Red/near-infrared luminescence tuning of group-14 element complexes of dipyrrins based on a central atom

Article abstract of DOI:10.1021/ic402116j

A dipyrrin complex has been one of the most utilized fluorescent dyes, and a variety of dipyrrin complexes show intriguing functions based on the various coordination structures of the central element. We now report the synthesis, structure, and photophysical properties of germanium and stannane complexes of the N2O2-type tetradentate dipyrrin, L·Ge and L·Sn, which are heavier analogues of the previously reported dipyrrin silicon complex, L·Si. The central group-14 atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the square-pyramidal (SP) character becomes higher as the central atom is heavier. Interestingly, L·Sn formed a dimeric structure in the crystal. All complexes L·Si, L·Ge, and L·Sn showed a fluorescence in the red/NIR region. Fluorescence quantum yields of L·Ge and L·Sn are higher than that of L·Si. These results indicated that the central atom on the dipyrrin complexes contributes not only to the geometry difference but also to tuning the fluorescence properties.

Full text of DOI:10.1021/ic402116j

Article
pubs.acs.org/IC
Red/Near-Infrared Luminescence Tuning of Group-14 Element
Complexes of Dipyrrins Based on a Central Atom
Masaki Yamamura,† Marcel Albrecht,‡ Markus Albrecht,‡ Yoshinobu Nishimura,† Tatsuo Arai,†
and Tatsuya Nabeshima*,†
†Graduate School of Pure and Applied Sciences & Tsukuba Research Center for Interdisciplinary Materials Science, University of
Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
‡Institut fur Organische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
S
* Supporting Information
ABSTRACT: A dipyrrin complex has been one of the most
utilized fluorescent dyes, and a variety of dipyrrin complexes
show intriguing functions based on the various coordination
structures of the central element. We now report the synthesis,
structure, and photophysical properties of germanium and
stannane complexes of the N2O2-type tetradentate dipyrrin, L·
Ge and L·Sn, which are heavier analogues of the previously
reported dipyrrin silicon complex, L·Si. The central group-14
atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the
square-pyramidal (SP) character becomes higher as the central atom is heavier. Interestingly, L·Sn formed a dimeric structure in
the crystal. All complexes L·Si, L·Ge, and L·Sn showed a fluorescence in the red/NIR region. Fluorescence quantum yields of L·
Ge and L·Sn are higher than that of L·Si. These results indicated that the central atom on the dipyrrin complexes contributes not
only to the geometry difference but also to tuning the fluorescence properties.
Recently, germanium and stannane complexes of the N2O2-
type dipyrrin, heavier analogues of the silicon complex, have
been reported as polymerization catalysts.4 However, their
fluorescent properties have not been investigated. We now
report the synthesis, structure, and photophysical properties of
the germanium and stannane complexes (Chart 1). The notable
finding in this study is the effect of the heavier atoms (Ge and
Sn) on the red shift and enhancement of the fluorescence.
INTRODUCTION
■
Development of fluorescent materials has been important for
applications to fluorescent sensors, biolabels, and laser dyes.
Among a huge number of fluorophores, a dipyrrin−boron
complex (BODIPY) has been one of the most utilized
fluorescent dyes because of their sharp and intense absorption
in the visible region, high fluorescent quantum yield, and high
chemical and photochemical stability.1 A variety of dipyrrin
complexes containing a central atom other than boron have
been found to show intriguing functions based on the various
coordination structures of the central element, for example, self-
assembly,2 anion sensing,3 polymerization catalysis,4 and
detoxification of a biological oxidant.5 We recently reported
the first synthesis of dipyrrin−silicon hypercoordinate com-
plexes6 and their strong luminescent properties utilizing the
N2O2-type tetradentate dipyrrins.7 The hypercoordinate
structure of the dipyrrin−silicon complexes is stabilized by a
chelate effect of the five-membered rings. The dipyrrin−silicon
complexes have a pentacoordinate silicon center (hyper-
coordinate structure) having one more substituent than the
N2O2-type BODIPYs. As the hypercoordinate silicon com-
pound features facile bond dissociation on the silicon center,8
the dipyrrin silicon complexes can be assembled and
disassembled via bond formation and dissociation as follows:
a dipyrrin−silicon complex bearing a Si−OH group was
dehydrated to form a dipyrrin dimer bridged through a Si−
O−Si bond. In addition, the dative Si−O−Si bond was
reversibly dissociated and reformed to switch the red/NIR
luminescence.
