NIR and CT luminescence spectra of [Yb(TFN)(S-BINAPO)] and [Yb(HFA)(S-BINAPO)] complexes

Article abstract of DOI:10.1016/j.saa.2014.03.109

The complexes [Yb(TFN)₃(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2- napthyl)-1,3-butanedione) (complex 1) and [Yb(HFA)₃(S-BINAPO)](HFA = hexafluoroacetylacetonate) (complex 2) were synthesized, characterized. The absorption as well as PL s

Full text of DOI:10.1016/j.saa.2014.03.109

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 37–40
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
NIR and CT luminescence spectra of [Yb(TFN)(S-BINAPO)]
and [Yb(HFA)(S-BINAPO)] complexes
b
Md. Abdus Subhan a,b, , Hiroyasu Nakata
⇑
a Department of Chemistry, Shah Jalal University of Science and Technology, Sylhet, Bangladesh
b Department of Arts and Science, Osaka Kyoiku University, Kashiwara, Osaka, Japan
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
NIR PL Spectra of [Yb(TFN)3(S-BINAPO)] (a) and CT luminescence of [Yb(TFN)3(S-BINAPO)] (b). The com-
plex, [Yb(TFN)3(S-BINAPO)] showed narrowed emission peak (half width ꢁ6 nm) at around 981 nm at
low temperature.
ꢀ
ꢀ
ꢀ
ꢀ
The complexes [Yb(TFN)3(S-BINAPO)]
and [Yb(HFA)3(S-BINAPO)] showed PL
at low temperature.
Complex [Yb(TFN)3(S-BINAPO)]
showed narrowed emission (half
width ꢁ6 nm) at 981 nm.
The complex [Yb(HFA)3(S-BINAPO)]
showed strong emission peak at
around 985 nm.
Complex [Yb(TFN)3(S-BINAPO)]
showed CT emission at 412–463 nm.
a r t i c l e i n f o
a b s t r a c t
Article history:
The complexes [Yb(TFN)3(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione) (complex 1)
and [Yb(HFA)3(S-BINAPO)](HFA = hexafluoroacetylacetonate) (complex 2) were synthesized, character-
ized. The absorption as well as PL spectra have been studied. The complex [Yb(TFN)3(S-BINAPO)] showed
narrowed emission peak (half width ꢁ6 nm) at around 981 nm in addition to several emission peaks in
NIR (near infrared) region. The complex [Yb(HFA)3(S-BINAPO)] showed strong emission peak at around
985 nm. The charge transfer luminescence of [Yb(TFN)3(S-BINAPO)] was also observed at 412–463 nm.
Ó 2014 Elsevier B.V. All rights reserved.
Received 21 December 2013
Received in revised form 24 March 2014
Accepted 29 March 2014
Available online 6 April 2014
Keywords:
NIR luminescence
Yb(III) complex
BINAPO
CT transitions
f–f transitions
Introduction
luminescent lanthanide complexes are significant for their applica-
tions in material as well as biological sciences. Highly emissive and
Lanthanide luminescence has numerous important applications
in optoelectronic devices, phosphorescent devices, anion sensing,
protein recognition, immunoassays, etc. [1–4]. Chiral as well as
enantiopure lanthanide complexes have been used as cellular
imaging and reactive probes by their interactions with DNA [5,6].
Population inversion in 4f orbitals in Ln(III) complexes is a great
benefit in the development of organic chelate laser and plastic
optical fiber applications [7–11]. Luminescences of Yb complexes
in 3d–4f and energy transfer processes have been reported
[12,13]. Luminescence from lanthanide ions in metal complexes
are very sensitive to solvents coordinated to the metal centers.
⇑
Corresponding author at: Department of Chemistry, Shah Jalal University of
Science and Technology, Sylhet, Bangladesh. Tel.: +880 821 713491x431, mobile:
+880 1716073270; fax: +880 821 715257.
