Platinum(II) complexes bearing 2-(9,9-dihexadecyl-7-R-fluoren-2-yl)-1,10- phenanthroline ligands: Synthesis, photophysics and reverse saturable absorption

Article abstract of DOI:10.1002/ejic.201300466

Six platinum(II) complexes bearing 2-(9,9-dihexadecyl-7-R-fluoren-2-yl)-1, 10-phenanthroline ligands (R = NO₂, CN, I, H, benzothiazole, thiophene for ligands 1-6, respectively) were synthesized and their photophysics and reverse saturable absorption (RSA) were systematically investigated. All complexes exhibit intense absorption bands between 350 and 450 nm, which are attributed to ¹π,π/¹ILCT (intraligand charge transfer) transitions, and broad ¹MLCT (metal to ligand charge transfer) transitions between 475 and 550 nm. All complexes are emissive at room temperature in a variety of solvents and at 77 K in butyronitrile glassy matrix, with the long-lived, structured emission appearing between 600 and 750 nm. The emitting states are assigned to predominantly the ³π, π* state with an admixture of ³MLCT characters. Upon ns laser excitation at 355 nm, all complexes display broad, moderately strong transient absorption from the visible to the near-IR region. As a result, RSA is observed from all complexes at 532 nm for ns laser pulses. The strength of the RSA for these complexes follows the trend: Pt-2 > Pt-3 > Pt-4 > Pt-1 >> Pt-5 > Pt-6, which correlates well with the trend of the estimated Φ_Tσ_ex/σ₀ values (where Φ_T is the triplet excited state quantum yield, and σ_ex and σ₀ are the excited-state and ground-state absorption cross-section, respectively) at 532 nm. It is revealed that substitution at the 7-position of the fluorenyl component exerts a distinct effect on the photophysics and RSA of the complexes. Aromatic substituents such as benzothiazol-2-yl and 2-thionyl cause pronounced red-shifts of the absorption bands, the emission bands, and the transient difference absorption bands, but a decrease of the RSA at 532 nm. Platinum(II) complexes bearing 2-(9,9-dihexadecyl-7-R-fluoren-2-yl)-1,10-phenanthroline ligands exhibit a long-lived, broadband-absorbing excited state and strong reverse saturable absorption (RSA) at 532 nm for ns laser pulses. The substituent at the 7-position of the fluorenyl component exerts a pronounced effect on both the photophysical properties and the RSA. Copyright

Full text of DOI:10.1002/ejic.201300466

FULL PAPER
DOI:10.1002/ejic.201300466
Platinum(II) Complexes Bearing 2-(9,9-Dihexadecyl-7-R-
fluoren-2-yl)-1,10-phenanthroline Ligands: Synthesis,
Photophysics and Reverse Saturable Absorption
Xu-Guang Liu[a] and Wenfang Sun*[a]
COVER PICTURE
Keywords: Platinum / Ligand design / Electronic structure / Time-resolved spectroscopy / Emission / Absorption
Six platinum(II) complexes bearing 2-(9,9-dihexadecyl-7-R-
fluoren-2-yl)-1,10-phenanthroline ligands (R = NO2, CN, I, H,
benzothiazole, thiophene for ligands 1–6, respectively) were
moderately strong transient absorption from the visible to the
near-IR region. As a result, RSA is observed from all com-
plexes at 532 nm for ns laser pulses. The strength of the RSA
synthesized and their photophysics and reverse saturable ab- for these complexes follows the trend: Pt-2 Ͼ Pt-3 Ͼ Pt-4 Ͼ
sorption (RSA) were systematically investigated. All com-
plexes exhibit intense absorption bands between 350 and
450 nm, which are attributed to 1π,π*/1ILCT (intraligand
charge transfer) transitions, and broad 1MLCT (metal to li-
gand charge transfer) transitions between 475 and 550 nm.
All complexes are emissive at room temperature in a variety
of solvents and at 77 K in butyronitrile glassy matrix, with the
long-lived, structured emission appearing between 600 and
750 nm. The emitting states are assigned to predominantly
the 3π,π* state with an admixture of 3MLCT characters. Upon
ns laser excitation at 355 nm, all complexes display broad,
Pt-1 ϾϾ Pt-5 Ͼ Pt-6, which correlates well with the trend of
the estimated ΦTσex/σ0 values (where ΦT is the triplet excited
state quantum yield, and σex and σ0 are the excited-state and
ground-state absorption cross-section, respectively) at
532 nm. It is revealed that substitution at the 7-position of the
fluorenyl component exerts a distinct effect on the pho-
tophysics and RSA of the complexes. Aromatic substituents
such as benzothiazol-2-yl and 2-thionyl cause pronounced
red-shifts of the absorption bands, the emission bands, and
the transient difference absorption bands, but a decrease of
the RSA at 532 nm.
ylides.[6b,7–9] Our group has designed and synthesized sev-
eral series of PtII complexes for nonlinear transmission ap-
plications, including bipyridyl PtII acetylide complexes,[7]
terpyridyl PtII acetylides or chlorides,[8] and 4,6-diphenyl-
2,2Ј-bipyridyl PtII acetylides or chlorides.[9] Some represen-
tative structures are shown in Scheme 1. Among these, PtII
Introduction
Square-planar platinum(II) terdentate complexes repre-
sent an interesting class of transition-metal complexes due
to their unique photophysical properties, such as room tem-
perature phosphorescence and broadband excited-state ab-
sorption.[1] In addition, the photophysical properties of the
PtII complexes can be readily tuned through structural
modifications to tailor the specific requirements for dif-
ferent applications, such as light-emitting devices,[2] chemo-
sensors,[3] chemical cells for hydrogen generation,[4] solar
cells,[5] and nonlinear optical devices.[6–9]
Among the various potential applications, our group is
particularly interested in the nonlinear absorption of
square-planar platinum complexes. Parallel to the growing
interest in the development of phosphane platinum com-
plexes as nonlinear absorbing materials,[6] there has also
been immense interest in the investigation of polypyridine
ligands (especially bipyridyl and terpyridyl) for PtII acet-
complexes
bearing
6-phenyl-2,2Ј-bipyridine
ligand
∧ ∧
(C N N) are particularly interesting because of their rela-
tively intense emission at room temperature compared with
the corresponding PtII terpyridyl complexes.[10] This feature
is attributed to the stronger π-donating ability of the phenyl
ring, which admixes the intraligand charge transfer (ILCT)
character into the lowest excited state. Meanwhile, the
∧ ∧
C N N ligand reduces the distortion of the square-planar
configuration around the PtII ion in comparison with the
terpyridine ligand, which decreases the nonradiative decay
∧ ∧
from the excited state. In addition, the Pt(C N N) com-
plexes exhibit broader and stronger nonlinear absorption in
the visible to the near-IR region.
∧ ∧
Intrigued by the merits of the C N N ligand, we recently
[a] Department of Chemistry and Biochemistry, North Dokota
State University,
replaced the 6-phenyl group at the bipyridine by the 6-
(fluoren-2-yl) group (structures shown in Scheme 1) to in-
crease the π-donating ability of the cyclometalated aryl ring
and thus enhance the intraligand charge transfer character
and nonlinear absorption in the PtII complex.[9d] Our
photophysical and nonlinear absorption studies revealed
Fargo, ND 58108-6050, USA
Fax: +1-701-231-8831
E-mail: Wenfang.Sun@ndsu.edu
Homepage: http://www.ndsu.nodak.edu/chemistry/people/
faculty/sun.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300466.
