eur. J. Inorg. Chem. 0000, 0–0
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M. Arca et al.
Table 4. Redox potentials E1/2 (vs. Fc+/Fc),[a] UV/Vis absorption only marginally affects the metal and generates the
FULL PAPER
II
·
–
∧
∧
maxima λmax, and the corresponding molar extinction coefficients
[Pt (N N )(S S)] species. A second reduction process
leading from the mono- to the dianionic form of complexes
26–28 and 32 (E1/2I) occurs at about –2.1 V vs. Fc+/Fc (ipc/
[c]
ε,[b] emission maxima λem
,
and quantum yields Φ[d] for 23–40.
II
III
E1/2I [V]
E1/2
E1/2
[V]
λmax
ε
λem
Φ
[V]
[nm] [103 m–1 cm–1] [nm]
[10–3]
ipa ≈ 1 and |Epc – EpaI| = 48–53 mV at 50 mVs–1). In the
I
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
–
–
–
–1.741 –0.135 604
–1.727 –0.135 603
–1.618 –0.076 592
–1.608 –0.004 581
6.7
5.9
–
374, 395
8.4
case of [Pt(Ph2-phen)(dtoc)] [Ph2-phen: 4,7-diphenyl-1,10-
phenanthroline; dtoc2– = 1,2-dithiolato-1,2-dicarba-closo-
dodecaborane(12)], the second reduction, detected by CV
in dmf (E1/2 = –2.14 V vs. Fc+/Fc), has been proposed to
be localized on the diimine,[63] although in analogy to what
has been reported for different [Pt(bipy)L2] (L = py, Me2N-
py, Cl), [Pt(bipy)LЈ] (LЈ = en), and [Pt(phen)py2] com-
plexes,[69] it could be tentatively attributed to the formation
374, 395 10.8
391, 410
374, 395 18.5
375, 405 7.2
375, 405 12.1
372, 391 8.8
375, 399 11.2
375, 399 15.5
372, 391 18.4
374, 400 13.4
374, 400 15.2
392, 411
372, 405
375, 404
373, 403 27.6
373, 394 18.3
–
–2.270
–2.256
–2.269
–
–
–
4.3
4.5
4.0
4.7
4.5
5.0
5.6
5.4
3.6
–
5.0
4.0
4.6
5.7
3.7
–1.609 0.008
–1.622 0.046
582
580
–1.730 –0.027 567
–1.740 –0.017 563
–1.692 –0.015 564
–1.563 –0.040 608
–1.715 –0.147 606
–1.728 –0.161 603
–1.620 –0.076 596
–1.620 –0.017 581
–1.620 –0.027 579
–2.112
I
I
·
2– [71]
∧
∧
of a dianionic Pt radical species [Pt (N N )(S S)] .
–
–
–
–
–
–
–
–
The oxidation of the neutral species (E1/2III), which oc-
curs for all complexes except 40 at about –0.1 V vs. Fc+/Fc,
is also a reversible process with ipc/ipa and |EpcIII – EpaIII| in
the ranges of 0.7–1.4 and 44–72 mV at 50 mVs–1, respec-
tively. Only for 28 and 36 do the ipc/ipa values fall outside
of these ranges so that, as concerns these two complexes,
the process should be considered as quasi-reversible. Be-
cause diimine-dithiolate complexes show the HOMO local-
ized on the dithiolate (see below), the oxidation of the neu-
–
8.2
9.2
–1.634 0.020
–1.561 –0.002 602
–1.789 549
581
–
384, 402
6.4
[a] CV potentials in anhydrous dmso at 298 K, supporting electro-
lyte 0.10 m TBAPF6, Ag/AgCl reference electrode, scan rate
50 mVs–1. Under these conditions, E1/2(Fc+/Fc) = +0.49 V. [b] UV/
Vis spectra recorded in dmso at 298 K. [c] Emission spectra re-
corded in dmso at 298 K. [d] Quantum yields determined by using
anthracene in ethyl alcohol solution as reference.
∧
tral species should be considered centered on the S S li-
gand.
The values of E1/2 and E1/2 can be rationalized by
analyzing separately the complexes grouped into the three
series described above.
II
III
∧
∧
1) Complexes belonging to Series 1 (N N = bipy, S S =
R-edt2– for 23–25 and R-dmet2– for 26–28) show an unam-
III
biguous dependence of the half-wave potentials E1/2 on
∧
the nature of the S S ligand. In particular, complexes 26–
28, bearing R-dmet2– ligands, show E1/2III values systemati-
cally more positive than those recorded for 23–25, bearing
R-edt2– dithiolates, which indicates that the HOMO ener-
gies of the former complexes should be lower than those of
the latter.
2) Similar observations can be made for the complexes
belonging to Series 2 (33–38) featuring 1,10-phenanthroline
in place of 2,2Ј-bipyridine.
3) An insight into the effect induced by the diimine can
be obtained by analyzing the potentials of the complexes of
Series 3 (26, 29–32, 36, 39, and 40) featuring the Me-dmet2–
1,2-dithiolate combined with different diimine ligands. A
comparison of the redox potentials of 26 and 36 suggests
that, on passing from 2,2Ј-bipyridine to 1,10-phen-
anthroline systems, no significant changes can be observed
in the value of the reduction potential (Table 4). An exami-
Figure 4. Cyclic voltammogram recorded for an anhydrous dmso
solution of 24 (298 K; scan rate 100 mVs–1; 0.1 m TBAPF6).
II
nation of the reduction potentials E1/2 of the complexes
An examination of the ipc/ipa and peak separation values bearing differently substituted 2,2Ј-bipyridine and 1,10-
for the reduction of the neutral species (E1/2II) clearly indi- phenanthroline ligands shows that in systems with phenyl
cates that this is a monoelectronic reversible process (ipc/ substituents on the diimine (32 and 39), the reduction pro-
II
ipa ≈ 1 and |Epc – EpaII| = 49–79 mV at 50 mVs–1 for all cess occurs at less negative potentials with respect to unsub-
complexes). According to the localization of the LUMO stituted systems (26 and 36), whereas the alkyl pendants
II
∧
mainly on the N N ligand in Pt diimine-dithiolate com- (29–31 and 40) induce the opposite effect. This suggests that
plexes (see below), and in agreement with previous studies phenyl substituents would induce stabilization in the
on different platinum(II) diimine complexes,[63,69,70] this re- LUMO of the corresponding Pt complexes, whereas alkyl
duction can be attributed to a diimine-centered process that substituents would cause destabilization.
