Study on the structureeproperty relationship in a series of novel BF2 chelates with multicolor fluorescence

Article abstract of DOI:10.1016/j.jorganchem.2013.06.012

A series of multicolor fluorescent N,O-bidentate BF2 complexes with variable ligand structures have been synthesized. These complexes exhibit the solvent-independent optical properties and large Stoke shifts. The electrochemical measurements demonstrate that all these chelates are better electron acceptors than the commonly used material Alq3. A qualitative structureeproperty relationship among these complexes has been established on the ground of the experimental data along with the density functional theory (DFT) calculations. The theoretically calculated results are in good agreement with those obtained by the experimental determinations.

Full text of DOI:10.1016/j.jorganchem.2013.06.012

Journal of Organometallic Chemistry 743 (2013) 1e9
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Study on the structureeproperty relationship in a series of novel BF2
chelates with multicolor fluorescence
*
Qi-Chao Yao, Ding-Er Wu, Ru-Zheng Ma, Min Xia
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of multicolor fluorescent N,O-bidentate BF2 complexes with variable ligand structures have been
synthesized. These complexes exhibit the solvent-independent optical properties and large Stoke shifts.
The electrochemical measurements demonstrate that all these chelates are better electron acceptors
than the commonly used material Alq3. A qualitative structureeproperty relationship among these
complexes has been established on the ground of the experimental data along with the density func-
tional theory (DFT) calculations. The theoretically calculated results are in good agreement with those
obtained by the experimental determinations.
Received 17 March 2013
Received in revised form
5 June 2013
Accepted 11 June 2013
Keywords:
Multicolor fluorescence
N,O-bidentate BF2 complex
Structureeproperty correlation
Photophysical performance
Electrochemical behavior
DFT calculation
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
than 30 nm) due to their rigid structures. Such small shifts usually
result in the serious self-absorption of fluorescence and the
Organoboron complexes are one of the most important types of
fluorescent dyes. Among them, boron dipyrromethenes (BODIPYs)
are the most well-known fluorophores with N,N-bidentate ligands
[1e3]. Due to the outstanding properties such as high fluorescence
quantum yields and extinction coefficients, excellent photochemical-
and chemical-stability, long excited-state lifetimes, large two-photon
cross-sections for multiphoton excitation, good solubility, and nar-
row emission spectra with high color purity, this type of complexes
are widely used as chemosensors [4e10], laser dyes [11,12], sensi-
tizers in solar cells [13,14], probes in detecting molecular rotor vis-
cosity [15,16] as well as agents in photodynamic therapy [17,18].
Apart from BODIPYs, other fluorescent organoboron complexes with
novel N,N-bidentate ligands such as pyridomethenes [19,20], pyr-
idylimidazoles [21e23] and others [24e30] have been continuously
developed.
decreased quantum yields. Contrarily, the shifts of N,O-bidentate
complexes are so much large (more than 40 nm [31e33]) that
discrimination against the incident and the emitted rays, which
is very crucial for fluorescent bioanalysis, can be dramatically
improved. Additionally, typical BODIPYs are faint or non-fluorescent
in solid state owning to the strong
pep stacking of the planar flu-
orophores, so that excitation energy through the electronic in-
teractions among molecules is substantially dissipated. Such
drawback can be efficiently overcome in cases of N,O-bidentate
organoboron complexes. Many of them turn to be intensely fluo-
rescent in aggregated or solid state [34,35]. This property enables
them to be as the appealing materials in field of organic electrolu-
minescence devices (OLEDs). Interestingly, a few of N,O-bidentate
organoboron complexes exhibit the attractive aggregation-induced
emission (AIE) effect [36]. These complexes with the AIE effect
can be exploited as indicators for viscosity and vapor pressure.
Therefore, it is quite necessary to develop more and more novel
N,O-bidentate organoboron complexes and explore their intriguing
properties.
However, compared with N,N-bidentate organoboron fluo-
rophores, the research on their cousins, N,O-bidentate complexes, is
relatively limited. Actually, N,O-bidentate compounds contain the
properties which are different from those of BODIPYs. For example,
the Stokes shifts of the typical BODIPYs are very small (usually less
Although we have carried out some primary research on the BF2
complexes with 2-(arylethylidene)-3,4-dihydroquinoxalin-2(1H)-
one ligands [37], it is still significant to reveal the structuree
property relationship for this type of BF2 chelates based on the
detailed measurements and the theoretic calculations. Herein we
* Corresponding author. Tel.: þ86 571 86843757.
E-mail address: xiamin@zstu.edu.cn (M. Xia).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.06.012

2
Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
describe the synthesis, characterization, determination of the op-
tical and electrochemical properties along with the DFT calcula-
tions of these multicolor-emitting BF2 chelates.
1a: 86% yield, yellow powder, m.p. 244.1e244.8 ꢁC; 1H NMR
(400 MHz, DMSO-d6)
13.67 (s, 1H), 12.05 (s, 1H), 7.98 (d, J ¼ 7.3 Hz,
2H), 7.63e7.47 (m, 4H), 7.15e7.12 (m, 3H), 6.83 (s, 1H); 13C NMR
(100 MHz, DMSO-d6) 188.36, 155.66, 145.60, 138.63, 131.81,
d
d
2. Experimental
128.66, 126.95, 126.71, 124.09, 123.92, 123.60, 116.49, 115.35, 89.14;
EI-MS (70 eV) m/z (%) 264 (Mþ,100), 235 (75),187 (43),159 (38),131
(36), 118 (19), 105 (88), 90 (18), 77 (93), 51 (30), 43 (34).
2.1. Materials and measurements
1b: 92% yield, yellow crystal, m.p. 219.8e220.6 ꢁC; 1H NMR
All the reagents used were analytically pure and some chemicals
were further purified by recrystallization or distillation. Melting
points were determined by an OptiMelt automated melting point
system. The 1H NMR (400 MHz), 13C NMR (100 MHz), 11B NMR
(128 MHz) and 19F NMR (376 MHz) spectra were obtained on a Bruker
Avance II DMX400 spectrometer using DMSO-d6 or CDCl3 as the
solvent. The 1H and the 13C NMR experiments were carried out using
(400 MHz, CDCl3)
d
14.06 (s, 1H), 8.04 (d, J ¼ 7.8 Hz, 2H), 7.53e7.46
(m, 3H), 7.26e7.21 (m, 3H), 7.16 (t, J ¼ 7.8 Hz, 1H), 7.11 (d, J ¼ 7.2 Hz,
2H), 7.06 (s, 1H), 6.98 (t, J ¼ 7.8 Hz, 1H), 6.57 (d, J ¼ 8.3 Hz, 1H), 3.90
(s, 3H); 13C NMR (100 MHz, CDCl3)
d 190.39, 159.98, 156.57, 145.00,
138.88, 131.90, 129.86, 129.39, 128.64, 128.53, 127.44, 125.11, 124.39,
123.53, 116.41, 116.32, 115.51, 91.20, 55.57; EI-MS (70 eV) m/z (%)
370 (Mþ, 76), 341 (83), 316 (14), 265 (21), 222 (25), 206 (17), 193
(20), 105 (100), 91 (20), 77 (60), 43 (36).
tetramethylsilane as the internal standard while the 11B and the 19
F
NMR spectra were recorded using BF3OEt2 (0 ppm) and CF3COOH
(76.5 ppm) as the external standards, respectively. The absorption
spectra were measured on a Shimadzu UV 2501(PC)S UVevis spec-
trometer and the fluorescence spectra were acquired on a Perkine
Elmer LS55 spectrophotometer. The quantum yields were measured
with quinine sulfate in 0.1 M sulfuric acid (Ff ¼ 0.55) or fluorescein in
0.1 N NaOH (Ff ¼ 0.91) as the reference. The cyclic voltammograms
were obtained on a ChenHua CHI660b electrochemical working
station with 2 mM sample in anhydrous acetonitrile solution of 0.1 M
tetrabutylammonium perchlorate, using a carbon glass as the
working electrode, a platinum wire as the counting electrode and a
Ag/AgNO3 (0.01 M) pair as the reference electrode. The scan rate was
at 30 mV/s with 0.5 mM ferrocene (Fc/Fcþ) as the internal standard.