Chart 1. Dipyrrin Complexes L·Si, L·Ge, and L·Sn
RESULTS AND DISCUSSION
■
Silicon complex L·Si was synthesized by reaction of the N2O2-
type ligand LH3 with PhSiCl3 in the presence of tertiary amine
(Scheme 1).7 The corresponding germanium and tin analogues,
L·Ge and L·Sn, were similarly obtained using PhGeCl3 and
PhSnCl3, respectively.
Received: August 19, 2013
Published: January 14, 2014
© 2014 American Chemical Society
1355
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360

Inorganic Chemistry
Article
bond. The reported N2O2-dipyrrin germanium and stannane
complexes similarly adopted TBP and octahedral structures,
respectively.4 A direct structural comparison of L·Ge and L·Sn
is difficult because their coordination numbers are different.
Monomeric structures of L·Si, L·Ge, and L·Sn were optimized
by DFT calculations.10 Structural parameters obtained by the
X-ray analysis and DFT calculations are summarized in Table 1.
The Nap−Ge−Oap angle (167.65(5)° (X-ray) and 166.08°
(calcd)) of L·Ge is distorted from the idealized value (180°) of
the TBP structure, whereas the silicon analogue L·Si has Nap−
Si−Oap angles (177.80(9)° (X-ray) and 172.73° (calcd)) closer
to 180°. The Nap−Sn−Oap angle (163.08°) of the calculated L·
Sn is narrower than that of L·Ge. Contrary to the Nap−E−Oap
angles, the Neq−E−Oeq angles widen in the order L·Si
(123.28°) < L·Ge (125.72°) < L·Sn (127.87°) in the calculated
structures. The distortions of these two angles are indicative of
the contribution of the square-pyramidal (SP) character. In the
three compounds, the Neq−E−Oeq of L·Si is the closest angle
to that of TBP (120°). In order to evaluate the SP
contributions, the τ values were calculated: τ = 1 for an
idealized TBP and τ = 0 for an SP.11 τ values based on the
calculated structures were 0.82, 0.67, and 0.59 for L·Si, L·Ge,
and L·Sn, respectively, which indicated that the order of the SP
character is in the order L·Si < L·Ge < L·Sn.
Scheme 1
X-ray structural analysis of a single crystal of L·Ge revealed a
distorted trigonal-bipyramidal (TBP) structure of the Ge center
(Figure 1). One pyrrole and one phenoxy group of L·Ge
One more striking structural difference is the bite angle on
the methine carbon bridging the two pyrrole rings (Cpy−
Cmeso−Cpy′). The bite angles become larger in the order L·Si <
L·Ge < L·Sn in both the experimental (L·Si 120.8(2)°, L·Ge
123.2(2)°, and L·Sn 126.5(2)°) and the calculated (L·Si
121.2°, L·Ge 122.7°, and L·Sn 125.0°) structures.
Figure 1. Perspective drawing of L·Ge (50% probability). Hydrogen
atoms are omitted for clarity.
Although the two pyrroles of L·Si, L·Ge, and L·Sn are
nonequivalent in the crystal and calculated structures, the
6
1
pyrrole units are equivalent in the H and 13C NMR spectra.
This fact suggests that the pyrroles at the apical and equatorial
positions are exchangeable according to the Berry pseudor-
otation mechanism.12
occupy the apical position of the TBP structure, and the other
three groups lie at equatorial positions. A similar TBP geometry
was observed in the silicon analogue L·Si. In contrast to L·Si
and L·Ge, L·Sn has a dimeric structure in the crystal (Figure 2),
which is formed by intermolecular Sn···O bonds (bond length
2.2537(18) Å). It is well known that many tin compounds
having Sn−O bonds undergo aggregation through the Sn···O
bonds (2.0−2.4 Å).9 L·Sn has an octahedral Sn center having
five valence bonds and one intermolecular Sn···O coordination
Absorption spectra of L·Si, L·Ge, and L·Sn were measured in
chloroform. Silicon complex L·Si showed an intense absorption
at 612 nm along with a shoulder ascribed to a vibrational band
(Figure 3, Table 2).6 The absorption spectral shape of L·Sn was
very similar to L·Si, but absorption of L·Sn was observed in the
red-shifted region (maximum 637 nm). Absorption of L·Ge is
broader, and the maximum value is intermediate (620 nm)
between those of L·Si and L·Sn.