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∧
∧
Scheme 1. Representative structures of some bipyridyl PtII acetylides, terpyridyl PtII acetylides, and C N N PtII acetylides or chlorides.
that the PtII complex with this new type of C N N ligand the frontier molecular orbitals are essentially localized on
∧ ∧
possesses longer triplet excited-state lifetime and broader- the fluorenylphenanthroline components.
band nonlinear absorption in comparison to complexes
with the 6-phenyl-2,2Ј-bipyridine ligand.[9c,9f] Che and co-
workers also discovered that the emission quantum yields
of the PtII C N N complexes with extended π-conjugation
∧ ∧
at the lateral rings of the cyclometalating ligands could in-
crease the emission quantum yields.[11] Encouraged by these
results, we recently reported PtII complexes with a new type
∧ ∧
of C N N ligand {2-[9,9-dihexadecyl-7-(4-R-phenyleth-
ynyl)-fluoren-2-yl]-1,10-phenanthroline},[12] in which a rigid
1,10-phenanthroline unit was used to replace the bipyridine
unit to favor metal binding (due to the juxtaposed nitrogen
atoms held by the rigidity of phenanthroline) and extend
the π-conjugation of the ligand (see structures depicted in
Scheme 2). In addition, the 4-R-phenylethynyl substituent
was introduced at the 7-position of the fluorenyl compo-
nent to further increase the π-conjugation of the ligand. It
Scheme 2. Structures for PtII chloride complexes containing the 2-
[9,9-dihexadecyl-7-(4-R-phenylethynyl)-fluoren-2-yl]-1,10-phen-
anthroline ligand or the 2-(9,9-dihexadecyl-7-R-fluoren-2-yl)-1,10-
phenanthroline ligand (Pt-1–6).
3
is found that all these complexes possess long-lived π,π*
excited states and give rise to moderate emission and broad-
band transient absorption. However, the reverse saturable
To remedy the deficiency of the PtII complexes contain-
absorption (RSA) of these complexes for nanosecond laser ing the 2-[9,9-dihexadecyl-7-(4-R-phenylethynyl)-fluoren-2-
pulse at 532 nm was very weak due to their small ratios of yl]-1,10-phenanthroline ligand, in this work, we designed
excited-state absorption cross-section relative to that of the and synthesized a series of new PtII 2-(fluoren-2-yl)-1,10-
ground-state absorption. Furthermore, the auxiliary sub- phenanthroline complexes (Pt-1–6) with different substitu-
stituent on the phenylethynyl motif exhibits a negligible ef- ents directly attached at the 7-position of the fluorene com-
fect on the electronic absorption and emission energies of ponent (structures shown in Scheme 2). Thiophene was
the complexes, indicating that the electron distributions of chosen as the electron-donating substituent and NO2, CN,
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I, and benzothiazole (BTZ) were chosen as electron-with-
Results and Discussion
drawing substituents. The photophysics of these complexes
were systematically investigated with the aim of under-
standing the structure-property correlations in order to im-
prove the RSA in the PtII complexes.
Synthesis
The synthetic routes to Pt-1–6 are outlined in Scheme 3,
and the synthetic details and characterization data for pre-
Scheme 3. Synthetic routes to PtII complexes Pt-1–6.
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cursors Ace-1–6 are provided in the Supporting Infor- component to the electron-withdrawing phenanthrolinyl
mation. The synthesis of Ace-3 was previously reported.[12] component. The 1ILCT nature of this shoulder is supported
Ace-1 was prepared through nitration of fluorene, followed by titration experiments of the ligand with TsOH. As exem-
by alkylation of 2-nitrofluorene, and acetylation of the al- plified in the inset of Figure 1 (a) for ligand L-4, the inten-
kylated 2-nitrofluorene using nitrobenzene as solvent.[13] sity of this shoulder increases and red-shifts with addition
Ace-2 was synthesized by converting the iodo group in Ace- of TsOH acid. This feature is attributed to the enhanced
3 into the corresponding cyano derivative using copper cya- electron-withdrawing ability of the phenanthrolinyl compo-
nide.[14] Ace-4 was synthesized by alkylation of fluorene, nent after protonation. Substitution at the 7-position of the
followed by mono-acetylation of the alkylated fluorene
3.[11c] Ace-5 and Ace-6 were synthesized by Stille coupling
reaction between Ace-3 and the corresponding stannyl com-
pounds.[15] Ligands L-1–6 were then obtained through the
Friedländer condensation reaction between the precursor
Ace-1–6 and 8-aminoquinoline-7-carbaldehyde. Finally, the
PtII complexes were synthesized by reacting K2PtCl4 with
the corresponding ligand under reflux in mixed acetic acid/
chloroform (10:1 v/v) solution.
It should be noted that the long alkyl chains were intro-
duced at the 9-position of fluorene to improve the solubility
of these cyclometalated PtII complexes, which is important
for the photophysical studies and for future device applica-
tions.
Electronic Absorption
The UV/Vis absorption of ligands L-1–6 and PtII com-
plexes Pt-1–6 was studied in CH2Cl2 solutions with dif-
ferent concentrations (1ϫ10–6 to 5ϫ10–4 mol/L). As exem-
plified in the inset of Figure 1 (b) for Pt-4, the absorption
of all ligands and complexes obeys Beer’s law in the concen-
tration range studied, indicating the absence of ground-state
aggregation in this concentration range. The UV/Vis ab-
sorption spectra of L-1–6 and Pt-1–6 are illustrated in Fig-
ure 1 and the band maxima and molar extinction coeffi-
cients of Pt-1–6 are listed in Table 1. For ligands L-1–6,
Figure 1. UV/Vis absorption spectra of (a) L-1–6 and (b) Pt-1–6 in
the intense absorption bands between 300 and 400 nm are
CH2Cl2. The inset in (a) shows the titration curves of L-4 in
dominated by 1π,π* transitions, whereas the low-energy
CH2Cl2 (5ϫ10–5 mol/L) with pTsOH (2 ϫ10–2 mol/L). The inset in
(b) manifests the Beer’s law of Pt-4 in CH2Cl2 at different wave-
shoulders have contributions from intraligand charge trans-
fer (1ILCT) transitions from the electron-donating fluorenyl lengths.
Table 1. Photophysical parameters for Pt-1–6.