The absolute HOMO energy level of Fc/Fcþ is assumed as ꢀ4.88 eV
[38]. The E1/2 potential of Fc/Fcþ against Ag/Agþ in 0.1 M Bu4NþClOꢀ4 /
MeCN was detected to be 0.085 V, which was very close to the re-
ported value [64,65]. ELUMO (eV) ¼ ꢀ(Ered/onset þ 4.88) [39,40], where
Ered/onset value was calibrated against the potential of Fc/Fcþ pair.
1c: 83% yield, orange powder, m.p. 217.1e217.5 ꢁC (decomp.); 1H
NMR (400 MHz, CDCl3)
d 14.24 (s, 1H), 10.57 (s, 1H), 8.03 (d,
J ¼ 7.1 Hz, 2H), 7.56e7.43 (m, 3H), 7.19 (d, J ¼ 8.5 Hz, 1H), 6.94 (s,
1H), 6.77 (d, J ¼ 8.9 Hz, 1H), 6.67 (s, 1H), 3.82 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) d 185.88,156.43,155.76,145.80,138.48, 131.57,
128.72, 128.23, 127.01, 126.76, 118.49, 110.43, 99.81, 88.21, 55.43; EI-
MS (70 eV) m/z (%) 294 (Mþ, 66), 265 (24), 217 (10),189 (13),161 (8),
118 (14), 105 (100), 77 (60), 51 (17), 43 (15).
1d: 78% yield, red powder, m.p. 245.7e246.4 ꢁC (decomp.); 1H
NMR (400 MHz, DMSO-d6)
(m, 2H), 7.65e7.45 (m, 3H), 7.33 (s, 1H), 6.84 (s, 1H), 6.76 (s, 1H),
3.81 (s, 3H), 3.77 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
184.69,
d 14.19 (s, 1H), 12.06 (s, 1H), 8.05e7.91
d
165.73, 155.07, 146.73, 146.40, 145.81, 138.38, 131.36, 128.65, 126.58,
118.06, 101.70, 99.15, 88.23, 55.99, 55.79; EI-MS (70 eV) m/z (%) 324
(Mþ, 100), 309 (38), 296 (12), 281 (15), 263 (11), 219 (20), 203 (8),
191 (11), 175 (11), 147 (20), 105 (100), 77 (91), 51 (26), 39 (7).
1e: 85% yield, yellow powder, m.p. 231.2e232.7 ꢁC (decomp.);
1H NMR (400 MHz, DMSO-d6)
d 13.59 (s, 1H), 12.00 (s, 1H), 7.98
EHOMO (eV) ¼ ꢀ(ELUMO
þ
optEg), where optEg was obtained from the
lowest-energy edge of UVevis absorption spectra.
(d, J ¼ 8.8 Hz, 2H), 7.48 (d, J ¼ 3.5 Hz, 1H), 7.136e7.10 (m, 3H), 7.07
(d, J ¼ 8.8 Hz, 2H), 6.79 (s, 1H), 3.85 (s, 3H); 13C NMR (100 MHz,
DMSO-d6)
d 169.79, 163.69, 153.46, 152.08, 130.48, 129.79, 128.18,
2.2. Computational details
124.36, 123.99, 123.87, 121.08, 116.34, 114.79, 89.34, 55.71; EI-MS
(70 eV) m/z (%) 294 (Mþ, 100), 265 (23), 251 (9), 186 (83), 158
(29), 135 (77), 107 (15), 92 (23), 77 (44), 64 (18), 51 (11), 39 (10).
1f: 73% yield, dark yellow powder, m.p. 232.4e233.0 ꢁC
The gas-phase geometries of the concerned complexes were
optimized without any symmetry restrictions in singlet ground
state using the density functional theory (DFT) method at the B3LYP
level [41,42]. The 6-31G (d, p) basis set was selected for all the el-
ements. The vibration frequency calculations were performed to
ensure that the optimized geometries represented the local minima
on the ground-state potential energy surface. All the calculations
were carried out with the Gaussian 09 program package in aid of
the GaussView visualization program [43]. The absorption spectra
based on the B3LYP optimized geometries were stimulated using
the time-dependent density functional theory (TD-DFT) and the
solvent effect was executed with the polarizable continuum model
(PCM) [44,45]. The geometric optimizations of the corresponding
excited singlet states were started from the optimized ground-state
geometries with the same functional and basis set. The emission
spectra were simulated with TD-DFT and PCM methods after the
check of the vibration frequencies.
(decomp.); 1H NMR (400 MHz, DMSO-d6)
d 11.74 (s, 1H), 11.06 (s,
1H), 7.40 (d, J ¼ 7.6 Hz, 1H), 7.15e6.95 (m, 3H), 5.50 (s, 1H), 4.16 (q,
J ¼ 7.0 Hz, 2H),1.24 (t, J ¼ 7.1 Hz, 3H); 13C NMR (100 MHz, DMSO-d6)
d
169.16, 155.53, 143.93, 125.11, 124.79, 123.36, 122.41, 115.25,
115.16, 83.73, 59.08, 14.28; EI-MS (70 eV) m/z (%) 232 (Mþ, 100), 186
(100), 158 (86), 130 (62), 103 (53), 90 (30), 77 (23), 63 (16), 52 (16),
39 (14).
2.4. Synthesis of ligand 1g
At room temperature and under nitrogen flow, sodium hydride
(60 wt% in oil, 1.80 g, 45 mmol) was added to the anhydrous THF
solution (30 mL) of 2-methylquinoline (30 mmol, 4.29 g) and ethyl
benzoate (40 mmol, 6.0 g). The solution was refluxed for 24 h. After
cooling to room temperature, the reaction mixture was added with
aq. NH4Cl and extracted with diethyl ether. The extract was dried
over MgSO4 and concentrated in vacuo. Column chromatography of
the residue on silica gel gave 1g (5.26 g, 71%) as a yellow powder.
1g: 73% yield, yellow powder, m.p. 271.4e272.1 ꢁC (decomp.); 1H
2.3. General procedure for synthesis of ligands 1aef
At room temperature, diamine (10 mmol) and substituted 2,4-
dioxo-butanoate (10 mmol) were added in dioxane (20 mL), the
resulted mixture was refluxed overnight to afford the precipitate.
After cooling to room temperature, the solid was filtrated and
washed with ethanol for several times. The ligand could be
recrystallized from ethanol.
