Aggregation induced emission (AIE) active β-ketoiminate boron complexes: Synthesis, photophysical and electrochemical properties

Article abstract of DOI:10.1016/j.dyepig.2015.06.020

New keto-enol tautomeric benzoxazolyl and benzthiazolyl-1,2-diaryl β-ketoiminate based organoboron complexes have been synthesised and their fluorescence properties investigated. Boron complexes are widely known for their fluorescent properties, here we have synthesized organoboron complexes that show bright fluorescence in solid state and hardly any fluoresce in solution. These compounds exhibit aggregation induced emission (AIE) activity. Density functional theory (DFT) was employed for geometry optimisation and molecular orbital distribution computations in the ground state of the molecules. Electrochemical study demonstrates that these molecules possess high electron affinities as compared to the current electroluminescent materials like tris(8-hydroxyquinoli- nato)-aluminium (Alq₃) and BODIPY, indicating the prospects of these boron complexes as an cient emitters in the optoelectronics.

Full text of DOI:10.1016/j.dyepig.2015.06.020

Accepted Manuscript
Aggregation induced emission (AIE) active β-ketoiminate boron complexes:
synthesis, photophysical and electrochemical properties
Haribhau S. Kumbhar, Ganapati S. Shankarling
PII:
S0143-7208(15)00238-7
10.1016/j.dyepig.2015.06.020
DYPI 4822
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 21 April 2015
Revised Date: 4 June 2015
Accepted Date: 11 June 2015
Please cite this article as: Kumbhar HS, Shankarling GS, Aggregation induced emission (AIE) active
β-ketoiminate boron complexes: synthesis, photophysical and electrochemical properties, Dyes and
Pigments (2015), doi: 10.1016/j.dyepig.2015.06.020.
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ACCEPTED MANUSCRIPT
Aggregation induced emission (AIE) active β-ketoiminate boron complexes:
synthesis, photophysical and electrochemical properties
Haribhau S. Kumbhar and Ganapati S. Shankarling*

ACCEPTED MANUSCRIPT
Aggregation induced emission (AIE) active β-ketoiminate boron complexes:
synthesis, photophysical and electrochemical properties
Haribhau S. Kumbhar and Ganapati S. Shankarling*
Dyestuff Technology Department, Institute of Chemical Technology, Matunga, Mumbai 400 019, India
E-mail: gsshankarling@gmail.com, gs.shankarling@ictmumbai.edu.in Tel.: +91 2233612708; fax: +91
2
2 33611020.
Abstract
New keto-enol tautomeric benzoxazolyl and benzthiazolyl-1,2-diaryl β� ketoiminate based
organoboron complexes have been synthesised and their fluorescence properties investigated.
Boron complexes are widely known for their fluorescent properties, here we have synthesized
organoboron complexes that show bright fluorescence in solid state and hardly any fluoresce
in solution. These compounds exhibit aggregation induced emission (AIE) activity. Density
functional theory (DFT) was employed for geometry optimisation and molecular orbital
distribution computations in the ground state of the molecules. Electrochemical study
demonstrates that these molecules possess high electron affinities as compared to the current
electroluminescent materials like tris(8-hydroxyquinoli- nato)-aluminium (Alq3) and
BODIPY, indicating the prospects of these boron complexes as an efficient emitters in the
optoelectronics.
Keywords: β� ketoiminate, Organoboron complex, Solid state fluorescence, AIEE.

ACCEPTED MANUSCRIPT
1
. Introduction
Design and synthesis of the highly solid state emissive compounds have gained great
attention in the field of the optoelectronic devices like, organic light emitting diodes, organic
solid state lasers and fluorescent molecular sensors[1–5]. Boron complexes, mainly boron
dipyrromethene (BODIPY) dyes[6–9] are the most important types of fluorescent dyes due to
their outstanding optical properties such as, high fluorescence quantum yields, extinction
coefficients, sharp absorption and fluorescence emission spectra. BODIPY dyes are
extensively used as a chemosensors[10–16], in the biolabeling[17,18], in dye-sensitized solar
cells[19,20] and photodynamic therapy[21,22]. However, their use as an electroluminescent
material is restricted due to their small stokes shifts which leads to self-quenching[23,24].
The high planarity and intermolecular π–π-stacking interactions in these BODIPY dyes result
in to the concentration quenching in the solid state which is known as aggregation caused
quenching (ACQ)[25–30]. Hence, they seldom exhibit photoluminescence in the solid
state[31]. Other than BODIPY, the boron complexes of pyridomethene[32], diketone [33],
iminoketone [34], azo dyes[35], β-enaminone[36] and β-ketoiminate also shows high
fluorescence. Some of them also show photoluminescence in the solid state as well as
aggregation induced emission enhancement (AIEE)[37]. Aggregation induced emission
(AIE) active molecules basically have two or more conjugated-aromatic moieties joined
through rotatable C-C single bond[38–41]. This free intramolecular rotation along the C-C
single bond occurs only in the solution, whereas in the aggregated state it gets inhibited. The
C-C single bond rotation results in to the fluorescence quenching whereas restricted C-C
single bond rotation is responsible for AIE phenomenon[42]. The best example for this
phenomenon is tetraphenylethene which exhibit excellent aggregation-induced emission
(AIE)[43]. These molecules does not show fluorescence in solution but they are highly
fluorescent in their aggregate state[44].