TD DFT calculations were performed to clarify the
excitations of the dipyrrin complexes.15 The excitation energies
to the S1 states for L·Si, L·Ge and L·Sn were determined to be
2.429 eV (f = 0.43), 2.402 eV (f = 0.45), and 2.431 eV (f =
0.52), respectively (Table 3). All S1 excitations of the three
compounds are assigned to the HOMO−LUMO transitions
with more than 97% contributions. The frontier Kohn−Sham
orbitals of the three complexes are very similar to each other,
and none of them includes the atomic orbitals of the central
atoms (Figure 4). The frontier orbital energies of L·Si are the
lowest among the three. This prediction was reproduced by
cyclic voltammetry (CV) measurements (Table 4, Figures S1−
S3, Supporting Information). CV of all complexes, L·Si, L·Ge,
and L·Sn, exhibited one reversible one-electron reduction wave
with ΔEp values of ∼70 mV and two quasi-reversible one-
electron oxidation waves with ΔEp values in the range of 80−97
mV at 100 mV/s. Electrochemical parameters are summarized
in Table 4. Both the oxidation and the reduction potential of L·
Figure 2. Perspective drawing of L·Sn (50% probability). Hydrogen
atoms and solvent molecule are omitted for clarity. Oxygen atom
involved in the intramolecular coordination is tentatively defined as
the Oeq of L·Sn, here.
1356
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360

Inorganic Chemistry
Article
Table 1. Coordination Parameters of Pentacoordinate Dipyrrin Complexes L·Si, L·Ge, and L·Sn
L·Si
L·Ge
L·Sn
a
X-ray6
calcd
X-ray
calcd
X-ray (octahedral)
calcd (TBP)
bond lengths (Å)
Nap−E
Neq−E
Oap−E
Oeq−E
1.904(2)
1.807(2)
1.732(2)
1.688(2)
1.828(3)
1.922
1.847
1.742
1.708
1.894
1.976(2)
1.919(2)
1.859(1)
1.825(1)
1.939(2)
1.996
1.924
1.880
1.842
1.935
2.125(2)
2.130
2.100
1.975
1.963
2.101
2.117(2)
2.0234(18)
2.1077(17)
2.147(3)
Ceq−E
Oap···E (intermolecular)
bond angles (deg)
Nap−E−Oap
Nap−E−Neq
Nap−E−Oeq
Nap−E−Ceq
Oap−E−Neq
Oap−E−Oeq
Oap−E−Ceq
Neq−E−Oeq
Neq−E−Ceq
Oeq−E−Ceq
Cpy−Cmeso−Cpy′
2.2537(18)
177.80(9)
88.22(9)
172.73
87.00
88.00
93.61
90.71
87.50
93.63
123.28
113.38
123.32
121.2
167.65(5)
88.12(5)
86.71(5)
97.14(5)
90.29(5)
84.93(5)
94.65(5)
129.93(5)
114.71(5)
115.35(5)
123.2(2)
166.08
87.43
86.80
98.18
90.21
83.46
95.24
125.72
115.23
119.02
122.7
166.97(8)
86.79(8)
84.21(8)
97.40(9)
89.40(8)
94.17(7)
95.62(9)
155.00(8)
106.66(9)
97.62(8)
126.5(2)
163.08
84.00
84.50
97.55
87.94
88.78
99.31
127.87
113.60
118.26
125.0
88.50(9)
90.56(10)
91.61(9)
89.72(9)
91.38(10)
121.45(10)
123.00(12)
115.45(12)
120.8(2)
a
Apical and equatorial positions of the octahedral L·Sn are defined as shown in Figure 2.