NMR (400 MHz, CDCl3)
d
15.69 (s, 1H), 7.96 (d, J ¼ 4.0 Hz, 2H), 7.61
(d, J ¼ 9.1 Hz, 1H), 7.55e7.38 (m, 6H), 7.26e7.21 (m, 1H), 6.83 (d,
J ¼ 9.1 Hz, 1H), 6.07 (s, 1H); 13C NMR (100 MHz, CDCl3)
d 183.99,
154.04, 139.70, 137.67, 136.07, 130.90, 130.33, 128.21, 127.50, 126.58,
123.61, 123.21, 122.21, 118.05, 89.78; EI-MS (70 eV) m/z (%) 247

Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
3
(Mþ, 92), 219 (52), 170 (46), 143 (54), 115 (40), 105 (100), 77 (78), 51
(29), 43 (31), 30 (6).
2d: 76% yield, dark red powder, m.p. 301.4e302.0 ꢁC (decomp.);
1H NMR (400 MHz, DMSO-d6)
12.80 (s, 1H), 7.99 (d, J ¼ 7.8 Hz, 2H),
7.74e7.34 (m, 4H), 7.15 (s, 1H), 6.82 (s, 1H), 3.79 (s, 3H), 3.75 (s, 3H);
13C NMR (100 MHz, DMSO-d6)
166.81, 153.21, 150.51, 149.67,
145.86, 132.70, 132.45, 129.19, 126.89, 126.61, 117.59, 103.78, 98.42,
d
d
2.5. General procedure for synthesis of complexes 2aeg
90.39, 55.89, 55.86; 19F NMR (376 MHz, DMSO-d6)
d
ꢀ123.85
At room temperature, triethylamine (5 mmol, 0.505 g, 0.71 mL)
was dropped into the suspension of the corresponding ligand
(1 mmol) in CH2Cl2 (10 mL), the mixture was stirred for 30 min and
then boron trifluoride etherate (5 mmol, 0.705 g, 0.63 mL) was
added. The resulted mixture was stirred for 12 h and the solid was
filtrated. The solid was washed with ether for several times and
dried in vacuo. Column chromatography on silica gel gave the
complex as a powder or microcrystal.
(d, J ¼ 34.9 Hz); 11B NMR (128 MHz, CDCl3)
d 2.26 (s); EI-MS (70 eV)
m/z (%) 372 (Mþ, 100), 357 (2), 329 (14), 309 (49), 281 (9), 105 (66),
77 (40), 51 (9).
2e: 81% yield, red powder, m.p. 281.5e282.1 ꢁC (decomp.); 1H
NMR (400 MHz, DMSO-d6)
7.21e7.14 (m, 2H), 7.12e7.05 (m, 2H), 7.01 (s, 1H), 6.96 (d, J ¼ 8.8 Hz,
2H), 3.88 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
169.79, 163.67,
d
12.98 (s, 1H), 7.99 (d, J ¼ 8.8 Hz, 2H),
d
153.46, 152.08, 130.48, 129.79, 128.17, 124.36, 123.99, 123.87, 121.08,
2a: 88% yield, red powder, m.p. 294.7e295.3 ꢁC; 1H NMR
116.34, 114.79, 89.34, 55.71; 19F NMR (376 MHz, DMSO-d6)
(400 MHz, DMSO-d6)
J ¼ 7.4 Hz, 1H), 7.61 (t, J ¼ 7.5 Hz, 2H), 7.51 (t, J ¼ 7.6 Hz, 1H), 7.39e
7.32 (m, 2H), 7.28 (s, 1H); 13C NMR (100 MHz, DMSO-d6)
169.29,
d 12.88 (s, 1H), 8.14e8.09 (m, 3H), 7.68 (d,
d
ꢀ125.02 (d, J ¼ 33.6 Hz); 11B NMR (128 MHz, DMSO-d6)
d 2.49 (s);
EI-MS (70 eV) m/z (%) 342 (Mþ,100), 313 (38), 294 (10), 277 (17),157
(13), 135 (61), 107 (11), 92(14), 77 (32), 63 (17), 51 (10).
d
153.40, 152.61, 133.29, 132.13, 130.94, 129.27, 128.76, 127.30, 123.93,
2f: 88% yield, yellow powder, m.p. 172.0e172.5 ꢁC (decomp.); 1H
123.82, 121.38, 116.42, 90.45; 19F NMR (376 MHz, DMSO-d6)
NMR (400 MHz, DMSO-d6)
d
12.53 (s, 1H), 7.84 (d, J ¼ 8.0 Hz, 1H),
d
ꢀ122.95 (d, J ¼ 32.1 Hz); 11B NMR (128 MHz, DMSO-d6)
d 2.74 (s);
7.34 (d, J ¼ 8.0 Hz, 1H), 7.27e7.23 (m, 2H), 5.91 (s, 1H), 4.48 (q,
EI-MS (70 eV) m/z (%) 312 (Mþ,100), 283 (70), 247 (12), 219 (12),179
(17), 142 (12), 105 (52), 90 (12), 77 (64), 51 (17), 45 (37).
J ¼ 7.0 Hz, 2H),1.37 (t, J ¼ 7.0 Hz, 3H); 13C NMR (100 MHz, DMSO-d6)
d
170.00, 153.55, 153.13, 128.65, 126.38, 124.10, 123.71, 119.57,
2b: 90% yield, orange powder, m.p. 192.5e193.2 ꢁC; 1H NMR
116.24, 75.70, 65.84,14.03; 19F NMR (376 MHz, DMSO-d6)
d
ꢀ123.54
(400 MHz, CDCl3)
d
8.45 (d, J ¼ 8.3 Hz, 1H), 8.12 (d, J ¼ 8.0 Hz, 2H),
(d, J ¼ 34.1 Hz); 11B NMR (128 MHz, DMSO-d6)
d 2.48 (s); EI-MS
7.59 (t, J ¼ 7.3 Hz, 1H), 7.51 (t, J ¼ 7.5 Hz, 2H), 7.37 (s, 1H), 7.34 (t,
(70 eV) m/z (%) 280 (Mþ, 63), 232 (43), 186 (100), 158 (87), 130
(60), 103 (55), 90(35), 76 (19), 63 (16), 51 (14), 39 (13).
J ¼ 7.8 Hz, 1H), 7.29e7.23 (m, 3H), 7.15 (d, J ¼ 8.3 Hz, 2H), 6.75 (d,
J ¼ 8.3 Hz, 1H), 3.92 (s, 3H); 13C NMR (100 MHz, CDCl3)
d 172.32,
2g: 86% yield, bright yellow crystal, m.p. 230.8e231.6 ꢁC
160.45,154.04,151.43,133.32, 133.06,132.72,129.09,128.89,128.26,
128.01, 127.85, 125.14, 125.00, 122.74, 116.61, 115.78, 91.35, 55.64;
(decomp.); 1H NMR (400 MHz, CDCl3)
d
8.75 (d, J ¼ 8.7 Hz, 1H), 8.16
(d, J ¼ 8.7 Hz,1H), 8.02 (d, J ¼ 7.6 Hz, 2H), 7.80 (t, J ¼ 8.0 Hz,1H), 7.76
(d, J ¼ 7.9 Hz, 1H), 7.54 (t, J ¼ 7.5 Hz, 1H), 7.51e7.44 (m, 3H), 7.25 (d,
19F NMR (376 MHz, CDCl3)
d
ꢀ125.21 (d, J ¼ 35.7 Hz); 11B NMR
(128 MHz, DMSO-d6) d
2.24 (s); EI-MS (70 eV) m/z (%) 418 (Mþ, 51),
J ¼ 9.6 Hz, 1H), 6.42 (s, 1H); 13C NMR (100 MHz, CDCl3)
d 164.99,
389 (18), 370 (78), 341 (74), 265 (19), 222 (27), 206 (14), 193 (22),
105 (100), 77 (81), 63 (12), 51 (20), 39 (6).