E-mail address: subhan-che@sust.edu (M.A. Subhan).
http://dx.doi.org/10.1016/j.saa.2014.03.109
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

38
M.A. Subhan, H. Nakata / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 37–40
(m, 8H), d 7.38–7.50 (m, 12H), d 7.79–7.87 (q, 4H), d 7.88–7.91(d,
2H) and d 7.93–7.96(d, 2H) ppm. The elemental analysis of S-
BINAPO ligand was performed; found C, 80.72%; H, 4.89% and cal-
culated for C44H32O2P2, C, 80.75%; H, 5.03%.
Synthesis of [Yb(TFN)3(S-BINAPO)] and [Yb(HFA)3(S-BINAPO)]
Yb(HFA)3 and Yb(TFN)3 were synthesized by dissolving ytter-
bium acetate monohydrate in ethanol in a beaker and then adding
slowly the ethanol solution of HFA or TFN with stirring in an ice
bath (ꢁ1:3 M ratio) according to the previous method [14]. An ace-
tone solution (100 mL) containing Yb(HFA)3 or Yb(TFN)3 and
BINAPO ligand (1:1 M ratio) was refluxed at ꢁ50 °C for 10 h with
continuous stirring to obtain a clear solution of desired complexes
[Yb(HFA)3(S-BINAPO)] and [Eu(TFN)3(S-BINAPO)], respectively. In
each case, the resulting mixture was concentrated and hexane
was added to it, which gave crystalline precipitate. For an example
synthesis of [Yb(TFN)3(S-BINAPO)] is given here. [Yb(TFN)3]ꢃ2H2O
(5 g, 5 mmol) was dissolved in 100 mL acetone in a round bottom
flask. Then (3 g, 5 mmol) of S-BINAPO was added to the above solu-
tion. A turbid mixture obtained was shaken and a clear solution was
obtained in a few min. This solution was refluxed for 10 h. The
resulting mixture was concentrated and hexane was added. A white
yellow crystalline solid obtained was filtered and dried in air (%
yield, 60%). Elemental analyses for the following complexes were
performed, results are as provided below: Calculated for, C90H56O8-
F9P2Yb, [Yb(TFN)3(S-BINAPO)], %H, 3.38, %C, 64.68; found, %H 3.58,
Scheme 1. Schematic diagram of (a) [Yb(TFN)3(S-BINAPO)] and (b) [Yb(HFA)3
(S-BINAPO)].
The quenching of the luminescence due to the excited state relax-
ation through solvent molecules usually observed in case of lan-
thanide complexes. Introduction of the suitable bulky neutral
ligand in a neutral lanthanide tris-(b-diketonato) complex can
replace the solvent molecules from the coordination sphere result-
ing in improved luminescence as well as photophysical properties
[14]. A comprehensive strategy to boost the luminescence of lan-
thanide complexes has been reported recently [15]. Phosphine
oxide ligands can produce antisymmetrical structures that pro-
mote faster radiation rates because coordination of phosphine
oxide moiety (1) prevents coordination of water or solvent mole-
cules and (2) lowers vibrations (P@O:1125 cmꢂ1) [16]. For this pur-
poses b-diketonato ligands with chiral BINAPO (1,10-binapthyl
phosphine oxide) ligand were chosen. The complexes [Yb(TFN)3
(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione)
(complex 1) and [Yb(HFA)3(S-BINAPO)](HFA = hexafluoroacetyl-
acetonate) (complex 2) were synthesized (Scheme 1), character-
ized and their absorption as well as PL spectra have been studied.
%C, 64.65; Calculated for,
C
59H35O8F18P2YbꢃC6H14
, [Yb(HFA)3
(S-BINAPO)]ꢃC6H14 %H, 3.22, %C, 50.86; found, %H 2.80, %C,
,
50.70; The ESI–MS data were collected for [Yb(HFA)3(S-BINAPO)]
and [Yb(TFN)3(S-BINAPO)]complexes. For [Yb(HFA)3(S-BINAPO)],
m = 1449, m/z 1242, [1449-hfa]+; m/z 1896, [1449-hfa+BINAPO]+
and [Yb(TFN)3(S-BINAPO)], m = 1623, m/z 655, BINAPO+H+; m/z
1358, [M-TFN]+; m/z 2012, [M-TFN+BINAPO]+ were obtained.