Table 3. Singlet Electronic Excitation of L·Si, L·Ge, and L·Sn
Based on TD DFT Using the M06-2X Functional
transition states
calcd (eV)
exp. (eV)
L·Si
S1 (97% HOMO−LUMO)
S2 (96% HOMO-1−LUMO)
S3 (84% HOMO-2−LUMO)
S1 (98% HOMO−LUMO)
S2 (96% HOMO-1−LUMO)
S3 (91% HOMO-2−LUMO)
S1 (98% HOMO−LUMO)
S2 (96% HOMO-1−LUMO)
S3 (92% HOMO-2−LUMO)
2.429 (f = 0.43)
3.406 (f = 0.23)
3.850 (f = 0.03)
2.402 (f = 0.45)
3.322 (f = 0.21)
3.750 (f = 0.06)
2.431 (f = 0.52)
3.400 (f = 0.21)
3.750 (f = 0.07)
2.01
2.87
3.85
1.99
2.83
3.84
1.94
2.85
3.84
L·Ge
L·Sn
Figure 3. UV−vis absorption spectra of L·Si6 (black), L·Ge (blue),
and L·Sn (red) in CHCl3 (3 μM).
Fluorescence spectra of L·Si, L·Ge, and L·Sn were measured
in chloroform with the excitation at 550 nm. All fluorescence
spectra of these complexes were mirror images of the
Si are the highest among the three, as expected from the
calculations.
Table 2. Spectroscopic and Photophysical Data of L·Si, L·Ge, and L·Sn
absorption
fluorescence
a
λabs/nm
ε/cm−1·M−1
λflu/nm
τ0/ns
Φ
kr × 10−7/s−1
knr × 10−7/s−1
b
b
b
L·Si
L·Ge
L·Sn
612
4.4 × 104
3.5 × 104
4.2 × 104
650
0.18
1.9
0.028 (0.028)
0.12 (0.13)
0.22
16
550
45
620
637
675
664
6.9
6.9
3.2
25
a
Quantum yields were determined by the absolute method using an integrating sphere instrument.13 The parentheses values of L·Si and L·Ge are
b
quantum yields determined by the relative method using L·Sn as a standard. Reference 14.
1357
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360

Inorganic Chemistry
Article
converted to the nonradiative rotation energy of the meso-Ph
group.
Although the contributions of the meso-Ph group to the
LUMOs of the three compounds are almost the same, L·Ge
and L·Sn have higher quantum yields, 12% and 22%,
respectively, than L·Si. This is probably because the wider
Cpy−Cmeso−Cpy′ bite angles in L·Ge and L·Sn force the two
pyrroles closer to the meso-Ph group, which inhibit internal
rotation of meso-Ph. Rate constants for S1 to S0 decay via
radiative (kr) and nonradiative (knr) processes are determined
by the fluorescence quantum yields and lifetimes (τ0, Table 2).
Radiative rate constants (kr) are in a range typical of BODIPY
analogues.16 There is a definite correlation between the
nonradiative rate constants (knr) and the bite angles of L·Si,
L·Ge, and L·Sn, supporting the assumption that the large bite
angle inhibits rotation of the meso-Ph group.
In summary, the germanium and stannane complexes of the
N2O2-type dipyrrin were synthesized. Structures of the
dipyrrin group-14 complexes were studied by X-ray analysis
and DFT calculations. The central group-14 atoms of the
monomeric complexes have geometries close to TBP, in which
the contribution of the SP character becomes higher as the
central atom is heavier. Interestingly, L·Sn formed a dimeric
structure in the crystal. All complexes showed a fluorescence in
the red/NIR region in CHCl3. Fluorescence wavelengths of L·
Ge and L·Sn are red shifted compared to that of L·Si.
Furthermore, fluorescence quantum yields increase according
to the order of the periodic table. These results indicated that
the central atom on the dipyrrin complexes contributes not
only to the geometry difference but also to tuning of the
fluorescence properties. These findings should be important in
the design of advanced red/NIR fluorescent materials.
Figure 4. Frontier Kohn−Sham orbitals of L·Si, L·Ge, and L·Sn.
