52
N. Almonasy et al. / Dyes and Pigments 108 (2014) 50e56
Table 1
2.6. Compound 5
Molecular structures of the investigated compounds 1e7.
Yellowish solid, overall yield over two steps 86%, Rf ¼ 0.32 (SiO2;
CH2Cl2/hexane 1:1), m.p. 216e218 ꢀC. 1H NMR (400 MHz, CDCl3,
Comp. Substituents Central -linker
p
X
Y
25 ꢀC):
d
¼ 7.55e7.45 (m, 10H; Ar), 6.79 (d, 3J(H,H) ¼ 8.8 Hz, 2H; Ar),
3.17 (s, 1H; CH), 3.00 ppm (s, 6H; N(CH3)2). 13C NMR (100 MHz,
CDCl3, 25 ꢀC):
d
¼ 150.4, 141.5, 132.3, 132.2, 131.6, 128.1, 127.8, 126.2,
1
NMe2
H
C^CH
C^CH
C^CH
124.2, 121.8, 120.4, 112.9, 92.0, 89.2, 83.6, 79.0, 40.7 ppm. IR (neat):
n
¼ 1670, 1594, 1507, 1346, 1217, 948, 813 cmꢂ1. MS (ESI): m/z (%):
1a
2
322 [M þ 1]þ. Elemental analysis: calcd (%) for C24H19N (321.41): C
89.68, H 5.96, N 4.36; found C 89.19, H 5.88, N 4.29.
NMe2
2.7. Compound 6
2a
2b
H
H
C^CH
H
Yellowish solid, overall yield over two steps 82%, Rf ¼ 0.30 (SiO2;
CH2Cl2/hexane 1:1), m.p. 189e190 ꢀC. 1H NMR (400 MHz, CDCl3,
25 ꢀC):
d
¼ 7.60e7.53 (m, 8H; Ar), 7.42 (d, 3J(H,H) ¼ 8.8 Hz, 2H; Ar),
3
NMe2
C^CH
6.66 (d, 3J(H,H) ¼ 8.8 Hz, 2H; Ar), 3.14 (s, 1H; CH), 2.99 ppm (s, 6H;
N(CH3)2). 13C NMR (100 MHz, CDCl3, 25 ꢀC):
133.0, 132.8, 131.9, 127.0, 127.0, 123.9, 121.3, 112.0, 110.1, 92.0, 87.4,
d
¼ 150.3, 141.0, 139.2,
3a
3b
H
H
C^CH
H
83.7, 78.1, 40.4 ppm.; IR (neat):
n
¼ 1668,1595,1515,1353,1136, 944,
818, 776 cmꢂ1. MS (ESI): m/z (%): 322 [M þ 1]þ. Elemental analysis:
calcd (%) for C24H19N (321.41): C 89.68, H 5.96, N 4.36; found C
89.85, H 5.98, N 4.39.
4
NMe2
C^CH
4a
4b
H
H
C^CH
H
2.8. Compound 7
Yellowish solid, overall yield over two steps 83%, Rf ¼ 0.50 (SiO2;
CH2Cl2/hexane 1:1), m.p. 238e239 ꢀC. 1H NMR (400 MHz, CDCl3,
5
6
7
NMe2
C^CH
25 ꢀC):
d
¼ 7.46 (br s, 8H; Ar), 7.40 (d, 3J(H,H) ¼ 8.8 Hz, 2H; Ar), 6.65
C^CH NMe2
(d, 3J(H,H) ¼ 8.8 Hz, 2H; Ar), 3.17 (s, 1H; CH), 2.99 ppm (s, 6H;
N(CH3)2). 13C NMR (100 MHz, CDCl3, 25 ꢀC):
131.7, 131.7, 131.4, 124.6, 123.9, 122.1, 121.9, 112.0, 109.8, 93.2, 91.6,
d
¼ 150.5, 133.0, 132.3,
NMe2
C^CH
90.5, 87.5, 83.5, 79.2, 40.4 ppm. IR (neat):
n
¼ 1606,1590, 1520, 1347,
1120, 939, 836, 819 cmꢂ1. MS (ESI): m/z (%): 346 [M þ 1]þ.
Elemental analysis: calcd (%) for C26H19N (345.44): C 90.40, H 5.54,
N 4.05; found C 90.77, H 5.60, N 4.09.
7a
7b
H
H
C^CH
H
3. Results and discussion
terminal acetylene carbon of the optimized molecule geometry)
seems to be the principal structural factor affecting the position of
the absorption maxima, the following observations and compari-
sons must also be taken into account:
3.1. Synthesis
Molecular structure of the studied molecules 1e7 is shown in
Table 1. Compounds 1e3 were synthesized by the methods
described in our earlier Ref. [30], the synthesis of extended mole-
cules 4e7 is outlined in Scheme 1 and follows protocols shown in
Ref. [21] and the experimental part. Two step synthesis involves
SuzukieMiyaura and Sonogashira cross-coupling reactions of
boronic acid pinacol esters 9e10 [30] and terminal acetylenes 2e3
with 4-iodophenylethynyltrimethylsilane 8 [21]. Subsequent tri-
methylsilyl group removal with tetrabutylammonium fluoride
(TBAF) provided desired compounds 4e7 in the overall yields of
81e86%. In this way, N,N-dimethylamino- and ethynyl-terminated
molecules with terphenyl (4), biphenylethynylphenyl (5), phenyl-
ethynylbiphenyl (6), and phenylethynylphenylethynylphenyl (7)
ꢃ
lmax values of compounds 2 and 4 are practically the same even
though 4 is longer by one benzene ring; the same relation was
found for the compounds 3 and 7;
lmax values of 5 and 6 are situated at shorter wavelengths than
for 3 even though 5 and 6 are larger;
ꢃ
ꢃ by going from 3 to 4, a strong hypsochromic shift was found
whereas compound 4 is longer.
Hence, the observed spectral behavior of 1e7 must be eluci-
dated in a more complex manner. As can be seen from Fig. 2 (left),
the measured lmax values split into two series (1, 2, and 3) and (1, 4,
5, 6, and 7) as a dependence on the molecular length. However,
structural genesis of these series is not clear especially by going
from compound 2 to 3 and from 4 to 7. The only feature of these
series is the molecular length and the number of phenyl rings (two
rings for 2 and 3; three rings for 4, 5, 6, and 7). On the contrary,
when considering the structural arrangement of 1e7, they can be
divided into two series A and B (Fig. 2). Whereas non-planar
chromophores 2 (biphenyl) and 4 (terphenyl) generate series A
(practically identical lmax values), planar compounds 1 (phenyl), 3
(phenylethynylphenyl), and 7 (phenylethynylphenylethynylphenyl)
belong to series B (strong bathochromic shift of the absorption
systematically evaluated central p-linker were synthesized.
3.2. Absorption spectra
The absorption spectra of the studied compounds are formed by
the non-structural broad bands appearing within the range 280e
400 nm (Fig. 1, Table 2). Although the changes of the absorption
spectra are relatively small, some relationships with the molecular
characteristics of studied compounds may be drawn. Despite the
molecular length (the distance between the amino nitrogen and the