ACCEPTED MANUSCRIPT
In this work, we have designed and synthesized novel solid state emissive 2-(benz[d]oxazol-
2
-yl)-1, 2-diphenylethanol and 2-(benz[d]thiazol-2-yl)-1, 2-diphenylethanol based
organoboron complexes where the BF chelation gives bright solid state fluorescence. The
2
electrochemical properties of the synthesised compounds are investigated by cyclic
voltammetry combined with computational study.
2
. Experimental
2
.1. General methods
All reagents and other chemicals were obtained from commercial suppliers and used without
further purification. Nuclear magnetic resonance spectra were recorded on Bruker 400 MHz
with TMS as an internal standard. Fluorescence spectra were performed with a Varian Cary
Eclipse fluorescence spectrofluorometer at room temperature. UV-Visible spectra were
performed with a Perkin-Elmer Lamda-25 spectrophotometer at room temperature.
2
.2. Synthesis of the 7a-c and 8a-c ligands Compound and their boron complexes
2
-Benzylbenzo[d]thiazole (4) and 2-benzylbenzo[d]oxazole (5) were synthesised by
previously reported method[50,51]. Further synthesis of the ligands 7a-c and 8a-c and their
complexes are as follows,
Synthesis of 7a
To the toluene (50 mL) solution of 2-benzylbenzo[d]oxazole (2.09 g, 10 mmol) and ethyl
benzoate (1.5 g, 10 mmol), sodium hydride (60 wt% in oil, 1.6 g, 40 mmol) was added in at
o
room temperature. The solution was refluxed for overnight. After cooling to 0 to 5 C, aq.
NH Cl was added to the reaction mixture and the product extracted with ethyl acetate. The
4
extract was dried over anhydrous Na SO and concentrated under vacuum. The crude product
2
4
obtained was purified by column chromatography using silica gel to give 7a (1.8 g, 57%) as a

ACCEPTED MANUSCRIPT
°
-1
pale yellow solid. mp: 118-120 C. FTIR (cm ): 1597, 1567, 1525, 1489, 1285, 1119, 1023,
1
7
41. H NMR (400 MHz, CDCl ) δ 13.90 (s, 1H), 7.66 (d, J = 7.8 Hz, 1H), 7.41 (d, J = 8.0
3
1
3
Hz, 1H), 7.29 (m, 10 H), 7.18 (t, J = 7.4 Hz, 2H). C NMR (101 MHz, CDCl ) δ 166.20,
3
1
1
65.67, 148.74, 139.46, 135.29, 134.39, 132.04, 129.51, 129.36, 129.26, 129.16, 129.08,
28.81, 128.42, 127.67, 127.37, 124.75, 124.24, 117.88, 110.60, 101.08. Mass (EI):
C H NO Calculated 313.4 (M+), found 314.7(M+1).
21
15
2
Synthesis of 7b
Synthesized by same procedure as 7a using diethyl terephthalate 6b and compound 4
o
-1
Yellow solid (Yield = 55%). mp. (134-136 C). FT-IR (cm ): 1703, 1598, 1523, 1457, 1273,
1
1
2
4
1
1
252, 1181, 1099, 835, 747. H NMR (400 MHz, CDCl ) δ 13.90 (s, 1H), 7.85 (d, J = 8.4 Hz,
3
H), 7.67 (d, J = 7.8 Hz, 1H), 7.40 (t, J = 7.7 Hz, 3H), 7.34 (m, 4H), 7.29 – 7.23 (m, 3H),
1
3
.34 (q, J = 7.1 Hz, 2H), 1.36 (t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl ) δ 166.07,
3
65.83, 164.26, 148.77, 139.57, 139.28, 133.87, 131.92, 130.80, 129.31, 128.91, 128.84,
28.60, 127.70, 124.89, 124.53, 118.03, 110.68, 102.15, 77.35, 77.03, 76.71, 61.06, 14.28.
Mass (EI): C H NO Calculated 385.41 (M+), found 386.11(M+1).
2
2
19
4
Synthesis of 7c
Synthesized by same procedure as 7a using 6c and compound 4
o
-1
Yellow solid (Yield = 60%). mp:178-180 C. FT-IR (cm ): 1655, 1590, 1545, 1454, 1375,
1
1
3
7
280, 1189, 743. H NMR (400 MHz, CDCl ) δ 7.94 (d, J = 9.0 Hz, 2H), 7.69 (dd, J = 5.8,
3
.0 Hz, 1H), 7.55 (d, J = 7.4 Hz, 2H), 7.47 (dd, J = 5.7, 3.2 Hz, 1H), 7.37 (t, J = 7.4 Hz, 2H),
1
3
.28 (m, 3H), 6.58 (d, J = 9.0 Hz, 2H), 6.27 (s, 1H), 3.00 (s, 6H). C NMR (101 MHz,
CDCl ) δ 190.96, 163.93, 153.63, 151.28, 141.26, 134.75, 131.41, 129.45, 128.93, 127.98,
3

