Synthesis and characterization of ultraviolet light-emitting organic acids

Article abstract of DOI:10.1007/s10895-014-1362-7

Three ultraviolet light-emitting organic acids of 3,3′-(4-phenyl-4H- 1,2,4-triazole-3,5-diyl)dibenzoic acid (Tz-1), 4,4′,4″-(4H-1,2,4- triazole-3,4,5-triyl)tribenzoic acid (Tz-2), and 4,4′-(4-(4′- carboxy-[1,1′-biphenyl]-4-yl)-4H-1,2,4-triazole-3,5-diyl)d

Full text of DOI:10.1007/s10895-014-1362-7

J Fluoresc
DOI 10.1007/s10895-014-1362-7
ORIGINAL PAPER
Synthesis and Characterization of Ultraviolet Light-Emitting
Organic Acids
Chun-Ai An & Ya n c h a o G u o & Zhenjun Si & Qian Duan
Received: 28 November 2013 /Accepted: 3 February 2014
#
Springer Science+Business Media New York 2014
Abstract Three ultraviolet light-emitting organic acids of
3,3′-(4-phenyl-4H-1,2,4-triazole-3,5-diyl)dibenzoic acid (Tz-
1), 4,4′,4″-(4H-1,2,4-triazole-3,4,5-triyl)tribenzoic acid (Tz-
2), and 4,4′-(4-(4′-carboxy-[1,1′-biphenyl]-4-yl)-4H-1,2,4-tri-
azole-3,5-diyl)dibenzoic acid (Tz-3) were successfully syn-
coverage of the applications, the heteroatoms such as the sulfer
atom [10] and the nitrogen atom [2, 11, 12] are often introduced
into the organic acids’ molecules for these heteroatoms could
endow the materials with some special structures and/or excel-
lent properties. For example, the picolinic acid was used to
prepare high-efficient organic electroluminescent IrIII complex
[7]. Meanwhile, the derivatives of 1,2,4-triazole (Tz-0) [13–15]
were widely applied in functional materials because of the fact
that these compounds possess the advantages including i) the
nitrogen atoms can coordinate to most metal ions, ii) the easy
modification of Tz-0 with different functional groups at 3-, 4-,
5- positions would furnish the Tz-0 derivatives with unexpect-
ed properties, and iii) the large energy gap of these compounds
could endow them with higher-energy light-emitting spectra.
Therefore, we designed and synthesized three ultraviolet light-
emitting compounds, 3,3′-(4-phenyl-4H-1,2,4-triazole-3,5-
diyl)dibenzoic acid (Tz-1), 3,4′,3″-(4H-1,2,4-triazole-3,4,5-
triyl)tribenzoic acid (Tz-2), and 3,3′-(4-(4′-carboxy-[1,1′-bi-
phenyl]-4-yl)-4H-1,2,4-triazole-3,5-diyl)dibenzoic acid (Tz-
3), which were characterized by 1H NMR, UV–Vis absorption
spectra and IR absorption spectra as well as that the crystal
structures of Tz-1 and Tz-2 were cultured by the hydrothermal
method and correctly resolved. At the same time, the
photophysical, the electrochemical, and the theoretical analyses
of Tz-1 ~ Tz-3 were also carried out.
1
thesized and fully characterized by the H NMR, the IR
absorption spectra, and the X-ray single crystal diffraction. It
was found that Tz-1, Tz-2, and Tz-3 could give out the
ultraviolet photoluminescent spectra centered at 369 nm,
365 nm and 350 nm, respectively. The luminescence quantum
yields of Tz-1 and Tz-2 were measured to be 0.20 and 0.14,
respectively. Additionally, the density functional theory
(DFT) and the time-dependent DFT calculations were also
carried out for Tz-1, Tz-2, and Tz-3.
.
Keywords Photoluminescence X-ray single crystal
.
diffraction Theoretical calculation
Introduction
In the past decades, the studies on the synthesis and the prop-
erties of the organic acids [1–12] appealed to many scientific
researchers because the organic acids, along with most metal
ions, can form diverse metal complexes which are potentially
applied in magnetism [1, 2], catalysts [3, 4], sensors [5, 6],
luminescence [7–9], etc. In order to further expand the
Experimental Section
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-014-1362-7) contains supplementary material,
which is available to authorized users.
Materials
:
:
:
N-(-chloro(m-tolyl)methylene)-3-methylbenzohydrazonoyl
chloride (A) were prepared according to the previously report-
ed methods [15]. The solvents used in the synthesis were dried
in the standard procedure [16], and all reactions were carried
out under nitrogen using Schlenk techniques.
C.<A. An Y. Guo Z. Si (*) Q. Duan (*)
School of Materials Science and Engineering, Changchun University
of Science and Technology, Changchun 130022, People’s Republic
of China
e-mail: szj@cust.edu.cn
e-mail: duanqian88@hotmail.com

J Fluoresc
Scheme 1 Synthetic route to Tz-1 ~ Tz-3. i) N,N-dimethylaniline, 145 °C, 24 h; ii) NaOH, KMnO4,H2O, reflux, 12 h
Synthesis of Tz-1
containing 120.0 mL distilled water and 20.0 mL pyridine and
heated up to 100 °C for 12 h and then cooled to room
temperature, 30.0 mL ethanol was added into the mixture
which was stirred for another 0.5 h, then the solid was filtered.
The filtrate was acidified with the diluted HCl aqueous (10 %)
to pH=3. The precipitated Tz-1 was obtained in yield of ca.
75 % by filtration. 1H NMR (400 MHz, DMSO-d6): δ=13.08
(s, 2H), 8.05–7.45 (d, 13H); IR (KBr)/cm−1: 3,500, 3,073,
2,923, 2,614, 1,926, 1,695, 1,612, 1,495.
The mixture of A (7.5 g, 24.590 mmol), aniline (2.3 mL,
25.190 mmol) and N,N-Dimethylaniline (45.0 mL) were
added into a 250.0 mL flask equipped with a magnetic stirrer
and reflux condenser and reacted 36 h at 145 °C. After being
cooled to the room temperature, diluted hydrochloric acid
(10 %, 80.0 mL) was added into the mixture and stirred for
another 2 h, then the white solid was filtered and washed with
the diluted hydrochloric acid (10 %, 50.0 mL×3) and pure
water successively, and then dried 12 h in vacuum at 30 °C to
give pure 4-phenyl-3,5-di-m-tolyl-4H-1,2,4-triazole (B-1) in
yield of ca. 60 %. The mixture of B-1 (3.25 g, 10.000 mmol),
KMnO4 (12.64 g, 80.000 mmol) and NaOH (8.13 g,
0.203 mol) were added into a 250.0 mL round-bottomed flask
Synthesis of Tz-2
The synthesis of Tz-2 was similar to that of Tz-1 by replacing
aniline with p-toluidine. Yield in total was 41.2 %. 1H NMR
(400 MHz, DMSO-d6): δ=13.18 (s, 3H), 8.07–7.96 (m, 6H);
7.60 (d, J=8Hz, 4H); 7.51 (t, J=8 Hz, 2H); IR (KBr)/cm−1:
3,419, 2,902, 2,615, 1,724, 1,606, 1,512, 1,461, 1,254.
Synthesis of Tz-3
The synthesis of Tz-3 was similar to that of Tz-1 by replacing
aniline with 4′-methyl-[1,1′-biphenyl]-4-amine. Yield in total
Ta b l e 1 Crystalline data of Tz-1 and Tz-2
Tz-1
Tz-2
Empirical formula
Formula weight
CCDC no.
Crystal system
Space group
a (Å)
C22H17N3O5
403.39
C23H15N3O6
429.38
956,492
Monoclinic
P21/c
935,264
Monoclinic
P21/n
12.038(2)
10.620(2)
15.528(3)
90.000
8.0474(16)
18.379(4)
13.095(3)
90
b (Å)
c (Å)
α (°)
β (°)
91.71(3)
90.000
96.48
γ (°)
90
V (Å3)
1984.3(7)
4
1924.4(7)
4
z
μ (mm−1
)
0.098
0.110
Fig. 1 ORTEP drawings of Tz-1(upper) and Tz-2 (lower) with 30 %
F(000)
840
888
thermal ellipsoids

J Fluoresc
Ta b l e 2 Selective bond distances (Å) and bond angles (o) of Tz-1 and
Tz-2
(integrated areas) of a standard sample (quinine sulfate)
and the unknown sample according to Eq. 1.
Tz-1
1.472(3)
Tz-2
1.475(3)
2
Φunk ¼ ΦstdðIunk=AunkÞðAstd=IstdÞðηunk=ηstd
Þ
ð1Þ
C(6)-C(8)
C(8)-N(2)
1.309(2)
1.378(2)
1.314(2)
1.376(3)
where Φunk is the LQY of the unknown sample; Φstd is the
LQY of quinine sulfate and taken as 0.546 [17]; Iunk and Istd
are the integrated fluorescence intensities of the unknown
sample and quinine sulfate at corresponding excitation wave-
length, respectively; Aunk and Astd are the absorbances of the
unknown sample and quinine sulphate at the corresponding
excitation wavelengths, respectively. The ηunk and ηstd are the
refractive indices of the corresponding solvents (pure solvents
were assumed). 1H NMR spectra was obtained using a Bruker
AVANVE 400 MHz spectrometer with tetramethylsilane as
the internal standard. The crystal structures of Tz-1 and Tz-2
were measured on a Bruker Smart Apex CCD single-crystal
diffractometer using λ (Mo Kα) radiation, 0.7107 Å at 293 K
and solved using the SHELXL-97 program [18–20]. The
cyclic voltammetry measurements were conducted on a
CHI825D electrochemical workstation with a polished Pt
plate as the working electrode, Pt mesh as the counter elec-
trode, and a commercially available saturated calomel elec-
trode (SCE) as the reference electrode, at a scan rate of 0.1 V/
s. The voltammograms were recorded using CH3CN/DMSO
(v/v=10/1) solutions with ~ 10−3 M sample and 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) as the
supporting electrolyte. Prior to each electrochemical measure-
ment, the solution was purged with nitrogen for ~10–15 min
to remove the dissolved O2 gas.
C(8)-N(1)
C(9)-N(1)
1.440(2)
1.445(3)
C(15)-N(3)
1.309(3)
1.313(3)
C(15)-N(1)
1.370(3)
1.379(2)
C(15)-C(16)
1.478(3)
1.470(3)
N(2)-N(3)
1.385(2)
1.381(2)
C(7)-C(6)-C(8)
C(5)-C(6)-C(8)
N(2)-C(8)-N(1)
N(2)-C(8)-C(6)
N(1)-C(8)-C(6)
C(14)-C(9)-N(1)
C(10)-C(9)-N(1)
N(3)-C(15)-N(1)
N(3)-C(15)-C(16)
N(1)-C(15)-C(16)
C(21)-C(16)-C(15)
C(17)-C(16)-C(15)
123.00(17)
117.89(18)
109.01(16)
124.26(17)
126.72(17)
119.22(18)
119.54(18)
109.77(16)
124.99(19)
125.24(17)
118.99(18)
121.46(19)
123.09(19)
118.07(19)
109.18(17)
123.18(18)
127.60(18)
118.69(17)
119.63(18)
109.26(18)
124.22(18)
126.50(18)
117.46(19)
123.87(19)
1
was 38.4 %. H NMR (400 MHz, DMSO-d6): δ=13.08 (s,
3H); 8.03 (t, J=10 Hz, 4H); 7.97 (d, J=8Hz, 2H); 7.87 (m, J=
8Hz, 4H); 7.68(d, J=8 Hz, 2H); 7.62(d, J=8 Hz, 2H); 7.52 (t,
J=8 Hz, 2H) IR (KBr)/cm−1: 3,288, 2,879, 2,553, 1,685,
1,610, 1,523, 1,425, 1,284.