6
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
Absorption UV/Vis/NIR Spectroscopy
sorption band is broadened or split into two bands, as has
∧
∧
Complexes 23–40 in dmso exhibit a broad band in the been observed previously for other [Pt(N N)(S S)] com-
visible region of the absorption spectra with the absorption plexes.[27]
wavelengths λmax between 549 and 608 nm and ε values in
The dependence of λmax values on the nature of the sol-
the range 3600–6700 m–1 cm–1 (Table 4 and Figure 5 for 23 vent for each compound is in agreement with the empirical
and 26). The absorption spectra of all the complexes exhibit scale proposed by Eisenberg,[28,72] as shown in Figure 6.
remarkable negative solvatochromism, as proven by re- Moreover, the analysis of the absorption spectra of com-
cording the absorption spectra in eight different solvents plexes 23–40 in each solvent shows that the λmax of the ab-
(CH2Cl2, CHCl3, CH3CN, acetone, thf, dmf, dmso, and tol- sorption in the visible region depends on the nature of the
uene, Table 5).
ligands.
For each complex, the λmax value of the absorption band
1) Complexes bearing an R-edt2– ligand (23–25 and 33–
varies by about 150 nm in the eight solvents considered, the 35) feature the solvatochromic absorption band at wave-
smallest wavelength being found in all cases in acetonitrile lengths systematically larger than those recorded for the
and the largest in toluene. The molar extinction coefficients corresponding complexes featuring an R-dmet2– ligand (26–
ε of the absorptions are also solvent-dependent (Table 5), 28 and 36–38), which suggests that the HOMO–LUMO en-
reaching about 8000 m–1 cm–1 in toluene for 23. In the ab- ergy gap is smaller for complexes featuring the former type
sorption spectra recorded in toluene, the solvatochromic ab- of 1,2-dithiolate than those featuring the latter.
Figure 5. UV/Vis/NIR absorption spectra recorded for 23 (continuous line) and 26 (dotted line) in dmso.
Table 5. Visible absorption maxima and molar extinction coefficients (in parentheses)[a] for 23–40 in different solvents.
λ [nm] (ε [m–1 cm–1])
CH2Cl2
CHCl3
CH3CN
Acetone
thf
dmf
dmso
Toluene
23 636 (6100)
24 637 (6200)
25 628 (–)
654 (4900)
667 (5500)
644 (–)
598 (5500)
601 (3900)
594 (–)
630 (6900)
629 (5100)
612 (–)
672 (7800)
675 (7100)
640 (–)
615 (6200)
615 (6300)
–
604 (6700)
603 (5900)
592 (–)
686 (7200), 743 (8000)
698 (–), 760 (–)
–
740 (–)
740 (4300)
731 (4600)
687 (–), 740 (–)
26 633 (5000)
27 635 (4800)
28 630 (4400)
29 603 (5000)
30 606 (4800)
31 607 (6200)
32 657 (5900)
33 634 (6300)
34 632 (3300)
35 620 (–)
36 631 (3600)
37 634 (4100)
38 628 (4900)
39 642 (5700)
40 571 (4500)
660 (5200)
670 (4600)
652 (4200)
623 (5300)
627 (5000)
627 (4800)
675 (5500)
653 (3600)
652 (5200)
–
656 (2400)
660 (4500)
635 (4000)
662 (5800)
586 (4300)
584 (3600)
577 (5900)
579 (3200)
565 (3600)
567 (3900)
564 (3500)
611 (3700)
598 (3800)
598 (4000)
–
589 (3100)
579 (3800)
577 (3700)
600 (4200)
543 (3700)
610 (4100)
604 (4600)
604 (3800)
585 (4700)
584 (5200)
588 (4600)
637 (4500)
632 (5400)
628 (4100)
606 (–)
619 (5000)
606 (3500)
603 (4700)
616 (4900)
563 (–)
645 (3600)
652 (4800)
651 (4600)
629 (6300)
635 (2700)
631 (5300)
682 (5500)
675 (6300)
675 (4100)
–
654 (2700)
655 (3600)
652 (5300)
672 (6200)
621 (–)
591 (4300)
586 (3000)
589 (3800)
570 (4900)
568 (4700)
570 (5200)
615 (4600)
618 (4300)
616 (5800)
–
591 (4900)
589 (3800)
591 (4600)
615 (5600)
561 (3100)
581 (4300)
582 (4500)
580 (4000)
567 (4700)
563 (4500)
564 (5000)
608 (5600)
606 (5400)
603 (3600)
596 (–)
581 (5000)
579 (4000)
581 (4600)
602 (5700)
549 (3800)
–
694 (3900), 755 (3700)
–
677 (5700), 736 (7000)
684 (6100), 732 (6800)
–
–
757 (–)
730 (4400)
–
–
[a] If not reported, the molar extinction coefficients were not determined for solubility reasons.
Eur. J. Inorg. Chem. 0000, 0–0
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M. Arca et al.
FULL PAPER
Figure 6. Correlation between Eisenberg empirical parameters
(ref.[28,72]) and experimentally measured λmax visible absorption
maxima recorded for 23 in eight solvents.
2) The effect of the nature of the diimine can be deduced
by examining the absorption spectra of the complexes be-
longing to Series 3, featuring the same Me-dmet2– dithiolate
and different diimines (26, 29–32, 36, 39, and 40). Although
no significant variation in the position of the solvato-
III
II
Figure 7. Correlation between E1/2 (top) and E1/2 (bottom) po-
tentials (Table 4) and the wavelengths λmax of the visible absorption
maxima determined for complexes belonging to Series 1 (top) and
∧
Series 3 (bottom), respectively. Top graph: S S = R-edt2– (᭿), R-
∧
dmet2– (ᮀ); bottom graph: N N = unsubstituted (᭛) 2,2Ј-bipyr-
idine (blue) or 1,10-phenanthroline (red) and alkyl (᭺)/aryl (Δ) de-
∧
chromic absorption band occurs on passing from N N =
rivatives.
2,2Ј-bipyridine to 1,10-phenanthroline in complexes 26 and
36, respectively, the introduction of alkyl substituents onto
the diimine ligand causes the absorption band to shift to
higher energies, while phenyl groups induce the opposite
effect, which suggests a lowering of the HOMO–LUMO en-
ergy gap.