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1
24.75, 124.11, 123.15, 120.12, 110.77, 110.72, 77.36, 77.04, 76.72, 54.06, 39.90. Mass (EI):
C H N O Calculated 356.42 (M+), found 357.08(M+1).
23
20
2
2
Synthesis of 8a
Synthesized by same procedure as 7a using 6a and compound 5
o
-1
Yellow solid (Yield = 65%). mp: 90-94 C. FT-IR (cm ): 1584, 1560, 1489, 1455, 1249,
1
1
159, 1084, 1059, 779. H NMR (400 MHz, CDCl ) δ 14.96 (s, 1H), 7.84 (d, J = 8.2 Hz, 1H),
3
7
.66 (d, J = 7.9 Hz, 1H), 7.53 (d, J = 7.5 Hz, 1H), 7.42 (dd, J = 13.8, 6.6 Hz, 2H), 7.3–7.13
1
3
(
m, 9H). C NMR (101 MHz, CDCl ) δ 195.28, 173.18, 163.94, 150.46, 137.71, 136.00,
3
1
1
7
33.61, 132.07, 131.91, 129.32, 129.08, 128.99, 128.93, 128.84, 128.77, 128.31, 127.94,
27.61, 126.47, 125.91, 124.96, 124.13, 123.06, 121.49, 121.14, 120.05, 107.68, 77.34,
7.03, 76.71, 58.29. Mass (EI): C H NOS Calculated 329.41 (M+), found 330.13 (M+1).
2
1
15
Synthesis of 8b
Synthesized by same procedure as 7a using 6b and compound 5
o
-1
Yellow solid (Yield = 50%). mp: 110-112 C. FT-IR (cm ): 1711, 1585, 1557, 1436, 1402,
1
1
268, 1086, 1059, 776, 751. H NMR (400 MHz, CDCl ) δ 14.97 (s, 1H), 7.84 (d, J = 8.4 Hz,
3
3
H), 7.66 (d, J = 7.9 Hz, 1H), 7.46 – 7.21 (m, 9H), 4.31 (q, J = 7.1 Hz, 2H), 1.34 (t, J = 7.1
13
Hz, 3H). C NMR (101 MHz, CDCl ) δ 172.87, 166.06, 162.63, 150.29, 140.31, 137.18,
3
1
31.78, 129.08, 129.00, 128.78, 128.24, 126.59, 124.37, 121.20, 120.18, 108.56, 60.98,
4.27. Mass (EI): C H NO S Calculated 401.48 (M+), found 402.14(M+1).
1
2
4
19
3
Synthesis of 8c
Synthesized by same procedure as 7a using 6c and compound 5

ACCEPTED MANUSCRIPT
o
-1
Yellow powder (Yield = 61%). mp:156-158 C. FT-IR (cm ): 1657, 1582, 1524, 1436, 1370,
1
1
192, 1154, 1059, 760, 707. H NMR (400 MHz, CDCl ) δ 8.03 – 7.95 (m, 3H), 7.81 (d, J =
3
8
.0 Hz, 1H), 7.56 (d, J = 7.5 Hz, 2H), 7.44 – 7.36 (m, 2H), 7.35 – 7.19 (m, 3H), 6.59 (d, J =
1
3
9
.0 Hz, 2H), 6.56 (s, 1H), 2.99 (s, 6H). C NMR (101 MHz, CDCl ) δ 192.98, 170.29,
3
1
53.70, 152.39, 137.50, 136.24, 132.10, 131.43, 130.48, 129.09, 128.69, 127.85, 125.70,
24.73, 123.34, 122.89, 121.46, 110.79, 110.73, 57.41, 39.89. Mass (EI): C H NO S
1
2
3
20
2
Calculated 372.48 (M+), found 373.09 (M+1).
Synthesis of 9a
Compound 7a (626 mg, 2 mmol) was dissolved in dry dichloromethane (12 mL),
triethylamine (0.5 mL, 4 mmol) and boron trifluoride diethyl ether complex (1.41 mL, 4
mmol) was added to the solution and stirred at room temperature for 5 hours. Addition of
water was done followed by extraction of product using CH Cl . The organic layer was
2
2
washed with water and dried over anhydrous MgSO4. The residue obtained after evaporating
the solvent was further purified by column chromatography using silica gel to afford
-1
compound 9a (630mg 55%) as a yellow solid. mp 170-172 °C. FT-IR (cm ): 1594, 1574,
1
1
1
1
1
523, 1487, 1296, 1116, 1100, 1024, 743. H NMR (400 MHz, CDCl ) δ 7.86 (d, J = 8.2 Hz,
3
1
3
H), 7.48 (m, 4H), 7.40 (m, 4H), 7.32 (m, 3H), 7.22 (m, 2H). C NMR (101 MHz, CDCl ) δ
3
70.36, 164.17, 148.36, 134.24, 131.53, 131.11, 130.94, 130.74, 130.08, 129.01, 128.36,
27.84, 126.84, 126.16, 115.68, 111.36, 98.83. Mass (EI): C H BF NO Calculated 361.15
2
1
14
2
2
(M+), found 361.55 (M+1).
Synthesis of 9b
Synthesized by same procedure as 9a using compound 7b
o
-1
Yellow solid (Yield= 68%). mp: 174-176 C. FT-IR (cm ): 1713, 1588, 1484, 1268, 1242,
1
1
180, 1093, 748. H NMR (400 MHz, CDCl ) δ 7.91 – 7.84 (m, 3H), 7.51 (m, 4H), 7.47 –
3

ACCEPTED MANUSCRIPT
1
3
7
.37 (m, 2H), 7.28 (m, 1H), 4.35 (q, J = 7.1 Hz, 2H), 1.37 (t, J = 7.1 Hz, 3H). C NMR (101
MHz, CDCl ) δ 168.80, 165.76, 163.89, 148.44, 138.29, 132.21, 131.43, 131.37, 130.57,
3
1
29.95, 129.45, 129.17, 128.93, 128.66, 127.02, 126.47, 115.82, 111.48, 99.88, 61.26, 14.26.
Mass (EI): C H BF NO Calculated 433.21 (M+), found 435.82 (M+2).
2
4
18
2
4
Synthesis of 9c
Synthesized by same procedure as 9a using compound 7c
°
-1
Yellow solid (Yield= 75%). mp: 206-208 C. FT-IR (cm ): 1604, 1549, 1476, 1439, 1361
1
CH bending, 1277, 1199, 745. H NMR (400 MHz, CDCl ) δ 7.79 (d, J = 7.8 Hz, 1H), 7.48
3
3
1
3
–
1
1
4
7.29 (m, 10H), 6.43 (d, J = 9.1 Hz, 2H), 2.97 (s, 6H). C NMR (101 MHz, CDCl ) δ
3
70.36, 164.40, 152.08, 148.23, 132.44, 132.27, 131.72, 131.15, 129.09, 128.03, 126.36,
25.25, 120.80, 115.08, 111.00, 110.40, 95.89, 39.88. Mass (EI): C H BF N O Calculated
2
3
19
2
2
2
04.22 (M+), found 405.21 (M+1).
Synthesis of 10a
Synthesized by same procedure as 9a using compound 8b
°
-1
Yellow solid (Yield= 72%). mp: 180-182 C. FT-IR (cm ): 1582, 1541, 1466, 1454, 1268,
1
1
111, 1074, 1040, 781, 769. H NMR (400 MHz, CDCl ) δ 8.23 (d, J = 8.3 Hz, 1H), 7.67 (d,
3
J = 8.0 Hz, 1H), 7.57 (t, J = 7.8 Hz, 1H), 7.42 (m, 6H), 7.34 – 7.26 (m, 3H), 7.18 (t, J = 7.7
13
Hz, 2H). C NMR (101 MHz, CDCl ) δ 172.44, 163.78, 143.33, 135.06, 134.17, 131.24,
3
1
30.58, 129.89, 129.63, 129.12, 128.99, 128.24, 127.79, 125.93, 121.61, 118.87, 106.76.
Mass (EI): C H BF NOS Calculated 377.21 (M+), found 378.14 (M+1).
2
1
14
2
Synthesis of 10b
Synthesized by same procedure as 9a using compound 8b

ACCEPTED MANUSCRIPT
°
-1
Yellow solid (Yield= 70%). mp: 158-160 C. FT-IR (cm ): 1714, 1577, 1547, 1467, 1439,
1
1
266, 1099, 1048, 754, 721. H NMR (400 MHz, CDCl ) δ 8.26 (d, J = 8.3 Hz, 1H), 7.86 (d,
3
J = 8.4 Hz, 2H), 7.71 (d, J = 8.1 Hz, 1H), 7.61 (t, J = 7.9 Hz, 1H), 7.51 (d, J = 8.4 Hz, 2H),
7
.45 (m, 4H), 7.34 – 7.28 (m, 1H), 7.28 – 7.14 (m, 1H), 4.34 (q, J = 7.1 Hz, 2H), 1.36 (t, J =
1
3
7
.1 Hz, 3H). C NMR (101 MHz, CDCl ) δ 172.29, 165.84, 162.35, 143.34, 138.32, 134.57,
3
1
31.88, 131.17, 131.11, 129.79, 129.29, 129.04, 128.89, 128.44, 128.23, 126.22, 125.30,
21.68, 119.14, 107.64, 61.22, 14.26. Mass (EI): C H BF NO S Calculated 449.28 (M+),
1
24
18
2
3
found 449.14 (M+).
Synthesis of 10c
Synthesized by same procedure as 9a using compound 8c
°
-1
Yellow solid (Yield = 85%). mp: 232-234 C. FT-IR (cm ): 1599, 1561, 1476, 1455, 1439,
1
1
363, 1195, 1104, 787, 716. H NMR (400 MHz, CDCl ) δ 8.15 (d, J = 8.3 Hz, 1H), 7.60 (d,
3
1
3
J = 8.0 Hz, 1H), 7.49 (m, 4H), 7.36 (m, 5H), 2.96 (s, 6H). C NMR (101 MHz, CDCl ) δ
3
1
1
4
72.10, 164.13, 151.85, 143.56, 136.45, 132.06, 131.49, 129.79, 128.74, 127.87, 125.12,
21.35, 118.26, 110.53, 39.88. Mass (EI): C H BF N OS Calculated 420.28 (M+), found
2
3
19
2
2
21.16 (M+)
2
.3. Computational methodology
Theoretical calculations were performed using the Turbomole-V6.5 program[52–54]
package. We have used B3LYP (Becke, 3-parameter, Lee-Yang-Parr)[55,56] which is
commonly used functional[57], in combination with def2-SV(P) basis set[58] which works as
perfect fit for the boron complexes[59]. Time dependant density functional (TDDFT)
calculations were also performed with B3LYP functional and the def2-SV(P) basis set in the
gas-phase.

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3
. Results and discussion
3
.1. Synthesis
The benzoxazolyl and benzthiazolyl-1,2-diaryl β� ketoiminate ligands 7a-7c and 8a-8c were
synthesised by refluxing compound 2-benzylbenzo[d]oxazole (4) or 2-
benzylbenzo[d]thiazole (5) with ethyl benzoate derivative (6a-6c) in the presence of sodium
hydride in toluene. These compounds were further treated with BF -etherate in
3
dichloromethane in the presence of triethyl amine to give desired organoboron compounds
9
a-9c and 10a-10c in good yield.
Scheme 1. Synthesis of benzoxazolyl and benzthiazolyl-1,2-diphenylethenol based
organoboron compounds
1
13
The synthesised compounds were characterized by FTIR, H NMR, C NMR and mass
1
spectra. The H NMR spectra showed that compound 7a and 7b are stable in the enol form
rather than keto form, whereas the compound 7c is present in the keto form. Similar trend