153.96, 141.25, 139.52, 133.52, 132.43, 131.52, 128.58, 128.41, 126.84,
126.64, 126.49, 122.95, 121.13, 94.02; 19F NMR (376 MHz, CDCl3)
2c: 83% yield, red powder, m.p. 294.9e295.4 ꢁC (decomp.); 1H
d
ꢀ126.79 (q, J ¼ 18.8 Hz); 11B NMR (128 MHz, DMSO-d6)
d 2.52
NMR (400 MHz, DMSO-d6) d 12.84 (s, 2H), 8.11e7.98 (m, 6H), 7.65 (t,
(t, J ¼ 19.2 Hz); EI-MS (70 eV) m/z (%) 294 ((M ꢀ 1)þ, 100), 274 (12),
J ¼ 7.2 Hz, 2H), 7.58 (t, J ¼ 7.4 Hz, 4H), 7.25 (t, J ¼ 7.4 Hz, 2H), 7.20 (s,
2H), 7.19e7.12 (m, 3H), 7.00 (dd, J1 ¼ 7.4, J2 ¼ 2.6 Hz, 2H), 6.83 (d,
J ¼ 2.6 Hz, 2H), 3.84 (s, 6H), 2.30 (s, 3H); 13C NMR (100 MHz, DMSO-
230 (23), 115 (21), 101 (8), 77 (28), 51 (15), 39 (7).
d6)
d
167.40, 159.36, 153.67, 150.05, 137.33, 132.84, 132.76, 132.37,
3. Results and discussion
129.21, 128.88, 128.18, 126.99, 125.29, 122.98, 118.11, 112.11, 99.31,
90.16, 55.68, 21.02; 19F NMR (376 MHz, DMSO-d6)
d
ꢀ125.04 (d,
3.1. Synthesis of complexes 2aeg
J ¼ 34.1 Hz); 11B NMR (128 MHz, DMSO-d6)
d 2.15 (s); EI-MS (70 eV)
m/z (%) 342 (Mþ, 64), 313 (12), 105 (60), 91 (100), 77 (37), 45 (42),
The synthetic routes to BF2 complexes 2aeg are illustrated
in Scheme 1. The dioxane solutions of o-phenylenediamines and
39 (21).
Scheme 1. The synthetic routes to BF2 complexes.

4
Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
Scheme 2. The tautomeric equilibrium of ligands 1aeg.
2,4-dioxo-butanoates are refluxed overnight without any catalyst
to offer the ligands 1aef as the precipitates. A Claisen ester-
condensation is taken place when 2-methylquinoline subse-
quently reacts with ethyl benzoate in the presence of sodium hy-
dride, providing the ligand 1g as a yellow solid. The preparation of
the complexes 2aeg can be readily accomplished in good to
excellent yields by treating the ligands with excessive tri-
fluoroboron etherate under the basic condition. These BF2 com-
plexes can be well dissolved in many solvents and stored in solid
state under the atmosphere for several months with the negligible
decomposition.
On the 1H NMR spectra, the most obvious variation between a
ligand and its corresponding BF2 chelate is the disappearance of the
proton signal in the lowest-field region. Additionally, due to the
chelation with BF2 group, the proton signals go through a different
extent down-field shift from a parent ligand to its complex. On the
13C NMR spectra, a remarkably shielding effect occurs on the C1
atom owning to its transformation from a carbonyl to an enol. Thus,
a considerably up-field shift of the C1 signal takes place from
w190 ppm in a parent ligand to w165 ppm in its BF2 complex.
The striking difference between 2aef and 2g occurs on the 11B
and the 19F NMR spectra (Fig. 1). For 2g, its 11B and 19F NMR exhibit
a well-resolved triplet and a quartet resonance respectively. It is
assumed that a fast ring-flipping process which results in an
exchange-averaged conformation with the symmetrically equiva-
lent fluorines might be responsible for the NMR performances of 2g
in solutions [47]. For each of 2aef, however, a broad singlet signal of
11B and a doublet signal of 19F can be observed. Actually, these
signals should be considered as the poor-resolved triplet and
quartet resonances. This dramatically diminished resolution is
presumably caused by the ultrafast ring-flipping process in solu-
tions. Obviously, the frequency of the ring-flipping is related to the
structure of a complex.
3.2. NMR spectra study
Theoretically, there are three tautomers for a parent ligand, they
are enolimine (I), ketoimine (II) and ketoenamine (III) (Scheme 2).
However, both the 1H and the 13C NMR spectra clearly demonstrate
that only a sole tautomer exists in the solution of a given ligand. For
1g, only 1-phenyl-2-(quinolin-2-yl)ethanol, the enolimine tautomer,
can be detected in the CDCl3 solution. The ketoimine tautomer can be
completely excluded since its characteristic resonance of methylene
H2 atoms in the 4e5 ppm region is unobservable. Moreover, it is safe
to announce that a ketoenamine tautomer is impossible to occur in
the solution of 1g since the destruction of an aromatic system is
unreasonable. For 1aef, the existence of ketoimines can also be
entirely eliminated due to the absence of the methylene H2 signals in
the 3e4 ppm region. The lack of the methylene C2 chemical shifts at
w50 ppm on the 13C NMR spectra is the other evidence for the
elimination of ketoimines. It seems that ketoenamines are more
likely to be existent than enolimines in solutions of 1aef, as the
3.3. Photophysical feature
In general, an excellent mirror-image relationship with the fine
vibrations between the absorption and the emission spectra can be
observable for each complex, which implies that the vibration
levels in the S1 state are similar to those in the S0 state [48]. The
spectra of 2a and 2g are selected to be illustrated in Fig. 2.
Furthermore, the high molar extinction coefficients of these com-
1
relatively low-field H NMR signals at w14 ppm can be ascribed to
the formation of the intramolecular hydrogen bonds between the
oxygen atoms on the keto carbonyls and the active protons on the
enamino [46]. The DFT calculations test the above assumption
and reveal that ketoenamines are more thermodynamically
preferred than enolimines. As for 1a, 3-(2-oxo-2-phenylethylidene)-
3,4-dihydroquinoxalin-2(1H)-one (ketoenamine) is more stable than
3-(2-hydroxy-2-phenylvinyl)quinoxalin-2(1H)-one (enolimine) by
0.477 kcal/mol in the DMSO solution at 25 ꢁC.
plexes suggest that permitted pep* transitions occur in the process
of excitation. They display the intensely multicolor fluorescence in
solutions. The photos of them in the CH2Cl2 solution under a hand-
held ultraviolet lamp are shown in Fig. 3.
It is found that a qualitative correlation between the optical
properties and the molecular structures can be connected among
these BF2 complexes (Table 1). When the benzoyl in 2a is
substituted by the carbethoxyl in 2f, a substantially hypsochromic
Fig. 1. 11B NMR spectra of 2g (a) and 2d (c) along with 19F NMR spectra of 2g (b) and 2d (d).

Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
5
UV for 2a
FL for 2a
UV for 2g
FL for 2g
shows the much larger red shifts than 2a in the spectral maxima,
the former has the decreased molar extinction coefficient than
that of the latter. It is suggested that a molecular bend caused by
the steric hindrance between the two vicinal methoxyl groups on
the quinoxalinone moiety may account for the decreased molar
extinction coefficient of 2d [33,49,50].