II
duction potentials E1/2 to more negative values in com-
plexes 32 and 39 in comparison with the unsubstituted sys-
tems 26 and 36. The presence of alkyl substituents results
in the opposite effect. This suggests that phenyl substituents
on the diimine lower the energy of the LUMO and thus
the HOMO–LUMO energy gap with respect to complexes
bearing the corresponding unsubstituted nitrogen ligands,
whereas alkyl groups cause an opposite effect.
To confirm the dependence of the solvatochromic ab-
sorption band energy and the CV potentials on the HOMO
and LUMO energies, the spectroscopic and electrochemical
data can be successfully cross-compared:
∧
1) As regards the members of Series 1 (N N = bipy) and
2
∧
Series 2 (N N = phen), a linear correlation [R = 0.93, Fig-
Emission Spectroscopy
ure 7, top, for Series 1; R2 = 0.87 for Series 2 (not shown)]
III
∧ ∧
Excitation of [Pt(N N)(S S)] complexes in the range
holds between λmax and the oxidation potentials E1/2
(Table 4). Complexes bearing an R-dmet2– ligand (26–28 350–500 nm reportedly results in a complex emission profile
and 36–38) feature oxidation potentials at more positive po- in the visible region, with emission maxima in the range
tentials and λmax at lower wavelengths than complexes fea- 500–800 nm.[27,28] Fluorescence measurements were carried
turing an R-edt2– ligand (23–25 and 33–35). Thus, the intro- out at room temperature in dmso (c = 3ϫ10–7–3ϫ10–5 m)
duction of an R-dmet2– ligand in place of an R-edt2– dithiol- on all complexes except 25 and 35. Emission spectra were
ate induces a lowering in the energy of the HOMO and recorded at excitation wavelengths λexc corresponding to the
increases the HOMO–LUMO energy gap. Concerning the absorption maxima observed by absorption spectroscopy
∧
[Pt(N N)(R-edt)] complexes (23–25 and 33–35), it is inter- (see above), but only emissive processes in the UV/Vis re-
esting to observe that according to the spectroscopic and gion (350–450 nm; quantum yields Φ between 6ϫ10–3 and
CV data, the 1-pyrenyl substituent at the ethylene-1,2-di- 3ϫ10–2, Table 4) were observed upon UV excitation (λexc
thiolate slightly lowers the energy of the HOMO with re- = 260–350 nm). The absorption and fluorescence spectra
spect to those of the corresponding phenyl- and 2-naphthyl- recorded for 23 are compared in Figure 8.
substituted systems.
A dependence of the fluorescence intensity If on the con-
2–
∧
2) Within Series 3 (S S = Me-dmet ), a linear corre- centration c of the solutions was observed, the value of If
lation (R2 = 0.91; Figure 7, bottom) can also be found be- decreasing when cϾ 1ϫ10–6 m (see Figure S8 in the Sup-
II
tween the λmax values and the reduction potentials E1/2
porting Information for 23), possibly due to self-quenching
(Table 4). In particular, considering the complexes bearing processes similar to those previously observed for different
[73]
∧
∧
differently substituted 2,2Ј-bipyridine or 1,10-phenan- [Pt(N N)(S S)] complexes.
throline ligands, the introduction of phenyl substituents
The emission spectra show approximately the same pro-
onto the diimine induces a lowering in the energy of the file for all complexes, with two emission maxima at about
solvatochromic absorption band and a shift of the re- 370 and 390 nm, respectively, which suggests that the pro-
8
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
Figure 8. Superimposed normalized UV/Vis (260–520 nm) absorption (solid line) and emission (dotted line; λexc = 327 nm) spectra re-
corded for 23 in dmso.
cesses leading to the emission should have the same origin these systems (see the Supporting Information). The calcu-
for all the compounds.[74] Interestingly, the emission energy lated data providing the best agreement with experimental
is not affected by the nature of the ligand and only the data were obtained by adopting the hybrid PBE0
fluorescence intensity varies upon changing both the di- (PBE1PBE) functional of Adamo and Barone,[76] and the
imine and the 1,2-dithiolate. In fact, an examination of the CRENBL BS with RECPs for Pt.[77] Moreover, given the
fluorescence quantum yields Φ shows that for complexes solvent-dependence of some of the features of these com-
33, 34, and 36–38 (Series 2) featuring a 1,10-phenanthroline plexes (see above), implicit solvation calculations were also
ligand, the Φ values are systematically larger than those carried out at the same level of theory by using the integral
found in the corresponding complexes bearing a 2,2Ј-bipyr- equation formalism of the polarizable continuous model
idine (23, 24, and 26–28, Series 1). In addition, a correlation (IEF-PCM) within the self-consistent reaction field (SCRF)
(R2 = 0.85) is observed between the values of Φ determined approach.[78]
for complexes belonging to Series 1 (23, 24, and 26–28) and
those belonging to Series 2 (33, 34, and 36–38) featuring the
same S S ligands.
A comparison of selected optimized bond lengths and
angles (see Table S6 in the Supporting Information) for 23–
40 shows that the structural parameters calculated in
CH2Cl2 solution are slightly different (usually by less than
0.02 Å and 1° for distances and angles, respectively) to
those optimized in the gas phase. The gas-phase optimized
∧
Theoretical Calculations
The availability of a complete set of structural, spectro- parameters are in very good agreement with the corre-
scopic, and electrochemical data for the 18 completely new sponding structural data determined by single-crystal X-ray
∧
∧
[Pt(N N)(S S)] complexes synthesized and characterized in diffraction for 27–29, 31, and 37, only the Pt–S distances
this work represented a challenging opportunity to investi- being slightly overestimated (by less than 0.08 Å). As found
gate in depth the electronic features of this class of com- experimentally, the optimized geometries show the metal
pounds by DFT. To determine an appropriate computa- coordinated in a square-planar fashion, with the complexes
tional setup, preliminary calculations were performed on 26 completely planar but for the substituents. For complexes
by using different functionals (both pure and hybrid) and featuring R-edt2– ligands (23–25 and 33–35), the torsion
various basis sets (BSs) for the Pt atom, all featuring relativ- angles of the aromatic substituents range between 28 and
istic effective core potentials (RECPs) to account for rela- 57° depending on the nature of the aryl group {in agree-
tivistic effects (see the Supporting Information). The all- ment with what has been found previously for bis(1,2-dithi-
electron double-ζ BSs with polarization functions from olene) complexes [Au(R-edt)2]x– (x = 0–2)}[49,50] and are re-
Schäfer, Horn, and Ahlrichs[75] were exploited for light duced by about 2° in CH2Cl2. The optimized distances are
atom species (C, H, N, and S). A comparison between the strictly dependent upon the nature of the ligands. In fact,
optimized geometries obtained with different combinations as far as the complexes of Series 1 are concerned, a depen-
of functionals and BSs for the Pt atom and the crystal dence of the bond lengths at the metal center on the nature
structure of complex 27, and between the simulated (see of the 1,2-dithiolate can be observed: complexes featuring
below) and experimental electronic spectra of 26, allowed an R-edt2– ligand show Pt–S and Pt–N bond lengths sys-
identification of a suitable computational methodology for tematically longer and shorter, respectively, than those con-
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M. Arca et al.