Results and discussion
BINAPO ligand and metal complexes have been synthesize and
characterized by elemental analyses, mass spectra and NMR. We
previously have reported the X-ray structure of [Yb(HFA)3
(S-BINAPO)], a square antiprism (SAP) structure was found [14].
Yb(III) has the most unique absorption among the rare earth series.
Materials and methods
2
The unique f–f transitions of Yb(III) from ground state F7/2 to
Materials
2
excited state F5/2 are split by the crystal field into four and three
doubly degenerate sublevels, respectively. This is magnetically
allowed (DJ = 1) transition of Yb(III). For the Yb(III) complexes
Ytterbium acetate monohydrate (99.9%), 1,1,1,5,5,5-hexafluoro-
2,4-pentanedione (HFA) were purchased from Wako Pure Chemical
Industries Ltd. 4,4,4-Trifluoro-1(2-napthyl)-1,3-butanedione (TFN)
was purchased from Aldrich Chemical Co. BINAP was purchased
from Wako Pure Chemical Industries Ltd. All chemicals and
reagents were of analytical grade and used as received.
within f13 electronic configuration, three absorption bands have
been observed at around 930 nm, 960 nm and 975 nm [6]. It has
been found that if the absorption spectrum is taken in acetone then
all the bands are well resolved for Yb(III) complex [6]. Absorption
spectra of the complexes (1 and 2) have been measured in acetone.
As shown in Fig. 1 three absorption bands were observed at 937,
957 and 975 nm for the complex 1. Absorption spectra showed
PL measurements
2
2
only few transitions from ground F7/2 to the excited F5/2 levels
Solid state NIR (near infrared) PL spectra of the complexes were
measured at low temperatures using a line of He–Cd laser as exci-
tation source (at 325 nm). The visible PL spectra were measured by
a spectrofluorophotometer (Shimadzu Corp., model RF-5301) using
Xenon lamp as an excitation source.
Synthesis and characterization of the BINAPO and metal complexes
The S-BINAPO ligand was prepared by oxidation of BINAP [17]
with H2O2 in THF at 0 °C for 12 h. The ligand was characterized
by IR, NMR and elemental analysis. 1H NMR (acetone d6, TMS)
peaks were obtained at d 6.63 (d, 2H), d 6.77 (t, 2H), d 7.30–7.36
Fig. 1. Absorption spectra of complex [Yb(TFN)3(S-BINAPO)] in acetone.

M.A. Subhan, H. Nakata / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 37–40
39
due to crystal field splitting (Fig. S1). However, multiple CD com-
ponents in the complexes ascended from the ligand field splitting
within the 2F7/2 ? 2F5/2 transitions of the Yb(III) chromophores
[14]. These are several transitions from four Kramers doublets of
2
2
the ground F7/2 states to three of the excited F5/2 states [14].
Fig. 2 shows the PL spectra of Yb(TFN)3(S-3BINAPO) at 20 K. A
sharp and strong NIR emission peak with narrowed band (half
width ꢁ6 nm) has been observed at around 981 nm. Three more
strong peaks were also observed at 1000, 1016 and 1030 nm. In
addition, small emission peaks were also observed at 947, 963,
1044, 1050 and 1061 nm. All these emissions are due to the tran-
sitions from the excited 2F5/2 states to the ground 2F7/2 states with
in the 2F5/2 ? 2F7/2 transitions of Yb(III) (Figs. 2 and 3). Fig. 4 shows
the PL spectra of complex Yb(TFN)3(S-3BINAPO) at 4 K, which is
very similar to that observed at 20 K. As shown in Fig. 5, absorption
spectra of complex 2 is similar to that observed for complex 1,
three absorption bands are also observed approximately at 938,
960 and 976 nm due to the 2F7/2 ? 2F5/2 transitions of Yb(III). For
the complex [Yb(HFA)3(S-BINAPO)] a strong and relatively broad
emission band compared to that found for [Yb(TFN)3(S-3BINAPO)]
has been observed at 4 K as well as 20 K at around 985 nm (Figs. 6
and 7) corresponding to the 2F5/2 ? 2F7/2 transitions of Yb(III). In
addition, few small emission peaks were also observed at 810,
855, 925, 1105 and 1140 nm. The emissions peaking at 925, 1105
and 1140 nm also originated from the 2F5/2 ? 2F7/2 transitions.