The investigation of 2b reveals that its photophysical perfor-
mance is almost identical to that of 2a. This demonstrates that the
imposing of a p-methoxylphenyl group onto the amide moiety has
700
600
500
400
300
200
100
0
0.6
0.5
0.4
0.3
0.2
0.1
0.0
little dedication to the extension of
p-conjugation. This assumption
is tested to be reasonable by the DFT calculation of 2b.
Complex 2a and 2g are selected to survey the solvent effect
on their optical behaviors. It is indicated in Table 2 that both
their UVevis and fluorescent spectra are insensitive to the sol-
vatochromism. Not only the maxima but also the quantum yields
have the minute response to the variation of solvent polarity. This
solvent-independent optical property infers that an intramolecular
charge transfer (ICT) excited state can barely exist in the photo-
induced excitation [51e54]. This presumption is also verified to
be reliable by the time-dependent density functional theory
(TD-DFT) calculations.
350
400
450
500
550
600
650
Wavelength / nm
Fig. 2. Normalized spectra of complex 2a and 2g (solid lines for absorption and dash
lines for emission).
3.4. Electrochemical behaviors
Fig. 3. Photos of complex 2aeg in CH2Cl2 solution under a hand-hold 365 nm ultra-
violet lamp.
It was reported by the previous research that BODIPYs are good
electron acceptors [55]. Therefore, our N,O-bidentate BF2 com-
plexes, which are the cousins of BODIPYs, are expected to have good
electron-accepting abilities. The electrochemical behaviors of 2a
and 2f along with those of 1a and 1f are investigated by the cyclic
voltammetry (CV).
It is observed that the onset reduction potentials of 2a and 2f
undergo the considerably positive shifts in comparison with those
of 1a and 1f. The onset reduction potentials of 2a and 2f are ꢀ1.22 V
and ꢀ1.55 V respectively while those of 1a and 1f are ꢀ1.66 V
and ꢀ1.96 V respectively. Such positive shift in reduction potentials
from a ligand to a BF2 complex is similar to the case of the N,O-
bidentate BF2 chelates with perylene tetracarboxlic diimide ligands
[56]. The relatively positive reduction potential of a complex in-
dicates that a large decrease of the electronic density happens on it
due to the chelation of BF2 group.
shift of the spectral maxima along with the remarkable decrease of
the molar extinction coefficient occur. Such difference of their op-
tical behaviors should be attributed to the reduced electronic
density on the NeBeO chromophore from in 2a to in 2f. Similarly,
when the quinolinyl ring in 2g replaces the quinoxalinone ring in
2a, the spectra of the former go through a strikingly blue shift.
Clearly, the amide group in 2a makes a large contribution to the
long-wavelength absorption and emission.
Additionally, when a methoxyl is located on either the benzoyl
or the quinoxalinone moiety, the spectra of the corresponding
complex exhibit a bathochromic shift in comparison with those of
2a. For 2c where a methoxyl is introduced on the quinoxalinone
moiety, its spectra have the larger red shifts than those of 2e where
a methoxyl is attached on the benzoyl moiety. However, 2c has the
lower molar extinction coefficient than that of 2e. Although 2d
The electronic states (HOMO/LUMO levels) of 2aeg are inves-
tigated by CV. The recorded CV curves (Fig. 4(A)) demonstrate that
Table 1
Photophysical properties of N,O-chelated BF2 complexes.
Complex
R1
R2
R4
X
Y
Dicholoromethanea
b
lab (nm)
lem (nm)
ε ( ꢂ104 Mꢀ1 cmꢀ1
)
fc
Ffd
2a
2b
2c
2d
2e
2f
H
H
CH3O
CH3O
H
H
H
H
CH3O
H
C6H5
C6H5
C6H5
C6H5
4-CH3OC6H4
OC2H5
C6H5
NH
C]O
C]O
C]O
C]O
C]O
C]O
]CH
419, 442, 470
419, 445, 472
438, 460, 490
483, 514
428, 451, 481
379, 400, 426
403, 425
481, 512
482, 515
505, 534
541
493, 523
437, 460
437, 461
4.09
4.20
4.28
3.62
4.97
2.25
3.12
0.8253
0.8461
0.8390
0.7019
1.0222
0.5286
0.8415
0.64
0.59
0.74
0.71
0.66
0.46
0.84
4-CH3OC6H4NH
NH
NH
NH
NH
]CH
H
H
H
H
2g
a
Measured in 1.0 ꢂ 10ꢀ5 mol/L at 25 ꢁC.
b
c
Measured at the underlined wavelength.
Oscillator strength of the absorptions obtained with TD-DFTePCM calculations at B3LYP level with 6-31G (d,p) basis set.
Using quinine sulfate (Ff ¼ 0.55 in 0.5 mol/L H2SO4 aqueous solution) as the standard for 2feg while using fluorescein (Ff ¼ 0.91 in 0.1 mol/L NaOH aqueous solution) as
d
the standard for 2aee.

6
Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
Table 2
Solvent effect on complex 2a and 2g.
Solvent
Complex 2a
lab (nm)
Complex 2g
lem (nm)
F
=
FCH
lab (nm)
lem (nm)
=
F FCH
2Cl2
2 Cl2
Benzene
CHCl3
EtOAc
422, 447, 474
419, 444, 471
421, 442, 469
420, 443, 468
419, 442, 470
421, 444, 472
424, 446, 477
421, 445, 478
422, 444, 478
482, 513
483, 514
482, 513
480, 515
481, 512
483, 515
485, 520
484, 523
485, 521
0.94
0.99
0.96
1.03
1.00
0.93
0.91
0.95
1.05
386, 406, 429
387, 404, 427
386, 402, 423
387, 403, 425
386, 403, 425
384, 400, 421
384, 401, 422
382, 399, 419
384, 404, 426
440, 463
436, 462
436, 462
439, 461
438, 461
437, 460
436, 459
438, 460
443, 464
0.99
0.96
0.94
1.03
1.00
0.99
1.00
0.93
1.04
THF
CH2Cl2
(CH3)2CO
CH3OH
CH3CN
DMSO
there is a reversible one-electron reduction wave for each complex
except 2c and each complex has an irreversible oxidation wave.
There are many reports in literature that the optical energy gap
obtained from the lowest-energy edge of UVevis absorption
spectra can be used to replace the electrochemical energy gap in
estimation of the absolute HOMO or LUMO levels [59,60], as these
two energy gaps are always quite close to each other [27,62,63]. For
complex 2aeg, each LUMO level is determined by the onset
reduction potential based on the standard reduction waves. How-
ever, due to the existence of some unknown small peaks on the
oxidation waves for several complexes, the accurate onset oxida-
tion potentials become hard to be determined. Therefore, the
HOMO levels are estimated with the optical energy gaps and the
results are listed in Table 3.
It is indicated that both the HOMO and the LUMO levels are
enhanced for 2c and 2d where one and two methoxyl groups are
located at the quinoxalinone moiety, compared with those of 2e
whose methoxyl group is imposed at the benzoyl moiety. However,
the enhancement of the HOMO levels makes the more contribution
to the reduced energy gaps of 2c and 2d than that of the LUMO
(ꢀ3.0 eV) [57]. These comparisons suggest that our BF2 chelates
have the better electron-accepting capability than them.