[a]
[c]
λabs [nm] (ε [103 Lmol–1 cm–1]) λem [nm]
(τ0 [μs]; kq [ϫ108 Lmol–1 s–1])[a]
Φem
λem [nm]
λT1–Tn [nm]
ΦT
(τem [μs])[b]
(τTA [μs]; εT1–Tn [Lmol–1 cm–1])[c]
Pt-1 341 (28.5), 387 (39.8), 421
(23.4), 484 (5.2), 515 (3.8)
Pt-2 338 (36.0), 369 (34.2), 416
(15.6), 488 (3.7), 518 (2.3)
Pt-3 341 (27.7), 386 (36.0), 421
(16.9), 488 (4.1), 519 (2.9)
Pt-4 340 (24.2), 383 (29.1), 421
(14.4), 491 (3.2), 520 (2.1)
Pt-5 327 (24.7), 354 (33.2), 397
(58.3), 423 (27.3), 488 (7.1),
523 (4.8)
618 (3.90; 10.4), 672 (4.02; 8.35)
612 (5.52; 11.3), 666 (5.35; 11.2)
614 (7.69; 11.4), 668 (7.97; 11.5)
614 (8.45; 13.8), 666 (8.60; 13.4)
624 (6.53; 7.13), 676 (6.13; 6.20)
0.061
0.087
0.137
0.128
0.079
607 (5.68), 664
(5.79)
600 (7.48), 655
(7.45)
598 (11.5), 653
(11.2)
598 (12.3), 652
(11.7)
455 (3.48; 35120), 655 (3.65; 39510) 0.34
420 (3.49; 44643), 565 (3.63; 49895) 0.38
420 (5.36; 37109), 565 (4.93; 65654) 0.18
420 (6.47; 39563), 490 (5.57; 55854) 0.21
465 (4.69; 22901), 640 (4.89; 41441) 0.46
611 (8.83), 668
(8.73)
Pt-6 350 (25.4), 400 (49.7), 426
(25.5), 495 (6.8), 526 (5.0)
630 (7.65; 7.90), 678 (6.66; 7.33)
0.062
618 (13.1), 673
(12.7)
465 (5.18; 24144), 655 (4.98; 39234) 0.50
[a] Measured at room temp. at a concentration of 1ϫ10–5 mol/L in CH2Cl2 solution. τ0 is the intrinsic lifetime at infinite dilute concentra-
tion, kq is the self-quenching rate constant. [b] Measured at 77 K at a concentration of 1ϫ10–5 mol/L in BuCN glassy matrix. [c] Measured
in toluene.
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fluorene component causes red-shifts and enhanced molar
It is noted that the auxiliary substituent at the 7-position
extinction coefficients of the ligand. This becomes more sa- of the fluorene motif exhibits a pronounced effect on the
lient in L-1, L-5, and L-6, which contain the strong elec- UV/Vis absorption of the PtII complexes. Similar to that
tron-withdrawing NO2 substituent, the aromatic BTZ, or observed in the ligands, substitution at the 7-position of the
thiophene substituents, respectively.
fluorene increases the molar extinction coefficients of the
The ligand-based 1π,π* transition bands between 350 and absorption bands in PtII complexes compared with those of
400 nm are red-shifted in complexes Pt-1–6 compared with Pt-4 (which has no substituent at the 7-position). However,
those of their respective ligands, implying the interactions the different substituents affect the transition energy in dif-
of the ligand-centered molecular orbitals with the platinum ferent ways. The absorption bands of complex Pt-2 with the
dπ orbitals, which result in delocalization of the molecular CN substituent are blue-shifted compared with those of Pt-
orbitals and red-shifted absorption bands. The 1ILCT 4; whereas the absorption bands in all of the other com-
bands at 420–430 nm in these complexes become more dis- plexes are red-shifted compared with those of Pt-4. The ba-
tinct and red-shifted in comparison with those in their li- thochromic shift and enhancement of the molar extinction
gands, reflecting the increased electron-deficiency of the coefficients are more significant in Pt-5 and Pt-6, which
phenanthrolinyl component after complexation with the contain conjugated aromatic substituents. It is noted that
PtII ion. Similar spectral features and assignments have the molar extinction coefficients of complexes Pt-5 and Pt-
been reported by Che’s group and our groups for PtII com- 6 at 532 nm are much larger than those of the other four
plexes containing the fluorene unit.[11c,12] In contrast to the complexes, which could decrease the reverse saturable ab-
ligands, all complexes possess two broad, moderately in- sorption (RSA) at 532 nm for these two complexes and will
tense absorption bands in the visible spectral region, i.e., be discussed later.
470–560 nm, which likely arise from metal-to-ligand charge
transfer (1MLCT) transitions. The appearance of two dis-
Emission
All complexes Pt-1–6 are emissive in solutions at room
temperature and in glassy matrix at 77 K. The normalized
emission spectra of these complexes in CH2Cl2 at a concen-
tration of 1ϫ10–5 mol/L are illustrated in Figure 3. The
emission lifetimes and quantum yields are summarized in
Table 1.
tinct bands in this region indicates two orbitally distinct
MLCT transitions due to unequal interaction of the ligand
field with the participating PtII d-orbitals of different sym-
metry. A similar feature has been reported by Schanze’s
group for diimine PtII bis-acetylide complexes[16] and by our
group for PtII terpyridyl acetylide complexes[8b] and for PtII
[12]
∧ ∧
complexes with a similar type of C N N ligand.
The
charge transfer nature of the low-energy absorption bands
is supported by the negative solvatochromic effects (i.e., the
absorption bands hyposochromically shift in polar solvents
such as CH3CN and CH2Cl2, but bathochromically shift in
less polar solvents such as hexane and toluene, as exem-
plified in Figure 2 for Pt-3 and in Figure S3 of the Support-
ing Information for Pt-1, Pt-2, and Pt-4–6), which is com-
[9a,9e,9f]
monly seen in many PtII C N N complexes
and in
∧ ∧
PtII terpyridyl complexes.[8b]
Figure 3. Normalized emission spectra of complexes Pt-1–6 in
CH2Cl2 at room temperature (c = 1ϫ10–5 mol/L). λex = 386 nm
for Pt-1; 370 nm for Pt-2; 386 nm for Pt-3; 370 nm for Pt-4; 396 nm
for Pt-5; and 398 nm for Pt-6.
As shown in Figure 3, upon excitation of CH2Cl2 solu-
1
tions of Pt-1–6 at their respective major π,π* absorption
bands, a structured emission appears at 612–630 nm and
a shoulder at 666–678 nm. The vibronic progressions are
1300 cm–1 for Pt-1, 1188 cm–1 for Pt-2, 1317 cm–1 for Pt-3,
1271 cm–1 for Pt-4, 1233 cm–1 for Pt-5, and 1124 cm–1 for
Pt-6, which all fall in the ring breathing mode of the aro-
matic rings. The lifetimes of the emission vary from approx-
imately 4.0 to 8.5 μs. Considering the large Stokes shifts
Figure 2. Normalized UV/Vis absorption spectra of Pt-3 in dif-
ferent solvents.
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(2950–3240 cm–1), the long lifetimes, and the distinct vib- concentrations (1ϫ10–6–1ϫ10–5 mol/L), and the intensity
ronic structures, we attribute the emission of Pt-1–6 at room reaches the maximum at a concentration of 1ϫ10–5 mol/L.
temperature predominantly to 3π,π* states. However, contri- When the concentration was higher than 1ϫ10–5 mol/L,
3
butions from the MLCT states should also be taken into the emission intensity continued to decrease. In contrast,
account in view of the salient negative solvatochromic effect the lifetime becomes shorter with increased concentration
exemplified in Figure 4 (a) for Pt-4 and in the Supporting from 1ϫ10–6 to 5ϫ10–4 mol/L. The reduced lifetime at
Information Figures S4 for the other complexes.
higher concentrations clearly indicates the occurrence of
self-quenching, which contributes partially to the reduced
emission intensity at higher concentrations. By plotting the
observed decay rate constants vs. concentrations, straight
lines are generated (exemplified in the inset b of Figure 4 for
Pt-4 at 614 nm). According to the Stern–Volmer equation
[Equation (1) in the experimental section], the self-quench-
ing rate constant (kq) can be obtained from the slope of the
plot, and the intrinsic lifetime (τ0) can be deduced from the
intercept of the plot. The τ0 and kq for Pt-1–6 are listed in
Table 1. The kq values for these complexes are of the order
108–109 Lmol–1 s–1, which are in accordance with the values
[9e,12]
∧ ∧
reported for other C N N Pt complexes
and for Pt
terpyridyl complexes.[17]
To further understand the nature of the emission from
the PtII complexes, the emission characteristics of the li-
gands and complexes in butyronitrile matrix at 77 K were
investigated. As exemplified in Figure S7 of the Supporting
Information for ligand L-4, the emission of all of the li-
gands at 77 K displays the same energies as those at room
temperature but with distinct vibronic structures, which is
attributed to low-temperature fluorescence. However, weak
phosphorescence from 480 to 600 nm was observed in ad-
dition to the fluorescence signal when an excess amount of
iodomethane (CH3I) was added due to enhanced intersys-
tem crossing from the heavy-atom effect. For complexes Pt-
1–6, owing to the rigidochromic effect,[18] the emission spec-
tra at 77 K are narrower and slightly blue-shifted with re-
spect to those at room temperature (shown in Figure S8).