ACCEPTED MANUSCRIPT
was observed for the compounds 8a to 8c. The stability of the keto–enol tautomeric pairs of
the compounds 7a-7c and 8a-8c is dependent upon the nature of their heteroatoms and the
substituents present on the ring[45]. We believe that the compounds with electron donating
group such as dimethyl amino group (compound 7c and 8c) may stabilize the keto form, on
the other hand compounds with an electron withdrawing substituent such as -COOCH CH3
2
1
13
ester or -H stabilises the enol form. This was further confirmed by the H and C NMR
1
spectroscopy. The H NMR shows signals at 13.9δ, 13.9δ, 14.95δ and 14.97 δ for enolic OH
proton in the compounds 7a, 7b, 8a and 8b, while in compounds 7c and 8c signals are seen
at 6.27 δ and 6.55 δ for CH proton adjacent to C=O group (Fig.1); this results were further
confirmed by FTIR spectra. The FTIR graph for the compounds 7c and 8c show carbonyl
-1
stretching (C=O) at 1657 and 1655 cm which disappeared after formation of BF complex
2
(Fig. 2). Those carbonyl stretching’s were not observed in compounds 7a, 7b, 8a and 8b
which suggest that the compound 7c and 8c exist in the keto-form while other compounds
exist in the enol-form.
1
Fig.1. H NMR of compound 7a-7c with the Keto enol tautomerization
Fig 2. IR spectra overlay of compound 8c and 10c
3
.2.UV-visible absorption and Photoluminescence property
The absorption and emission spectra of the organoboron compounds (9a-c and 10a-c) were
recorded in tetrahydrofuran. The thiazole ring comprising derivative showed bathochromic
shift as compared to those with oxazole ring (Fig.3). The compounds 9a, 9c, 10a and 10c
showed higher molar absorption coefficient than 9b and 10b. Compound 9c and 10c showed
bathochromic shift due to presence of electron donating (dimethyl-amino) group. These
compounds fluoresce weakly at wavelength (Fmax) ranging from 389 to 507nm with lower
quantum yields (Table 1), which may be due to conjugated C-C single bond rotation in

ACCEPTED MANUSCRIPT
solution molecular state (Scheme 2). Therefore, in order to evaluate AIE property we have
recorded the photoluminescence spectra in solution state as well as in aggregated state. In
case of compound 10c, extensive enhancement in the photoluminescence was observed. This
result shows that the compound 10c exhibit extensive enhancement in the photoluminescence
as shown in Fig.4 (A). The graph of percent fraction of water added versus the
photoluminescence intensity shows maximum photoluminescence enhancement for the 90%
water-THF system Fig.4 (B). Amongst all synthesized compounds, compound 9c and 10c
shows strong AIE activity with higher quantum yields, 0.154 and 0.142 respectively in their
aggregates as compared to other derivatives. This proves that all the synthesized compounds
are AIE active (Fig.S1-S5).
The solid state fluorescence data for the synthesized compounds were summarized in Table
1
. It was observed that, the compound 9c and 10c has intense photoluminescence in solid
state as compared to others. We believe that, it could be due to electron donating dimethyl-
amino group shown in Fig.5. The presence of aryl rings across the C-C double bond may
increase the steric hindrance which prevents the compact packing of the molecules. Few
intermolecular interactions between molecules and large stokes shifts eliminate self-
quenching and enhance their solid state fluorescence[46].
Scheme 2. (A) Molecular structure of AIE active Tetra phenylethene, molecular structure of
(9a) and (10a)
Table 1. Photophysical properties of 9a-c and 10a-10c in THF

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Solid State
In Tetrahydrofuran
b
Compounds
Φ
f
Stoke
Shift
a
λAbs (ε)
λPL
(nm)
λAbs
λPL
Φ
f
(nm)
(nm)
(nm)
(nm)
0
0
0
0
0
.013
.011
.011
.014
.011
0.061
0.048
0.154
0.065
0.056
0.142
370
390
465
380
440
458
9
a
344 (7554)
350 (7034)
414 (9750)
360 (23200)
389
400
476
446
45
50
62
86
494
540
505
499
9
b
9
c
1
0a
0b
0c
1
374 (15866)
446 (26850)
482
507
108
61
535
531
1
0.010
a
b
Quantum yield measured in tetrahydrofuran, Quantum yield in THF/water mixture ( 10:90
). Measured using quinine sulfate in 0.1N H SO as standard (Φ = 0.54).
%
2
4
f
Fig.3. (A) Absorbance (B) Emission spectra of compound (9a-c, 10a-c) in THF.
Fig.4. (A) PL spectra of 10c solutions in THF–water mixtures. (B) Photoluminescence of 10c
versus solvent composition of the THF–water mixture
Fig. 5. Solid state fluorescence spectra and photograph of compound 9a-c and 10a-c.
3
.3. Electrochemical Properties
The cyclic voltammetry study (CV) was performed in acetonitrile solution with 0.5 mM
concentration of compounds 9a-c and 10a-c along with 0.1 M tetrabutyl ammonium
+
hexaflourophosphate as a supporting electrolyte. Platinum disk, platinum wire and Ag/Ag
were used as working electrode, counter electrode and reference electrode respectively. All
the measurements were recorded with 100 mV/s scan rate. The cyclic voltammograms of the
compounds 9a-9c and 10a-10c are shown in Fig.6. The graph obeys the quasi reversible