3.5. Theoretical study
For the better understanding of the optical and electrochemical
properties displayed by 2aef, the DFT calculations are performed
under the polarizable continuum model (PCM) at the B3LYP level,
using the 6-31G (d,p) basis set for all atoms.
Complex 2f is chosen as an example to compare the simulated
and the experimental spectra (Fig. 5). Although the short-
wavelength regions cannot be acquired due to the limitations in
the instrument, the measured spectra are in good agreement with
the calculated ones in the long-wavelength regions. Regardless of
the fine vibrations, the calculated maxima are very close to the
experimental ones.
Table 3
Electrochemical data for complex 2aeg (vs Ag/Agþ) in anhydrous acetonitrile and
HOMOeLUMO gaps determined from spectroscopy and TD-DFT calculations.
levels. Similarly, owning to the shortage of the
p-conjugation
optEg
EHOMO
ELUMO
CalEg
a
b
b
c
d
d
d
Comp
Ered/onset
EHOMO
ELUMO
devoted by the p-methoxylphenyl group, the electrochemical per-
formance of 2b is almost identical to that of 2a. For 2f and 2g, it is
investigated that they show the much lower reduction potentials
and higher LUMO levels than those of 2aee. The greatly enhanced
LUMO levels should be responsible for the enlarged energy gaps of
2f and 2g. Fig. 4(B) clearly illustrates the relationship of the frontier
MOs among these complexes.
The electrochemical data show that the LUMO levels of our
complexes are lower than that of 1,3,5,7-tetramethyl-8-phenyl-
BODIPY (ꢀ3.05 eV) [27,32] which is a widely used BODIPY deriva-
tive and the commonly used electron-transport material Alq3
(V)
(eV)
(eV)
(eV)
(eV)
(eV)
(eV)
2a
2b
2c
2d
2e
2f
ꢀ1.22
ꢀ1.21
ꢀ1.28
ꢀ1.31
ꢀ1.23
ꢀ1.55
ꢀ1.63
ꢀ6.23
ꢀ6.23
ꢀ6.04
ꢀ5.89
ꢀ6.17
ꢀ6.18
ꢀ6.20
ꢀ3.66
ꢀ3.67
ꢀ3.60
ꢀ3.57
ꢀ3.65
ꢀ3.33
ꢀ3.25
2.57
2.56
2.44
2.32
2.52
2.85
2.85
ꢀ6.35
ꢀ6.27
ꢀ5.75
ꢀ5.48
ꢀ5.81
ꢀ6.21
ꢀ6.18
ꢀ3.14
ꢀ3.08
ꢀ2.70
ꢀ2.64
ꢀ2.65
ꢀ2.64
ꢀ2.65
3.21
3.19
3.05
2.84
3.16
3.57
3.59
2g
Calibrated Ered/onset with Fc/Fcþ as the internal standard.
ELUMO (eV) ¼ ꢀ(Ered/onset þ 4.88), EHOMO (eV) ¼ ꢀ(ELUMO
Calculated by lowest-energy edge of absorption spectra.
Obtained by MO calculations in acetonitrile.
a
b
c
þ
optEg).
d
Fig. 4. (A) Cyclic voltammograms for 2aeg (The wave at 0 V potential corresponds to Fc/Fcþ pair. All voltammograms are calibrated to the ferrocene anodic peak.); (B) Diagram on
HOMO and LUMO energy level of 2aeg.

Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
7
600
1.0
0.8
0.6
0.4
0.2
0.0
Experimental
Calculated
Experimental
Calculated
500
400
300
200
100
0
150 200 250 300 350 400 450 500 550
150 200 250 300 350 400 450 500 550 600 650 700
Wavelength / nm
Wavelength / nm
Fig. 5. Normalized absorption and emission spectra of 2f (solid lines for the experimental curves and dash lines for the simulated curves).
Complex 2a, 2f and 2g are screened as the candidates to run the
calculations so that the deep insight of their transition features can
be afforded. It is indicated in Table 4 that both the excitation and the
radiation transitions between the S0 and the S1 state are domi-
nantly contributed by the HOMO and the LUMO of each complex. In
the low-lying electronic states of these complexes, it is easy to
judge from the oscillator strengths that the S2 states are the “dark”
S2 states in which the involved absorptions and the emissions are
prohibited. There is a general assumption that the red shift emis-
sion is related to the enlarged dipole moment in the excited state
[58], as an excited state with the enlarged dipole moment can be
more stabilized in a polar solvent than a ground state. Conse-
quently, a tiny change of the dipole moments between the ground
and the excited state usually leads to the little solvatochrimism. The
data in Table 4 demonstrate that there is a minute variation of the
dipole moments between the S0 and the S1 state for each examined
complex. Hence, the nature for the solvent-insensitive optical be-
haviors of these complexes is clearly revealed by the theoretical
calculations.
properties of 2b are almost identical to those of 2a. For each of the
calculated complexes, the ICT transition rarely occurs in the photo-
induced excitation and the transition from the HOMO to the LUMO
should be assigned to a pep* transition.
The calculated HOMO and LUMO levels of 2aeg are listed in
Table 3. It is indicated that the calculated HOMO levels are in good
agreement with those obtained from the measured optical energy
gaps, but the computed LUMO levels are considerably over-
estimated. This overestimation of LUMO levels is very common for
the DFT calculations [27,59,60]. In spite of this overestimation, the
trend of HOMO-LUMO energy gaps in the theoretic study is still
entirely consistent with that in the experimental investigation. By
reference to 2a, the reduced energy gaps of 2cee predominantly
derive from the increase of the HOMO levels due to the extension of
the conjugated regions, while the enlarged energy gaps of 2feg
mainly result from the enhancement of the LUMO levels owning to
the diminished electron density on the NeBeO chromophores.
These calculation outcomes reasonably account for the spectral
performance of these BF2 chelates.
The visualized HOMOs and LUMOs of 2a, 2b, 2f and 2g are
illustrated in Fig. 6. Evidently, the distribution of the HOMO and the
LUMO in 2a, 2f and 2g is approximately donated by the atomic
orbitals throughout the whole molecule. For both the HOMO and
the LUMO of 2b, however, the electrons are completely excluded
from the p-methoxylphenyl moiety. Such exclusion results in the
Usually, homologous compounds have the structure-reliant
oscillator strengths [61]. Considering 2aef as a system, it is indi-
cated in Table 1 that 2e which has a methoxyl group at the benzoyl
moiety has the largest oscillator strength, but 2f where a carbe-
thoxyl takes the place of a benzoyl has the smallest one. The trend
of the calculated oscillator strengths among these complexes is in
perfect accordance with that of the measured molar extinction
coefficients. In term of 2g whose chemical structure is substantially
absence of the
p-conjugation participated by the p-methox-
ylphenyl moiety. Consequently, the optical and the electrochemical
Table 4
Selected electronic transition energies and corresponding oscillator strengths (f), main compositions and CI coefficients of the low-lying electronic excited states of complex 2a,
2f, 2g.