The vibronic spacing is approximately 1400 cm–1 for all
complexes, and the thermally induced Stokes shifts vary
from 293 to 436 cm–1 for these complexes. These features
(the similar shape and vibronic spacing of the spectra at
77 K and at room temperature, and the small thermally in-
duced Stokes shift) suggest that the emission of Pt-1–6 at
77 K should also arise predominantly from the ligand-local-
Figure 4. (a) Normalized emission spectra of Pt-4 in different sol-
vents at room temperature (λex = 436 nm). (b) Concentration-de-
pendent emission spectra of Pt-4 in CH2Cl2 at room temperature
(λex = 370 nm). The inset shows the Stern–Volmer plot of Pt-4 at
614 nm.
3
ized π,π* state.
The emission energies of the complexes are influenced by
the substituents at the 7-position of the fluorene motif. A
strong electron-withdrawing substituent (NO2) or aromatic
substituents (BTZ and thiophene) cause pronounced red-
shifts of the emission spectra in Pt-1, Pt-5, and Pt-6 in com-
Transient Absorption
The nanosecond transient difference absorption (TA)
parison to the spectrum of Pt-4. This trend is consistent spectra of Pt-1–6 in toluene were studied to understand the
with that observed from the UV/Vis absorption spectra. spectral features of the triplet excited state and deduce its
However, weaker electron-withdrawing substituents (CN lifetime. Figure 5 (a) illustrates the TA spectra of Pt-1–6 in
and I) exhibit only a minor effect on the emission energies degassed toluene solution at zero delay after 355 nm exci-
of Pt-2 and Pt-3.
tation. All complexes exhibit a bleaching band below
1
The emission of Pt-1–6 in CH2Cl2 at different concentra- 450 nm, which is consistent with the position of the π,π*/
tions at room temperature was studied, and the results are 1ILCT transition bands in their respective UV/Vis absorp-
exemplified in Figure 4 (b) for complex Pt-4 and in the Sup- tion spectra. Above 450 nm, broad positive absorption
porting Information Figures S5 for the other five com- bands are observed. The shapes of the TA spectra are quite
plexes. It is clear that the emission intensity increases at low similar for Pt-1, Pt-5, and Pt-6, with two distinct absorption
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bands in the visible to the near-IR region. In contrast, the Reverse Saturable Absorption (RSA)
TA spectra of Pt-2 and Pt-3 resemble each other, with a
RSA is a nonlinear absorption phenomenon in which the
excited state of the molecule absorbs stronger than the
ground state, resulting in decreased transmission with in-
creased incident energy as illustrated in Figure 6. For an
ideal reverse saturable absorber, the molecule should have
weak ground-state absorption in order to populate the mo-
lecule from the ground state to the excited state through
one-photon absorption, and the excited-state absorption
should be much stronger than that of the ground state.
Namely, the ratio of the excited-state absorption cross-sec-
tion to that of the excited state (σex/σg) should be much
larger than 1. Meanwhile, the excited states should be long-
lived (at least longer than the laser pulse width), and the
triplet excited-state quantum yield should be high in the
case of using the triplet excited-state absorption to reach
RSA. RSA can be utilized for optical pulse shaping and
smoothing, laser pulse compression, and optical switching,
etc.[19] The TA experiments discussed above reveal that
complexes Pt-1–6 exhibit stronger excited-state absorption
than the ground state and long-lived triplet excited states
in the visible to the near-IR region. Consequently, reverse
saturable absorption is anticipated to occur in this spectral
region. To confirm this notion, nonlinear transmission ex-
periments were conducted for Pt-1–6 using 4.1 ns laser
pulses at 532 nm. For easy comparison, the linear trans-
mission of all the complex solutions was adjusted to 80%
at 532 nm in a 2-mm cuvette, which guarantees identical
excitation of Pt-1–6 to the singlet excited state. The ob-
served different degrees of RSA would then be attributed
to the difference in the excited-state absorption, which is
related to the excited-state absorption cross-section, life-
time, and quantum yield.
narrow absorption band at ca. 425 nm and two other broad
absorption bands at approximately 485 and 560 nm. How-
ever, the band at 560 nm is more salient in Pt-2 and Pt-3
compared to that of Pt-4. In line with the trend observed
from the UV/Vis and emission spectra, the low-energy TA
band is significantly red-shifted in Pt-1, Pt-5, and Pt-6,
which contain strong electron-withdrawing or aromatic sub-
stituents with respect to those in the other three complexes.
Figure 5. (a) Triplet transient difference absorption spectra of Pt-
1–6 at zero time delay following 355 nm excitation in toluene; (b)
Time-resolved triplet transient difference absorption spectra of Pt-
6 in toluene. For all measurements, λex = 355 nm, A355 nm = 0.4 in
a 1-cm cuvette.
The time-resolved TA spectra are exemplified in Figure 5
(b) for Pt-6 and in Figure S9 of Supporting Information
for the other complexes. The TA for all complexes decay
monoexponentially throughout the whole spectral range,
and the lifetimes deduced from the decay of the TA are in
Figure 6. Optical response curve for reverse saturable absorption.
As shown in Figure 7, the transmission of complexes Pt-
line with those measured from the decay of the emission in 1–6 decreases drastically when the incident energy increases,
the same solution. This feature implies that the TA likely which is a clear indication of RSA. The degree of RSA
emanates from the same excited state that emits, i.e., pre- decreases in this order: Pt-2 Ͼ Pt-3 Ͼ Pt-4 Ͼ Pt-1 ϾϾ Pt-5
3
3
dominantly π,π* state possibly mixed with some MLCT Ͼ Pt-6. Complex Pt-2, which contains the CN substituent,
characters.
displays the strongest RSA; whereas Pt-5 and Pt-6, which
Eur. J. Inorg. Chem. 2013, 4732–4742
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bear aromatic substituents, exhibit the weakest RSA. To ra- trend of RSA. It appears that aromatic substitution on this
∧ ∧
tionalize the observed difference in RSA for these com- new type of C N N ligand reduces the RSA at 532 nm for
plexes, the ratios of the excited-state absorption cross-sec- Pt-5 and Pt-6. However, considering the reduced ground-
tion relative to that of the ground state (σex/σg), which is a state absorption and much stronger excited-state absorption
critical parameter for RSA, were estimated by following the at the longer wavelengths (Ͼ 550 nm), it is reasonable to
method described previously.[20] The resultant ratios are predict that the RSA for these two complexes could be
presented in Table 2. According to our previous study on much stronger at wavelengths longer than 550 nm.
