Two-photon excited fluorescence properties and anions recognition of a trivalent organoboron compound

Article abstract of DOI:10.1016/j.molstruc.2011.06.008

A trivalent organoboron compound with diethylamino as an electron donor group and dimesitylboryl as an electron acceptor group has been synthesized. Its single- and two-photon excited fluorescence properties have been examined. Pumped by 820 nm laser puls

Full text of DOI:10.1016/j.molstruc.2011.06.008

Journal of Molecular Structure 1000 (2011) 145–149
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Two-photon excited fluorescence properties and anions recognition
of a trivalent organoboron compound
b
b
b,
Yunlong Deng a, Yunhui Sun a, Duxia Cao a,b, , Ying Chen , Zhiqiang Liu , Qi Fang
⇑
⇑
a School of Material Science and Engineering, University of Jinan, Jinan 250022, Shandong, China
b State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A trivalent organoboron compound with diethylamino as an electron donor group and dimesitylboryl as
an electron acceptor group has been synthesized. Its single- and two-photon excited fluorescence prop-
erties have been examined. Pumped by 820 nm laser pulses in femtosecond regime, it showed strong
two-photon excited fluorescence at 527 nm in toluene with two-photon absorption cross-section being
859GM. The compound has been found to be a sensitive chemosensor for fluoride and cyanide anions
in THF solutions.
Received 13 March 2011
Received in revised form 8 June 2011
Accepted 9 June 2011
Available online 14 June 2011
Keywords:
Organoboron
Ó 2011 Elsevier B.V. All rights reserved.
Chemosensor
Two-photon excited fluorescence
Fluoride anion
Cyanide anion
1. Introduction
electron acceptor. After decades of exploration, people have synthe-
sized a large number of stable organoboron compounds, which dis-
Two-photon absorption (TPA) is a nonlinear process, in which a
molecule simultaneously absorbs two photons to access an excited
state. In recent years, a considerable interest has been devoted to
the research into organic molecules with strong TPA and two-pho-
ton excited fluorescence (TPEF) due to their potential use in ad-
vanced photonic applications such as three-dimensional optical
data storage [1], up-converted lasing [2], two-photon fluorescence
excitation microscopy [3,4], lithographic microfabrication, laser
device fabrication [5] and photodynamic therapy [6]. Series of
compounds with strong TPEF have been reported, which promoted
both the theory and application research of TPA and TPEF [7–10].
From the viewpoint of molecular engineering, structural fea-
tures such as electron donor or acceptor terminal group and the
length of conjugated bridge all play an important role in tuning
nonlinear optical properties of materials. A number of studies
found that nonlinear optical effect increases with the increase of
the length of conjugated bridge and molecular planarity [11,12].
Boron atom has an empty p-orbital and this p-orbital can form
played great potentials in fields of nonlinear optical, luminescent
materials and electronic transmission [13–15]. Another important
role of organoboron compounds is as Lewis acid-based fluoride
[16–24] or cyanide [23–29] anions sensors. So, organoboron com-
pounds combine TPEF, fluoride and cyanide anions together very
well.
Our group has been interested in fluoride sensors and TPEF
based on organoboron compounds for several years [30–32]. We
herein report the synthesis of a D-p-A motif organoboron com-
pound with long conjugated bridge. We have measured its linear
and two-photon photophysical properties and examined its poten-
tial for fluoride and cyanide anions sensors.
2. Experimental
2.1. Chemicals and instruments
Nuclear magnetic resonance spectra were recorded on a Mercu-
ryPlus-400 spectrometer. Elemental analyse was carried out on a
PE 2400 autoanalyzer. Mass spectrum was obtained on an Agilent
5973N MSD spectrometer. n-Butyllithium in hexane solution was
obtained from Aldrich Ltd. Dimesitylboron fluoride (BF(Mes)2,
Mes = 2,4,6-trimethylphenyl) was purchased from Aldrich Ltd.