FULL PAPER
taining R-dmet2– 1,2-dithiolates. An analogous effect is Pt–S distances being the most affected (by only 0.01 Å) and
shown on comparing the same distances in complexes be- showing the largest values in dmso and dmf.
∧
∧
longing to Series 1 (N N = bipy) and Series 2 (N N =
The descriptions of the ground-state (GS) bonding
phen), both in the gas phase and in CH2Cl2, in agreement schemes for 23–40 based on the DFT calculations are in
with experimental observations for 27 and 37. In addition, agreement with the results of previous calculations carried
[39]
∧
∧
an examination of the bond lengths optimized for the com- out on different [Pt(N N)(S S)] complexes.
plexes belonging to Series 3 (26, 29–32, 36, 39, and 40)
The frontier Kohn–Sham (KS) MO scheme calculated
clearly shows that aryl substituents induce a shortening of for 26 in the gas phase is depicted in Figure 9 and the con-
the Pt–N distances with respect to the corresponding un- tributions from the central platinum atom and the two li-
substituted systems, whereas alkyl substituents exert an op- gands to the composition of each MO are summarized in
posite effect.
Figure 10. The HOMO (MO 99) is π in nature and is pre-
To gain a deeper insight into the dependence of the prop- dominantly localized on the 1,2-dithiolate with only a
erties of the complexes on the nature of the solvent, sol- minor participation of the Pt 5d atomic orbital (AO; 3%).
vation DFT calculations were performed on 26, simulating The LUMO (MO 100) is almost exclusively localized on
the seven other solvents used for absorption spectrophoto- the diimine with a contribution of the metal similar to that
metric measurements. As summarized in Table 6 (see also calculated for the HOMO (6%). No significant differences
Table S6 in the Supporting Information), the optimized pa- can be found in the compositions of the frontier MOs of
rameters vary only slightly upon changing the solvent, the complexes 23–40, only the HOMOs showing slight changes
Table 6. Selected optimized bond lengths [Å] and angles [°] for 26 in the gas phase and in different solvents.[a,b]
Gas
CH2Cl2
CHCl3
CH3CN
Acetone
thf
dmf
dmso
Toluene
Pt–S1
Pt–S2
Pt–N1
Pt–N2
S1–C1
S2–C2
C1–C2
S1–Pt–S2
N1–Pt–N2
N1–Pt–S1–C1
2.284
2.280
2.041
2.039
1.738
1.731
1.363
90.13
79.58
180.00
2.299
2.298
2.051
2.049
1.744
1.740
1.361
90.38
79.56
180.00
2.297
2.296
2.050
2.048
1.744
1.739
1.360
90.38
79.56
180.00
2.301
2.300
2.052
2.050
1.744
1.740
1.361
90.38
79.57
180.00
2.301
2.300
2.052
2.050
1.744
1.740
1.361
90.37
79.58
180.00
2.299
2.298
2.051
2.049
1.744
1.739
1.361
90.38
79.57
180.00
2.301
2.300
2.052
2.050
1.745
1.740
1.361
90.38
79.57
180.00
2.302
2.301
2.052
2.049
1.745
1.740
1.361
90.39
79.59
180.00
2.292
2.292
2.048
2.045
1.742
1.737
1.360
90.31
79.55
180.00
[a] IEF-PCM SCRF model. [b] Atom labeling scheme as in Figure 1.
Figure 9. Kohn–Sham molecular orbital scheme and isosurface drawings calculated for 26 in the gas phase (Cs point group). Contour
value: 0.05 e.
10
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
in composition in terms of the metal, diimine, and 1,2-di- 2.36, 2.32, 2.19, 2.36, 2.37, and 1.83 eV in CH2Cl2, CHCl3,
thiolate fragments, mostly depending on the nature of the CH3CN, acetone, thf, dmf, dmso, and toluene, respectively,
∧
S S ligand (see Table S7 in the Supporting Information). for 26).
Calculations carried out in CH2Cl2 for all complexes and
Further insight into the electronic features of the com-
in the presence of the reaction field of each solvent for 26 plexes derives from a charge distribution analysis carried
show that both the composition and the KS eigenvalues of out by examining Mulliken[82,83] and natural charges deriv-
the frontier MOs are scarcely affected by the nature of the ing from a NBO analysis[84] performed both in the gas
solvent (see Tables S8 and S9 in the Supporting Infor- phase and in CH2Cl2 (Tables S13–S15 in the Supporting In-
mation).
formation). In the gas phase, all complexes are calculated
to have a large charge separation between the two ligands
of about 0.6–1.0e. In fact, the 1,2-dithiolates show negative
∧
charges for all complexes (|QS S| = 0.500–0.624e and 0.350–
0.486e at the Mulliken and NBO levels, respectively),
whereas the diimines bear positive charges of about 0.1–
∧
0.4e (|QN N| = 0.124–0.237e and 0.267–0.375e at the Mul-
liken and NBO levels, respectively), the remaining positive
charge being carried by the metal.[85] For calculations per-
formed by the SCRF approach (solvent: CH2Cl2), a further
increase of about 0.4e in the charge separation between the
ligands (see Tables S12 and S15 in the Supporting Infor-
mation) was calculated. As expected, the charge separation
also shows a solvent-dependence, as testified by calculations
on 26 in the solvents mentioned above (see Table S13 in the
Supporting Information).