[9d]
a PtII complex with similar C N N core structure,
the
∧ ∧
excited-state that is the dominant contributor to the RSA
of ns laser pulses is the triplet excited state. In such a case,
the different triplet excited state quantum yields of these
complexes also contribute to the observed RSA. Taking
both factors into account, the combined ΦTσex/σ0 values
shown in Table 2 roughly correspond to the observed RSA
trend for these PtII complexes. The inconsistence between
the ΦTσex/σ0 value and the observed RSA for Pt-1 could
possibly be attributed to the different solvents used in our
TA and RSA measurements. The TA measurement was per-
formed in toluene (because the PtII complexes are more
stable in toluene than in CH2Cl2 upon several hundreds of
355 nm laser irradiation during the TA measurement), but
the RSA was measured in CH2Cl2 (because of the better
solubility of the sample in CH2Cl2 than in toluene). It was
found that the ground-state absorption cross-section in
CH2Cl2 is smaller than that in toluene at 532 nm (as impli-
cated in Figure S3 of the Supporting Information), which
would increase the ΦTσex/σ0 value in CH2Cl2 and result in
stronger RSA. Nevertheless, the trend of the estimated
ΦTσex/σ0 values are generally in good agreement with the
Conclusion
The PtII complexes bearing 2-(9,9-dihexadecyl-7-R-
fluoren-2-yl)-1,10-phenanthroline ligands exhibit 1π,π*/
1ILCT transitions below 450 nm and broad MLCT transi-
1
tions between 475 and 550 nm. Substitution at the 7-posi-
tion of the fluorenyl component increases the molar extinc-
tion coefficients of Pt-1–3, Pt-5 and Pt-6 compared with
that of Pt-4, which has no substituent at the 7-position of
fluorene. Aromatic substituents (BTZ and thiophene) cause
pronounced red-shifts of the absorption bands. All com-
plexes exhibit long-lived, structured π,π*/3MLCT emission
3
at room temperature and at 77 K, with the emission ener-
gies being significantly lowered for Pt-5 and Pt-6, which
contain aromatic substituents. Upon ns laser excitation at
355 nm, all complexes possess broad, moderately strong
transient absorption from the visible to the near-IR region,
with the maximum absorption band drastically red-shifted
for complexes with strong electron-withdrawing substituent
(NO2) or aromatic substituents (BTZ or thiophene). How-
ever, due to the stronger ground-state absorption of these
three complexes (Pt-1, Pt-5, and Pt-6) at 532 nm, the ΦTσex/
σ0 values for them are smaller than those of the other three
complexes. As a result, the RSA of these three complexes
(especially the complexes Pt-5 and Pt-6) are weaker than
the other complexes at 532 nm. The strength of the RSA
for these complexes follows the trend: Pt-2 Ͼ Pt-3 Ͼ Pt-4
Ͼ Pt-1 ϾϾ Pt-5 Ͼ Pt-6. However, it is believed that the
RSA of Pt-1, Pt-5, and Pt-6 could be stronger at longer
wavelength in view of the decreased ground-state absorp-
tion but increased excited-state absorption in the near-IR
region.
Experimental Section
Materials and Characterizations: All of the reagents and solvents
were purchased from Alfa Aesar or Aldrich Chemical Co., and
were used as received unless otherwise stated. The precursor 8-
amino-7-quinolinecarbaldehyde was prepared as described pre-
viously.[21] The precursors were characterized by NMR spectro-
scopic analysis, whereas the final platinum complexes were fully
characterized by 1H NMR, 13C NMR, electrospray ionization
high-resolution mass spectrometry (ESI-HRMS), and elemental
analyses.
Figure 7. Nonlinear transmission of complexes Pt-1–6 in CH2Cl2
solution for 4.1 ns laser pulses at 532 nm. The linear transmission
is 80% in a 2-mm cuvette at 532 nm.
Table 2. Ground-state (σ0) and excited-state (σex) absorption cross-
sections of the PtII complexes in toluene at 532 nm.
Pt-1
Pt-2
Pt-3
Pt-4
Pt-5
Pt-6
σ0 [10–17 cm2]
1.44
0.95
11.6
12.2
0.38
4.63
0.88
18.3
20.8
0.18
3.74
0.65
9.45
14.5
0.21
3.05
1.77
11.2
6.28
0.46
2.89
1.58
6.10
3.85
0.50
1.93
NMR spectra were obtained with a Varian Oxford-400 VNMR or
a Varian Oxford-500 VNMR spectrometer. ESI-HRMS analyses
were conducted with a Bruker Daltonics BioTOF III mass spec-
trometer. Elemental analyses were carried out by NuMega Reso-
nance Laboratories, Inc., San Diego, California.
σex [10–17 cm2] 8.01
σex/σ0
ΦT
ΦTσex/σ0
5.57
0.34
1.89
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The synthetic routes for ligands L-1–6 and PtII complexes Pt-1–6
are outlined in Scheme 3 and the synthetic details and characteriza-
tion data are provided below.
1 H, Ar), 9.21–9.23 (m, 1 H, Ar) ppm; 13C NMR (100 MHz,
CDCl3): δ = 14.0, 22.6, 23.8, 29.24, 29.27, 29.4, 29.5, 29.9, 31.8,
40.4, 55.2, 120.02, 120.06, 129.9, 121.8, 122.73, 122.79, 125.9,
126.2, 126.7, 127.2, 127.3, 127.6, 128.9, 135.8, 136.6, 138.8, 140.6,
142.4, 146.1, 146.4, 150.3, 151.1, 151.3, 158.2 ppm; HRMS: m/z
calcd. for [C57H80IN2 + H]+ 793.6394; found 793.6406. C57H80IN2
(920.18): calcd. C 86.30, H 10.17, N 3.53; found C 86.04, H 10.02,
N 3.48.
Typical Friedländer Condensation[22] for the Synthesis of Ligands
L-1–6: A mixture of 8-aminoquinoline-7-carbaldehyde (1.0 equiv.),
Ace-1–6 (1.1 equiv.), and KOH (2.5 equiv.) in absolute EtOH was
heated to reflux for 18–24 h under argon and cooled to room tem-
perature. The solvent was evaporated under vacuum and the resi-
due was extracted with ethyl acetate. The organic phase was washed
with water three times and dried with anhydrous Na2SO4. After
removal of the solvent, the residue was purified by column
chromatography (neutral Al2O3 gel; hexane/ethyl acetate, 10:1–4:1
v/v) to give the pure ligand.