Complex
Dipole moment (D)
Electronic transition
TD-DFT/PCM/B3LYP/6-31G (d, p) (in CH2Cl2)
Energy (eV)
Oscillator strength (f)
Composition
CI
2a
4.033 (S0)
3.836 (S1)
S0
S0
S1
S2
S1
S2
S0
S0
2.84 (437 nm)
3.33 (372 nm)
2.51 (494 nm)
3.09 (401 nm)
0.8484
0.0489
0.8287
0.0429
H
H-1
L
L
0.7054
0.7000
0.7080
0.7008
L
H
H-1
L
2f
1.527 (S0)
1.307 (S1)
S0
S0
S1
S2
S1
S2
S0
S0
3.22 (385 nm)
3.73 (332 nm)
2.69 (461 nm)
3.02 (411 nm)
0.5500
0.0091
0.4420
0.0143
H
H-1
L
L
L
L
0.7036
0.6981
0.6996
0.1190
0.6861
L
H
H-3
H-1
2g
7.570 (S0)
7.512 (S1)
S0
S0
S1
S2
3.11 (399 nm)
3.80 (327 nm)
0.8250
0.0075
H
H-1
H
L
0.7034
0.6580
0.2331
0.6943
0.1110
0.5949
0.1181
0.3351
L
L þ 1
S1
S2
S0
S0
2.70 (460 nm)
3.35 (370 nm)
0.5690
0.0092
L
H
L þ 1
H
L
H-1
L þ 1
L þ 1
H-1
H

8
Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
Fig. 6. The selected frontier molecular orbitals of complex 2a, 2f, 2g and 2b.
Table 5
Selected electronic transition energies and corresponding oscillator strengths (f), main compositions and CI coefficients of the lowest electronic excited states of complex 2f.
Solvent
Dipole moment (D)
Electronic transition
TD-DFT/PCM/B3LYP/6-31G (d, p)
Energy (eV)
Oscillator strength (f)
Composition
CI
Benzene
1.235 (S0)
1.031 (S1)
S0
S1
S1
S0
3.21 (386 nm)
2.76 (450 nm)
0.5572
0.5092
H
L
L
H
0.70377
0.70737
Dichloromethane
Acetonitrile
1.527 (S0)
1.307 (S1)
S0
S1
S1
S0
3.22 (385 nm)
2.69 (461 nm)
0.5500
0.4420
H
L
L
H
0.70362
0.69957
1.722 (S0)
1.425 (S1)
S0
S1
S1
S0
3.23 (384 nm)
2.78 (446 nm)
0.5286
0.4874
H
L
L
H
0.70321
0.70734
distinct from that of 2a, no correlation between their oscillator
strengths and molar extinction coefficients can be connected.
Taking 2f as an example, we examine the solvent effect on the
dipole moments and the results are listed in Table 5. It is found that
the dipole moments of the S1 and the S0 state are increased as the
solvent polarity is enhanced, but the dipole moment of the excited
state is slightly smaller than that of the ground state in each of the
tested solvents. The minute difference of the dipole moments be-
tween the S0 and the S1 state in different solvents implies that the
transitions of 2f should be solvent-independent. Actually, the
spectral maxima, oscillator strengths, main compositions and CI
coefficients are all insensitive to the solvent polarity.
correlation has been established via the detailed measurements
and verified by the DFT calculations. It is revealed that (i) the
dramatically blue-shifted spectral bands along with the substan-
tially decreased molar extinction coefficient occur if a benzoyl is
substituted by a carbethoxy on a complex; (ii) the amide moiety
makes a large contribution for the long-wavelength fluorescence of
complexes, but the substituent on the amide moiety is barely
helpful for the extension of the p-conjugation; (iii) a complex with
an electron-donating group at the quinoxalinone moiety has the
larger red shifts of spectral bands and the less stability toward
oxidation than the one with an electron-donating group at the
benzoyl moiety; (iv) the increase of the HOMO levels may account
for the long-wavelength emission while the short-wavelength
fluorescence may be caused by the enhancement of the LUMO
levels; and (v) these BF2 chelates have the solvent-independent
photophysical performance due to the minute change of the
dipole moments between the S0 and the S1 state.
4. Conclusion
Herein we describe the synthesis along with the property
and the calculation study on a series of novel BF2 complexes with
N,O-bidentate ligands. These complexes are ready to be prepared in
good yields by simple operation and exhibit intense fluorescence in
solutions with multiple colors. A qualitative structureeproperty
Moreover, the electrochemical investigation shows that these
novel N,O-bidentate BF2 chelates are better electron acceptors than
the commonly used electron-transport material Alq3. The further

Q.-C. Yao et al. / Journal of Organometallic Chemistry 743 (2013) 1e9
9
[28] G.M. Fischer, E. Daltrozzo, A. Zumbusch, Angew. Chem. Int. Ed. 50 (2011)
1406e1409.
[29] F. Ito, T. Nagai, Y. Ono, K. Yamaguchi, H. Furuta, T. Nagamura, Chem. Phys. Lett.
435 (2007) 283e288.
research on exploiting them as electron-transporting materials is
on the progress.
[30] Y. Yang, X. Su, C.N. Carroll, I. Aprahamian, Chem. Sci. 3 (2012) 610e613.
[31] Y.-Y. Wu, Y. Chen, G.-Z. Gou, W.-H. Mu, X.-J. Lv, M.-L. Du, W.F. Fu, Org. Lett. 14
(2012) 5226e5229.
[32] Y. Zhou, Y. Xiao, S.-M. Chi, X.-H. Qian, Org. Lett. 10 (2008) 633e636.
[33] Y. Kubota, H. Hara, S. Tanaka, K. Funabiki, M. Matsui, Org. Lett. 13 (2011)
6544e6547.
[34] Y. Zhou, J.W. Kim, M.J. Kim, W.-J. Son, S.J. Han, H.N. Kim, S. Han, Y. Kim, C. Lee,
S.-J. Kim, D.H. Kim, J.-J. Kim, J. Yoon, Org. Lett. 12 (2010) 1272e1275.
[35] R.-Z. Ma, Q.-C. Yao, X. Yang, M. Xia, J. Fluorine Chem. 137 (2012) 93e98.
[36] Y. Kubota, S. Tanaka, K. Funabiki, M. Matsui, Org. Lett. 14 (2012) 4682e4685.
[37] M. Xia, B. Wu, G.F. Xiang, J. Fluorine Chem. 129 (2008) 402e408.
[38] Z.B. Henson, G.C. Welch, T. van der Poll, G.C. Bazan, J. Am. Chem. Soc. 134
(2012) 3766e3799.
Acknowledgments
We are grateful for the financial support of the Natural Science
Foundation of Zhejiang Province (Y4100034) and Zhejiang Province
Key Innovation Team (2012R 10038-09).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.06.012.
[39] Y. Liang, Y. Wu, D. Feng, S.-T. Tsai, H.-J. Son, G. Li, L. Yu, J. Am. Chem. Soc. 131
(2009) 56e57.
[40] Y. Kubo, K. Watanabe, R. Nishiyabu, R. Hata, A. Murakami, T. Shoda, H. Ota,
Org. Lett. 13 (2011) 4574e4577.
References
[41] A.D. Becke, J. Chem. Phys. 98 (1993) 5648e5652.
[1] A.C. Benniston, G. Copley, Phys. Chem. Chem. Phys. 11 (2009) 4124e4131.
[2] R. Ziessel, G. Ulricha, A. Harrimanb, New J. Chem. 31 (2007) 496e501.
[3] G. Ulrich, R. Ziessel, Anthony Harriman, Angew. Chem. Int. Ed. 47 (2008)
1184e1201.
[4] X. Zhang, H.-S. Zhang, Spectrochim. Acta A 61 (2005) 1045e1049.
[5] T. Matsumoto, Y. Urano, T. Shoda, H. Kojima, T. Nagano, Org. Lett. 9 (2007)
3375e3377.