Other reagents were purchased from Shanghai Reagents and were
used as received directly without further purification. All of the
solvents were freshly distilled before using.
p-p type orbital charge transfer with the p-orbital of the conju-
gated system connecting with boron atoms. It has strong electronic
affinity. So, groups with trivalent boron atoms can serve as a good
⇑
Corresponding authors. Address: School of Material Science and Engineering,
University of Jinan, Jinan 250022, Shandong, China. Tel.: +86 531 8973 6751; fax:
+86 531 8797 4453.
E-mail addresses: duxiacao@ujn.edu.cn (D. Cao), fangqi@sdu.edu.cn (Q. Fang).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.06.008

146
Y. Deng et al. / Journal of Molecular Structure 1000 (2011) 145–149
2.2. Synthesis
ether (1:9) as eluent. Red powders with yield 45% were obtained.
1H NMR(CDC13, 400 MHz), dH (ppm): 1.11(t, J = 7.0 Hz, 6H),
1.96(s, 12H), 2.23(s, 6H), 3.31(q, J = 7.0 Hz, 4H), 6.52(d,
J = 12.4 Hz, 1H), 6.59(d, J = 8.6 Hz, 2H), 6.74(s, 4H), 6.77(d,
J = 12.4 Hz, 1H), 6.93(d, J = 16.0 Hz, 1H), 7.05(d, J = 16.4 Hz, 1H),
7.12(d, J = 8.0 Hz, 1H), 7.16–7.24(m, 2H), 7.32(t, J = 8.6 Hz, 3H),
7.38–7.45(m, 4H). MS: m/z (%) 601(M+, 100). Anal. calcd for
The synthetic strategy of the title compound 1 is outlined in
Scheme 1 [33]. 4-[4-(N,N-diethylamino)styryl]aldehyde (S-1) and
the phosphonium salt (S-2) were synthesized according to proce-
dures described in the literatures [34,35]. Then 4-(4-(4-bromosty-
ryl)styryl)-N,N-diethylbenzenamine (10) was prepared by Wittig
reactions using S-1 and one equivalent S-2. Finally, the title com-
pound 1 was obtained by substitution of the Br atom of S-3 using
dimesitylboryl group.
C44H48BN: C, 87.83; H, 8.04; N, 2.33. Found: C, 87.68; H, 8.06; N,
2.37.
2.3. Measurements
2.2.1. 4-(4-(4-Bromostyryl)styryl)-N,N-diethylbenzenamine (10)
By reaction of S-1 with one equivalent S-2 via Wittig reaction, 10
was obtained as a green solid with a yield of 50%. 1H NMR(CDC13,
400 MHz), dH (ppm): 1.11(t, J = 7.2 Hz, 6H), 3.31(q, J = 7.1 Hz, 4H),
6.40(d, J = 12.4, 1H), 6.52(d, J = 12.4, 1H), 6.58 (d, J = 8.4, 2H), 6.76
(d, J = 16.4, 1H), 6.95(d, J = 16.4, 1H), 7.10(t, J = 9.0, 3H), 7.25–
7.35(m, 6H), 7.41(s, 1H). MS: m/z (%) 431(M+, 100), 416([M-
CH3]+, 100). Anal. calcd for C26H26BrN: C, 72.22; H, 6.06; N, 3.24.
Found: C, 72.38; H, 6.03; N, 3.28.
UV/vis absorption and single-photon excited fluorescence
(SPEF) spectra with C = 1.0 ꢁ 10ꢀ5 mol Lꢀ1 were recorded on Shi-
madzu UV 2550 and FLS920 fluorescence spectrometer, respec-
tively. The SPEF quantum yields
U were measured by using a
standard method [36] with coumarin 307 [37] as the standard.