2-[7-(Benzo[d]thiazol-2-yl)-9,9-dihexadecyl-9H-fluoren-2-yl]-1,10-
1
phenanthroline (L-5): Yield 180 mg (59%); yellow solid. H NMR
(500 MHz, CDCl3): δ = 0.69–0.76 (m, 4 H, CH2), 0.87 (t, J =
7.0 Hz, 6 H, CH3), 1.05–1.29 (m, 52 H, CH2), 2.17–2.21 (m, 4 H,
CH2), 7.40 (t, J = 8.0 Hz, 1 H, Ar), 7.52 (t, J = 8.0 Hz, 1 H, Ar),
7.67 (dd, J1 = 4.0, J2 = 8.0 Hz, 1 H, Ar), 7.80 (d, J = 9.0 Hz, 1 H,
Ar), 7.85 (d, J = 9.0 Hz, 1 H, Ar), 7.89 (d, J = 8.0 Hz, 1 H, Ar),
7.94 (t, J = 8.0 Hz, 2 H, Ar), 8.09–8.14 (m, 2 H, Ar), 8.18–8.20 (m,
3 H, Ar), 8.27–8.29 (m, 1 H, Ar), 8.36 (d, J = 8.5 Hz, 1 H, Ar),
8.50 (d, J = 7.5 Hz, 1 H, Ar), 9.27 (dd, J1 = 2.0, J2 = 4.5 Hz, 1 H,
Ar) ppm; 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.6, 23.8, 29.2,
29.3, 29.53, 29.56, 29.6, 29.9, 31.9, 40.4, 55.7, 120.5, 120.8, 121.1,
121.52, 121.55, 121.9, 122.9, 123.0, 125.0, 126.24, 126.28, 126.3,
127.1, 127.5, 127.9, 129.1, 132.5, 135.0, 136.0, 136.8, 139.7, 141.4,
143.8, 146.2, 146.4, 150.4, 151.9, 152.2, 154.3, 158.0, 168.7 ppm;
HRMS: m/z calcd. for [C64H83N3S + H]+ 926.6380; found
926.6399. C64H83N3S (926.44): calcd. C 82.97, H 9.03, N 4.54;
found C 83.42, H 9.34, N 4.62.
2-(9,9-Dihexadecyl-7-nitro-9H-fluoren-2-yl)-1,10-phenanthroline (L-
1
1): Yield 210 mg (57%); yellow oil. H NMR (400 MHz, CDCl3):
δ = 0.55–0.68 (m, 4 H, CH2), 0.82 (t, J = 7.0 Hz, 6 H, CH3), 1.00–
1.24 (m, 52 H, CH2), 2.08–2.16 (m, 4 H, CH2), 7.62 (dd, J1 = 4.4,
J2 = 8.0 Hz, 1 H, Ar), 7.75–7.85 (m, 3 H, Ar), 7.92 (d, J = 8.0 Hz,
1 H, Ar), 8.12–8.16 (m, 2 H, Ar), 8.20–8.28 (m, 3 H, Ar), 8.32 (d,
J = 8.4 Hz, 1 H, Ar), 8.46–8.49 (m, 1 H, Ar), 9.21–9.23 (m, 1 H,
Ar) ppm; 13C NMR (100 MHz, CDCl3): δ = 14.0, 22.6, 23.8, 29.2,
29.4, 29.5, 29.6, 29.8, 31.9, 40.1, 56.0, 118.2, 120.2, 121.1, 121.6,
122.1, 123.0, 123.3, 126.3, 126.5, 127.6, 128.2, 129.1, 136.1, 136.9,
139.8, 141.0, 146.2, 146.3, 147.2, 147.2, 150.4, 152.5, 152.8,
157.5 ppm; HRMS: m/z calcd. for [C57H79N3O2 + H]+ 838.6245;
found 838.6230. C57H79N3O2 (838.27): calcd. C 81.67, H 9.50, N
5.01; found C 81.34, H 9.84, N 5.02.
2-[9,9-Dihexadecyl-7-(thiophen-2-yl)-9H-fluoren-2-yl]-1,10-phen-
anthroline (L-6): Yield 130 mg (47%); yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 0.70–0.73 (m, 4 H, CH2), 0.86 (t, J =
6.8 Hz, 6 H, CH3), 1.05–1.29 (m, 52 H, CH2), 2.07–2.15 (m, 4 H,
CH2), 7.11 (dd, J1 = 3.6, J2 = 5.2 Hz, 1 H, Ar), 7.25–7.30 (m, 1 H,
Ar), 7.39–7.41 (m, 1 H, Ar), 7.60–7.65 (m, 3 H, Ar), 7.77 (d, J =
8.4 Hz, 2 H, Ar), 7.82 (d, J = 8.8 Hz, 1 H, Ar), 7.87 (d, J = 8.0 Hz,
1 H, Ar), 8.14–8.17 (m, 2 H, Ar), 8.24 (dd, J1 = 1.6, J2 = 8.0 Hz,
9,9-Dihexadecyl-7-(1,10-phenanthrolin-2-yl)-9H-fluorene-2-carbo-
nitrile (L-2): Yield 140 mg (34%); yellow oil. H NMR (400 MHz,
1
CDCl3): δ = 0.56–0.65 (m, 4 H, CH2), 0.83 (t, J = 6.8 Hz, 6 H,
CH3), 1.01–1.25 (m, 52 H, CH2), 2.02–2.11 (m, 4 H, CH2), 7.61–
7.65 (m, 3 H, Ar), 7.76–7.83 (m, 3 H, Ar), 7.89 (d, J = 8.0 Hz, 1
H, Ar), 8.11–8.14 (m, 2 H, Ar), 8.25 (d, J = 8.0 Hz, 1 H, Ar), 8.33
(d, J = 8.4 Hz, 1 H, Ar), 8.45 (d, J = 8.0 Hz, 1 H, Ar), 9.21–9.23
(m, 1 H, Ar) ppm; 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.6,
23.8, 29.2, 29.3, 29.51, 29.55, 29.6, 29.9, 31.9, 40.2, 55.8, 110.1,
119.8, 120.6, 121.1, 121.3, 122.0, 123.0, 126.3, 126.5, 127.6, 128.1,
129.1, 131.3, 136.1, 136.9, 140.2, 140.7, 145.3, 146.2, 146.4, 150.4,
151.9, 152.0, 157.6 ppm; HRMS: m/z calcd. for [C58H79N3 + H]+
818.6347; found 818.6358. C58H79N3·0.5H2 O: calcd. C 84.21, H
9.75, N 5.08; found C 83.95, H 10.02, N 4.93.
1 H, Ar), 8.31 (d, J = 8.4 Hz, 1 H, Ar), 8.45 (dd, J1 = 1.6, J2
=
8.0 Hz, 1 H, Ar), 9.25 (dd, J1 = 1.6, J2 = 4.4 Hz, 1 H, Ar) ppm;
13C NMR (100 MHz, CDCl3): δ = 14.1, 22.6, 23.8, 29.2, 29.3, 29.5,
29.6, 30.0, 31.9, 40.4, 55.4, 120.2, 120.5, 121.0, 121.9, 122.8, 122.9,
124.5, 124.9, 126.1, 126.4, 127.4, 127.7, 128.0, 129.0, 133.4, 136.0,
136.7, 138.9, 140.3, 141.9, 145.2, 146.2, 146.4, 150.3, 151.3, 152.2,
158.2 ppm; HRMS: m/z calcd. for [C61H82N2S + H]+ 875.6271;
found 875.6294. C61H82N2S·toluene (967.5 = 875.39+92.1): calcd.
C 84.41, H 9.38, N 2.90; found C 84.62, H 9.51, N 3.42.