Table 4. Electrochemical Data of L·Si, L·Ge, and L·Sn
a
electrochemical data/V (ΔEp/mV)
Ered
Eox1
Eox2
1/2
1/2
1/2
L·Si
L·Ge
L·Sn
−1.131 (74)
−1.436 (72)
−1.422 (70)
0.826 (80)
0.397 (90)
0.512 (82)
1.082 (90)
0.848 (89)
0.995 (97)
a
Potentials versus Fc/Fc+ = 0.20 V in 0.1 M Bu4NClO4/CH2Cl2. Scan
rate: 100 mV/s. Glassy carbon working, platinum wire counter, and
Ag/Ag+ reference electrodes. E1/2 = (Epa + Epc)/2, ΔEp = Epa − Epc.
EXPERIMENTAL SECTION
■
General. All chemicals were reagent grade and used without further
purification. All reactions were performed under a nitrogen
atmosphere. Melting points were determined using a Yanaco and are
uncorrected. 1H NMR spectra were recorded on a Varian Inova 400 at
400 MHz. 13C NMR spectra were recorded by a Varian Inova 400 at
100 MHz. In these NMR measurements, tetramethylsilane was used as
the internal standard (0 ppm). IR spectra were recorded by a PE-
1760FT spectrometer. High-resolution mass spectra (ESI-TOF,
positive mode) were recorded by a Thermo Finnigan LCQ Deca XP
Plus and ThermoFischer Scientific LTQ Ortitrap XL.
corresponding absorption spectra (Figure 5). The fluorescence
of L·Sn is slightly red shifted compared to L·Si. L·Ge has the
Synthesis of L·Ge. To a solution of 1,9-bis(2-hydroxyphenyl)-5-
(phenyl)dipyrrin (LH3)18 (40 mg, 0.1 mmol) in 20 mL of dry THF
were added N,N-diisopropylethylamine (0.34 mL, 2.0 mmol) and
phenylgermanium trichloride (77 mg, 0.3 mmol). The mixture was
stirred at room temperature for 40 h; then 4 mL of methanol was
added. After evaporation of the solvent, the crude product was
dissolved in dichloromethane (20 mL) and washed with a saturated
aqueous Na2CO3 solution. After drying over MgSO4 and evaporation
of the solvent, crude product was purified by column chromatography
(neutral alumina, CH2Cl2). P roduct was isolated as a green metallic
solid of L·Ge (34 mg, 73%).
Figure 5. FL spectra of L·Si (black), L·Ge (blue), and L·Sn (red) in
CHCl3 (3 μM, λex = 550 nm).
longest fluorescence wavelength (675 nm) of the three
complexes (Table 2). Noteworthy is that the fluorescence
quantum yields are also significantly dependent on the central
atom. The quantum yield of L·Si is very low (2.8%) because the
internal rotation of the meso-Ph group should cause an efficient
nonradiative decay.16 This prediction is suggested by the
LUMO orbitals that contain the orbitals on the meso-Ph
group.17 The delocalization of the LUMO orbital to the meso-
Ph group is responsible for the decrease in the transition energy
upon the Ph ring rotation. Thus, the excitation energy is
Mp 259−260 °C. 1H NMR (400 MHz, CDCl3): δ 6.86 (td, J = 1.3,
7.5 Hz, 2H), 6.88 (d, J = 4.5 Hz, 2H), 7.00 (d, J = 4.5 Hz, 2H), 7.14−
7.25 (m, 7H), 7.29 (td, J = 1.6, 7.6 Hz, 2H), 7.44−7.63 (m, 5H), 7.62
(dd, J = 1.6, 4.0 Hz, 2H). 13C NMR (100 Hz, CDCl3): δ 115.5, 117.0,
119.2, 121.5, 127.0, 127.9, 128.3, 129.3, 130.3, 130.6, 131.8, 132.3,
133.6, 135.9, 136.2, 139.3, 139.6, 158.6, 161.8. IR(KBr): ν (cm−1)
3053, 1601, 1546, 1492, 1428, 1333, 1242, 1198, 1124, 1059, 1026,
933, 849, 788, 749, 690. ESI-TOF MS observed m/z: 575.07861 [M +
Na]+, calcd for C33H22O2N2GeNa 575.07853. Anal. Calcd for
C33H22N2O2Ge: C, 71.91; H, 4.02; N, 5.08. Found: C, 71.48; H,
3.78; N, 4.94.