Two-photon excited fluorescence spectra of the compounds in tol-
uene and THF with C = 1.0 ꢁ 10ꢀ4 mol Lꢀ1 were performed with a
femtosecond Ti:sapphire laser (80 MHz, 80 fs pulse width, Spec-
tra-Physics Inc., Tsunami 3941-M1 BB) over the range 740–
880 nm as pump source. The input laser powder was 150 mW for
all measurements, which was carefully monitored to ensure suffi-
cient TPEF intensity.
2.2.2. 4-(4-(4-Dimesitylborylstyryl)styryl)-N,N-diethylbenzenamine
(1)
2.0 g (4.6 mmol) 10 in freshly distilled THF was injected into a
three-necked flask under the cover of N2. Then the flask was cooled
to ꢀ78 °C by dry ice-acetone bath and then 15 mmol n-Butyllith-
ium in hexane solution was dropped. The flask was kept at
ꢀ78 °C for about 1 h, then warmed naturally to room temperature
and stirred for 2 h to get the lithium salt. Then the mixture was
cooled to ꢀ78 °C again and 1.25 g (4.6 mmol) dimesitylboron fluo-
ride, which had been resolved in 5 mL freshly distilled THF, was in-
jected quickly via a dried injector. The mixture was continuously
stirred overnight and then was poured into 200 mL distilled water
and extracted with dichloromethane. After a rotary evaporator re-
moved the organic solvent, the product was purified through col-
umn chromatography on silica gel using chloroform–petroleum
3. Results and discussion
3.1. Linear absorption and single-photon excited fluorescence
properties
Linear photophysical properties of compound 1 in various sol-
vents are shown in Table 1 and Fig. 1. As shown in Table 1 and
Fig. 1, one can see that absorption peak position and absorbance
show little dependence on polarity of the solvents. In contrast, its
emission properties display an obvious solvatochromic effect. With
increasing polarity of the solvents, the emission maximum of
Scheme 1. Synthetic strategy of the title compound 1.

Y. Deng et al. / Journal of Molecular Structure 1000 (2011) 145–149
147
Table 1
Linear photophysical properties of compounds 1’ and 1 in various solvents.
Solvents
kabs
(nm)
e
kfluo
(nm)
U
s (ns)
(104 Mꢀ1cmꢀ1
)
1
Hexane
Toluene
THF
414
424
422
417
6.22
5.35
5.61
5.82
468, 503
525
602
0.52
0.45
0.21
0.02
1.1
1.5
2.3
–
Acetonitrile
677
10
Hexane
Toluene
THF
395
401
400
395
4.7
4.2
5.1
4.9
439, 464
470, 496
523
0.38
0.36
0.32
0.25
0.9
1.0
1.5
2.2
Acetonitrile
566
Fig. 2. Changes in UV–vis absorption spectra of compound 1 at 20 °C in THF upon
the addition of different equivalents of TBAF (a) or TBACN (b).
absorption and fluorescence emission wavelength and more obvi-
ous solvatochromism relative to 1’ that indicating that compound
1 possesses larger polarity.
3.2. Spectral response to fluoride and cyanide anions
As a general adapted method, n-Bu4NF (TBAF) or n-Bu4NCN
(TBACN) as fluoride or cyanide source was progressively added to
a THF solution of compound 1. The linear absorption and single-
photon excited fluorescence emission spectra of solutions contain-
ing increasing concentration of fluoride anions or cyanide anions
were recorded to examine the complexation between 1 and Fꢀ or
CNꢀ. Compound 1 shows an obvious spectral response to the added
TABF and TBACN. As shown in Fig. 2, upon complexation with fluo-
ride or cyanide anions, the characteristic intense charge-transfer
absorption at 420 gradually decreases and a new peak at 396 nm
appears. When 4.5 equivalents TBAF or 3.5 equivalents TBACN
were added, the absorption peak at 420 nm disappeared com-
pletely. So 1 can recognize for fluoride and cyanide anions with
similar bonding ability. The phenomenon upon is contributed to
the formation of the 1:1 adduct 1-F or 1-CN.