Computational Details
Measurements
The geometrical structures of the ground states were optimized
at b3lyp/6-31 g* level [21] in gas phase by the density func-
tional theory (DFT) [22], On the basis of the optimized ground
state geometry structures, the absorption spectral properties in
methanol media were calculated by time-dependent DFT
(TDDFT) method [23–25] associated with the polarized con-
tinuum model (PCM) [26] in methanol media. All the calcula-
tions were performed with the Gaussian 09 package [27].
The IR spectra was acquired using a FTIR-8400S
SHIMADZU spectrophotometer in the 4,000–400 cm−1
region with KBr pellets. The UV-Vis absorption and
photoluminescent (PL) spectra of methanol solutions
with ca. 10−4 mol/L samples were recorded on a Perkin
Elmer Lambda 900 UV/Vis/NIR spectrophotometer
and a SHIMADZU RF-5301 PC spectrofluorophotometer,
respectively. The luminescence quantum yields (LQYs)
were measured by comparing fluorescence intensities
Results and Discussion
Ta b l e 3 Hydrogen bond distances (Å) in Tz-1 and Tz-2
Molecular Structures
Tz-1
Tz-2
As presented in Scheme 1, the B-1, 3,5-di-m-tolyl-4-(p-tolyl)-
4H-1,2,4-triazole (B-2) and 4-(4′-methyl-[1,1′-biphenyl]-4-
yl)-3,5-di-m-tolyl-4H-1,2,4-triazole (B-3) were prepared from
the precursors of A and aniline derivatives in N,N-
Dimethylaniline at 145 °C, and then converted into the target
compounds of Tz-1 ~ Tz-3 in hot KMnO4/NaOH aqueous
O(3)-H(5B)-O(5)
O(4)-H(4A)-O(5)
N(2)-H(5A)-O(5)
N(3)-H(2A)-O(2)
2.874
2.553
2.793
2.760
O(1)-H(2)-O(2)
N(2)-H(6A)-O(6)
N(3)-H(3A)-O(3)
2.622
2.689
2.783

J Fluoresc
Fig. 2 Single-layer (a) and
double-layer (b) 2D
supermolecular structures of Tz-1
Fig. 3 Intermolecular hydrogen
bond interactions between 1,2,4-
triazole moiety and the acid
group(A) and the 3D
supermolecular structure of Tz-2
solution. The monoclinic crystals of Tz-1 with space group of
P21/n and Tz-2 with space group of P21/c were cultured by the
hydrothermal methods. The corresponding ellipsoid crystal
structures of Tz-1 and Tz-2 were prepared in 30 % thermal
ellipsoids and presented in Fig. 1. The crystal data and the
selective bond distances and angles are listed in Tables 1 and
2, respectively, while intermolecular hydrogen bond interac-
tions (IHBIs) are listed in Table 3.
double-layer based 2D supermolecules (Fig. 2b) with the help
of the IHBIs of O(3)⋅⋅⋅H(5B)−O(5) (d=2.874 Å). After adding
another carboxylic group, in Tz-2, The IHBIs of
N ( 2 ) ⋅ ⋅ ⋅ H ( 6 A ) − O ( 6 ) w i t h d o f 2 . 6 8 9 Å a n d
N(3)⋅⋅⋅H(3A)−O(3) with d of 2.783 Å connect Tz-2 molecules
to be the 2D supermolecules (Fig. 3a) which are further
The dihedral angles between the Tz-0 moiety and the
phenyl groups on 3-, 4-, 5-positions of the Tz-0 moiety were
measured to be 44.640(59)°, 70.655(53)°, and 28.365(54)° for
Tz-1, and 28.884(41)°, 84.118(57)° and 21.887(43)° for Tz-2,
respectively. These data suggest that the π-conjunction be-
tween 3- (or 5-) aryl groups and the Tz-0 moiety should be
better than that between 4-aryl group and the Tz-0 moiety as
well as that the size of the 4-aryl group could greatly affect the
π-conjunction interaction between 4-aryl groups and Tz-0
moiety. In Tz-1, the bond distance (d) of IHBIs of
N(2) ⋅⋅⋅H(5A )−O(5), N(3)⋅⋅⋅H(2A) −O(2), and
O(5)⋅⋅⋅H(4A)−O(4) are 2.793 Å, 2.760 Å, and 2.553 Å, re-
spectively. These IHBIs connect Tz-1 molecules to be the
single-layer based 2D supermolecules (Fig. 2a). These
single-layer based 2D supermolecules further expand to the
Fig. 4 UV–Vis absorption spectra (Abs) and the emission spectrum (Em)
of Tz-1 ~ Tz-3 in methanol at room temperature

J Fluoresc
peaked at 369 nm with full width at half maximum (HWHM)
of ca. 81 nm, 366 nm with HWHM of 44.5 nm, 350 nm with
HWHM of 38 nm, respectively. The LQYs of Tz-1, Tz-2 and
Tz-3 were measured reference to the quinine sulfate (LQY=
0.546) to be 0.20, 0.14, and 0.06, respectively, the higher
LQYs of Tz-1 and Tz-2 should be partially attributed to their
inflexible molecular structures [28].