Time-dependent DFT (TD-DFT) calculations were car-
ried out on complexes 23–40 in their GS optimized geome-
tries both in the gas phase and in CH2Cl2 (Table 7 for 26)
at the same level of theory as discussed above. As expected
on the basis of the solvatochromism previously described,
a comparison between experimental spectra and those sim-
ulated from vertical excitation energies and oscillator
strengths confirms that solvation is essential to simulate re-
Figure 10. Frontier Kohn–Sham molecular orbital (90–105; KS-
HOMO = 99, KS-LUMO = 100) composition calculated for 26 in
∧
the gas phase [fragments: platinum atom (light gray); S S ligand
(dark gray); N N ligand (medium gray)].
∧
Although Koopman’s theorem does not apply to DFT, liably the experimental spectral features.[86] Notably, a care-
the energy difference ΔEKSH–KSL between KS-HOMO and ful choice of the computational setup along with the IEF-
KS-LUMO can be considered as a valuable parameter,[79–81] PCM approach resulted in a very good agreement between
and ΔEKSH–KSL values in the range 1.47–1.89 eV (see simulated and experimental spectra, in particular in com-
Table S10 in the Supporting Information) reflect the experi- parison with the results reported previously for similar sys-
mental electrochemical and spectroscopic trends discussed tems.[26] For all the complexes, the S0ǞS1 vertical transi-
above. In fact, among the complexes featuring R-edt2– li- tion responsible for the solvatochromic absorption band ev-
gands, 25 and 35 (R = Pyr) show the largest ΔEKSH–KSL idenced experimentally in the visible region should be at-
values (1.88 and 1.89 eV, respectively), induced by KS- tributed to an almost pure (99% for 26, Table 7) one-elec-
HOMO stabilization with respect to their phenyl- and tron excitation involving the frontier molecular orbitals
naphthyl-substituted analogues, in agreement with CV mea- (KS-MOs 99 and 100 for 26, Table 7). Since the contri-
surements. Within Series 3, complexes 32 and 39 (featuring bution of metal 5d AOs to both KS-MOs is very small and
phenyl-substituted diimines) show the smallest ΔEKSH–KSL of the same magnitude (see above), this transition should
values (1.47 and 1.50 eV, respectively) with respect to the be best considered as an interligand charge-transfer (ILCT)
∧
corresponding complexes featuring unsubstituted N N li- process from the negatively charged 1,2-dithiolate to the di-
gands because of the stabilization of the KS-LUMO and, imine with a positive partial charge rather than a mixed-
accordingly, the experimental reduction potentials are less metal/ligand-to-ligand CT process (MMLLЈCT), as pre-
negative. Opposite considerations can be drawn for com- viously
proposed.[38,39]
As
a
consequence, the
plexes with alkyl-substituted diimines, also in this case in HOMOǞLUMO transition results in a lowering of the
agreement with electrochemical measurements. In CH2Cl2, charge separation in the first excited state compared with
the values of ΔEKSH–KSL (in the range 2.12–2.44 eV) were the GS, in agreement with the negative solvatochromism
calculated to be systematically higher by about 0.8 eV than observed experimentally.[87]
∧
the values calculated in the gas phase (see Table S10). As is
For complexes featuring the same class of S S ligands,
predicted, a dependence of ΔEKSH–KSL on the nature of the good agreement can be found between the experimental
solvent field applied can also be found, ΔEKSH–KSL being and calculated trends of the absorption wavelengths
larger in relatively polar solvents (ΔEKSH–KSL = 2.22, 2.08, (Table 5 and Table S16 in the Supporting Information). For
Eur. J. Inorg. Chem. 0000, 0–0
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M. Arca et al.
FULL PAPER
Table 7. Main electronic transitions (fϾ 0.015) calculated for 26 in CH2Cl2 at the IEF-PCM SCRF TD-DFT level. For each transition,
the excitation energy E, the absorption wavelength λ, the oscillator strength f, and the MO composition of the excited-state functions
along with the fragments in which the KS-MOs involved are mainly localised are reported.
Exc. state
E [eV]
λ [nm]
f
Composition[a]
%
Molecular fragments
∧
∧
S1
S5
1.675
2.765
740.0
448.4
0.144
0.015
99Ǟ100
97Ǟ100
99Ǟ102
96Ǟ100
99Ǟ104
97Ǟ102
96Ǟ101
96Ǟ101
94Ǟ100
96Ǟ102
93Ǟ100
94Ǟ100
93Ǟ100
94Ǟ100
96Ǟ102
93 Ǟ100
98Ǟ103
92Ǟ100
99
12
86
96
95
91
5
91
36
58
57
13
18
37
24
15
76
80
S S(90%)ǞN N(92%)
∧
∧
S S(67%) + Pt(30%) ǞN N(92%)
∧
∧
S S(90%)ǞN N(98%)
∧ ∧
S8
S10
S14
3.205
3.664
4.012
386.8
338.8
309.0
0.046
0.227
0.065
S S(80%)ǞN N(92%)
∧
∧
S S(90%)ǞS S(99%)
∧
∧
S S(67%) + Pt(30%)ǞN N(98%)
∧
∧
S S(80%)ǞN N(89%)
∧ ∧
S17
S20
4.212
4.302
294.4
288.2
0.023
0.055
S S(80%)ǞN N(89%)
∧
∧
∧
N N(92%)ǞN N(92%)
∧
S S(80%)ǞN N(98%)
∧
∧
S23
S24
4.465
4.479
277.6
276.8
0.186
0.265
Pt(50%) + S S(37%)ǞN N(92%)
∧
∧
N N(92%)ǞN N(92%)
∧
∧
Pt(50%) + S S(37%)ǞN N(92%)
∧
∧
∧
N N(92%)ǞN N(92%)
∧
S S(80%)ǞN N(98%)
∧
∧
S26
S27
4.532
4.547
273.6
272.7
0.213
0.142
Pt(50%) + S S(37%)ǞN N(92%)
∧
∧
N N(99%)ǞS S(39%) + Pt(42%)
∧
∧
S S(47%) + Pt(34%)ǞN N(92%)
[a] MOs are labeled in accord with Figure 9.
example, as regards complexes featuring S S = R-edt2– (23– trast, λmax assumes smaller values for complexes bearing
25 and 33–35), the pyrenyl-substituted compounds feature alkyl-substituted diimines (29–31 and 40).