Fig. 1. Linear absorption (a) and single-photon excited fluorescence (b) spectra of
compound 1 in various solvents.
compound 1 varies from 503 nm in hexane to 677 nm in CH3CN
with a shift of nearly 174 nm. Also, with the increase of solvent
polarity, the fluorescence intensity and fluorescent quantum yield
show a substantial reduction. Phenomenon above can be explained
by twisted intramolecular charge transfer (TICT) [38,39]. All these
cases indicate that typical intramolecular charge-transfer takes
place during the excitation process, which results in a highly polar-
ized excited state.
A direct comparison of the organoboron compound 1 with its
precursor 1’ clearly indicates that the former possesses much im-
proved photophysical properties. Compound 1 exhibits higher
fluorescence quantum yields and longer fluorescence lifetime rela-
tive to 1’ (shown in Table 1), which indicates that the –B(Mes)2
group acts as a fluorophore. Compound 1 shows longer linear
As shown in Fig. 3, the single-photon excited fluorescence emis-
sion spectra recorded with excitation at 410 nm also displayed
obvious changes when fluoride or cyanide anions were added.
The strong emission band of 1 at 602 nm gradually decreased,
and a new emission band at 473 nm (Fꢀ) or 475 nm (CNꢀ) ap-
peared. When 4.8 equivalents TBAF or 4.4 equivalents TBACN were

148
Y. Deng et al. / Journal of Molecular Structure 1000 (2011) 145–149
Fig. 5. Two-photon excited fluorescence (TPEF) spectra of 1 in toluene and THF
with excitation wavelength 820 nm and C = 1.0 ꢁ 10ꢀ4 mol Lꢀ1
.
Fig. 3. Changes in single-photon excited fluorescence spectra of compound 1 at
20 °C in THF upon the addition of different equivalents of TBAF or TBACN. Inset:
Titration curves at 473 nm (TBAF) or 475 nm (TBACN).
Fig. 6. Molecular structure of compound DEB.
1-F and 1-CN is accompanied by the disappearance of orange col-
our in solution.
3.3. Two-photon excited fluorescence properties
TPEF was collected at a direction perpendicular to the pump
beam. From linear absorption spectra (Fig. 1a), one can see that
the compound is linear optical penetrable in the range from 500
to 1000 nm. Therefore, any emission induced by excitation at this
wavelength range should be derived from multiphoton absorption
process. As shown in Fig. 4, TPEF intensity of compound 1 is pro-
portional to the square of the input laser power from 50 mW to
210 mW, which suggests the two-photon excitation mechanism.
Two-photon excitation (TPE) spectra of compound 1 in toluene
and THF with excitation wavelength from 740 nm to 880 nm were
shown in Fig. 4. From Fig. 4, one can see the optimal excitation
wavelengths in both solvents are 820 nm, which are almost twice
those of the corresponding linear absorption maxima.
TPEF spectra of the compounds shown in Fig. 5 were taken
when they were excited at 820 nm. Compound 1 exhibits strong
TPEF emission in toluene (527 nm) and THF (606 nm). TPEF inten-
sity of compound 1 in toluene is almost four times that in THF,
which is similar to SPEF. The phenomenon above exhibits that
stronger polarity solvent THF induces obvious fluorescence quench
of 1. TPEF intensity of compound 1 in toluene is almost four times
that of the precursor 1’, which indicates the replacement of bro-
mine atom using boron atom is beneficial to TPEF.
Fig. 4. Two-photon excitation (TPE) spectra of compound 1 in toluene and THF with
C = 1.0 ꢁ 10ꢀ4 mol Lꢀ1. Inset: The output fluorescence intensity vs. the input power
square for 1 in THF.
added, the fluorescence peak at 602 nm disappeared completely.
This phenomenon also indicates the recognition of compound 1
for fluoride and cyanide anions. Interestingly, conversion of 1 into

Y. Deng et al. / Journal of Molecular Structure 1000 (2011) 145–149
149
[8] L.Y. Chiang, P.A. Padmawar, T. Canteenwala, L.S. Tan, G.S. He, R. Kannan, R. Vaia,
T.C. Lin, Q.D. Zheng, P.N. Prasad, Chem. Commun. (2002) 1854.
