J. Isaad, A. Perwuelz / Tetrahedron Letters 51 (2010) 5328–5332
5331
O
HN
c2-,Na2+
O
O
O
O
O
O
O
O
N
R
11e-h
HN
N
HN
N
NH
N
HN
N
a
Br
Br
O
b
R
R
R
R
4a-d
11a-d
12a-d
Scheme 4. Synthetic sequences for the H-chromophore dyes 12a–d. Reagents and conditions: (a) AcOH, Br2, 0 °C–rt, 12 h (b) NaH, THF, rt, 12 h.
Table 2
Spectral properties of the pyrazolidine-3-5-dione dyes in different solvents
Dyes
Dimethyl sulfoxide
Acetonitrile
Chloroform
kmax (nm)
e
(Mꢁ1 cmꢁ1
)
kmax (nm)
e
(Mꢁ1 cmꢁ1
)
kmax (nm)
e
(Mꢁ1 cmꢁ1
)
8a
8b
8c
8d
8e
8f
8g
8h
10a
10b
10c
10d
12a
12b
12c
12d
369
414
438
404
377
429
443
418
377
421
451
417
521
547
573
522
27165
29574
30473
28562
38756
40973
43883
39563
28342
30174
33564
29749
31467
33583
34538
32376
361
406
428
399
366
411
432
401
369
411
435
405
511
523
559
513
26563
28444
28175
27482
35278
37785
41674
37438
27894
29016
31734
28093
30728
31629
32853
31004
365
408
433
401
371
417
439
411
372
419
441
412
525
537
566
518
27675
28923
27895
27057
34156
38359
42383
37643
26735
28563
32153
27538
29649
32555
33945
29624
with kmax ranging from 369 to 573 nm can be assigned to the intra-
molecular charge-transfer transitions, which involve the whole
electronic system of the compounds with a considerable charge-
transfer character, which originate mainly from the substituted
phenyl moiety and pointing toward the azo group. The position
of this band is strongly influenced by the structure of the com-
pounds, for example, the type of substitution pattern in the donor
and the acceptor moieties. Communication between the electron
donating and accepting termini can be evaluated by comparing
the kmax values. The influence of the strength of the acceptor group
is demonstrated by comparing the absorption maximum of com-
pounds 8a, 8b, and 8c as the longest wavelength transition is
shifted from 369 nm in 8a (Table 2, dye 8a), 414 nm for 8b (Table
2, dye 8b) to 438 nm for 8c (Table 2, dye 8c). This difference might
be attributed to the stronger electron-withdrawing effect of the ni-
tro group.
the withdrawing group on the phenyl-azo moiety and the type of
substituent on the nitrogen atom of the pyrazolidine-3-5-dione ring
have significant influence on the UV–vis absorption properties.
Acknowledgments
This work is financially supported by GEMTEX Laboratory —
France. The authors thank Doctor Ayham Alruhban very much for
their helpful and valuable comments on the text.
Supplementary data
Supplementary data associated with this article can be found, in
References and notes
The effect of the solvent polarity on the optical properties of the
dyes synthesized in this study has been investigated, because
many azo dyes depend on the solvent polarity, and their optical
characteristics change (Table 2). All of the synthesized dyes exhib-
ited some small blue shifts along with a decreased solvent polarity
and optical characteristic of the pyrazolidine-3,5-dione dyes exhib-
ited similar trends but these dyes don’t show regular variations
with the polarity of solvents (solvent polarity: DMSO >
acetonitrile > chloroform).
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3. Conclusions
In summary, we have achieved the first synthesis of a series of
azo and H-chromophore dyes pyrazolidine-3-5-dione-based 8a–h,
10a–b, and 12a–d, and have measured their UV–vis absorptions.
By comparing the derivatives synthesized, it can be noticed that
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