A family of the C,N-cyclometalated species [Pt(ppy)Cl(PPh3)], [Pt(ppy)Cl(CNCy)],
[Pt(ppy)(CNCy)(PPh3)](OTf),
and [Pt(ppy)(CNCy)2](BF4) (ppy = 2-phenylpyridinato-C
2,N; Cy = cyclohexyl) was generated
from [Pt(ppy)(μ-Cl)]2, CNCy, and PPh3.
The obtained platinum(II) complexes were characterized by high-resolution
ESI+-MS, IR, and 1D (1H, 13C{1H}, 195Pt{1H}) and 2D (1H,1H-NOESY; 1H,13C-HSQC; 1H,13C-HMBC) NMR spectroscopy, and the latter three complexes
were investigated by X-ray diffraction. All four platinum species
were examined as hydrosilylation catalysts (c 10–4–10–3 M; 80–120 °C;
[Pt(ppy)Cl(PPh3)] exhibited the highest catalytic activity)
for the cross-linking of vinyl-terminated polydimethylsiloxane and
polymethylhydrosiloxane to achieve luminescent silicone rubbers. Each
solid complex and the appropriate silicone rubber exhibited the same
emission spectra in the green region and strong phosphorescence with
a solid-state quantum yield of up to 12.5% (measured for the silicone
elastomer obtained with the [Pt(ppy)(CNCy)2](BF4) catalyst). The resulting luminescent silicone rubbers can be potentially
used for protective coatings (to facilitate the thickness control)
and as a component for phosphor-converted white light-emitting diodes
(to transform a UV part of the LED emission to the visible spectrum).
Cyclometalated platinum(II) complexes [Pt(ppy)Cl(CNAr)]
(ppy =
2-phenylpyridinato-C
2
,
N
; Ar = C
6
H
4
-2-I
1
, C
6
H
4
-4-I
2
, C
6
H
3
-2-F-4-I
3
, and
C
6
H
3
-2,4-I
2
4
) bearing
ancillary isocyanide ligands were obtained by the bridge-splitting
reaction between the dimer [Pt(ppy)(μ-Cl)]
2
and 2
equiv any one of the corresponding CNAr. Complex
2
was
crystallized in two polymorphic forms, namely,
2
I
and
2
II
, exhibiting green (emission
quantum yield of 0.5%) and orange (emission quantum yield of 12%)
phosphorescence, respectively. Structure-directing non-covalent contacts
in these polymorphs were verified by a combination of experimental
(X-ray diffraction) and theoretical methods (NCIplot analysis, combined
electron localization function (ELF), and Bader quantum theory of
atoms in molecules (QTAIM analysis)). A noticeable difference in the
spectrum of non-covalent interactions of
2
I
and
2
II
is seen in the Pt···Pt
interactions in
2
II
and absence of these metallophilic
contacts in
2
I
. The other solid luminophores,
namely,
1
,
3
I–II
,
4
, and
4
·CHCl
3
, exhibit green
luminescence; their structures include intermolecular C–I···Cl–Pt
halogen bonds as the structure-directing interactions. Crystals of
1
,
2
I
,
3
I
,
3
II
,
4
, and
4
·CHCl
3
demonstrated a reversible mechanochromic color change achieved
by mechanical grinding (green to orange) and solvent adsorption (orange
to green).
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