Electrochemistry
In order to investigate the distribution of the frontier molecular
orbitals, the electrochemical properties of Tz-1 ~ Tz-3 are
studied in CH3CN/DMSO (v/v=10:1) solution through cyclic
voltammetry using TBAPF6 as the supporting electrolyte
(Fig. 5). The irreversible anodic waves peak at +1.18 V with
an onset oxidation potential (Vonset(OX)) of +0.98 V for Tz-1,
+1.16 V with Vonset(OX) of +0.98 V for Tz-2, and +1.26 V
with Vonset(OX) of +1.01 V for Tz-3, respectively. The ener-
gies of the highest occupied molecular orbital (EHOMO) are
Fig. 5 Electrochemistry of Tz-1 ~Tz-3 in CH3CN/DMSO (v/v=10:1)
solution with 0.1 M TBAPF6 as the supporting electrolyte
connected to be 3D supermolecules by the IHBIs of
O(1)⋅⋅⋅H(2)−O(2) (d=2.622 Å) (Fig. 3b).
Photophysical Properties
obtained according to the following equation: EHOMO=[VSCE
−
The UV−Vis absorption spectra and the emission spectra of
Tz-1 ~ Tz-3 are presented in Fig. 4. According to the previous
reports [13] and the theoretical analysis (vide infra), the ab-
sorption band peaked at ~ 200 nm should be mainly attributed
to the π → π* transitions and the shoulder band in the range
240 ~ 320 nm should be assigned to the contribution of the
intramolecular charge transfer (ICT) transitions and the π →
π* transitions. Upon the UV excitation, Tz-1, Tz-2 and Tz-3
give out in their ethanol solutions the ultraviolet PL spectra
V
onset(OX)] eV [17], where the VSCE is the electrode potential of
the SCE which should be—4.74 eV in a vacuum, and the
values of EHOMO of Tz-1, Tz-2, and Tz-3 are calculated to
be −5.72 eV, −5.72 eV, and −5.75 eV, respectively. At the same
time, the values for the energy of the lowest unoccupied
molecular orbital (ELUMO) are calculated with the equation of
ELUMO=[VSCE − Vonset(Red)] eV [17], where the Vonset(Red) is
the onset reduction potential which should be −1.83 V,
−1.78 V, and −1.72 V for Tz-1, Tz-2, and Tz-3, respectively.
Fig. 6 Electron density plots of
the HOMO and LUMO of Tz-1 ~
Tz-3 in gas phase at DFT/
B3LYP1/6-31G* level
Tz-1
Tz-2
Tz-3
HOMO
LUMO

J Fluoresc
Ta b l e 4 Frontier molecular orbital compositions (%) of Tz-1 ~ Tz-3
calculated in the gas phase at the DFT/B3LYP/6-31 g* level
Therefore, the values of the ELUMO should be −2.91 eV,
−2.96 eV, and −3.02 eV, respectively, and the energy gap
(ΔE) between HOMO and LUMO of Tz-1 ~ Tz-3 should be
2.81 eV, 2.76 eV, and 2.73 eV, respectively. These results
present the fact that the ELUMO and ΔE of Tz-1 ~ Tz-3 are
in the order of Tz-1 > Tz-2 > Tz-3, which is in accordance
with the theoretical studies (vide infra). It is also found that the
ΔEs of Tz-2 ~ Tz-3 are higher than that of the triplet energy
gape of the typical blue triplet emitter of Firpic (2.62 eV) [29],
which suggests that Tz-1 ~ Tz-3 might be used as the host
materials of the blue phosphorescent light-emitting devices.