ACCEPTED MANUSCRIPT
nature and the onset of oxidation potentials were found to be 1.29, 1.34 and 0.54 for the
compounds 9a-9c whereas 1.23, 1.29 and 0.47 for compounds 10a-10c respectively. The
electronic states (HOMO, LUMO)[47,48] and band gap were summarized in Table 2. The
lowering in the band gap was observed for the compounds 9c and 10c. It may due to the
electron donating dimethyl-amino substituent. The LUMO energies of the compounds 9a-9c
and 10a-10c were comparable with the existing electron transport material such as tris(8-
hydroxyquinolinato)-aluminium (Alq )[49] and BODIPY[24]. This indicates that these
3
compounds have electron-accepting feature which can find potential applicability in charge
transport material.
–
1
Fig. 6. Cyclic voltammograms of the 9a-9c and 10a-10c CH CN at a scan rate of 0.1 Vs
3
Table 2 Electrochemical and computational data of compound 9a-c and 10a-c
b
Experimental (eV)
Theoretical (eV)
λ cut off
1
/2
a
e
c
d
Compound (nm)
E ox (V)
HOMO
LUMO
Eg opt
HOMO LUMO
Eg
9
a
397
412
462
423
452
492
1.29
1.34
0.54
1.23
1.29
0.47
-6.39
-6.44
-5.64
-6.33
-6.39
-5.57
-3.27
-3.43
-2.96
-3.40
-3.65
3.12
3.01
2.68
2.93
2.74
2.52
-6.02
-6.12
-5.36
-5.97
-6.07
-5.32
-2.14
-2.41
-1.80
-2.22
-2.46
-1.89
3.88
3.71
3.56
3.75
3.61
3.43
9
b
9
c
1
0a
0b
0c
1
1
-3.05
a
b
c
On-set determined using Cyclic voltammetry in acetonitrile, Density functional theory, calculated from
d
e
optical band gap and the HOMO energy level, optical bandgap E g =1240/ λcut-off, EHOMO = − (Eox onset Vs
Fc /Fc+ 5.1) eV.
+
3
.4. Computational Study
The optimised structures of the compounds 9a and 10a were shown in Fig.7. The two aryl
rings across C=C were non-planar to the boron chelate including benzoxazolyl/benzthiazolyl

ACCEPTED MANUSCRIPT
part which was more explained by top view. The torsion angle for 9a and 10a was found to
be 60.68°, 34.07° and 68.00°, 33.26° for ring A and ring B respectively (Table.S1). This
suggests that these compounds were non-planar which may minimise the stacking of
molecules and thus avoid molecular interactions that result in to the solid state luminescent
material. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) of 9a-9c and 10a-10c complex were computed. HOMO/LUMO energies are
in well agreement with the experimental values and thus showing similar trend. The rise in
LUMO energies of the compounds 9c and 10c and lowering of the band gap indicate the
charge transfer from dimethyl amino group to electron withdrawing BF chelate (Fig.8).
2
TDDFT calculations were also performed with B3LYP functional and the def2-SV(P) basis
set to analyze absorption pattern of synthesized organo-boron complexes. The calculated λmax
values are in well accordance with the experimental values. In all cases, absorptions are
mostly due to the first S -S transitions (HOMO to LUMO). HOMO orbitals are distributed
0
1
over whole molecule and the LUMO orbitals are localized over the heterocyclic boron
chelated electron withdrawing part of the molecules, representing the charge transfer (CT).
The larger dipole moment for the compounds 9c and 10c indicate charge separation between
the dimethyl-amino group and BF chelate. The calculated λmax, the main orbital transition,
2
and oscillator strength (f) are shown in Table S2.
Fig.7. DFT optimized structure of 9a and 10a, by applying B3LYP functional along with
def2-SV (P) method.(9a’ and 10a’ top view)
Fig.8. Molecular orbital energy diagram and isodensity surface plots of the HOMO and
LUMO of 9a-c and 10a-c
4
. Conclusion
In summary, the synthesised benzoxa/thiazolyl-1,2-diaryl β� ketoiminate derivatives shows
keto-enol tautomerization. Amongst all, compound with electron donating N, N-dimethyl