[6] X. Peng, J. Du, J. Fan, J. Wang, Y. Wu, J. Zhao, S. Sun, T. Xu, J. Am. Chem. Soc. 129
(2009) 1500e1501.
[7] A. Coskun, M.D. Yilmaz, E.U. Akkaya, Org. Lett. 9 (2007) 607e609.
[8] M. Baruah, W. Qin, R.A.L. Valle0e, D. Beljonne, T. Rohand, W. Dehaen, N. Boens,
Org. Lett. 7 (2005) 4377e4380.
[42] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789.
[43] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken,
C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas,
J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.02,
Gaussian, Inc., Wallingford CT, 2009.
[9] J.-P. Malval, I. Leray, B. Valeur, New J. Chem. 29 (2005) 1089e1094.
[10] R. Ziessel, G. Ulrich, A. Harriman, M.A.H. Alamiry, B. Stewart, P. Retailleau,
Chem. Eur. J. 15 (2009) 1359e1369.
[44] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 24 (2003) 669e681.
[45] N.M. O’Boyle, A.L. Tenderholt, K.M. Langner, J. Comput. Chem. 29 (2008)
839e845.
[11] C.F.A. Gómez-Durán, I. García-Moreno, A. Costela, V. Martin, R. Sastre,
J. Bañuelos, F. López Arbeloa, I. López Arbeloa, E. Peña-Cabrera, Chem. Com-
mun. 46 (2010) 5103e5105.
[46] L.-X. Wu, K. Burgess, J. Am. Chem. Soc. 130 (2008) 4089e4096.
[47] P.M. Felipe, C. Gwengo, S.V. Lindeman, M.D. Smith, J.R. Gardinier, Eur. J. Inorg.
Chem. (2008) 3200e3211.
[12] M.J. Ortiz, I. Garcia-Moreno, A.R. Agarrabeitia, G. Duran-Sampedro, A. Costela,
R. Sastre, F. López Arbeloa, J. Bañuelos Prieto, I. López Arbeloa, Phys. Chem.
Chem. Phys. 12 (2010) 7804e7811.
[48] Z.R. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 103 (2003) 3899e4031.
[49] L.G.S. Brooker, F.L. White, R.H. Sprague, S.G. Dent, G. Van Zandt, Chem. Rev. 41
(1947) 325e351.
[50] H.C. Longuet-Higgins, J. Chem. Phys. 18 (1950) 265e274.
[51] D. Huang, Y. Chen, J. Zhao, Dyes Pigm. 95 (2012) 732e742.
[52] G.J. Huang, J.H. Ho, C. Prabhakar, Y.H. Liu, S.M. Peng, J.S. Yang, Org. Lett. 14
(2012) 5034e5037.
[53] B. Wang, H. Liao, H. Yeh, W. Wu, C. Chen, J. Lumin. 113 (2005) 321e328.
[54] C. Cornelissen-Gude, W. Rettig, J. Phys. Chem. A 103 (1999) 4371e4377.
[55] G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. Int. Ed. 46 (2007) 2e20.
[56] J.-Q. Feng, B.-L. Liang, D.-L. Wang, L. Xue, X.-Y. Li, Org. Lett. 10 (2008) 4437e
4440.
[13] S. Ertan-Ela, M.D. Yilmaz, B. Icli, Y. Dede, S. Icli, E.U. Akkaya, Org. Lett. 10
(2008) 3299e3302.
[14] T. Rousseau, A. Cravino, T. Bura, G. Ulrich, R. Ziessel, J. Roncali, Chem. Com-
mun. (2009) 1673e1675.
[15] M.K. Kuimova, G. Yahioglu, J.A. Levitt, K. Suhling, J. Am. Chem. Soc. 130 (2008)
6672e6673.
[16] M.A.H. Alamiry, A.C. Benniston, G. Copley, K.J. Elliott, A. Harriman, B. Stewart,
Y.-G. Zhi, Chem. Mater. 20 (2008) 4024e4032.
[17] J.F. Lovell, T.W.B. Liu, J. Chen, G. Zheng, Chem. Rev. 110 (2010) 2839e2857.
[18] S. Ozlem, E.U. Akkaya, J. Am. Chem. Soc. 131 (2009) 48e49.
[19] Y. Kubota, Y. Tsuzuki, K. Funabiki, M. Ebihara, M. Matsui, Org. Lett. 12 (2010)
4010e4013.
[57] P.E. Burrows, Z. Shen, V. Bulovic, D.M. McCarty, S.R. Forrest, J.A. Cronin,
M.E. Thompson, J. Appl. Phys. 79 (1996) 7991e8006.
[20] J. Bañuelos, F. López Arbeloa, V. Martinez, M. Liras, A. Costela, I. García Mor-
eno, I. López Arbeloa, Phys. Chem. Chem. Phys. 13 (2011) 3437e3445.
[21] M.F. Mao, S.Z. Xiao, T. Yi, K. Zou, J. Fluorine Chem. 132 (2011) 612e616.
[22] Q. Cao, S.Z. Xiao, M.F. Mao, X.H. Chen, S. Wang, L. Li, K. Zou, J. Organometal.
Chem. 717 (2012) 147e151.
[58] N.J. Turro, Modern Molecular Photochemistry, University Science Books, Mill
Valley, 1991.
ꢀ
[59] J. Schäer, M. Scheurer, B. Speiser, W. Kuznik, I.V. Kityk, Spectrochim. Acta A:
Mol. Biomol. Spectro. 95 (2012) 193e198.
[60] J.-M. Zhao, H.-Y. Lu, J. Cao, Y. Jiang, C.-F. Chen, Tetrahedron Lett. 50 (2009)
[23] M.F. Mao, S.Z. Xiao, J.F. Li, Y. Zou, R.H. Zhang, J.R. Pan, F.J. Dan, K. Zou, T. Yi,
Tetrahedron 68 (2012) 5037e5041.
219e222.
[24] A. Esparza-Ruiz, A. Peña-Hueso, H. Nöth, A. Flores-Parra, R. Contreras,
J. Organometal. Chem. 694 (2009) 3814e3822.
[61] Q.T. Miao, H.Q. Sun, J. East China Inst. Chem. Technol. 18 (1992) 765e771.
[62] K. Krumova, G. Cosa, J. Am. Chem. Soc. 132 (2010) 17560e17569.
[63] T. Wang, Y. Chen, X. Bao, Z. Du, J. Guo, N. Wang, M. Sun, R. Yang, Dyes Pigm. 98
(2013) 11e16.
[64] J.-C. Chen, C.-J. Chiang, Y.C. Liu, Synth. Met. 160 (2010) 1953e1961.
[65] V.V. Pavlishchuk, A.W. Addison, Inorg. Chim. Acta 298 (2000) 97e102.
[25] K. Perumal, J.A. Garg, O. Blacque, R. Saiganesh, S. Kabilan,
K.K. Balasubramanian, K. Venkatesan, Chem. Asian J. 7 (2012) 2670e2677.
[26] H.J. Li, W.-F. Fu, L. Li, X. Gan, W.-H. Mu, W.-Q. Chen, X.-M. Duan, H.-B. Song,
Org. Lett. 12 (2010) 2924e2927.
[27] Y. Zhou, Y. Xiao, D. Li, M.-Y. Fu, X.-H. Qian, J. Org. Chem. 73 (2008) 1571e1574.