Orbital
E(eV)
Distribution (%)
3- and 5-R1
Tz-0
21.5
4-R2
84.9
Tz-1
L+3
L+2
L+1
L
−0.79
−1.13
−1.42
−1.57
4.57
76.1
91.6
86.6
ΔE
H
−6.14
−6.73
−7.15
−7.20
47.3
52.3
83.9
Theoretical Calculations
H-1
H-2
H-3
Tz-2
L+3
L+2
L+1
L
66.0
89.2
19.7
89.2
Simulation on the Ground State Molecules
According to the optimized ground-state molecular structures
of Tz-1 ~ Tz-3 (Fig. 6), the dihedral angles between the Tz-0
moiety and the phenyl groups on its 3-, 4-, 5-positions were
simulated to be 33.31°, 69.56°, and 29.61° for Tz-1, 29.34°,
80.37° and 26.32° for Tz-2, and 28.51°, 93.11°, and 24.01° for
Tz-3, respectively. These data indicate that the π-conjunction
between the Tz-0 moiety and the aryl group on its 4-positon
should be in the following order: Tz-1 > Tz-2 > Tz-3, that is,
the increase of the size of aryl group on 4-position of Tz-0
moiety could weaken the π-conjunction, which is consistent
with the fact that the peaks of the PL spectra of Tz-1 ~ Tz-3
locates at 369 nm, 366 nm, and 350 nm, respectively [30, 31].
The distributions of the simulated HOMOs and LUMOs of
Tz-1 ~ Tz-3 are presented in Fig. S1 ~ S3, respectively, while
the compositions of the simulated frontier molecular orbitals
of Tz-1 ~ Tz-3 are listed in Table 4. The HOMO of Tz-1 is
composed of the π orbitals of Tz-0 moiety with 52.3 %
contributions and 3- and 5-PhCOOH moieties with 47.3 %
contributions. The LUMO of the Tz-1 is mainly contributed
by the π* orbitals on 3- and 5-PhCOOH moieties with 86.6 %
contributions. The HOMO of Tz-2 (Tz-3), similar to that of
Tz-1, is composed of the π orbitals of Tz-0 moiety with
50.5 % (50.8 %) contributions and 3-/5-PhCOOH groups
attached to Tz-0 moiety with 49.4 % (49.0 %) contributions,
while the LUMO of Tz-2 (Tz-3) is comprised with the π*
orbitals on the 4-PhCOOH (4-Ph2COOH) group with 89.2 %
(94.7 %) contributions. These data suggest that the composi-
tion of LUMOs of the derivatives of Tz-0 can be more
obviously affected by the groups attached to their 4-position
than that of their HOMOs. At the same time, the EHOMOs and
the ELUMOs are calculated to be −6.14 eV and −1.57 eV for
Tz-1, −6.23 eV and −1.67 eV for Tz-2, and −6.16 eV and
−1.63 eV for Tz-3, respectively. Therefore, the ΔE are calcu-
lated to be 4.57, 4.23, and 4.19 eV for Tz-1, Tz-2, and Tz-3,
respectively, which are bigger than those from the experimen-
tal measurements. But the values of these theoretically calcu-
lated data and the above mentioned electrochemically
−1.19
−1.51
−1.67
−2.00
4.23
70.7
90.6
82.1
ΔE
H
−6.23
−6.91
−7.31
−7.34
49.4
50.5
86.3
H-1
H-2
H-3
Tz-3
L+3
L+2
L+1
L
95.6
97.5
−1.17
−1.47
−1.63
−1.97
4.19
68.7
90.9
83.5
94.7
ΔE
H
−6.16
−6.67
−7.08
−7.29
49.0
94.3
50.8
50.6
59.3
H-1
H-2
H-3
44.0
29.0
R1 = –PhCOOH, R2 = -Ph for Tz-1, –PhCOOH for Tz-2, and –Ph2COOH
for Tz-3,respectively
measured data are in the same changing trend. The difference
between the experimental measurements and the theoretical
calculations should be mainly attributed to the ignorance of
the solution effect during the optimization of the geometrical
structures of Tz-1 ~ Tz-3.