1358
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360

Inorganic Chemistry
Article
Synthesis of L·Sn. To a solution of 1,9-bis(2-hydroxyphenyl)-5-
(phenyl)dipyrrin (LH3) (40 mg, 0.1 mmol) in 20 mL of dry THF were
added N,N-diisopropylethylamine (0.34 mL, 2.0 mmol) and phenyltin
trichloride (91 mg, 0.3 mmol). The mixture was stirred at room
temperature for 20 h; then 4 mL of methanol was added. After
evaporation of the solvent, crude product was purified by column
chromatography (neutral alumina, CH2Cl2:MeOH, 2:1). Product was
isolated as a green metallic solid of L·Sn (48 mg, 80%).
ASSOCIATED CONTENT
* Supporting Information
X-ray crystallographic data, details of electrochemical and
photochemical experiments, DFT calculations, and CIF files.
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
Mp > 300 °C. 1H NMR (400 MHz, CDCl3): δ 6.71 (d, J = 4.5 Hz,
2H), 6.76 (td, J = 1.1, 7.5 Hz, 2H), 6.91 (d, J = 4.5 Hz, 2H), 7.06 (d, J
= 8.3 Hz, 2H), 7.17 (td, J = 1.6, 7.7 Hz, 2H), 7.23−7.30 (m, 5H), 7.43
(m, 2H), 7.49−7.52 (m, 5H). 13C NMR (100 Hz, CDCl3): δ 116.7,
118.4, 119.1, 123.1, 127.6, 127.7, 128.2, 128.9, 128.9, 130.6, 131.8,
133.7, 135.2, 137.1, 137.1, 140.1, 140.7, 160.4, 162.1. IR(KBr): ν
(cm−1) 3060, 2853, 2115, 1599, 1534, 1482, 1429, 1327, 1296, 1257,
1195, 1123, 1083, 1055, 1023, 846, 790, 752, 718. ESI-TOF MS obsd
m/z 637.03259 [M + K]+, calcd for C33H22O2N2KSn 637.03348. Anal.
Calcd for C33H22N2O2Sn·0.5CH2Cl2: C, 62.90; H, 3.62; N, 4.38.
Found: C, 63.07; H, 3.32; N, 4.23.
AUTHOR INFORMATION
Corresponding Author
*E-mail: nabesima@chem.tsukuba.ac.jp.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was financially supported by Grants-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan and by the Tokyo
Biochemical Research Foundation.
X-ray Crystallography. X-ray diffraction measurements of L·Ge
and L·Sn were performed using a Bruker APEXII ULTRA. X-ray
diffraction intensities were collected on a CCD diffractometer at 120 K
using Mo Kα (graphite monochromated, λ = 0.71073 Å) radiation.
Data were integrated with SAINT (Bruker, 2004), and an empirical
absorption correction (SADABS)19 was applied. The structure was
solved by the direct or Peterson method of SHELXS-97 and refined
using the SHELXL-97 program.20 All of the positional parameters and
thermal parameters of non-hydrogen atoms were anisotropically
refined on F2 by the full-matrix least-squares method. Hydrogen
atoms were placed at the calculated positions and refined riding on
their corresponding carbon atoms. Crystallographic data for L·Ge and
L·Sn were deposited with the Cambridge Crystallographic Data
Center as supplementary publications CCDC-955085 and 955086,
respectively. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax
(+44) 1223-336-033; email deposit@ccdc.cam.ac.uk).
REFERENCES
■
(1) (a) Treibs, A.; Kreuzer, F.-H. Justus Liebigs Ann. Chem. 1968, 718,
208. (b) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891.
(c) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008,
47, 1184.
(2) (a) Zhang, Y.; Thompson, A.; Rettig, S. J.; Dolphin, D. J. Am.
Chem. Soc. 1998, 120, 13537. (b) Yu, L.; Muthukumaran, K.;
Sazanovich, I. V.; Kirmaier, K.; Hindin, E.; Diers, J. R.; Boyle, P. D.;
Bocian, D. F.; Holten, D.; Lindsey, J. S. Inorg. Chem. 2003, 42, 6629.