[9] R. Anémian, Y. Morel, P.L. Baldeck, B. Paci, K. Kretsch, J.M. Nunzi, C. Andraud, J.
Mater. Chem. 13 (2003) 2157.
[10] G. Bordeau, R. Lartia, G. Metge, C. Fiorini-Debuisschert, F. Charra, M. Teulade-
Fichou, J. Am. Chem. Soc. 130 (2008) 16836.
[11] M. Albota, D. Beljonne, J.L. Brédas, J.E. Ehrlich, J.Y. Fu, A.A. Heikal, S.E. Hess, T.
Kogej, M.D. Levin, S.R. Marder, D. McCord-Maughon, J.W. Perry, H. Röckel, M.
Rumi, G. Subramaniam, W.W. Webb, X.L. Wu, C. Xu, Science 281 (1998) 1653.
[12] L. Ventelon, S. Charier, L. Moreaux, J. Mertz, M. Blanchard-Desce, Angew.
Chem. Int. Ed. 40 (2001) 2098.
TPA cross-sections of 1 in toluene and THF at 820 nm are ob-
tained using two-photon excited fluorescence method with couna-
rin307 as Ref. [40], which are 859GM and 522GM, respectively. TPA
cross-section of 1 in toluene is about four times that of 1’ (206GM)
in same solvent. TPA cross-section of 1 in THF is almost three times
that of the corresponding short-chain analogue (DEB, Fig. 6) with
one phenyl-vinyl compound (194GM) in THF solution [35], which
indicates that the extending conjugated system is beneficial to
nonlinear optical properties of the compounds.
[13] Z.Q. Liu, Q. Fang, D. Wang, G. Xue, W.T. Yu, Z.S. Shao, M.H. Jiang, Chem.
Commun. (2002) 2900.
[14] Z. Yuan, C.D. Entwistle, J.C. Collings, D. Albesa-Jové, A.S. Batsanov, J.A.K.
Howard, N.J. Taylor, H.M. Kaiser, D.E. Kaufmann, S.-Y. Poon, W.-Y. Wong, C.
Jardin, S. Fathallah, A. Boucekkine, J.-F. Halet, T.B. Marder, Chem. Eur. J. 12
(2006) 2758.
[15] C.D. Entwistle, T.B. Marder, Chem. Mater. 16 (2004) 4574.
[16] Z.Q. Liu, M. Shi, F.Y. Li, Q. Fang, Z.H. Chen, T. Yi, C.H. Huang, Org. Lett. 7 (2005)
5481.
[17] C.R. Wade, A.E.J. Broomsgrove, S. Aldridge, F.P. Gabbaï, Chem. Rev. 110 (2010)
3958.
[18] H.Y. Zhao, F.P. Gabbaï, Nat. Chem. 2 (2010) 984.
[19] S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 123 (2001) 11372.
[20] X.Y. Liu, D.R. Bai, S. Wang, Angew. Chem. Int. Ed. 45 (2006) 5475.
[21] Q. Zhao, F.Y. Li, C.H. Huang, Chem. Soc. Rev. 39 (2010) 3007.
[22] W.J. Xu, S.J. Liu, H.B. Sun, X.Y. Zhao, Q. Zhao, S. Sun, S. Cheng, T.C. Ma, L.X. Zhou,
W. Huang, J. Mater. Chem. 21 (2011) 7572.
4. Conclusion
In summary, a D-p-A dipolar organoboron compound with long
conjugated bridge was synthesized. Its single and two-photon re-
lated photophysical properties and the property for fluoride and
cyanide bonding are measured. The compound exhibits strong
two-photon up-converted yellow fluorescence and large two-pho-
ton absorption cross-sections (859GM in toluene and 522GM in
THF) with 820 nm laser excitation. The compound can recognize
for fluoride anions and cyanide anions.