UV−Vi s A bs or pt io n S pe ct ra
As presented in Table 5, the lowest lying singlet → singlet
absorptions with the configurations of HOMO → LUMO are
calculated at 299 and 322, and 312 nm for Tz-1, Tz-2, and Tz-
3, respectively, which means that the lowest lying transitions
should be described as the π → π* and the intramolecular

J Fluoresc
Ta b l e 5 Calculated absorption of
Tz-1 ~ Tz-3 in methanol media
according to the TDDFT/B3LYP/
6-31 g* calculations
State
Transition (%)
E (eV)/λ (nm)
Osc. strength
Assign
Tz-1
1
H→L (94)
4.14/299
4.50/276
5.04/246
5.47/226
6.28/197
0.3142
0.4873
0.1378
0.1906
0.1027
ICT/π→π*
ICT/π→π*
π→π*
3
H→L+2 (90)
H-3→L (46)
H-5→L+1 (64)
H-10→L+1 (20)
11
21
44
Tz-2
1
ICT/π→π*
π→π*
H→L (99)
3.85/322
4.14/299
4.48/277
0.0025
0.4534
0.4457
ICT
2
H→L+1 (95)
H→L+3 (88)
H-3→L+1 (38)
H-4→L+2 (38)
H-9→L (20)
ICT/π→π*
ICT/π→π*
4
17
5.09/244
5.58/222
0.1922
0.1846
ICT/π→π*
ICT/π→π*
30
Tz-3
1
H→L (96)
3.98/312
4.11/301
4.36/284
4.45/278
5.08/244
0.0131
0.4181
0.6622
0.4658
0.1439
ICT
2
H→L+1 (94)
H-1→L (84)
H→L+3 (86)
H-4→L+1 (28)
ICT/π→π*
ICT/π→π*
ICT/π→π*
π→π*
4
6
19
charge transfer (ICT) based on the π(Tz-0 + 3-/5-PhCOOH)
→ π*(3-/5-PhCOOH) transitions for Tz-1, the ICT based on
the π(Tz-0 + 3-/5-PhCOOH) → π*(4-PhCOOH) transfer for
Tz-2 and the ICT based on the π(Tz-0 + 3-/5-PhCOOH) →
π*(4-PhPhCOOH) transfer for Tz-3, respectively.
and 0.14, respectively. Therefore, the titled organic acids Tz-1
~ Tz-3 could be used as the host materials in blue phospho-
rescent light-emitting devices.
Acknowledgments The authors are grateful to financial aid from the
National Natural Science Foundation of China (Grant No. 21271033).
The absorptions with the largest oscillator strengths are
simulated to be at 276 nm with the configuration of HOMO
→ LUMO + 2 for Tz-1, 299 nm with the configuration of
HOMO → LUMO + 1 for Tz-2, and 284 nm with the config-
uration of HOMO-1 → LUMO for Tz-3, respectively. Ac-
cording to the fact that the LUMO + 2 of Tz-1, the LUMO + 1
of Tz-2, and the HOMO-1 of Tz-3 are mainly comprised of
the π*(3-/5-PhCOOH + Tz-0), π*(3-/5-PhCOOH), and π (4-
Ph2COOH + Tz-0) (Table 4), respectively, these largest oscil-
lator strengths based absorption should be with the character
of π → π*/ICT transitions. At the same time, the absorptions
with the moderate oscillator of Tz-1 ~ Tz-3 are calculated to
be the mixture transitions of the π →π*/ICT transitions.
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