2-(9,9-Dihexadecyl-7-iodo-9H-fluoren-2-yl)-1,10-phenanthroline (L-
1
3): Yield 543 mg (59%); yellow oil. H NMR (400 MHz, CDCl3):
δ = 0.66–0.67 (m, 4 H, CH2), 0.85 (t, J = 6.4 Hz, 6 H, CH3), 1.04–
1.29 (m, 52 H, CH2), 1.96–2.12 (m, 4 H, CH2), 7.48 (d, J = 8.0 Hz,
1 H, Ar), 7.59–7.68 (m, 3 H, Ar), 7.73–7.82 (m, 3 H, Ar), 8.08–
8.12 (m, 2 H, Ar), 8.21–8.23 (m, 1 H, Ar), 8.29 (d, J = 8.4 Hz, 1
H, Ar), 8.39–8.42 (m, 1 H, Ar), 9.21–9.23 (m, 1 H, Ar) ppm; 13C
NMR (100 MHz, CDCl3): δ = 14.1, 22.6, 23.7, 29.2, 29.3, 29.5,
29.6, 29.8, 31.9, 40.3, 55.6, 120.3, 121.0, 121.7, 121.8, 122.8, 126.2,
126.3, 127.4, 127.8, 129.0, 132.1, 135.9, 136.0, 136.7, 139.5, 140.4,
141.3, 146.2, 146.4, 150.4, 150.6, 153.7, 158.0 ppm; HRMS: m/z
calcd. for [C58H79IN2 + H]+ 919.5361; found 919.5366. C58H79IN2
(931.18): calcd. C 74.48, H 8.66, N 3.05; found C 74.55, H 8.64, N
3.05.
Typical Procedures for Complexation with PtII:[11c,12] A mixture of
L-x (1.00 equiv.), [K2PtCl4] (1.25 equiv.) in a mixture of chloroform
and acetic acid (1:10 v/v) was heated to reflux for 24 h under argon.
The orange solid was filtered, washed with water and diethyl ether
several times, and then dried.
Complex Pt-1: Yield 106 mg (59%); orange solid. 1H NMR
(400 MHz, CDCl3): δ = 0.62–0.74 (m, 4 H, CH2), 0.82 (t, J =
6.8 Hz, 6 H, CH3), 1.04–1.24 (m, 52 H, CH2), 2.01–2.10 (m, 4 H,
CH2), 7.41 (s, 1 H, Ar), 7.73–7.77 (m, 4 H, Ar), 7.94 (d, J = 8.4 Hz,
1 H, Ar), 8.15–8.18 (m, 3 H, Ar), 8.27 (dd, J1 = 1.2, J2 = 8.4 Hz,
1 H, Ar), 8.40 (d, J = 8.0 Hz, 1 H, Ar), 9.04 (d, J = 4.0 Hz, 1 H,
Ar) ppm; 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 23.9, 29.3,
29.5, 29.60, 29.63, 30.0, 31.9, 40.3, 55.4, 118.0, 118.7, 119.6, 121.1,
2-(9,9-Dihexadecyl-9H-fluoren-2-yl)-1,10-phenanthroline (L-4):
1
Yield 260 mg (66%); yellow oil. H NMR (400 MHz, CDCl3): δ =
0.65–0.72 (m, 4 H, CH2), 0.84 (t, J = 5.6 Hz, 6 H, CH3), 1.02–1.26 123.4, 126.1, 126.3, 126.7, 127.0, 127.8, 131.0, 136.5, 137.2, 140.9,
(m, 52 H, CH2), 1.99–2.10 (m, 4 H, CH2), 7.28–7.37 (m, 3 H, Ar),
7.58 (dd, J1 = 4.4, J2 = 8.0 Hz, 1 H, Ar), 7.69–7.77 (m, 3 H, Ar),
7.86 (d, J = 7.6 Hz, 1 H, Ar), 8.10–8.13 (m, 2 H, Ar), 8.19 (d, J =
142.2, 146.2, 147.2, 147.4, 148.1, 148.2, 149.4, 152.6, 165.2 ppm;
HRMS: m/z calcd. for [C57H78ClN3O2Pt + Na]+ 1089.5323; found
1089.5488. C57H78ClN3O2Pt (1067.81): calcd. C 64.12, H 7.36, N
8.0 Hz, 1 H, Ar), 8.26 (d, J = 8.4 Hz, 1 H, Ar), 8.42 (d, J = 8.0 Hz, 3.94; found C 63.86, H 7.70, N 4.04.
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Complex Pt-2: Yield 60 mg (47%); orange solid. 1H NMR 144.8, 145.2, 145.9, 146.5, 147.5, 149.1, 152.4, 165.2 ppm; HRMS:
(400 MHz, CDCl3): δ = 0.59–0.72 (m, 4 H, CH2), 0.82 (t, J = m/z calcd. for [C61H81ClN2PtS + Na]+ 1126.5349; found 1126.5367.
6.8 Hz, 6 H, CH3), 1.04–1.24 (m, 52 H, CH2), 1.97–2.02 (m, 4 H, C61H81ClN2PtS (1104.93): calcd. C 66.31, H 7.39, N 2.54; found C
CH2), 7.38 (s, 1 H, Ar), 7.58 (s, 1 H, Ar), 7.64 (d, J = 8.0 Hz, 1 H,
Ar), 7.72–7.77 (m, 4 H, Ar), 7.91 (d, J = 8.0 Hz, 1 H, Ar), 8.11–
8.18 (m, 2 H, Ar), 8.39 (d, J = 8.0 Hz, 1 H, Ar), 9.04 (d, J = 4.8 Hz,
1 H, Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 23.9,
29.3, 29.5, 29.60, 29.65, 30.0, 31.9, 40.3, 55.2, 110.3, 118.6, 119.5,
119.9, 121.5, 126.0, 126.2, 126.7, 126.9, 127.5, 131.0, 131.4, 136.4,
137.2, 140.9, 142.7, 145.5, 146.2, 146.8, 147.3, 148.1, 149.4, 152.1,
66.16, H 7.33, N 2.62.
Photophysical Measurements: The UV/Vis absorption spectra were
acquired with an Agilent 8453 spectrophotometer in HPLC grade
solvents. The steady-state emission spectra were recorded with a
SPEX fluorolog-3 fluorometer/phosphorometer in different sol-
vents. The emission quantum yields of the PtII complexes were de-
termined by a comparative method in degassed solutions,[23] in
which a degassed aqueous solution of [Ru(bpy)3]Cl2 (Φem = 0.042,
λex = 436 nm) was used as the reference.[24] The excited-state life-
times, the triplet excited-state quantum yields, and the triplet tran-
sient difference absorption spectra were measured in degassed solu-
tions with an Edinburgh LP920 laser flash photolysis spectrometer.
The third harmonic output (355 nm) of a Nd:YAG laser (Quantel
Brilliant, pulsewidth ca. 4.1 ns, repetition rate was set at 1 Hz) was
used as the excitation source. Each sample was purged with argon
for at least 30 min prior to measurement.
165.3 ppm; HRMS: m/z calcd. for [C58H78ClN3Pt
+
Na]+
1069.5429; found 1069.5424. C58H78ClN3Pt·H2O·Et2O (1140.0 =
1047.82+18.0+74.1): calcd. C 65.33, H 7.96, N 3.69; found C 65.42,
H 7.73, N 4.20.