(c) Wood, T. E.; Dalgleish, N. D.; Power, E. D.; Thompson, A.; Chen,
́
X.; Okamoto, Y. J. Am. Chem. Soc. 2005, 127, 5740. (d) Beziau, A.;
Baudron, S. A.; Guenet, A.; Hosseini, M. W. Chem.Eur. J. 2013, 19,
3215.
(3) Kobayashi, J.; Kushida, T.; Kawashima, T. J. Am. Chem. Soc. 2009,
131, 10836.
Electrochemical Studies. Cyclic voltamograms were recorded by
a BAS ALS/CHI model 750A. A Ag/AgNO3 reference electrode was
used. The working electrode was a 1-mm-diameter glassy carbon with
a platinum wire acting as the counter electrode. CV measurement was
taken at a scan rate of 100 mV/s. After measurements in 0.1 M
Bu4NClO4/CH2Cl2 without any internal reference, ferrocene was
added to the same sample and the electrochemical potential was
adjusted to ferrocenium/ferrocene as the internal reference (Fc/Fc+ =
0.0 V).
Photophysical Studies. UV−vis absorption spectra were
recorded by a JASCO V-660 spectrophotometer. Fluorescence spectra
and absolute quantum yields were recorded by a JASCO FP-8600
spectrometer and a Hamamatsu Photonics absolute PL quantum yield
measurement system C9920-02, respectively.13 Fluorescence decay
measurements were performed using a time-correlated single-photon
counting method.21 Laser excitation at 410 nm was achieved using a
diode laser (PicoQuant, LDH-P-C-405) with a power control unit
(PicoQuant, PDL 800-B) in a repetition rate of 2.5 MHz. Temporal
profiles of fluorescence decay were detected using a microchannel
plate photomultiplier (Hamamatsu, R3809U) equipped with a TCSPC
computer board module (Becker and Hickl, SPC630). Full-width at
half-maximum (fwhm) of the instrument response function was 51 ps.
Values of χ2 and Durbin−Watson parameters were used to determine
the quality of the fit obtained by nonlinear regression.22
(4) Nakano, K.; Kobayashi, K.; Nozaki, K. J. Am. Chem. Soc. 2011,
133, 10720.
(5) Rausaria, S.; Kamadulski, A.; Rath, N. P.; Bryant, L.; Chen, Z.;
Salvemini, D.; Neumann, A. L. J. Am. Chem. Soc. 2011, 133, 4200.
(6) Sakamoto, N.; Ikeda, C.; Yamamura, M.; Nabeshima, T. J. Am.
Chem. Soc. 2011, 133, 4726.
(7) (a) Bloom, S. M.; Garcia, P. P. US Pat. 3,691,161, 1972. (b) Kim,
H.; Burghart, A.; Welch, M. B.; Reibenspies, J.; Burgess, K. Chem.
Commun. 1999, 1889.
(8) (a) Corriu, R. J. P.; Young, J. C. In The Chemistry of Organic
Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Willey & Sons:
Britain, 1989, 1241. (b) Hosomi, A. Acc. Chem. Res. 1988, 21, 200.
(c) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. Rev. 1993,
93, 1371. (d) Holmes, R. R. Chem. Rev. 1990, 90, 17.
(9) (a) Smith, P. J.; White, R. F. M.; Smith, L. J. Organomet. Chem.
1972, 40, 341. (b) Choi, J.-C.; Sakakura, T.; Sako, T. J. Am. Chem. Soc.
1999, 121, 3793. (c) Whittleton, S. R.; Rolle, A. J.; Boyd, R. J.;
Grindley, T. B. Organometallics 2010, 29, 6384.
(10) In the preliminary calculations of L·Si and L·Ge, the M06-2X
functional affords the best results among the various functionals
(B3LYP, PBE1PBE, B3PW91, and X3LYP), which are closest to the
experimental values. Thus, geometry optimization of L·Sn was
performed by utilizing the M06-2X functional with 6-31G(d,p) basis
set for C, H, N, and O and LANL2DZ for Sn. M06-2X functional:
Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215.
(11) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton. Trans. 1984, 1349.