∧
the S0ǞS1 transition at shorter wavelengths than com-
plexes with Ar = Ph and Naph, in agreement with the high- vents (calculated λmax = 740, 798, 689, 702, 753, 690, 686,
est-calculated ΔEKSH–KSL energy gaps (see Table S10). and 908 nm, in CH2Cl2, CHCl3, CH3CN, acetone, thf, dmf,
Moreover, calculations performed on 26 in different sol-
A linear correlation holds between the experimental and dmso, and toluene, respectively) show, as anticipated, a de-
calculated trends of the absorption wavelengths of the com- pendence of the λmax value of this absorption on the nature
2–
∧
plexes featuring S S = Me-dmet (Series 3, Figure 11). In of the solvent, according to the different values of the calcu-
particular, complexes 32 and 39 bearing phenyl-substituted lated HOMO–LUMO energy gaps discussed above and in
2,2Ј-bipyridine and 1,10-phenanthroline ligands show both perfect agreement (R2 = 0.98) with the solvatochromism ob-
the experimental and calculated absorptions at longer wave- served experimentally (Figure 12).
lengths than the unsubstituted systems (26 and 36, respec-
Concerning the experimental electronic absorptions of all
tively) due to their smaller HOMO–LUMO energy gaps the complexes in the region 300–400 nm (Figure 5 for 23
(Table S10 in the Supporting Information), whereas, in con- and 26) and calculated at the TD-DFT level in the same
Figure 11. Correlation between IEF-PCM TD-DFT calculated and experimental λmax values in CH2Cl2 of the solvatochromic visible
∧
∧
absorption band for complexes belonging to Series 3. S S = Me-dmet2–; N N = unsubstituted (᭛) 2,2Ј-bipyridine (blue) or 1,10-phen-
anthroline (red) and alkyl (᭺) or phenyl (Δ) derivatives.
12
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
Figure 12. Correlation between IEF-PCM TD-DFT calculated and experimental λmax values of the solvatochromic visible absorption
band for 26 in different solvents.
spectral region (see Figure S9 in the Supporting Infor- mation). Therefore the emissive processes that occur when
mation for 26), the corresponding transitions can be attrib- the complexes are excited in this wavelength range (see
uted to monoelectronic excitations occurring between KS- above) should be regarded exclusively as excitations involv-
∧
MOs mainly localized on the 1,2-dithiolates. In particular, ing MOs localized on the N N ligand given the very similar
for 26, the most intense electronic transition calculated in emission profiles observed for all 23–40 complexes, which
∧
this spectral region is S0ǞS10 (f = 0.227, Table 7), which do not seem to be affected by the nature of the S S ligand.
mainly results from a one-electron excitation between KS-
Finally, the lack of inversion center in the title complexes
MOs 99 and 104 (HOMOǞLUMO+4 excitation), both of suggests a possible application as second-order nonlinear
which are mainly localized on the S S ligand (90 and 99%, optical (SONLO) materials.[17,19,88] In this context,
∧
respectively). prompted by the results obtained by TD-DFT, static dipole
The absorptions in the UV region in the range 250– moments μ and static first (quadratic) hyperpolarizabilities
300 nm have been assigned to electronic transitions involv- βtot were calculated for 23–40 both in the gas phase and in
ing MOs mainly localized on the diimine (S1ǞS23/24/26/ CH2Cl2 (Table 8). To have an absolute reference to evaluate
27 for 26, Table 7 and Figure S9 in the Supporting Infor- the order of magnitude of the values of βtot, the same calcu-
Table 8. Static first hyperpolarizabilities βtot and static dipole moments μ calculated for 23–41 in the gas phase and in CH2Cl2.
[a]
Gas phase
CH2Cl2
βtot [104 a.u.]
βtot [10–30 esu]
|μ| [D]
βtot [104 a.u.]
βtot [10–30 esu]
|μ| [D]
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
2.01
1.71
1.76
4.16
4.25
4.29
4.30
4.65
5.31
7.68
2.40
2.06
2.13
4.89
4.94
4.95
7.68
5.34
2.33
174
147
152
360
367
370
371
402
459
664
208
178
184
423
427
428
664
461
201
2.85
4.98
2.29
7.46
7.41
7.98
8.01
9.25
6.98
7.85
4.77
5.16
2.62
5.67
7.59
8.15
6.65
6.57
1.80
3.46
3.45
3.09
4.68
4.74
4.61
3.88
3.82
3.94
8.00
3.74
3.73
3.36
4.83
4.79
4.68
6.99
3.38
3.42
299
298
267
404
409
398
335
330
340
691
323
322
290
418
414
404
604
292
296
4.43
7.63
3.07
11.31
11.22
4.93
11.79
13.51
9.95
11.58
7.37
7.77
3.50
8.59
11.32
12.34
9.62
9.29
3.10
[a] IEF-PCM SCRF model.
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M. Arca et al.
FULL PAPER
lations were also performed at the same level of theory on atomic orbitals of the central metal ion. Interestingly, struc-
[Pt(phen)(tdt)] (41, tdt2– = 3,4-toluenedithiolate), a diimine- tural modifications on both the diimine and 1,2-dithiolate
dithiolate Pt complex showing a very large hyperpolariz- ligands result in the modulation of the eigenvalues of the
ability among those investigated experimentally by two MOs, enabling their electrochemical and spectroscopic
EFISH measurements (λmax = 583 nm, βμ = –28ϫ10–30 esu properties to be fine-tuned separately:
with
ω
=
1.569ϫ1011 GHz; zero-frequency β0
=
1) Planar R-dmet2– 1,2-dithiolates show a larger delocal-
ization than R-edt2– ligands, as reflected in the more nega-
–16ϫ10–30 esu).[18]
As expected, on taking into account solvation, a dra- tive eigenvalues of the HOMOs of the complexes based on
∧
matic increase in βtot was calculated for most complexes the former class of ligands. Not surprisingly, [Pt(N N)(R-
(βtot = 147–664 and 267–691ϫ10–30 esu in the gas phase dmet)] complexes show larger oxidation potentials than
∧
and in CH2Cl2, respectively). Complexes featuring R- [Pt(N N)(R-edt)] complexes. Aromatic
R substituents
dmet2– ligands show larger hyperpolarizabilities compared cause a further stabilization of the HOMOs of the
with those containing the R-edt2– ligands (Table 8). In com- [Pt(N N)(R-dmet)] complexes, whereas in the cases of
∧
∧
plexes featuring the same class of 1,2-dithiolates, no signifi- [Pt(N N)(R-edt)] compounds, HOMO stabilization results
cant changes could be observed in the values of βtot upon from the increase in the size of the aryl pendant.