Complex Pt-3: Yield 77 mg (39%); orange solid. 1H NMR
(400 MHz, CDCl3): δ = 0.69–0.84 (m, 10 H, CH2 + CH3), 1.07–
1.25 (m, 52 H, CH2), 1.93–1.98 (m, 4 H, CH2), 7.24 (s, 1 H, Ar),
7.50 (d, J = 8.8 Hz, 1 H, Ar), 7.53–7.60 (m, 4 H, Ar), 7.66–7.69
(m, 2 H, Ar), 7.89 (s, 1 H, Ar), 7.94 (d, J = 8.8 Hz, 1 H, Ar), 8.24
(d, J = 8.0 Hz, 1 H, Ar), 8.77 (d, J = 4.0 Hz, 1 H, Ar) ppm; 13C
NMR (100 MHz, CDCl3): δ = 14.3, 22.9, 24.2, 29.5, 29.6, 29.82,
29.86, 30.3, 32.1, 40.6, 55.2, 93.7, 118.3, 119.6, 122.9, 125.9, 126.1,
126.6, 126.8, 126.9, 131.1, 132.1, 136.2, 136.4, 137.2, 140.8, 141.2,
143.9, 145.6, 145.9, 146.0, 147.7, 149.3, 154.1, 165.3 ppm; HRMS:
m/z calcd. for [C57H78ClIN2Pt + Na]+ 1170.4438; found 1170.4441.
C57H78ClIN2Pt (1148.70): calcd. C 59.60, H 6.84, N 2.44; found C
59.66, H 7.06, N 2.39.
The self-quenching rate constants (kq) in dichloromethane were de-
duced from the Stern–Volmer equation,
kobs = kq[c] + k0
(1)
where kobs is the measured radiative decay rate constant of the
emission (kobs = 1/τem) at a given concentration, kq is the self-
quenching rate constant, [c] is the concentration of the complex in
mol/L, and k0 (k0 = 1/τ0) is the decay rate constant of the excited
state at infinite dilute solution. A plot of the observed decay rate
constant vs. concentration should give a straight line. The slope of
the straight line corresponds to kq and the intercept corresponds
to k0.
Complex Pt-4: Yield 44 mg (23%); orange solid. 1H NMR
(400 MHz, CDCl3): δ = 0.67–0.84 (m, 10 H, CH2 + CH3), 1.07–
1.26 (m, 52 H, CH2), 1.95–2.05 (m, 4 H, CH2), 7.28–7.38 (m, 4 H,
Ar), 7.52–7.59 (m, 4 H, Ar), 7.85 (d, J = 6.8 Hz, 1 H, Ar), 7.96–
7.99 (m, 2 H, Ar), 8.26 (d, J = 8.0 Hz, 1 H, Ar), 8.82 (d, J = 4.4 Hz,
1 H, Ar) ppm; 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.6, 24.1,
29.3, 29.4, 29.60, 29.64, 30.2, 31.9, 40.6, 54.7, 118.0, 119.5, 121.1,
125.5, 125.9, 126.5, 126.8, 126.9, 127.7, 130.9, 136.3, 137.0, 140.9,
141.0, 144.7, 144.9, 145.9, 146.3, 147.4, 149.1, 151.5, 165.4 ppm;
HRMS: m/z calcd. for [C57H79ClN2Pt + Na]+ 1044.5472; found
1044.5508. C57H79ClN2Pt (1022.81): calcd. C 66.94, H 7.79, N 2.74;
found C 67.20, H 8.14, N 2.65.
The triplet excited-state absorption coefficient (εT) at the absorp-
tion band maximum was measured by the singlet depletion
method,[25] in which the optical density changes during transient
absorption at the minimum of the bleaching band (ΔODS) and the
maximum of the positive band (ΔODT) were recorded; εT was then
calculated using Equation (2)[25]
εs ϫΔODT
Complex Pt-5: Yield 110 mg (73%); orange solid. 1H NMR
(400 MHz, CDCl3): δ = 0.62–0.84 (m, 10 H, CH2 + CH3), 1.05–
1.23 (m, 52 H, CH2), 2.00–2.14 (m, 4 H, CH2), 7.35–7.39 (m, 2 H,
Ar), 7.49 (t, J = 7.6 Hz, 1 H, Ar), 7.67–7.68 (m, 4 H, Ar), 7.89–
7.95 (m, 2 H, Ar), 8.04–8.13 (m, 5 H, Ar), 8.34–8.35 (m, 1 H, Ar),
8.98 (d, J = 3.2 Hz, 1 H, Ar) ppm; 13C NMR (100 MHz, CDCl3):
δ = 14.3, 22.9, 24.2, 29.5, 29.6, 29.8, 30.3, 32.1, 40.7, 55.4, 118.6,
119.8, 121.5, 121.7, 121.8, 123.2, 125.2, 126.0, 126.3, 126.5, 126.9,
127.0, 127.3, 127.5, 131.2, 133.0, 135.3, 136.6, 137.3, 141.0, 144.1,
144.3, 145.9, 146.3, 147.5, 148.1, 149.5, 152.6, 154.5, 165.6,
εT
=
(2)
ΔODS
where εs is the ground-state molar extinction coefficient at the elec-
tronic absorption band maximum.
The quantum yield of the triplet excited state formation (ΦT) was
determined by using the comparative method,[26] in which SiNc in
benzene (ΦT = 0.20, εT,590 = 70,000 m–1 cm–1)[27] was used as the
reference. All the solutions were optically matched at the excitation
wavelength (355 nm), and ΦT was calculated using Equation (3)[26]
169.0 ppm; HRMS: m/z calcd. for [C64H82ClN3PtS
+
Na]+
1177.5458; found 1177.5717. C64H82ClN3PtS·H2O: calcd. C 65.48,
H 7.21, N 3.58; found C 65.11, H 7.19, N 3.61.
(3)
where ΔODTs and ΔODTref are the maximum optical density change
during transient absorption from the sample and the reference,
respectively; εTref and εTs are the triplet molar extinction coefficients
of this transition at the wavelength where ΔODT is measured for
the reference and the sample, respectively. ΦT is the triplet ex-
cited-state quantum yield of the reference.
Complex Pt-6: Yield 60 mg (40%); orange solid. 1H NMR
(400 MHz, CDCl3): δ = 0.73–0.85 (m, 10 H, CH2 + CH3), 1.12–
1.25 (m, 52 H, CH2), 2.01–2.10 (m, 4 H, CH2), 7.11 (dd, J1 = 3.6,
J2 = 5.2 Hz, 1 H, Ar), 7.29–7.31 (m, 2 H, Ar), 7.41 (d, J = 4.0 Hz,
1 H, Ar), 7.52–7.66 (m, 6 H, Ar), 7.84 (d, J = 8.0 Hz, 1 H, Ar),
7.95 (s, 1 H, Ar), 7.98 (d, J = 8.4 Hz, 1 H, Ar), 8.27 (d, J = 8.0 Hz,
1 H, Ar), 8.83 (d, J = 4.4 Hz, 1 H, Ar) ppm; 13C NMR (100 MHz,
ref
Nonlinear Transmission Measurements: The experimental setup was
CDCl3): δ = 14.1, 22.6, 24.1, 29.3, 29.4, 29.6, 30.2, 31.9, 40.6, 54.9, similar to a system that has been described previously.[28] The light
118.1, 119.5, 119.9, 121.5, 123.0, 124.6, 125.1, 125.5, 125.9, 126.4,
126.5, 126.8, 128.1, 130.9, 133.8, 136.2, 137.0, 140.5, 141.0, 144.4,
source was the second harmonic output (λ = 532 nm) of a 4.1 ns
(fwhm), 10 Hz, Q-switched Quantel Brilliant Nd:YAG laser. A f =
Eur. J. Inorg. Chem. 2013, 4732–4742
4741
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www.eurjic.org
FULL PAPER
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Received: April 10, 2013
Published Online: July 9, 2013
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim