The Journal of Physical Chemistry A
Article
Pt-2. Starting from 19 mg of (bpy)PtCl2, 20 mg of orange
solid was obtained as the product (yield: 54%). H NMR (500
RESULTS AND DISCUSSION
Electronic Absorption. The electronic absorption of L-1−
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1
MHz, CDCl3): δ 0.18 (t, J = 7.5 Hz, 12H, CH3), 0.77−0.93 (m,
24H, CH3), 1.08−1.43 (m, 34H, CH2), 1.56−1.78 (m, 16H,
CH3), 1.86−1.94 (m, 4H, CH2), 2.91−2.94 (m, 2H, CH),
7.26−7.29 (m, 6H, Ar), 7.33−7.36 (m, 6H, Ar), 7.42−7.54 (m,
12H, Ar), 7.58 (d, J = 7.5 Hz, 2H, Ar), 7.63 (d, J = 8.0 Hz, 2H,
Ar), 7.7−7.72 (m, 4H, Ar), 7.91 (d, J = 8.0 Hz, 2H, Ar). 13C
NMR (100 MHz, CDCl3): δ 8.4, 10.1, 10.7, 14.0, 14.1, 22.9,
23.1, 25.1, 26.2, 28.2, 28.7, 32.2, 32.6, 32.9, 36.1, 36.3, 40.6,
41.3, 56.0, 86.8, 103.3, 110.3, 119.3, 119.7, 120.9, 122.9, 123.1,
123.9, 126.9, 127.5, 127.6, 128.3, 128.6, 129.8, 131.2, 137.2,
137.4, 138.1, 143.08, 143.12, 149.7, 149.8, 151.4, 153.3, 156.2,
159.9. HRMS: m/z Calcd for [C108H126N6Pt]+, 1701.9744;
found, 1701.9795. Anal. Calcd for C108H126N6Pt·0.5CH2Cl2·
(iPr)2NH: C, 74.46; H, 7.75; N, 5.31. Found: C, 74.12; H, 6.91;
N, 5.77%.
L-3 and Pt-1−Pt-3 was studied in CH2Cl2 at different
concentrations (1 × 10−6−5 × 10−4 mol/L). The Beer’s law
is obeyed in this concentration range by all of these
compounds, indicating that neither dimerization nor oligome-
rization occurs at the ground state for these compounds (see
Supporting Information Figure S1). Figure 1 depicts the UV−
Pt-3. Starting from 68 mg of (bpy)PtCl2, 30 mg of orange
1
solid was obtained as the product (yield: 23%). H NMR (500
MHz, CDCl3): δ 0.18 (t, J = 7.0 Hz, 12H, CH3), 0.78−0.92 (m,
24H, CH3), 1.07−1.40 (m, 34H, CH2), 1.60−1.69 (m, 16H,
CH3), 1.83−1.89 (m, 4H, CH2), 2.91−2.94 (m, 2H, CH), 7.13
(s, 2H, Ar), 7.32−7.33 (m, 6H, Ar), 7.42 (d, J = 5.5 Hz, 2H,
Ar), 7.51 (s, 2H, Ar), 7.54−7.57 (m, 6H, Ar), 7.63 (d, J = 7.5
Hz, 2H, Ar), 7.72−7.79 (m, 8H, Ar), 7.82 (d, J = 8.0 Hz, 2H,
Ar), 8.17−8.22 (m, 4H, Ar), 9.79 (d, J = 5.0 Hz, 2H, Ar). 13C
NMR (100 MHz, CDCl3): δ 8.5, 10.1, 10.7, 14.0, 14.1, 22.9,
23.1, 25.1, 26.2, 28.2, 28.7, 32.2, 32.5, 32.9, 36.0, 36.3, 40.5,
40.6, 40.7, 41.2, 41.3, 56.0, 86.6, 103.3, 119.3, 119.7, 120.9,
127.8, 126.8, 126.9, 127.4, 128.4, 128.6, 128.7, 129.1, 129.6,
129.8, 131.1, 136.9, 138.3, 139.5, 141.0, 141.3, 142.6, 149.5,
149.8, 151.4, 153.8, 154.0, 156.2, 159.8, 159.9. HRMS: m/z
Calcd for [C110H126N6Pt]+, 1725.9744; found: 1725.9788. Anal.