∧
changing the substituent on the 1,2-dithiolate core. How-
2) As far as the N N ligands are concerned, although
ever, larger effects on the βtot values were calculated when the extension of the π-electron system on passing from 2,2Ј-
∧
the N N ligand was varied. In particular, complexes featur- bipyridine to 1,10-phenanthroline scarcely affects the
∧
ing substituted and unsubstituted 1,10-phenanthroline LUMO eigenvalues, within each class of N N ligand, the
show static hyperpolarizabilities systematically larger than introduction of phenyl substituents stabilizes the LUMO,
those calculated for the corresponding complexes with whereas alkyl groups have an opposite effect. Thus, re-
∧
N N = 2,2Ј-bipyridine and substituted derivatives. More- duction potentials reversibly leading to the monoanionic
over, the introduction of substituents into the diimine li- form are determined almost exclusively by the nature of the
∧
gands results in an increase in βtot values relative to those substituents on the N N ligands.
calculated for complexes with unsubstituted diimines. In
Because the solvatochromic visible absorption band
particular, complexes 32 and 39 feature the largest calcu- arises from a HOMO–LUMO vertical electronic transition,
lated βtot values, which suggests that the introduction of as clearly indicated by TD-DFT calculations, the balance
∧
aryl substituents into the N N ligands is a key feature in of the structural modifications on the two ligands deter-
the design of potential NLO chromophores based on di- mines on the one hand the energy of the transition and on
imine-dithiolate platinum complexes. In this context it is the other the change in the polarity that occurs on passing
worth noting that the values of βtot calculated for 23–40 are from the ground state to the first accessible excited state,
generally significantly larger than those computed for 41 thus directly affecting the energy of the transition and its
(by up to 450ϫ10–30 esu, Table 8), which further suggests solvatochromism, respectively.
the title complexes represent extremely promising candi-
dates for applications in the field of SONLO.
Among the complexes synthesized and reported in this
work, those featuring phenyl-substituted diimines coupled
to R-dmet2– 1,2-dithiolates show the most promising sec-
ond-order nonlinear optical (SONLO) properties. Very
interestingly, large nonlinearities have been calculated for
complexes 32 and 39 in comparison to the most active di-
imine-dithiolate Pt complexes reported so far as SONLO
Conclusions
∧
∧
The first examples of complexes [Pt(N N)(S S)] deriving materials, such as 41.
from variously substituted 2,2Ј-bipyridine and 1,10-phen- Finally, the incorporation of the title complexes into a
2–
anthroline N N diimines and R-edt and R-dmet2– S S multiplicity of macroscopic structures of technological im-
1,2-dithiolates have been synthesized. In total, 18 diimine- portance for applications as varied as optical processing,
dithiolate platinum complexes have been prepared and switching, and second harmonic generation (SHG) is con-
characterized by spectroscopic and electrochemical meth- ceivable due to their high chemical and thermal stability
ods. The experimental data, supported by a comparative compatible with the fabrication processes.
theoretical DFT investigation and the structural characteri-
∧
∧
zation of five compounds by X-ray diffraction, allowed rela-
tionships between the structural features of the complexes
and their electrochemical and linear and nonlinear optical
properties to be determined. In fact, both the ability of the
Experimental Section
Chemicals: 2,2Ј-Bipyridine, 1,10-phenanthroline, and derivatives
(Scheme 1 and Table 1) were obtained from commercial sources,
and when necessary they were purified according to standard tech-
niques.
platinum diimine-dithiolate complexes to reversibly access
differently charged states and the peculiar solvatochromism
in the visible region are determined by the composition of
the HOMO and LUMO frontier molecular orbitals local-
∧
∧
Synthesis of Complexes: Platinum dichlorodiimine complexes[61,62]
ized on the S S and N N ligands, respectively, with mar-
∧
∧
ginal (1–7% in the gas phase) contributions from the 5d (diimine N N: 1–8; [Pt(N N)Cl2]: 9–16, Scheme 1 and Table 1)
14 Eur. J. Inorg. Chem. 0000, 0–0
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
∧
and the precursors of the S S 1,2-dithiolate ligands [arene-1,3-di-
DFT Calculations: Theoretical calculations were performed with
the Gaussian 03 (Rev. D.01) and 09 (Rev. A.02)[96] suite of pro-
grams at the density functional theory (DFT)[43] level. A prelimi-
nary investigation was carried out on 26 by systematically testing
different density functionals (PW91PW91,[97,98] PBEPBE,[99,100]
thiol-2-ones, arene: Ph (17), Naph (18), and Pyr (19), and N-meth-
yl- (20), ethyl- (21), and phenyl (22)-substituted 4,5-bis(2-cyano-
ethylthio)-2-thioxothiazoline] were prepared according to pub-
lished procedures.[49,58,60] Platinum diimine-dithiolate complexes
[Pt(N N)(S S)] (23–40; Table 2) were synthesized according to the
following general procedure: an eight-fold excess of NaOEt in ethyl
alcohol was added dropwise under nitrogen to a solution of the
desired 1,2-dithiolate precursor in the same solvent. An equimolar
∧
∧
wPBEhPBE,[101]
PBEhPBE,[102]
B3LYP,[103]
PBE1PBE,[76]
PBEh1PBE,[102] mPW1PW,[104] long-range corrected[105] LC-
PBEhPBE/LC-PBEPBE and LC-PW91PW91) and ECP-equipped
basis sets (CRENBL,[77] LanL2DZ,[106] LanL2TZ,[107] SBKJC
VDZ,[108] and Stuttgart RSC 1997[109]) for the central metal ion
(details and Tables S1–S4 are available in the Supporting Infor-
mation). Eventually, all calculations were performed by adopting
the PBE0 (PBE1PBE) hybrid functional,[76] Schäfer, Horn, and
Ahlrichs double-ζ plus polarization all-electron basis sets (BSs) for
C, H, N, and S,[75] and CRENBL BS[77] with relativistic effective
core potentials (RECPs)[110,111] for the heavier Pt species.[112] Ge-
ometry optimizations were performed starting from structural data
when available. Tight SCF convergence criteria (SCF = tight key-
word) and fine numerical integration grids [Integral(FineGrid) key-
word] were used and the nature of the minima of each optimized
structure was verified by harmonic frequency calculations (freq =
raman keyword). Natural[84] and Mulliken[82] atomic charge distri-
butions were calculated at the optimized geometries at the same
level of theory and electronic transition energies and oscillator
strengths were calculated at the TD-DFT level (200 states). The
electronic spectra were simulated by a convolution of Gaussian
functions centered at the calculated excitation energies. To deter-
mine the influence of the solvent on the properties of the com-
plexes, calculations were also carried out in the presence of a set
of different solvents (CH2Cl2, CHCl3, CH3CN, acetone, thf, dmf,
dmso, and toluene), implicitly taken into account by means of the
polarizable continuum model (PCM) approach in its integral equa-
tion formalism variant (IEF-PCM), which describes the cavity of
the solute within the reaction field (SCRF) through a set of over-
lapping spheres.[78] The total static (i.e., under zero frequency)[113]
second-order (quadratic) hyperpolarizability (the first hyperpolar-
izability)[114] βtot was calculated as described by Mendes et al.[88]
from Equation (1) in which each static component βi (i = x, y, z) is
obtained from Equation (2).