The emission peaks detected at 810 and 855 nm may have some
contribution from charge transfer transitions. The broad emission
band (half width ꢁ80 nm) observed at 985 nm for the complex
[Yb(HFA)3(S-BINAPO)] may be due to the considerable reorganiza-
tion of the charge density distribution around the metal ion. This
reorganization is accompanied by an expansion of the
metal–ligand bonds in the excited state, which gives rise to the
observation of a relatively broad band.
Fig. 4. PL spectra of Yb(TFN)3(S-3BINAPO) at 4 K.
Fig. 5. Absorption spectra of complex [Yb(HFA)3(S-BINAPO)] in acetone.
Fig. 2. PL spectra of Yb(TFN)3(S-3BINAPO) at 20 K.
Fig. 6. PL spectra of Yb(HFA)3(S-3BINAPO) at 20 K.
3'
2F5/2
2'
1'
4f13
4
3
2
2F7/2
Spin-orbit coupling
1
Ligand field
splitting
Fig. 3. Schematic diagram showing four major transitions from excited 2F5/2 states to ground 2F7/2 states (1, 2, 3, 4 represents ground state levels and 10, 20, 30 are excited state
levels).

40
M.A. Subhan, H. Nakata / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 37–40
due to the CT transition from ligand to Yb(III) 4f levels (2F5/2 or
2F7/2). The CT transitions may involve a considerable reorganiza-
tion of the charge density distribution around the Yb(III) ion. This
reorganization is accompanied by an expansion of the metal–ligand
bonds in the excited state, which gives rise to the observation of large
Stokes shifts and broad luminescence bands in visible region for the
[Yb(TFN)3(S-BINAPO)] [20]. The excitation spectra for the [Yb(TFN)3
(S-BINAPO)] were measured in acetone. Broad and similar excitation
peaks were observed at 398 and 399 nm when monitored at 434 and
454 nm respectively (Fig. 9).
Conclusion
The complexes [Yb(TFN)3(S-BINAPO)](TFN = 4,4,4-trifluoro-1
(2-napthyl)-1,3-butanedione) (complex 1) and [Yb(HFA)3(S-BINAP-
O)](HFA = hexafluoroacetylacetonate) (complex 2) were synthe-
sized, characterized and their absorption as well as PL spectra were
studied. The complex [Yb(TFN)3(S-BINAPO)] showed narrowed
emission peak (half width ꢁ6 nm) at around 981 nm in addition to
several emission peaks in NIR region at low temperature. The
complex [Yb(HFA)3(S-BINAPO)] showed strong emission peak at
around 985 nm (half width ꢁ80 nm). The CT luminescence for the
[Yb(TFN)3(S-BINAPO)] was observed in 412–463 nm region. The
broadening of some PL peaks may be due to the considerable reorga-
nization of the charge density distribution around the Yb(III) ions
accompanied by an expansion of the metal–ligand bonds in the
excited state.
Fig. 7. PL spectra of Yb(HFA)3(S-3BINAPO) at 4 K.
