S. Y. Park et al.
(3.70 g, 26.8 mmol) were dissolved in pyridine (50 mL) and the solution
stirred for 30 min. Triphenyl phosphite (7.0 mL, 26.7 mmol) was added to
this solution. The mixture was heated to 1008C for 2 h. The reaction mix-
ture was poured into cold water and extracted with dichloromethane.
The solution was dried with anhydrous magnesium sulfate. After removal
of the solvent, the crude product was purified by column chromatography
on silica gel with ethyl acetate/n-hexane (1/4). The product was recrystal-
lized from ethanol to give 2.30 g of pure product (yield 30%). 1H NMR
(CDCl3, 300 MHz): d=12.40 (s, 1H), 8.08 (d, 1H), 7.55 (s, 1H), 7.46 (t,
1H), 7.00 (m, 3H), 4.05 (s, 3H), 4.01 ppm (s, 3H); m/z (MS-EI) calcd:
299.28, found 299; elemental analysis calcd (%) for C16H13NO5: C 64.21,
H 4.38, N 4.68; found: C 64.26, H 4.40, N 4.55.
ior of gelators is attributed to its rigid structure, which pre-
ꢀ
cludes extensive twisting about the Ar CO bond along the
reaction coordinate.
Conclusion
Low-molecular-weight organogelators 3 and 4 containing
salicylanilide-based ESIPT moieties were synthesized and
characterized. Highly fluorescent organogels are easily
formed in nonpolar solvents such as dodecane and n-hexane
by virtue of the self-assembled lamellar and hexagonal col-
umnar structures of 3 and 4, respectively. By combining the
results of UV/Vis absorption and photoluminescence studies
and DFT and semiempirical (AM1) calculations, the molec-
ular packing model in the gel phase was deduced. The gela-
tors are self-assembled into complex 3D networks, and their
aggregation into fibrous superstructures is driven by p-stack-
ing interactions between the central salicylanilide moieties,
hydrogen-bonding interactions among the amide groups,
and van der Waals interactions among the alkyl groups. In-
terestingly, the fluorescence emission intensity of the orga-
nogels is 10–50-fold higher than that of the solution phase.
Nonradiative relaxation via a TICT is reduced in the hydro-
gen-bonded supramolecular assembly and gel states, and
this leads to enhanced ESIPT fluorescence emission.
N-Heptyl-2-(2-hydroxybenzamido)benzamide (3): Compound
1 (1.0 g,
4.2 mmol) and n-heptylamine (0.60 g, 5.2 mmol) were dissolved in pyri-
dine (50 mL). The solution was heated at 1008C and refluxed under N2
atmosphere for 24 h. The reaction mixture was poured into cold water
and neutralized with 1n HCl solution, after which the precipitate was
collected by filtration. The crude product was purified by column chro-
matography on silica gel with ethyl acetate/n-hexane (1/10). The product
was recrystallized from ethanol to give 1.50 g of pure product (yield
59%). 1H NMR (CDCl3, 300 MHz), d=12.37 (s, 1H), 12.34 (s, 1H), 8.67
(d, 1H), 7.80 (d, 1H), 7.52 (m, 2H), 7.43 (t, 1H), 7.16 (t, 1H),7.00 (m,
2H), 6.18 (s, 1H), 3.50 (q, 2H), 1.62 (m, 2H), 1.30 (m, 8H), 0.88 ppm (t,
3H); IR (KBr pellet): n˜ =3300 (nOH or NH), 1655 (nCO) cmꢀ1; m/z (MS-EI)
calcd: 354.44, found: 354; elemental analysis calcd (%) for C21H26N2O3:
C 71.16, H 7.39, N 7.90; found: C 71.40, H 7.50, N 7.87.
N-Heptyl-2-(2-hydroxybenzamido)-4,5-dimethoxybenzamide (4): Com-
pound 2 (1.0 g, 3.3 mmol) and n-heptylamine (1.0 g, 8.6 mmol) were dis-
solved in pyridine (30 mL). The solution was heated to reflux at 1008C
for 24 h. The reaction mixture was poured into cold water and neutral-
ized with 1n HCl solution. The precipitate was collected by filtration.
The crude product was purified by column chromatography on silica gel
with ethyl acetate/n-hexane (1/10). The product was recrystallized from
ethanol to give 0.90 g of pure product (yield 65%). 1H NMR (CDCl3,
300 MHz): d=12.60 (s, 1H), 12.40 (s, 1H), 8.40 (s, 1H), 7.79 (d, 1H),
7.41 (t, 1H), 7.00–6.92 (m, 3H), 6.23 (s, 1H), 3.99 (s, 3H), 3.89 (s, 3H),
3.46 (q, 2H), 1.63 (m, 2H), 1.34 (m, 8H), 0.86 ppm (t, 3H); 13C NMR
(CDCl3, 75 MHz): d=168.85, 168.76, 162.01, 152.21, 144.52, 134.65,
134.31, 126.37, 119.23, 118.40, 115.06, 112.23, 109.24, 105.16, 56.43, 56.09,
40.16, 31.67, 29.48, 28.90, 26.92, 22.53, 14.01 ppm; IR (KBr pellet): n˜ =
3312 (OH or nNH), 1650 (nCO) cmꢀ1; m/z (MS-EI) calcd: 414.49, found:
414; elemental analysis calcd (%) for C23H30N2O5: C 66.65, H 7.30, N
6.76; found: C 66.51, H 7.35, N 6.74.
Experimental Section
General: 1H NMR spectra were recorded on
a Jeol JNM-LA300
(300 MHz) spectrometer in CDCl3 or [D6]acetone with TMS as internal
standard. Molar masses of compounds were measured on a Jeol JMS-
AX505WA in electron-impact (EI) mode. Elemental contents of com-
pounds were measured with an EA1110 (CE Instruments, Italy). FTIR
studies were performed on a Jasco 200 model spectrometer. Solid sam-
ples were recorded as intimate mixtures with powdered KBr. Liquid and
gel samples were recorded in a liquid cell equipped with CaF2 windows
and a 0.2 mm lead spacer. Data were registered at 2 cmꢀ1 resolution with
32 scans. UV/Vis absorption and fluorescence spectra were recorded on
Shimadzu UV-1650PC and Shimadzu RF-500 spectrofluorimeter, respec-
tively, with emission and excitation slit width of 3 nm each. Field-emis-
sion scanning electron microscopy (FESEM) images were obtained with
a JSM-6330F (Jeol). X-ray diffraction studies were performed in trans-
mission mode with Cu K Co radiation by NICEM (Bruker D5005 diffrac-
tometer).
2-Phenyl-4H-3,1-benzoxazin-4-one (5): Anthranilic acid (1.0 g, 7.3 mmol)
was dissolved in pyridine (20 mL) and the solution stirred for 10 min.
Benzoyl chloride (2.05 g, 14.6 mmol) was added to this solution. The so-
lution was stirred for 2 h at room temperature. The reaction mixture was
poured into cold water and the precipitate collected by filtration. The
crude product was recrystallized from ethanol to give 0.65 g of pure prod-
uct (yield 40%). 1H NMR ([D6]acetone, 300 MHz): d=8.32 (t, 1H), 8.29
(d, 1H), 8.21 (d, 1H), 7.97 (m, 1H), 7.73 (d, 1H), 7.68–7.61 ppm (m,
4H); m/z (MS-EI) calcd: 223.23, found: 223; elemental analysis calcd
(%) for C14H9NO2: C 75.33, H 4.06, N 6.27; found: C 75.26, H 4.01, N
6.22.
2-(2-Hydroxyphenyl)-4H-3,1-benzoxazin-4-one (1): Anthranilic acid
(10.0 g, 72.9 mmol) and salicylic acid (10.10 g, 73.1 mmol) were dissolved
in pyridine (100 mL) and the solution stirred for 30 min. Triphenyl phos-
phite (72.5 mol, 19.0 mL) was added and the solution was stirred at
1008C for about 2 h. The reaction mixture was poured into cold water
and extracted with dichloromethane. The solution was dried with anhy-
drous magnesium sulfate. After removal of the solvent, the crude product
was purified by column chromatography on silica gel with ethyl acetate/
n-hexane (1/3). The product was recrystallized from ethanol to give
3.10 g of pure product (yield 18%). 1H NMR (CDCl3, 300 MHz): d=
12.45 (s, 1H), 8.23 (d, 1H), 8.07 (d, 1H), 7.84 (t, 1H), 7.61 (d, 1H), 7.50
(m, 2H), 7.05 (d, 1H), 6.97 ppm (t, 1H); m/z (MS-EI) calcd: 239.23;
found: 239; elemental analysis calcd (%) for C14H9NO3: C 70.29, H 3.79,
N 5.86; found: C 70.39, H 3.79 N 5.80.
6,7-Dimethoxy-2-phenyl-4H-3,1-benzoxazin-4-one (6): 2-Amino-4,5-dime-
thoxybenzoic acid (1.0 g, 5.1 mmol) was dissolved in pyridine (20 mL)
and stirred for 10 min. Benzoyl chloride (1.4 g, 10.0 mmol) was added to
this solution and the mixture was stirred for 2 h at room temperature.
The reaction mixture was poured into cold water and the precipitate col-
lected by filtration. The crude product was recrystallized from ethanol to
give 0.78 g of pure product (yield 54%).1H NMR (CDCl3, 300 MHz): d=
8.29 (d, 2H), 7.58–7.51 (m, 4H), 7.13 (s, 1H), 4.05 (s, 3H), 4.01 ppm (s,
3H); m/z (MS-EI) calcd: 283.28, found: 283; elemental analysis calcd
(%) for C16H13NO4: C 67.84, H 4.63, N 4.94; found: C 67.89, H 4.65, N
4.92.
2-Benzamido-N-heptylbenzamide (7): Compound 5 (0.5 g, 2.2 mmol) and
n-heptylamine (0.80 g, 6.9 mmol) were dissolved in pyridine (20 mL). The
solution was heated to reflux at 1008C for 24 h. The reaction mixture was
2-(2-Hydroxyphenyl)-6,7-dimethoxy-4H-3,1-benzoxazin-4-one (2): 2-
Amino-4,5-dimethoxybenzoic acid (5.0 g, 25.3 mmol) and salicylic acid
7444
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7437 – 7447