Calcd for C110H126N6Pt: C, 76.49; H, 7.35; N, 4.87. Found: C,
76.45; H, 6.99; N, 5.07%.
Photophysical Measurements. The UV−vis absorption
spectra and steady-state emission spectra of Pt-1−Pt-3 were
measured in different HPLC grade solvents. An Agilent 8453
spectrophotometer was used for the UV−vis absorption
measurement, and a SPEX fluorolog-3 fluorometer/phosphor-
ometer was utilized for the steady-state emission study. A
comparative method32 with a degassed aqueous solution of
[Ru(bpy)3]Cl2 (Φem = 0.042, λex = 436 nm)33 being used as the
reference was applied to determine the emission quantum
yields of Pt-1−Pt-3 in degassed solutions. An Edinburgh LP920
laser flash photolysis spectrometer was utilized to acquire the
triplet excited-state lifetimes and the triplet transient difference
absorption spectra in degassed solutions. The excitation source
was the third harmonic output (355 nm) of a Nd:YAG laser
(Quantel Brilliant, pulsewidth ≈ 4.1 ns, repetition rate was set
at 1 Hz). Each sample was degassed with argon for at least 30
min prior to measurement.
Figure 1. UV−vis absorption spectra of Pt-1−Pt-3 (a) and L-1−L-3
(b) in CH2Cl2.
vis absorption spectra of L-1−L-3 and Pt-1−Pt-3 in CH2Cl2,
and Table 1 lists their absorption band maxima and molar
extinction coefficients. In line with the Pt(II) diimine
bis(acetylide) complexes reported in the literature,3−27 the
UV−vis absorption spectra of Pt-1−Pt-3 (Figure 1a) are
composed of two groups of bands: the major absorption bands
below 400 nm are ascribed to the 1π,π* transitions localized on
the acetylide ligand; while the tails above 400 nm are attributed
to the 1LLCT (ligand-to-ligand charge transfer)/1MLCT
(metal-to-ligand charge transfer) transitions. The assignment
of 1π,π* transitions to the major absorption bands is supported
by the facts that the energies of these bands resemble those of
their corresponding acetylide ligands (Figure 1b) and that the
solvatochromic effect of these bands (Figure 2 for Pt-2 and
Supporting Information Figure S2 for Pt-1 and Pt-3) are quite
minor. However, these bands are clearly red-shifted in
comparison to those of their respective ligands, suggesting
the delocalization of the ligand-centered molecular orbitals via
the interactions with the platinum dπ orbitals. In contrast to the
major absorption bands, the low-energy tails in these complexes
shift to longer wavelengths in hexane and toluene compared to
those in CH3CN and CH2Cl2 (examplified in Figure 2 for
complex Pt-2), manifesting a clear negative solvatochromic
effect. The negative solvatochromic effect is a characteristic
Nonlinear Transmission Measurements. The experi-
mental setup resembled that reported by our group before.34
The second harmonic output (λ = 532 nm) of a Q-switched
Quantel Brilliant Nd:YAG laser (4.1 ns (fwhm), 10 Hz) was
used as the light source. The focal length of the plano-convex
lens used was 30 cm, which focused the laser beam to ∼96 μm
(radius) at the center of a 2 mm thick sample cuvette. The
incident and output energies were monitored using two
Molectron J4-09 pyroelectric probes and an EPM2000
energy/power meter.
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feature for LLCT/1MLCT transitions as reported for many
other Pt(II) diimine bisacetylide complexes.8−16
Emission. Pt-1−Pt-3 are luminescent in fluid solutions at
room temperature and in glassy matrix at 77 K. Figure 3 shows
the normalized emission spectra of these complexes in CH2Cl2
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dx.doi.org/10.1021/jp500397g | J. Phys. Chem. A XXXX, XXX, XXX−XXX