For the complex [Yb(TFN)3(S-BINAPO)] the visible luminescence
spectra at 390–410 nm excitations were also recorded in acetone
(Fig. 8). When excited at 390 nm three peaks were observed at
412, 434 and 458 nm. Excitations at 398 and 400 nm provided
two emission peaks for each at 436 and 455 nm (Fig. 8). A broad
peak centering at 463 nm was observed corresponding to 400 nm
excitation. Yb(III)(4f13) is an ion for which charge transfer (CT)
luminescence can be expected [18,19]. In this ion, the only excited
4f state, F5/2, is located around 10,000 cmꢂ1 above the ground
state F7/2. Because of the large energy difference between the
charge transfer state and the highest excited 4f state, the charge
transfer luminescence in Yb(III) can be observed [20]. In our
present case the violet-blue region emissions (412–463 nm) are
2
2
Acknowledgement
Professors Yanagida Shozo of Osaka University, Japan and
Yasuchika Hasegawa of Hokkaido University, Japan are thankfully
acknowledged for their cooperation.
Appendix A. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.saa.2014.03.109.
References
[1] G.F. de Sa´, O.L. Malta, C. de Mello Donega´, A.M. Simas, R.L. Longo, P.A. Santa-
Cruz, E.F. da Silva Jr., Coord. Chem. Rev. 196 (2000) 165–195.
[2] S. Shinoda, H. Tsukube, Analyst 136 (2011) 431–435.
[3] G. Wang, Q. Peng, Y. Li, Acc. Chem. Res. 44 (2011) 322–332.
[4] A.K. Hagan, T. Zuchner, Anal. Bioanal. Chem. 400 (2011) 2847–2864.
[5] J.C. Frias, G. Bobba, M.J. Cann, C.J. Hutchison, D. Parker, Org. Biol. Chem. 1
(2003) 905–907.
Fig. 8. PL spectra of [Yb(TFN)3(S-BINAPO)] excitation at 390 nm (blue–), 398 nm
(red–), 400 nm (green–), 410 nm (violet–). (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
[6] M.A. Subhan, S. Rahman, K. Alam, M. Mahmud Hasan, Spectrochim. Acta, A 118
(2014) 944.
[7] F. Gan, Laser Materials, World Scientific, Singapore, 1995. p 70.
[8] E.J. Schimitschek, E.G.K. Schwarz, Nature 196 (1962) 832.
[9] H. Samelson, C. Brecher, V. Brophy, Appl. Phys. Lett. 5 (1964) 173.
[10] T. Kobayashi, S. Nakatsuka, T. Iwafuji, K. Kuriki, N. Imai, N. Nakamoto, C.D.
Claude, K. Sasaki, Y. Koike, Y. Okamoto, Appl. Phys. Lett. 71 (1997) 2421–2423.
[11] K. Kuriki, Y. Koike, Y. Okamoto, Chem. Rev. 102 (2002) 2347.
[12] A. Beeby, R.S. Dickins, S.F. Gerald, L.J. Govenlock, C.L. Maupin, D. Parker, J.P.
Riehl, G. Siligardic, J.A. Gareth Williams, Chem. Commun. (2000) 1183–1184.
[13] M.A. Subhan, T. Suzuki, J.H. Choi, H. Nakata, S. Kaizaki, J. Lumin. (2003) 101–
307.
[14] M.A. Subhan, Y. Hasegawa, T. Suzuki, S. Kaizaki, S. Yanagida, Inorg. Chim. Acta
362 (2009) 136–142.
[15] Nathalia B.D. Lima, Simone M.C. Goncalves, Severino A. Junior, Alfredo M.
Simas, Sci. Rep. 3:2395 (2013) 1–8.
[16] Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa, Y. Kai, S. Yanagida, J. Phys.
Chem. A 107 (2003) 1697–1702.
[17] Q. Lin, T.E. Long, J. Poly. Sci. Part A 38 (2000) 3736.
[18] E. Nakazawa, Chem. Phys. Lett. 56 (1978) 161.
[19] E. Nakazawa, J. Lumin. 18 (19) (1979) 272.
[20] L. van Pieterson, M. Heeroma, E. de Heer, A. Meijerink, J. Lumin. 91 (2000) 177–
193.
Fig. 9. Excitation spectra of [Yb(TFN)3(S-BINAPO)] excitation at 434 nm (blue–),
454 nm (red–). (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)