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conjugate system to lower the HOMO-LUMO gap;[10] (3) We gratefully acknowledge the financial support by the National
largeStokes shifts, which play a decisive role in the field of optical Natural Science Foundation of ChinDaOI:(1201.16073291/3D20)C,C0C44h5i2nKa
whiteners and brighteners.[11] In this article, in order to explore the Postdoctoral Science Foundation (2018M631119) and the
photophysical properties of these naphtho[c]coumarin derivatives, Fundamental Research Funds for the Central Universities
further modification were conducted. According to principles (GK202003026).
discussed above, we introduced a π-conjugated system (arylethynyl
or aryl groups) or electron-acceptor group (cyano group) to the 7-
position of compound 3a, which has owned an electron-donor group
Conflicts of interest
(isopropoxyl group) at 3-position, to improve the fluorescence
properties. As shown in Table 3, the compound 3a could easily
transform to triflate 5, followed by cross-coupling reactions of
compound 5 with various coupling partners, such as alkyne arene,
arylboronic acid and zinc cyanide to give the corresponding
alkylation products (6a-d), arylation products (6e-i), and the
cyanidation product (6j) in good yields. The structure of 6h was
confirmed by the X-ray crystallographic analysis.
As expected, the emission wavelengths of all of the coupling
products (6a-j) are bathochromically shifted compared to 3a, and the
fluorescence quantum yields were improved (Table 4). The
compounds containing arylethynyl groups (6a-d) exhibited dramatic
high fluorescence quantum yield up to 78%. Furthermore, most of
these naphtho[2,3-c]coumarins showed blue-green flurescence in the
range of approximately 460-570 nm with large Stokes shift.
Surprisingly, the compound 6i, bearing a 4-(diphenylamino)phenyl
substituent group at 7-position, exhibited fluorescence maximum at
563 nm with Stockes shift of 173 nm.
There are no conflicts to declare.
Notes and references
1
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Table 4 Spectral properties of 5 in dichloromethane solution (10-5 mol/L)
Stokes
shift (nm)
No.
abs (nm)
ex (nm)
em (nm)
F (%)
3a
5
390
394
413
419
412
415
384
385
386
388
392
413
389
392
415
420
414
417
386
386
387
387
390
412
459
483
496
511
496
502
463
464
472
480
563
514
70
17
19
78
77
78
74
28
31
36
39
14
39
91
81
6a
6b
6c
6d
6e
6f
91
82
85
77
78
6g
6h
6i
85
93
173
102
6j
5
6
7
8
9
X. Huang, T. Zhu, Z. Huang, Y. Zhang, Z. Jin, G. Zanoni, Y. R. Chi,
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In conclusion, an efficient and easily operated synthetic procedure to
construct the 7-hydroxy-6H-naphtho[2,3-c]coumarin derivatives was
developed via TsOH-mediated aldol reaction, lactonization, Friedel-
crafts
reaction
using
available
1-(2-hydroxyphenyl)-2-
phenylethanone and meldrum’s acid. Control experiments indicated
the meldrum’s acid served as both reagent and catalyst in the
reaction, and the TsOH promoted the total process. Furthermore,
transformations of compounds 3 by cross-coupling reaction were
achieved to afford three types of 7-substituted-6H-naphtho[2,3-
c]coumarin derivatives in good to equivalent yield. Most of these
compounds have significantly bathochromic shifts, and exhibit high
fluorescence quantum yields and large Stokes shifts. Further studies
on the synthetic application and physical properties examination are
currently ongoing.
10 M. Staderini, M. A. Martín, M. L. Bolognesi, J. C. Menéndez, Chem.
Soc. Rev. 2015, 44, 1807.
11 L. Chen, T.-S. Hu, Z.-J. Yao, Eur. J. Org. Chem. 2008, 2008, 6175.
4 | J. Name., 2012, 00, 1-3
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