Computational Methods. DFT calculations were performed
using the Gaussian09 packages23 with the M06-2X functional.10 Basis
sets 6-31G(d,p) for C, H, N, O, Si, and Ge and LANL2DZ for Sn were
used for geometry optimizations and vibrational analysis, and 6-311+
+G(d,p) for C, H, N, O, Si, and Ge and LANL2DZ for Sn were used
for time-dependent calculations. The effective core potential24 was
included in LANL2DZ basis sets.
(12) Berry, R. S. J. Chem. Phys. 1960, 32, 933.
(13) (a) Suzuki, K.; Kobayashi, A.; Kaneko, S.; Takehira, K.;
Yoshihara, T.; Ishida, H.; Shiina, Y.; Oishi, S.; Tobita, S. Phys. Chem.
Chem. Phys. 2009, 11, 9850. (b) Ishida, H.; Tobita, S.; Hasegawa, Y.;
Katoh, R.; Nozaki, K. Coord. Chem. Rev. 2010, 254, 2449.
1359
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360

Inorganic Chemistry
Article
(14) The λmax value of L·Si (650 nm) is a little different from the
previous reported one (660 nm). See ref 6. In this study, the spectral
difference was observed after repeated recrystallization of L·Si.
Fluorescence decay of the recrystallized sample showed a single
component (Figure S6, Supporting Information), indicating the high
purity of L·Si in spectroscopic grade. The high purity of L·Ge and L·
Sn was also supported by the fluorescence decay (Figures S7 and S8,
Supporting Information).
(15) Calculation methods for the excitation states of the dipyrrin
complex derivatives have been thoroughly tested. We selected M06-
2X, which is the most adequate functional predicting a reliable
excitation state consistent with experimental results. Generally, the
theoretical transition energies in this calculation are much higher than
the experimental ones. However, the systematically constant deviation
enables a comparison of the different derivatives. Although the energy
differences among the three complexes are so small that the calculated
S1 excitation energy is not comparable to the experimental value,
deviations in our compounds are within acceptable limits. See:
Chibani, S.; Le Guennic, B.; Charaf-Eddin, A.; Laurenta, A. D.;
Jacquemin, D. Chem. Sci. 2013, 4, 1950.
(16) (a) Li, F.; Yang, S. I.; Ciringh, Y.; Seth, J.; Martin, C. H., III;
Singh, D. L.; Kim, D.; Birge, R. R.; Bocian, D. F.; Holten, D.; Lindsey,
J. S. J. Am. Chem. Soc. 1998, 120, 10001. (b) Sazanovich, I. V.;
Kirmaier, C.; Hindin, E.; Yu, L.; Bocian, D. F.; Lindsey, J. S.; Holten,
D. J. Am. Chem. Soc. 2004, 126, 2664. (c) Kee, H. L.; Kirmaier, C.; Yu,
L.; Thamyongkit, P.; Youngblood, W. J.; Calder, M. E.; Ramos, L.;
Noll, B. C.; Bocian, D. F.; Scheidt, W. R.; Birge, R. R.; Lindsey, J. S.;
Holten, D. J. Phys. Chem. B 2005, 109, 20433.
(17) At 77 K in THF/CH2Cl2 (2:3 v/v) glass matrix under aerobic
conditions all complexes showed emission spectra similar to those at
room temperature (Figure S4, Supporting Information).
(18) Ikeda, C.; Ueda, S.; Nabeshima, T. Chem. Commun. 2009, 2544.
(19) Sheldrick, G. M. SADABS, Program for empirical absorption
correction; Universitat Gottingen: Gottingen, Germany, 1996.
̈
̈
̈
(20) Sheldrick, G. M. SHELX97, Program for crystal structure
determination; Universitat Gottingen: Gottingen, Germany, 1997.
̈
̈
̈
(21) Nishimura, Y.; Kamada, M.; Ikegami, M.; Nagahata, R.; Arai, T.
J. Photochem. Photobiol. A 2006, 178, 150.
(22) Boens, N.; Tamai, N.; Yamazaki, I.; Yamazaki, T. Photochem.
Photobiol. 1990, 52, 911.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.;
Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. GAUSSIAN 09,
Revision A.02; Gaussian, Inc.: Wallingford CT, 2009.
(24) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.;
Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
1360
dx.doi.org/10.1021/ic402116j | Inorg. Chem. 2014, 53, 1355−1360