Acknowledgements
[23] T.W. Hudnall, F.P. Gabbaï, J. Am. Chem. Soc. 129 (2007) 11978.
[24] T. Agou, M. Sekine, J. Kobayashi, T. Kawashima, Chem. Eur. J. 15 (2009) 5056.
[25] J.O. Huh, Y. Do, M.H. Lee, Organometallics 27 (2008) 1022.
[26] K. Parab, K. Venkatasubbaiah, F. Jäkle, J. Am. Chem. Soc. 128 (2006) 12879.
[27] C.-W. Chiu, F.P. Gabbaï, Dalton Trans. (2008) 814.
[28] R. Badugu, J.R. Lakowicz, C.D. Geddes, J. Am. Chem. Soc. 127 (2005) 3635.
[29] J.V. Ros-Lis, R. Martínez-Máñez, J. Soto. Chem. Commun. (2005) 5260.
[30] D.X. Cao, Z.Q. Liu, G.H. Zhang, G.Z. Li, Dye. Pigm. 81 (2009) 193.
[31] Y.L. Deng, Y. Chen, D.X. Cao, Z.Q. Liu, G.Z. Li, Sens. Actuators B 149 (2010) 165.
[32] D.X. Cao, Z.Q. Liu, G.Z. Li, Sens. Actuators B 133 (2008) 489.
[33] Cao DX. Design, Synthesis and Properties of Several Series of Novel Two-
Photon Excited Up-Converted Fluorescence Compounds. Jinan: Doctoral
Dissertation of Shandong University; 2004, p. 40.
This work was supported by the National Natural Science
Foundation of China (20802026, 50803033), Natural Science
Foundation of Shandong Province (Q2008F02), Shandong
Encouraging Fund for Excellent Scientists (BS2009CL013) and the
Fund of Innovation Project of Graduate of University of Jinan
(YCX09001).
References
[34] D.X. Cao, Z.Q. Liu, G.H. Zhang, F.X. Cao, H.Y. Chen, G.Z. Li, Dye. Pigm. 76 (2008)
118.
[35] Z.Q. Liu, Q. Fang, D. Wang, D.X. Cao, G. Xue, W.T. Yu, H. Lei, Chem. Eur. J. 9
(2003) 5074.
[36] J.N. Demas, G.A. Crosby, J. Phys. Chem. 75 (1971) 991.
[37] G.A. Reynolds, K.H. Drexhage, Opt. Commun. 13 (1975) 222.
[38] N. Sarkar, K. Das, D.N. Nath, K. Bhattacharyya, Langmuir 10 (1994) 326.
[39] Z.R. Grabowski, J. Dobkowski, Pure Appl. Chem. 55 (1983) 245.
[40] C. Xu, W.W. Webb, J. Opt. Soc. Am. B 13 (1996) 481.
[1] D.A. Parthenopoulos, P.M. Rentzepis, Science 245 (1989) 843.
[2] G.S. He, C.F. Zhao, J.D. Bhawalkar, P.N. Prasad, Appl. Phys. Lett. 67 (1995) 3703.
[3] W. Denk, J.H. Strickler, W.W. Webb, Science 248 (1990) 73.
[4] Q. Xu, K. Shi, S. Yin, Z. Liu, J. Microsc. 235 (2009) 79.
[5] C.F. Zhao, G.S. He, J.D. Bhawalkar, C.K. Park, P.N. Prasad, Chem. Mater. 7 (1995)
1979.
[6] H. Stiel, K. Teuchner, A. Paul, W. Freyer, D. Leupold, J. Photochem. Photobiol. A:
Chem. 80 (1994) 289.
[7] S.J.K. Pond, M. Rumi, M.D. Levin, T.C. Parker, D. Beljonne, M.W. Day, J.L. Brédas,
S.R. Marder, J.W. Perry, J. Phys. Chem. A 106 (2002) 11470.