Z. Si et al. / Journal of Organometallic Chemistry 694 (2009) 3742–3748
3743
9.22–9.24 (2H, m), Anal. Calc. for C16H11N3: C, 78.35; H, 4.52; N,
17.13. Found: C, 78.69; H, 4.33; N, 16.98%. IR (KBr): 743, 1481,
1625, 3085 cmꢀ1
the reference electrode, at a scan rate of 0.1 V/s. The voltammo-
grams were recorded in CH3CN solutions with ꢁ10ꢀ3 M sample
and 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as
the supporting electrolyte. In order to precisely calculate the en-
ergy levels of the HOMO and the LUMO, the offset potentials are
determined by the point of intersection of the tangential lines near
the beginning part of the redox peaks. Prior to each electrochemi-
cal measurement, the solution was purged with nitrogen for ꢁ10–
15 min to remove the dissolved O2 gas.
m
.
2.1.2. Synthesis of Phen–Re
Phen (0.036 g, 0.200 mmol), Re(CO)5Br (0.081 g, 0.200 mmol)
and 15 mL toluene were refluxed in a flask for 9 h. After the mix-
ture was cooled to RT, the solvent was removed in a water bath un-
der reduced pressure. The resulting yellow solid was washed with
CH2Cl2. Yield: 0.085 g (80%). 1H NMR (CDCl3, 400 MHz): d 7.87–
7.91 (2H, m), 8.045 (2H, s), 8.55–8.57 (2H, tetr), 9.43–9.45 (2H,
tetr). Anal. Calc. for C15H8BrN2O3Re: C, 33.97; H, 1.52; N, 5.28.
2.3. Computational details
Found: C, 34.38; H, 1.24; N, 5.44%. IR (KBr):
m 1425, 1895, 1929,
The geometrical structures of the ground states were optimized
by the density functional theory (DFT) [14] with Becke’s LYP
(B3LYP) exchange-correlation functional [15]. On the basis of the
optimized ground state geometry structures, the absorption spec-
tral properties in CH2Cl2 media were calculated by time-dependent
DFT (TDDFT) [16] approach associated with the polarized contin-
uum model (PCM) [17]. To investigate solvent effect, the singlet
absorption spectra of Phen–Re and PyPh–Re in the gas phase were
also theoretically studied at the same level. The 6-31G* [18–20] ba-
sis set was employed on C, H, N, O, and Br atoms, and LANL2DZ ba-
sis set was adopted on Re atom. To intuitively understand the
transition process, the calculated isosurface plots for the frontier
molecular orbitals of Phen–Re and Pyph–Re involved in the tran-
sitions were prepared by using the GAUSSVIEW 3.07 software and
shown in Figs. 4 and 5, respectively. All the calculations were per-
formed with the GAUSSIAN 03 software package [21].
2017, 3083 cmꢀ1
.
2.1.3. Synthesis of Pyph–Re
The procedure is similar to that of Phen–Re. Yield: 84%. 1H NMR
(CDCl3, 400 MHz): d 7.86–7.93 (2H, m), 8.01 (2H, s), 8.48–8.56 (2H,
m), 9.44–9.48 (2H, m). Anal. Calc. for C19H11BrN3O3Re: C, 38.33; H,
1.86; N, 7.06. Found: C, 38.52; H, 1.60; N, 7.27%. IR (KBr):
m 1479,
1894, 1920, 2022, 3047 cmꢀ1
.
2.2. Measurements
The IR spectra were acquired using a Magna560 FT-IR spectro-
photometer. Element analyses were performed using a Vario Ele-
ment Analyzer. 1H NMR spectra were obtained using a Bruker
AVANVE 400 MHz spectrometer with tetramethylsilane as the
internal standard. The absorption and PL spectra of the degassed
solution with 10ꢀ4 mol/L sample were recorded on a Lambda 750
spectrometer and a Hitachi model F–4500 fluorescence spectro-
photometer, respectively. The luminescence quantum yields
(LQYs) were measured by comparing fluorescence intensities (inte-
grated areas) of a standard sample (quinine sulfate) and the un-
known sample according to the following equation:
3. Results and discussion
3.1. Synthesis and characterization
As depicted in Scheme 1, Pyph was synthesized from the reac-
tion between Phen–NH2 and DMOTHF in HOAc [22]. Phen–Re
and Pyph–Re were obtained in a previously reported approach
[23]. The structures of Pyph, Pyph–Re, and Phen–Re were fully
verified with elemental analysis, IR, UV–Vis, and 1H NMR
spectroscopy.
2
Uunk
¼
UstdðIunk=AunkÞðAstd=IstdÞðgunk
=
gstd
Þ
where Uunk is the LQY of the unknown sample; Ustd is the LQY of
quinine sulfate and taken as 0.546 [12]; Iunk and Istd are the inte-
grated fluorescence intensities of the unknown sample and quinine
sulfate with the excitation wavelength of 400 nm for bromo Re(I)
complexes and 364 nm for quinine sulfate. Aunk and Astd are the
absorbances of the unknown sample at 400 nm and quinine sulfate
at 364 nm, respectively. The gunk and gstd are the refractive indices
of the corresponding solvents (pure solvents were assumed). The
excited-state lifetimes were detected by a system equipped with
a TDS 3052 digital phosphor oscilloscope pulsed Nd:YAG laser with
a THG 299 nm output and a computer-controlled digitizing oscillo-
scope according to the reported method [13]. The ORIGIN 7.0 program
by OriginLab Corporation was used for the curve-fitting analysis.
The absorption and emission spectral data of Phen–Re and Pyph–
Re in CH2Cl2 media and solid state are listed in Table 1.
3.2. Photophysical properties
Fig. 1 presents the powder-sample based excitation and PL
spectra and the CH2Cl2 solution based UV–Vis absorption spectra
of Phen–Re and Pyph–Re. The higher-energy absorption bands
of Phen–Re and Pyph–Re in ca. 230–330 nm region should be as-
signed to the admixture of ligand-based charge-transfer
p ? p*
(ILCT/LLCT) transitions, and the lower-energy features in ca. 330–
500 nm are tentatively assigned to the metal-to-ligand charge-
transfer dp (Re) ? p*(N-N) (MLCT) transitions. These assignments
are confirmed by the UV–Vis absorption spectra of the free ligands
and the theoretical calculations (vide infra).
Cyclic voltammetry measurements were conducted on a vol-
tammetric analyzer (CH Instruments, Model 620B) with a polished
Pt plate as the working electrode, Pt mesh as the counter electrode,
and a commercially available saturated calomel electrode (SCE) as
Similar to the previous reports, the broad and lower-energy
bands in the absorption spectra partially resolve into two bands
in scanning the excitation spectra, namely, 1MLCT transition states
with peaks at 390, 410 nm and 3MLCT transition states with peaks
Table 1
Absorption, excitation, and emission spectral parameters of Phen–Re and Pyph–Re in CH2Cl2 and solid state at RT.
Complex
Medium
Absorption
k/nm
Excitation
Emission
k/nm
kmax (W1/2)/nm
u (degass)
Phen–Re
Pyph–Re
CH2Cl2
Solid
CH2Cl2
Solid
267, 292, 377, 411
310, 420
354, 453
372, 464
269, 329, 365, 488
554 (90)
527 (76)
588 (88)
578 (73)
0.015
254, 290, 323, 402
0.011