∧
suspension of the appropriate [Pt(N N)Cl2] complex in thf was
then added and the reaction mixture was stirred for 7 d. The dark
precipitate was collected by filtration and washed with ethyl alcohol
and water. Yields varied between 24 and 90%, and elemental analy-
ses corresponded to the expected values in all cases except for 25
and 35, which were not isolated as pure solids, although spectro-
scopic and electrochemical data could be collected. Details on the
synthesis and characterization of all the complexes are available in
the Supporting Information. X-ray quality crystals were obtained
by slow diffusion of diethyl ether (in the case of 27, 29, and 37),
petroleum ether (for 31), or n-hexane (for 28) into a thf (for 27),
acetone (for 28), or CH2Cl2 (for 29, 31, and 37) solution of the
complex.
Characterization: Elemental analyses were performed with an
EA1108 CHNS-O Fisons instrument (T = 1000 °C). IR spectra
were recorded with a Thermo-Nicolet 5700 spectrometer at room
temperature: KBr pellets with a KBr beam-splitter and KBr win-
dows (4000–400 cm–1, resolution 4 cm–1) were used. 1H NMR mea-
surements were recorded with a Varian INOVA 400 MHz spec-
trometer at 298 K and referenced to Si(CH3)4. Absorption spectra
were recorded at 298 K in a quartz cell of 10.00 mm optical path
with a Thermo Evolution 300 (190–1100 nm) spectrophotometer.
Uncorrected emission spectra were collected at 298 K with a Varian
Cary Eclipse spectrophotometer equipped with a xenon lamp.
Quantum yields were determined relative to anthracene in ethyl
alcohol (c = 1–5ϫ10–6 m, λexc = 334–359 nm) by calculating the
integrated emission intensity of both the sample and the reference
through a decomposition of the spectra in their constituent
Gaussian curves. Spectral decomposition was carried out by using
the software Fytik.[89] Cyclic voltammetry measurements (scan rate
25–1000 mVs–1) were performed at room temperature in anhydrous
dmso in a Metrohm voltammetric cell, with a combined platinum
working and counter-electrode and a standard Ag/AgCl reference
electrode with a Metrohm Autolab PGSTAT 10 potentiostat (sup-
porting electrolyte 0.10 m TBAPF6). Reported data are referred to
the reversible Fc+/Fc couple.
(1)
(2)
X-ray Crystallography: Single-crystal X-ray diffraction data were
collected with a Rigaku MM007/Mercury diffractometer with Mo-
Kα radiation at 93(2) K for 27·1/2thf, and with the St Andrews
Robotic diffractometer at 125(2) K for 28 and 37.[90] The structures
were solved by direct methods with SHELXS-97[91] and refined on
F2 by using SHELXL-97.[91] X-ray structure determinations for 29
and 31 were carried out at 150(2) K with a Bruker-AXS dif-
fractometer (Centre de diffractométrie X, Université de Rennes 1).
The structures were solved by direct methods by using the SIR97
program,[92] and then refined by the full-matrix least-squares
method based on F2 (SHELXL-97) with the aid of the WINGX
program.[93] All the structures were validated by using the Check-
CIF[94] and enCIFer programs.[95]
By using Kleinman symmetry relationships,[115] the final Equa-
tion (3) was obtained.
(3)
The programs Gabedit 2.1.0[116] and Molden 4.9[117] were used to
investigate the charge distributions and molecular orbital shapes.
The software GaussSum 2.1[118] was used to calculate the molecular
orbital contributions (MOC) from groups of atoms along with the
contribution of singly excited configurations to each electronic
transition and to generate all the necessary data to simulate absorp-
tion spectra.
CCDC-876442 (for 27·1/2thf), -876443 (for 28), -876444 (for 29),
-876445 (for 31), and -876446 (for 37) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Details for the synthesis and characterization of 23–40, com-
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Arca et al.
FULL PAPER
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PtII Diimine-Dithiolate Nonlinear Optical Chromophores
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Received: April 5, 2012
Published Online: ᭿
18
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Job/Unit: I20346
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Date: 29-06-12 09:37:32
Pages: 19
PtII Diimine-Dithiolate Nonlinear Optical Chromophores
Nonlinear Optical Chromophores
∧
∧
∧
Eighteen [Pt(N N)(S S)] complexes (N N
A. Pintus, M. C. Aragoni, N. Bellec,
F. A. Devillanova, D. Lorcy, F. Isaia,
V. Lippolis, R. A. M. Randall, T. Roisnel,
A. M. Z. Slawin, J. D. Woollins,
∧
= diimine; S S = arylethylene-1,2-dithiol-
ate, N-substituted 2-thioxothiazoline-4,5-
dithiolate) have been prepared. All com-
plexes feature a notable negative solvato-
chromism and potential SONLO properties
on the basis of their GS electronic struc-
tures.
M. Arca* ........................................ 1–19
Structure–Property Relationships in PtII
Diimine-Dithiolate Nonlinear Optical
Chromophores Based on Arylethylene-1,2-
dithiolate and 2-Thioxothiazoline-4,5-di-
thiolate
Keywords: Solvatochromism / Platinum /
Nonlinear optics / Density functional cal-
culations / N ligands / S ligands
Eur. J. Inorg. Chem. 0000, 0–0
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