ACCEPTED MANUSCRIPT
amino substituent exists in the keto form whereas other derivative shows enol form
predominantly. Their organoboron complexes exhibit intense photoluminescence in the solid
state and weak photoluminescence in solution. These compounds also exhibit emission
enhancement in their aggregate state. The computational and electrochemical studies show
that these organoboron complexes have good electron affinity that suggest their
multifunctional application.
Acknowledgment
Author HSK is thankful to UGC-CAS for providing fellowship and IIRBS Kottayam
1
13
recording H NMR, C NMR spectra.
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Schemes and Figures
Scheme 1. Synthesis of benzoxazolyl and benzthiazolyl-1,2-diphenylethenol based
organoboron compounds.
Scheme 2. (A) Molecular structure of AIE active Tetra phenylethene, molecular structure of
(9a) and (10a)

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1
Fig.1. H NMR of compound 7a-7c with the Keto enol toutomerization
Fig 2. IR spectra overlay of compound 8c and 10c

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Fig.3. (A) Absorbance (B) Emission spectra of compound (9a-c, 10a-c) in THF 1ppm
solution.
Fig.4. (A) PL spectra of 10c solutions in THF–water mixtures. (B) Photoluminescence of 10c
versus solvent composition of the THF–water mixture

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Fig. 5. Solid state fluorescence spectra and photograph of compound 9a-c and 10a-c.
–
1
Fig. 6. Cyclic voltammograms of the 9a-9c and 10a-10c CH CN at a scan rate of 0.1 Vs
3

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Fig.7. DFT optimized structure of 9a and 10a, by applying B3LYP functional along with
def2-SV (P) method.(9a’ and 10a’ top view)

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Fig.8. Molecular orbital energy diagram and isodensity surface plots of the HOMO and
LUMO of 9a-c and 10a-c

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Highlights
1. Synthesis of new benzoxa/thiazolyl-1,2-diaryl β
ketoiminate boron complexes
2
.
The synthesized boron complexes show intense fluorescence in solid state
All these complexes exhibit aggregation-induced emission characteristics
3
4
.
.
3
The complexes show better electron affinity compare to Alq and BODIPY

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Aggregation induced emission (AIE) active
β
-ketoiminate boron complexes:
synthesis, photophysical and electrochemical properties
Haribhau S. Kumbhar and Ganapati S. Shankarling*
Fig.S1. (A) PL spectra of 9c solutions in THF–water mixtures. (B) Photoluminescence of 9c
versus solvent composition of the THF–water mixture
Fig.S2. (A) PL spectra of 9a solutions in THF–water mixtures. (B) Photoluminescence of 9a
versus solvent composition of the THF–water mixture
Fig.S3. (A) PL spectra of 9b solutions in THF–water mixtures. (B) Photoluminescence of 9b
versus solvent composition of the THF–water mixture
Fig.S4. (A) Absorbance (B) Emission spectra of 10a in various solvents (C) PL spectra of 10a
solutions in THF–water mixtures. (D) Photoluminescence of 10a versus solvent composition of
the THF–water mixture
Fig.S5. (A) PL spectra of 10b solutions in THF–water mixtures. (B) Photoluminescence of 10b
versus solvent composition of the THF–water mixture
Table.S1. The bond lengths and ring torsion of the compound 9a-9c and 10a-10c at the
B3LYP/def2-SV(P) level
Fig.S6. DFT optimized structure of 9b, 10b and 9c, 10c by applying B3LYP functional along
with def2-SV (P) method
Table.S2. Absorption maxima (nm), main orbital transitions, and oscillator strengths (f)
calculated by TDDFT at the B3LYP/def2-SV(P) level
1
Fig.S7. H NMR of compound 8a-8c with the Keto-enol toutomerization
Fig.S8-S19. IR spectra of compound 7a-c, 8a-c, 9a-c and 10a-c
1
13
FigS20-S42. H and C NMR of compound 7a-c, 8a-c, 9a-c and 10a-c