A. Yoshida et al. / Tetrahedron xxx (2017) 1e8
7
Fig. 11. Schematic representation of morphological differences between a) emissive and b) less emissive crystals of the long-chained compounds in series 1.
Strong van der Waals interactions stemming from long alkyl chains
result in stable face-to-face and face-to-edge packing motifs, which
enable the unprecedented off/on polymorphic control of crystalline
fluorescence. This work clearly demonstrates the importance of the
face-to-edge structure (that is, perpendicular packing of the fluo-
rescent platform) as a prerequisite for intense solid-state emission,
as well as the negative effects of consecutive stacking arrange-
ments. These findings are expected to make a significant contri-
bution to various fields related to the study of solid-state emissions.
bromohexadecane (2.61 g, 8.56 mmol) in toluene (25 mL) was
stirred at 100 C for 18 h under Ar. After removal of the solvent
ꢀ
under reduced pressure, BBr
3
(2.00 mL, 20.8 mmol) and CH
2
Cl
2
ꢀ
(40 mL) was added to the resulting imidazolium bromide at 0 C,
and the mixture was stirred at room temperature for 18 h. After
removal of the solvent under reduced pressure, the resulting
demethylated imidazolium bromide was subjected to column
chromatography (Chromatorex NH-DM1020, Fuji Silysia Chemical,
Japan, CH
3
CN/CH
3
OH ¼ 10/1) to give 1e (0.606 g, 38%) as a colorless
ꢀ
solid. m.p. 119e120 C; IR (KBr): 3165, 3118, 2920, 2850, 1585, 1556,
4
. Experimental section
1527, 1476, 1409, 1327, 1217, 1150, 1109, 1051, 961, 868, 797,
ꢃ1
1
7
48 cm ; H NMR (500 MHz, DMSO-d
eCH
), 1.20e1.29 (m, 26 H), 1.81 (tt, J ¼ 7.2, 7.2 Hz, 2 H,
eNCH CH e), 6.76 (dd, J ¼ 8.4,
e), 4.26 (t, J ¼ 7.2 Hz, 2 H, eNCH
1.5 Hz, 1 H, H ), 6.95 (dd, J ¼ 8.4, 4.2 Hz, 1 H, H ), 7.15 (dd, J ¼ 4.2,
6
)
d
0.85 (t, J ¼ 7.2 Hz, 3 H,
4.1. General
3
2
2
2
6
7
Melting points were measured in a glass capillary with a Büchi
8
2
B-545 melting point apparatus. IR spectra were recorded on a Jasco
1.5 Hz, 1 H, H ), 7.82 (dd, J ¼ 1.9, 1.5 Hz, 1 H, H ), 8.41 (dd, J ¼ 1.9,
3 1 13
1
13
FT/IR-410 and a Bruker EQUINOX55 spectrometers. H and C NMR
spectra were recorded on Varian Unity-Inova 500 spectrometer.
Mass spectra were obtained with a JEOL JMS-DX 303 spectrometer.
Elemental analyses were performed with a Perkin Elmer 2400II
CHN elemental analyzer. Diffuse reflectance UVevis spectra of
crystals were obtained on a JASCO V-570 spectrometer equipped
with an integrating sphere ISN-470. Emission spectra were ob-
tained using a Jasco FP-6500 spectrometer, after correction of the
wavelength-dependent characteristics of the detection unit.
Quantum yields were measured by the absolute method using a
Jasco FP-6500 spectrometer equipped with an integrating sphere.
Emission lifetime measurements were conducted with an Optical
Building Blocks EasyLife V instrument using a 366 nm LED for
excitation. Single crystals for photophysical studies were obtained
1.5 Hz, 1 H, H ), 10.81 (dd, J ¼ 1.5, 1.5 Hz, 1 H, H ); C NMR
(125 MHz, DMSO-d 14.0, 22.1, 25.6, 28.4, 28.7, 28.8, 28.9, 28.98,
28.99, 29.02, 29.6, 31.3, 48.7, 118.1, 120.7, 124.9, 125.3, 128.8, 133.8,
6
) d
135.7, 159.2; HRMS (FAB): m/z calcd for C24
H
40
N
3
O: 386.3172;
þ
found: 386.3172 [M þ H] . Anal. Calcd for C24
H
40
N
3
O: C, 74.56; H,
10.43; N, 10.87. Found C, 74.35; H, 10.12; N, 10.84.
4.2.1. 2-(3-Butyl-1H-imidazolium-1-yl)pyridin-3-olate (1a)
ꢀ
Colorless solid (36%); m.p. 135e136 C; IR (KBr): 3117, 3039,
2959, 2931, 2872, 1673, 1582, 1559, 1526, 1474, 1410, 1349, 1327,
ꢃ1
1
1271, 1219, 1148, 1109, 1052, 1012, 964, 880, 849, 796, 748 cm ; H
NMR (500 MHz, DMSO-d ), 1.29 (tq,
0.91 (t, J ¼ 7.2 Hz, 3 H, eCH
J ¼ 7.2, 7.2 Hz, 2 H, eCH CH ), 1.81 (tt, J ¼ 7.2, 7.2 Hz, 2 H,
eNCH CH e), 6.78 (dd, J ¼ 8.4,
e), 4.27 (t, J ¼ 7.2 Hz, 2 H, eNCH
1.5 Hz, 1 H, H ), 6.96 (dd, J ¼ 8.4, 4.2 Hz, 1 H, H ), 7.16 (dd, J ¼ 4.2,
6
)
d
3
2
3
2
2
2
6
7
by recrystallization from CH
Et O (condition B in Table 1).
3
CN (condition A in Table 1) or i-PrOH/
8
2
2
1.5 Hz, 1 H, H ), 7.82 (dd, J ¼ 1.9, 1.5 Hz, 1 H, H ), 8.41 (dd, J ¼ 1.9,
3 1 13
1
.5 Hz, 1 H, H ), 10.77 (dd, J ¼ 1.5, 1.5 Hz, 1 H, H ); C NMR
4.2. Synthesis of 2-(3-alkyl-1H-imidazolium-1-yl)pyridin-3-olates
(125 MHz, DMSO-d 13.3, 18.9, 31.6, 48.4, 118.3, 120.8, 125.3,
6
) d
1
125.8, 128.7, 133.9, 135.7, 158.5; HRMS (FAB): m/z calcd for
þ
C H
12 16
N
3
O: 218.1293; found: 218.1294 [M þ H] .
The synthesis of zwitterionic imidazolium 2-pyridin-3-olates
1
a-e is exemplified by the preparation of 2-(3-hexadecyl-1H-imi-
4.2.2. 2-(3-Octyl-1H-imidazolium-1-yl)pyridin-3-olate (1b)
ꢀ
dazolium-1-yl)pyridine-3-olate (1e). A solution of 2-(1H-imid-
Colorless solid (45%); m.p. 145e146 C; IR (KBr): 3165, 3087,
azole-1-yl)-3-methoxypyridine (1.50 g, 8.56 mmol) and 1-
2928, 2855, 1760, 1652, 1585, 1556, 1523, 1475, 1408, 1375, 1349,
Please cite this article in press as: Yoshida A, et al., Solid-state fluorescence of zwitterionic imidazolium pyridinolates bearing long alkyl chains: