Effect of alkoxy side chain length on the solid-state fluorescence behaviour of bisazomethine dyes possessing dipropylamino terminal group

Article abstract of DOI:10.1016/j.dyepig.2016.08.043

A study was conducted on the optical properties of alkoxy-substituted bisazomethine dyes possessing a dipropylamino terminal group in solution and the solid state. All of the derivatives had similar optical properties in chloroform solution, showing weak

Full text of DOI:10.1016/j.dyepig.2016.08.043

Accepted Manuscript
Effect of alkoxy side chain length on the solid-state fluorescence behavior of
bisazomethine dyes possessing dipropylamino terminal group
Hyung-Wook Yu, Byung-Soon Kim, Shinya Matsumoto
PII:
S0143-7208(16)30503-4
10.1016/j.dyepig.2016.08.043
DYPI 5423
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 16 June 2016
Revised Date: 8 August 2016
Accepted Date: 19 August 2016
Please cite this article as: Yu H-W, Kim B-S, Matsumoto S, Effect of alkoxy side chain length on the
solid-state fluorescence behavior of bisazomethine dyes possessing dipropylamino terminal group, Dyes
and Pigments (2016), doi: 10.1016/j.dyepig.2016.08.043.
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ACCEPTED MANUSCRIPT
Effect of alkoxy side chain length on the solid-state fluorescence behavior of
bisazomethine dyes possessing dipropylamino terminal group
Hyung-Wook Yu, Byung-Soon Kim, Shinya Matsumoto*

ACCEPTED MANUSCRIPT
Effect of alkoxy side chain length on the solid-state fluorescence
behaviour of bisazomethine dyes possessing a dipropylamino
terminal group
Hyung-Wook Yua, Byung-Soon Kima, Shinya Matsumotoa, *
a Graduate School of Environment and Information Sciences, Yokohama National
University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
Abstract: A study was conducted on the optical properties of alkoxy-substituted
bisazomethine dyes possessing a dipropylamino terminal group in solution and the solid
state. All of the derivatives had similar optical properties in chloroform solution,
showing weak fluorescence quantum yield of 5%. In the solid state, the fluorescence
behaviour was found to be dependent on the length of the alkoxy side chain. The solid-
state fluorescence intensity of the derivatives with the short alkoxy side chains (methoxy,
propoxy, and butoxy) was rather low compared to that of the other derivatives in the
near-infrared region. However, in the case of the derivatives with the ethoxy side chain
the red solid-state fluorescence quantum efficiency improved to 13% at around 700 nm.
On the other hand, the derivatives with the middle (pentyloxy to octyloxy) to long
(dodecyloxy, hexadecyloxy, and eicosanoxy) alkoxy side chains emitted at around 680
nm, producing enhanced red fluorescence compared to that of the chloroform solution.
In particular, the derivative with the hexyloxy side chain showed the highest
fluorescence quantum efficiency of over 20% in the solid state. To determine the
influence of the alkoxy side chain length on the observed solid-state fluorescence
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behaviour, X-ray structure analysis was carried out focusing on the molecular
arrangement of bisazomethine dyes in crystals. The crystal structures were analysed
based on the molecular arrangements of their geometrical characteristics. The result
indicated that their solid-state fluorescence depends on the relative positional
relationship of the neighbouring molecules and the intermolecular distance resulting
from the alkoxy side chain length.
Keywords: Bisazomethine dye, Substituent effects, Crystal structure, Solid-state fluorescence,
Near-infrared fluorescence
1. Introduction
Recently, organic fluorescent materials have attracted considerable interest because
of their extensive and direct applications in organic semiconducting devices [1–3]. In
particular, the enhanced fluorescence of π-conjugated organic materials is essential for
the development of optoelectronic devices such as organic light-emitting diodes
(OLEDs) [4–6]. However, organic materials that fluoresce in dilute solutions cannot
efficiently fluoresce in the solid state because of the aggregation-caused quenching
(ACQ) effect. The ACQ effect results from strong intermolecular π-π interactions
caused by molecular aggregation [7, 8]. Fluorescence quenching in the solid state
hindered the development of a near-infrared fluorophore, which has an extended π-
conjugated system, reducing the HOMO-LUMO energy gap. Consequently, this system
facilitates increased intermolecular interactions in the tightly packed crystalline state or
amorphous solid phase such as a thin film, leading to a weak emission or non-emission
[9–18].
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Solid-state optical properties, including fluorescence quenching, are considered to be
strongly correlated with the molecular arrangement and packing pattern [19–26]. J-
aggregate is a typical example, exhibiting a sharp red-shifted absorption band with
strong resonance fluorescence, based on its unique electronic states derived from the
characteristic low-dimensional molecular arrangement [27–29]. Some interesting results
regarding the effect of substitution have been reported with bisazomethine (BAM) dyes,
which can form J-aggregates in vapour-deposited films [30, 31]. In the vapour-
deposited films, however, it is difficult to determine the effect of molecular arrangement
and packing pattern on the intermolecular interactions and, consequently, the resulting
optical and electronic properties [27, 28, 32]. Moreover, enhancement of the
fluorescence intensity by molecular design of pure J-aggregate formation in the
crystalline state remains to be a challenge [33, 34]. To design efficient solid-state
organic materials, fluorescence quenching of the fluorophore must be prevented by
controlling the molecular arrangement. A common method to obtain improved
fluorescent intensity in the solid state is the introduction of substituent groups to
fluorophores [23, 35–40]. The length of the substituted alkoxy chain can particularly
affect the molecular arrangement and the three-dimensional aggregation of molecules,
adjusting light emission in the solid state [24, 34, 41–43].
We studied BAM dyes forming J-aggregates in vapour-deposited films [30, 31, 44–
51], and observed that the fluorescence properties of some derivatives drastically
changed with the length of the alkoxy side chain in the crystalline state. Herein, we
report the absorption and emission properties for a range of alkoxy-substituted BAM
dyes possessing a dipropylamino terminal group (Fig. 1), in solution and the solid state.
X-ray structure analysis was carried out to determine the effect of molecular
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arrangement on the solid-state optical properties. The observed difference in the solid-
state fluorescence behaviour of the BAM dyes was interpreted in the context of their
molecular arrangements in the crystalline state.
<Insert Fig. 1>
2. Experimental
2.1. Materials and instruments
3-Aminophenol (98.5%), alkyl bromides (98%), alkyl iodides (98%), and phosphoryl
chloride (99%) were obtained from Tokyo Chemical Industry (TCI) Co.
Diaminomaleonitrile (98%) was purchased from Wako Pure Chem. Ind. Ltd. Wako
silica gel C-300 (45–75 ꢀm) was used for the column chromatography. 1H-NMR spectra
were recorded on a DRX 300 MHz NMR instrument (Bruker Co.) with TMS as the
internal standard. Elemental analyses of carbon, hydrogen, and nitrogen were performed
with a CHNOS Elemental Analyzer Vario ELIII Elemental (Elementar Co.). The IR
spectra were collected with a PerkinElmer Spectrum BX FTIR system
spectrophotometer. Melting point (Tm) was measured by differential scanning
calorimetry (DSC) on a Rigaku ThermoPlus DSC 8230 at a heating rate of 10 ℃/min
under an air flow rate of 10 mL/min. UV-Vis absorption spectra were obtained with a
Perkin Elmer Lambda 750 UV-Vis spectrometer and fluorescence spectra were collected
on a Jasco FP-8500 spectrofluorometer using solution concentrations of 1.0×10-5 M. For
the solid-state optical properties, the absorption and fluorescence spectra were measured
using an optical waveguide SIS-50 surface/interface spectrometer (SIC Co.) and a Jasco
FP-8500 spectrofluorometer, respectively. The fluorescence quantum efficiency (ΦF)
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was estimated by using a Jasco FP-8500 spectrofluorometer. All of the optical
measurements were performed in triplicate at room temperature.
2.2. Synthesis and characterisation
Novel BAM dyes were synthesised according to a previously described method [30],
and their chemical structures were confirmed by nuclear magnetic resonance
spectroscopy (1H-NMR), Fourier transform infrared spectroscopy (FT-IR), and
elemental analysis (EA). The synthetic route is illustrated in Fig. 1. 3-
(Dipropylamino)phenol [52] and 4-(Dipropylamino)salicylaldehyde [53] were
synthesised according to previously reported methods.
2.2.1. 4-(Dipropylamino)-2-alkoxybenzaldehyde (DP1a–DP20a)
A mixture of 4-(Dipropylamino)salicylaldehyde (0.66 g, 3 mmol) and potassium
carbonate (0.9 g, 6 mmol) was dissolved in 15 mL of dry DMF. The alkyl halide (9
mmol) was added to the mixture and then the subsequent mixture was refluxed at 60 ℃
for 8h. The reaction mixture was cooled to room temperature and filtered to remove
potassium carbonate. The mixture was then poured into ice water and extracted with
ethyl acetate. The combined organic layer was washed with water and brine and dried
over magnesium sulphate. The solvent was evaporated under reduced pressure and then
purified by column chromatography by eluting with ethyl acetate/n-hexane (ethyl
acetate : n-hexane=1 : 3 v/v). DP1a, Yield: 89% (0.63 g); 1H-NMR (300 MHz, CDCl3):
δ (ppm): 10.16 (s, 1H), 7.71 (d, 1H, J= 9 Hz), 6.25 (dd, 1H, J= 6 Hz and J= 3 Hz), 6.01
(d, 1H, J= 3 Hz), 4.10 (s, 3H), 3.31 (t, 4H, J= 9 Hz), 1.62 (m, 4H), 0.98 (t, 6H, J= 9 Hz);
IR(KBr): 1657 (C=O) cm-1. DP2a, Yield: 83% (0.62 g); 1H-NMR (300 MHz, CDCl3): δ
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(ppm): 10.16 (s, 1H), 7.70 (d, 1H, J= 9 Hz), 6.25 (dd, 1H, J= 6 Hz and J= 3 Hz), 6.00
(d, 1H, J= 3 Hz), 4.10 (q, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.66 (m, 4H), 1.46 (t, 3H,
J= 9 Hz), 0.93 (t, 6H, J= 9 Hz); IR(KBr): 1657 (C=O) cm-1. DP3a, Yield: 68% (0.54 g);
1H-NMR (300 MHz, CDCl3): δ (ppm): 10.19 (s, 1H), 7.71 (d, 1H, J= 9 Hz), 6.25 (dd,
1H, J= 6 Hz and J= 3 Hz), 6.00 (d, 1H, J= 3 Hz), 3.98 (t, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9
Hz), 1.90 (m, 2H), 1.69 (m, 4H), 1.09 (t, 3H, J= 9 Hz), 0.93 (t, 6H, J= 9 Hz); IR(KBr):
1
1662 (C=O) cm-1. DP4a, Yield: 81% (0.67 g); H-NMR (300 MHz, CDCl3): δ (ppm):
10.17 (s, 1H), 7.69 (d, 1H, J= 9 Hz), 6.24 (dd, 1H, J= 6 Hz and J= 3 Hz), 6.00 (d, 1H,
J= 3 Hz), 4.03 (t, 2H, J= 9 Hz) 3.30 (t, 4H, J= 9 Hz), 1.84 (m, 2H), 1.72 (m, 4H), 1.54
(m, 2H), 1.01 (t, 3H, J= 9 Hz), 0.98 (t, 6H, J= 9 Hz); IR(KBr): 1656 (C=O) cm-1. DP5a,
Yield: 78% (0.68 g); 1H-NMR (300 MHz, CDCl3): δ (ppm): 10.18 (s, 1H), 7.70 (d, 1H,
J= 9 Hz), 6.24 (dd, 1H, J= 6 Hz and J= 3 Hz), 6.00 (d, 1H, J= 3 Hz), 4.02 (t, 2H, J= 9
Hz), 3.30 (t, 4H, J= 9 Hz), 1.85 (m, 2H), 1.65 (m, 4H), 1.59–1.40 (m, 4H), 0.98–0.91 (t,
1
9H, J= 9 Hz); IR(KBr): 1661 (C=O) cm-1. DP6a, Yield: 83% (0.76 g); H-NMR (300
MHz, CDCl3): δ (ppm): 10.17 (s, 1H), 7.70 (d, 1H, J= 9 Hz), 6.24 (dd, 1H, J= 6 Hz and
J= 3 Hz), 6.00 (d, 1H, J= 3 Hz), 4.02 (t, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.84 (m,
2H), 1.69 (m, 4H), 1.54–1.34 (m, 6H), 0.98–0.88 (t, 9H, J= 9 Hz); IR(KBr): 1666 (C=O)
cm-1. DP7a, Yield: 75% (0.71 g); 1H-NMR (300 MHz, CDCl3): δ (ppm): 10.18 (s, 1H),
7.71 (d, 1H, J= 9 Hz) 6.24 (dd, 1H, J= 6 Hz and J= 3 Hz), 5.99 (d, 1H, J= 3 Hz), 4.02 (t,
2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.87–1.44 (m, 14H), 1.30 (t, 3H, J= 9 Hz), 0.95 (t,
1
6H, J= 9 Hz); IR(KBr): 1667 (C=O) cm-1. DP8a, Yield: 78% (0.78 g); H-NMR (300
MHz, CDCl3): δ (ppm): 10.18 (s, 1H), 7.71 (d, 1H, J= 9 Hz), 6.24 (dd, 1H, J= 6 Hz and
J= 3 Hz), 5.99 (d, 1H, J= 3 Hz), 4.04 (t, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.87–1.44
(m, 16H), 1.30 (t, 3H, J= 9 Hz), 0.96 (t, 6H, J= 9 Hz); IR(KBr): 1651 (C=O) cm-1.
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DP12a, Yield: 62% (0.72 g); 1H-NMR (300 MHz, CDCl3): δ (ppm): 10.18 (s, 1H), 7.70
(d, 1H, J= 9 Hz), 6.24 (dd, 1H, J= 6 Hz and J= 3 Hz), 5.99 (d, 1H, J= 3 Hz), 4.01 (t, 2H,
J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.87–1.24 (m, 27H), 0.93 (t, 6H, J= 9 Hz); IR(KBr):
1
1668 (C=O) cm-1. DP16a, Yield: 63% (0.84 g); H-NMR (300 MHz, CDCl3): δ (ppm):
10.18 (s, 1H), 7.71 (d, 1H, J= 9 Hz), 6.26 (dd, 1H, J= 6 Hz and J= 3 Hz), 5.99 (d, 1H,
J= 3 Hz), 4.01 (t, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.85–1.45 (m, 35H), 0.93 (t, 6H,
1
J= 9 Hz); IR(KBr): 1668 (C=O) cm-1. DP20a, Yield: 80% (1.21 g); H-NMR (300
MHz, CDCl3): δ (ppm): 10.18 (s, 1H), 7.71 (d, 1H, J= 9 Hz), 6.25 (dd, 1H, J= 6 Hz and
J= 3 Hz), 5.99 (d, 1H, J= 9 Hz), 4.01 (t, 2H, J= 9 Hz), 3.30 (t, 4H, J= 9 Hz), 1.85–1.46
(m, 43H), 0.93 (t, 6H, J= 9 Hz); IR(KBr): 1668 (C=O) cm-1.
2.2.2. BAM dyes (DP1b–DP20b)
A mixture of diaminomaleonitrile (0.11 g, 1 mmol) and 2 mmol of the prepared 4-
(Dipropylamino)-2-alkoxybenzaldehyde were added to 20 mL of benzene; the resulting
mixture was stirred. Piperidine was added dropwise for a total of 5–6 drops during the
reaction. Reflux was continued at 70 ℃ for 8h with a Dean-Stark trap. After 8h, the
reaction mixture was cooled to room temperature. The precipitated crude product was
filtered and washed with methanol. The product was then purified by column
chromatography using chloroform to get purple or red compounds. DP1b, Yield: 12%
(0.07 g); M.p. 253–254 ℃. 1H-NMR (300 MHz, CDCl3): δ (ppm): 8.99 (s, 2H), 8.11 (d,
2H, J= 9 Hz), 6.32 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J= 3 Hz), 3.88 (s, 6H),
3.33 (t, 8H, J= 9 Hz), 1.68 (m, 8H), 0.96 (q, 12H, J= 9 Hz); EA: Found: C, 70.40; H,
7.97; N, 12.70. Calc. For C32H42N6O2: C, 70.82; H, 7.80; N, 15.49; O, 4.89; IR(KBr):
2205 (C≡N) cm-1, 1615 (CH=N) cm-1. DP2b, Yield: 19% (0.11 g); M.p. 250–251 ℃.
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1H-NMR (300 MHz, CDCl3): δ (ppm): 9.00 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.31 (dd, 2H,
J= 6 Hz and J= 3 Hz), 6.02 (d, 2H, J= 3 Hz), 4.10 (q, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9
Hz), 1.67 (m, 8H), 1.49 (t, 6H, J= 9 Hz), 0.96 (t, 12H, J= 9 Hz); EA: Found: C, 71.97;
H, 8.72; N, 13.41. Calc. For C34H46N6O2: C, 71.55; H, 8.12; N, 14.72; O, 5.61; IR(KBr):
2204 (C≡N) cm-1, 1615 (CH=N) cm-1. DP3b, Yield: 13% (0.08 g); M.p. 224–225 ℃.
1H-NMR (300 MHz, CDCl3): δ (ppm): 9.02 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.32 (dd, 2H,
J= 6 Hz and J= 3 Hz), 6.02 (d, 2H, J= 3 Hz), 3.99 (t, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9
Hz), 1.92 (m, 4H), 1.70 (m, 8H), 1.09 (t, 6H, J= 9 Hz), 0.91 (t, 12H, J= 9 Hz); EA:
Found: C, 62.16; H, 7.14; N, 11.66. Calc. For C37H51N6O2Cl3: C, 61.88; H, 7.16; N,
11.70; O, 4.46; IR(KBr): 2205 (C≡N) cm-1, 1612 (CH=N) cm-1. DP4b, Yield: 6% (0.04
1
g); M.p. 215–216 ℃. H-NMR (300 MHz, CDCl3): δ (ppm): 9.01 (s, 2H), 8.10 (d, 2H,
J= 9 Hz), 6.32 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.02 (d, 2H, J= 3 Hz), 4.03 (t, 4H, J= 9
Hz), 3.32 (t, 8H, J= 9 Hz), 1.85 (m, 64H), 1.68 (m, 8H), 1.31 (m, 4H), 1.01 (t, 6H, J= 9
Hz), 0.91 (t, 12H, J= 9 Hz); EA: Found: C, 73.73; H, 9.43; N, 10.27. Calc. For
C38H54N6O2: C, 72.81; H, 8.68; N, 13.41; O, 5.10; IR(KBr): 2208 (C≡N) cm-1, 1614
1
(CH=N) cm-1. DP5b, Yield: 48% (0.31 g); M.p. 217–218 ℃. H-NMR (300 MHz,
CDCl3): δ (ppm): 9.01 (s, 2H), 8.09 (d, 2H, J= 9 Hz), 6.31 (dd, 2H, J= 6 Hz and J= 3
Hz), 6.01 (d, 2H, J= 3 Hz), 4.02 (t, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9 Hz), 1.86 (m, 4H),
1.69 (m, 8H), 1.53–1.37 (m, 8H), 1.01 (t, 6H, J= 9 Hz), 0.95 (t, 12H, J= 9 Hz); EA:
Found: C, 72.18; H, 8.93; N, 12.76. Calc. For C40H58N6O2: C, 73.36; H, 8.93; N, 12.83;
O, 4.89; IR(KBr): 2205 (C≡N) cm-1, 1613 (CH=N) cm-1. DP6b, Yield: 51% (0.35 g);
M.p. 203–204 ℃. 1H-NMR (300 MHz, CDCl3): δ (ppm): 9.01 (s, 2H), 8.10 (d, 2H, J= 9
Hz), 6.31 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J= 3 Hz), 4.02 (t, 4H, J= 9 Hz),
3.32 (t, 8H, J= 9 Hz), 1.86 (m, 4H), 1.67 (m, 8H), 1.54–1.35 (m, 12H), 0.99–0.89 (t,
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18H, J= 9 Hz); EA: Found: C, 72.07; H, 9.10; N, 12.04. Calc. For C42H62N6O2: C,
73.86; H, 9.15; N, 12.30; O, 4.69; IR(KBr): 2204 (C≡N) cm-1, 1612 (CH=N) cm-1.
1
DP7b, Yield: 11% (0.08 g); M.p. 174–175 ℃. H-NMR (300 MHz, CDCl3): δ (ppm):
9.01 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.30 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J=
3 Hz) 4.02 (t, 4H, J= 9 Hz), 3.33 (t, 8H, J= 9 Hz), 1.86 (m, 4H), 1.66 (m, 8H), 1.51–1.23
(m, 16H), 0.99–0.89 (t, 18H, J= 9 Hz); EA: Found: C, 64.10; H, 8.36; N, 9.81. Calc. For
C45H67N6O2Cl3: C, 65.09; H, 8.13; N, 10.12; O, 3.85; IR(KBr): 2203 (C≡N) cm-1, 1612
1
(CH=N) cm-1. DP8b, Yield: 30% (0.22 g); M.p. 160–161 ℃. H-NMR (300 MHz,
CDCl3): δ (ppm): 9.01 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.31 (dd, 2H, J= 6 Hz and J= 3
Hz), 6.01 (d, 2H, J= 3 Hz), 4.02 (t, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9 Hz), 1.86 (m, 4H),
1.65 (m, 8H), 1.52–1.30 (m, 20H), 1.09–0.86 (t, 18H, J= 9 Hz); EA: Found: C, 74.17;
H, 9.66; N, 12.29. Calc. For C46H70N6O2: C, 74.75; H, 9.55; N, 11.37; O, 4.33; IR(KBr):
2204 (C≡N) cm-1, 1613 (CH=N) cm-1. DP12b, Yield: 6% (0.05 g); M.p. 134–135 ℃.
1H-NMR (300 MHz, CDCl3): δ (ppm): 9.00 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.32 (dd, 2H,
J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J= 3 Hz), 4.01 (t, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9
Hz), 1.83 (m, 4H), 1.68 (m, 8H), 1.50–1.12 (m, 36H), 1.06–0.85 (t, 18H, J= 9 Hz); EA:
Found: C, 75.00; H, 9.83; N, 9.62. Calc. For C54H86N6O2: C, 76.19; H, 10.18; N, 9.87;
O, 3.76; IR(KBr): 2203 (C≡N) cm-1, 1614 (CH=N) cm-1. DP16b, Yield: 8% (0.08 g);
M.p. 115–116 ℃. 1H-NMR (300 MHz, CDCl3): δ (ppm): 9.00 (s, 2H), 8.09 (d, 2H, J= 9
Hz), 6.31 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J= 3 Hz), 4.02 (t, 4H, J= 9 Hz),
3.32 (t, 8H, J= 9 Hz) 1.96 (m, 4H), 1.68 (m, 8H), 1.50–1.26 (m, 52H), 1.03–0.86 (t,
18H, J= 9 Hz); EA: Found: C, 72.30; H, 10.16; N, 8.18. Calc. For C62H102N6O2: C,
77.29; H, 10.67; N, 8.72; O, 3.32; IR(KBr): 2205 (C≡N) cm-1, 1610 (CH=N) cm-1.
1
DP20b, Yield: 2% (0.02 g); M.p. 108–109 ℃. H-NMR (300 MHz, CDCl3): δ (ppm):
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9.00 (s, 2H), 8.11 (d, 2H, J= 9 Hz), 6.31 (dd, 2H, J= 6 Hz and J= 3 Hz), 6.01 (d, 2H, J=
3 Hz), 4.01 (t, 4H, J= 9 Hz), 3.32 (t, 8H, J= 9 Hz), 1.85 (m, 4H), 1.65 (m, 8H), 1.50–
1.25 (m, 68H), 1.06–0.86 (t, 18H, J= 9 Hz); EA: Found: C, 77.59; H, 11.19; N, 7.75.
Calc. For C70H118N6O2: C, 78.16; H, 11.06; N,7.81; O, 2.97; IR(KBr): 2205 (C≡N) cm-1,
1610 (CH=N) cm-1.
2.3. Crystallography
X-ray diffraction experiments were performed on a Rigaku RAXIS-RAPID imaging
plate diffractometer with a graphite-monochromatic CuKα radiation at room
temperature (296 K) for DP2b, DP5b, and DP8b (40 kV and 30 mA). Single crystal X-
ray diffraction data were recorded on a Rigaku AFC-7R Mercury 70 imaging plate
diffractometer equipped with a graphite-monochromatic MoKα radiation at 223.2 K for
DP3b, DP4b, DP6b, DP16b, and DP20b (50 kV and 80 mA) and at 93 K for DP7b and
DP12b (50 kV and 100 mA). The structure was solved by direct method of SIR2011
[54] and refined by full-matrix least-squares techniques. Non-hydrogen atoms were
anisotropically refined. Hydrogen atoms were located at the calculated positions and
refined using the riding model. All of the calculations were performed using the
CrystalStructure 4.2.1 crystallographic software package [55]. The crystal structure was
visualised using Mercury 3.6 [56]. All of the suitable crystals were obtained through a
solvent-diffusion method. Chloroform was used as a good solvent and n-hexane for
DP1b–DP8b and methanol for DP12b–DP20b were used as a poor solvent to grow
crystals, respectively.
3. Results and discussion
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3.1. Optical properties
The synthesised BAM dyes were soluble in chloroform solution (1.0×10-5 M). UV-
Vis absorption and fluorescence spectra in chloroform are illustrated in Fig. 2. Their
optical characteristics are summarised in Table 1. DP1b–DP20b showed a similar
absorption band characterised by an absorption maximum (λmax) at 558 nm and a small
shoulder around 520 nm with a molar extinction coefficient (εmax) in the range of 1.1–
1.2×105. The λmax with large εmax values for the BAM dyes are due to the intramolecular
charge transfer (ICT) of the π-conjugate push-pull system from the arylamine moiety as
the donor to the central dicyanoethylene moiety as the acceptor [30, 57]. All of the
derivatives exhibited a sharp fluorescence band with the maximum fluorescence (Fmax
)
in the range of 609–612 nm. In addition, the fluorescence quantum yield was low and
similar (ΦF < 0.05) for all the dyes. Excitation spectra for the observed Fmax were in
good agreement with the absorption spectra (Fig. S1 (a)). No remarkable difference in
the optical properties was found in chloroform solution. In the present series of BAM
dyes, the length of alkoxy substituents did not lead to large alterations of absorption and
fluorescence spectra in chloroform solution.
<Insert Fig. 2>
As shown in Fig. 3, the absorption and fluorescence properties of all the BAM dyes
were also measured in the crystalline state. Their optical properties in the crystalline
state are summarised in Table 1. None of the derivatives exhibited any significant
difference in the absorption band, with an absorption maximum at around 610 nm,
which is red-shifted compared to that in chloroform solution. Significant differences
11

ACCEPTED MANUSCRIPT
were observed in the fluorescence behaviour of the dyes in the crystalline state, as
shown in Fig. 3 (b) and Table 1. The derivatives with short alkoxy side chains (DP1b–
DP4b) exhibited slightly red-shifted fluorescence spectra with Fmax of about 700 nm. In
particular, the derivatives with short alkoxy side chains with the exception of DP2b had
a relatively lower ΦF (of about 5%) compared to that of the other derivatives. DP2b
exhibited the enhanced near-infrared solid-state fluorescence with ΦF of 13%. The
derivatives with short side chains might have dissimilarities in their intermolecular
interactions, weakening the emission. In the case of the derivatives with longer alkoxy
side chains (DP5b–DP20b), however, Fmax of the fluorescence spectra was observed in
the range of 680–690 nm producing a stronger fluorescence intensity of over 12%
greater than that of solution. These results suggest that the length of the side chain could
decrease intermolecular interactions, leading to enhanced fluorescence in the solid state.
Therefore, a particular length of the side chain in this dye system could give the most
favoured packing structure with minimised intermolecular interactions in the solid state.
There is no significant difference of excitation spectra for the observed Fmax in the
crystalline state (Fig. S1 (b)). As listed in Table 1, DP6b with its hexyloxy side chain
exhibited the highest ΦF of 20% in the present series. These dyes have the potential to
be used as near-infrared fluorescent materials, which usually suffer from low quantum
efficiencies [11, 13]. On the other hand, there was little difference in its λmax in the solid
state, which was red-shifted compared to that in solution. The length of the side chain
affects fluorescence behaviour in the solid state, whereas it does not significantly
modify absorption spectra based on interactions such as excitonic interactions [38, 58].
<Insert Table 1>
12

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3.2. Crystal structures
In order to interpret the fluorescence behaviour of DP2b–DP20b in the solid state, X-
ray structure analysis was carried out. The crystallographic data are summarised in
Table 2. A suitable single crystal of DP1b for the analysis was not obtained. The core of
the BAM dyes corresponding to the π-conjugated push-pull system is almost planar and
has a crystallographic centre of symmetry in the crystal. Moreover, the substituted side
chains, except for the hexyloxy side chain in DP6b, adopt a trans-zigzag conformation.
There is no critical short contact between the stacked molecules of all BAM dye
derivatives (Table S1). Intermolecular distance and slip angles were measured between
the closest stacked molecules to investigate the relationship between molecular
arrangement and the length of the alkoxy side chain. The slip angles were calculated in
two directions: along the long molecular axis as viewed from the side of the π-
conjugated part from the terminal arylamine moiety to the other terminal arylamine
moiety, and along the short molecular axis as viewed from the side of the π-conjugated
part from the central dicyanoethylene moiety to the other central dicyanoethylene
moiety. This geometrical examination allowed us to divide the crystal structures into
three groups. DP2b, DP4b, DP5b, DP6b, DP8b, and DP12b with short and middle
lengths of the alkoxy side chain are in Group 1; DP16b and DP20b with long lengths of
the alkoxy side chain belong to Group 2; and DP3b and DP7b with solvated crystals are
assigned to Group 3 (Table S2). The most remarkable structural difference between
Groups 1 and 2 was found in the slip angle along the short molecular axis. Molecules
are stacked with this slip angle in the range of 56–58° in Group 1, whereas a larger
slippage of about 80° along this direction was found in the derivatives in Group 2. The
13

ACCEPTED MANUSCRIPT
π-conjugated part of molecules in Group 2 overlapped more by the enlarged slip angle
along the short molecular axis compared to that in Group 1. The intermolecular distance
in Group 2 is under 3.41 Å, which is smaller than that in Group 1 members except for
DP4b. In the case of the derivatives of Group 3, these structural features are similar to
those of Group 1 unless the chloroform solvent is included in the crystal. Interestingly,
the molecules in all the groups were stacked with similar small slip angles in the range
of 25–30° along the long molecular axis forming a staircase arrangement [28, 33]. This
structural feature can be regarded as one of structural components for J-type aggregates
causing enhanced fluorescence compared to those of the monomer [27, 28].
The molecules of DP4b in Group 1 are π-π stacked in a layer parallel to the ac plane
(Fig. 4 (a)). The intermolecular distance is the shortest length of 3.35 Å in the present
series (Fig. 4 (b)). The slip angles are calculated to be 27° along the long molecular axis
and 56° along the short molecular axis. The short intermolecular distance of DP4b
between the π-conjugated molecules might have the potential to form tight molecular
packing in the crystalline state leading to stronger intermolecular interactions as a short
intermolecular distance between π-conjugated molecules has been known to correlate
with significant intermolecular interactions in solid-state fluorescence quenching [13,
20, 26, 35]. The strong intermolecular interactions between the π-conjugated molecules
could lead to the weakened fluorescence of the chromophore [36, 37]. This result agrees
with the relatively low fluorescence quantum yield of DP4b compared to that of the
other derivatives in the solid state. Fig. 5 depicts the molecular arrangement of DP5b.
The crystal system of DP5b is different from the others as it belongs to a monoclinic
system with P21/c space group. However, its molecular arrangement is categorised as
Group 1. As shown in Fig. 5, the molecules are stacked along the c axis with an
14

ACCEPTED MANUSCRIPT
intermolecular distance of 3.47 Å. They form two-dimensional staircase arrangements
with slip angles of 27° and 57° along the long and short molecular axes, respectively.
The only structural difference from the other derivatives in Group 1 is that the two-
dimensional staircase layers do not align in a completely parallel way as indicated in Fig.
5 (a). This result suggests that the influence of the small difference in the interlayer
alignment is negligible for the purposes of fluorescence quenching in the solid state of
these dyes. Fig. 6 shows the molecular arrangement of DP6b. The molecular
arrangement of DP2b (Fig. S2), DP8b (Fig. S3) and DP12b (Fig. S4) is similar to that
of DP6b as listed in Table S2. The molecules are arranged in parallel with an
intermolecular distance of 3.48 Å. The two types of small slip angles are 28° along the
long molecular axis and 58° along the short molecular axis (Fig. 6 (b)). The derivatives
in Group 1 have similar molecular arrangements. An almost similar fluorescence
behaviour of the derivatives in this Group could be interpreted by this structural
similarity, except for DP4b having a relatively small fluorescence quantum yield
correlated with its short intermolecular distance.
<Insert Fig. 4>
<Insert Fig. 5>
<Insert Fig. 6>
The crystal structure of DP16b in Group 2 is shown in Fig. 7. The structure of
DP20b is isomorphic with DP16b (Table S2 and Fig. S5). The intermolecular distance
is 3.40 Å for DP16b and 3.41 Å for DP20b. The two slip angles along the long and
short molecular axes are 25° and 81° for DP16b and 25° and 80° for DP20b,
15

ACCEPTED MANUSCRIPT
respectively. The conformation of the long alkoxy side chain is not horizontal to the
planar core plane with a typical zigzag conformation. There is no significant difference
in the optical properties of the derivatives in Group 2. In the view along the long
molecular axis, the molecules of DP16b and DP20b are also aligned in the head-to-tail
arrangement like Group 1. However, Group 2 dyes have a tendency to form different
molecular pairs along the short molecular axis from those of Group 1. The long side
chain causes a molecule to be closer to neighbouring molecules with large slip angles of
about 80° along the short molecular axis. The small intermolecular distance and
enlarged slip angle along the short molecular axis of the longer side chains lead to
further overlapping of the π-conjugated part of molecules, resulting in an increase in
intermolecular interactions. The long side chain may cause an increase in intermolecular
interactions, leading to a decrease in the fluorescence intensity of DP16b and DP20b
compared to those of the derivatives in Group 1 (with the exception of DP4b).
<Insert Fig. 7>
In the solvated crystal of DP3b and DP7b in Group 3, the chloroform molecules are
arranged between the two-dimensional layers, as illustrated in Fig. 8 (a). These solvated
crystals have two unsymmetrical half-molecular units. In the solvated crystal of DP3b,
these two different molecular units are almost planar and are stacked in a parallel
fashion, thereby forming the staircase arrangement as recognised in the derivatives of
Groups 1 and 2. Two intermolecular distances were identified in the crystal of DP3b,
because of two different unsymmetrical units. They are 3.45 Å and 3.52 Å. The slip
angle is calculated to be 26–28° and 56° along the long and short molecular axes,
16

ACCEPTED MANUSCRIPT
respectively. In the solvated crystal of DP7b, two different molecular units are slightly
distorted. The molecules in this solvated crystal also form the staircase arrangement
with two different intermolecular distances. The molecules of DP7b are packed in
almost parallel with intermolecular distance of 3.33 Å and 3.48 Å. The slip angle is
measured as 27–29° and 50–53° along the long and short molecular axes, respectively
(Fig. S6 and Table S2). From this structural perspective, it seems that there would be no
significant difference in fluorescence behaviour of these two solvated crystals. However,
fluorescent characteristics of two derivatives are not the same. Powder X-ray
measurement for the ground sample of DP3b showed that there was no structural
change of its solvate by grinding, whereas we found that a slight structural change
occurred by the grinding process in the DP7b solvate. This may cause their different
fluorescence behaviour.
<Insert Fig. 8>
<Insert Table 2>
4. Conclusions
Eleven novel BAM dyes possessing a dipropyl terminal amino group with different
alkoxy side chains on the phenyl ring were synthesised and their optical properties were
investigated. All the synthesised BAM dyes exhibited similar absorption and
fluorescence behaviour in chloroform solution. Further, there was no significant
difference in the absorption spectra among the derivatives in the crystalline state. On the
other hand, the dyes exhibited red-shifted fluorescence spectra, with enhanced
fluorescence quantum efficiency in the crystalline state compared to that in the
chloroform solution. The difference in the solid-state fluorescence behaviour was found
17

ACCEPTED MANUSCRIPT
to be dependent on the length of the alkoxy side chains. The BAM dyes were grouped
by analysing their molecular arrangement in their crystal structure. The derivatives in
the same group showed similar fluorescence behaviour because of their structural
similarities with the exceptions of DP3b, DP4b, and DP7b. DP3b and DP7b belong to
the same group – a solvated crystal – but exhibit dissimilar fluorescence behaviour in
the solid state. Low solid-state fluorescence quantum yield of DP4b is correlated with
its closed intermolecular distance. The present result suggests that the solid-state
fluorescence of BAM dyes is influenced by the molecular arrangement dependent on the
alkoxy side chain length in the crystalline state.
18

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References
[1] Thomas SW, Joly GD, Swager TM. Chemical sensors based on amplifying
fluorescent conjugated polymers. Chem Rev 2007;107:1339–86.
[2] Samuel IDW, Turnbull GA. Organic semiconductor lasers. Chem Rev
2007;107:1272–95.
[3] Basabe-Desmonts L, Reinhoudt DN, Crego-Calama M. Design of fluorescent
materials for chemical sensing. Chem Soc Rev 2007;36:993–1017.
[4] Minaev B, Baryshnikov G, Agren H. Principles of phosphorescent organic light
emitting devices. Phys Chem Chem Phys 2014;16:1719–58.
[5] Geffroy B, Roy Pl, Prat C. Organic light-emitting diode (OLED) technology:
materials devices and display technologies. Polym Int 2006;55:572–82.
[6] Chen CT. Evolution of red organic light-emitting diodes: materials and devices.
Chem Mater 2004;16:4389–400.
[7] Hong Y, Lam JWY, Tang BZ. Aggregation-induced emission. Chem Soc Rev
2011;40:5361–88.
[8] Tang BZ, Qin A. Aggregation-induced emission: fundamentals. John Wiley & Sons;
2013.
[9] Wang ZY. Near-infrared organic materials and emerging applications. CRC Press;
2013.
[10] Achilefu S. The insatiable quest for near-infrared fluorescent probes for molecular
imaging. Angew Chem Int Ed, 2010;49:9816–18.
[11] Massin J, Dayoub W, Mulatier JC, Aronica C, Bretonniere Y, Andraud C. Near-
infrared solid-state emitters based on isophorone: synthesis, crystal structure and
spectroscopic properties. Chem Mater 2011;23:862–73.
19

ACCEPTED MANUSCRIPT
[12] Wu XT, Chen L. Structure-property relationships in non-linear optical crystals I:
the UV-Vis region. Springer; 2012.
[13] Matsui M, Ikeda R, Kubota Y, Funabiki K. Red solid-state fluorescent
aminoperfluorophenazines. Tetrahedron Lett 2009;50:5047–9.
[14] Okada N, Eto R, Horiguchi-Babamoto E, Kobayashi T, Naito H, Shiro M,
Takahashi H, Matsumoto S. Optical properties of three differently colored crystal
modifications of a 2,3-dicyanopyrazine dye. Bull Chem Soc Jpn 2015;88:716–21.
[15] Yu J, Zhang X, Hao X, Zhang X, Zhou M, Lee CS, Chen X. Near-infrared
fluorescence imaging using organic dye nanoparticles. Biomaterials 2014;35:3356–64.
[16] Abd-El-Aziz AS, Strohm EA, Okasha RM. Design and spectroscopic
characterization of novel series of near infrared indocyanine dyes. J Mol Struct
2015;1091:228–35.
[17] Redy-Keisar O, Huth K, Vogel U, Lepenies B, Seeberger PH, Haag R, Shabat D.
Enhancement of fluorescent properties of near-infrared dyes using clickable
oligoglycerol dendrons. Org Biomol Chem 2015;13:4727–32.
[18] Clark M. Handbook of textile and industrial dyeing, volume 1: principles,
processes and types of dyes. Woodhead Publishing; 2011.
[19] Davis R, Kumar NSS, Abraham S, Suresh CH, Rath NP, Tamaoki N, Das S.
Molecular packing and solid-state fluorescence of alkoxy-cyano substituted
diphenylbutadienes: structure of the luminescent aggregates. J Phys Chem C
2008;112:2137–46.
[20] Kitamura C, Tsukuda H, Yoneda A, Kawase T, Kobayashi T, Naito H. 1,4,7,10-
Tetraisoalkyltetracenes: tuning of solid-State optical properties and fluorescence
quantum yields by peripheral modulation. Eur J Org Chem 2010;3033–40.
20

ACCEPTED MANUSCRIPT
[21] Park SY, Ebihara M, Kubota Y, Funabiki K, Matsui M. The relationship between
solid-state fluorescence intensity and molecular packing of coumarin dyes. Dyes Pigm
2009;82:258–67.
[22] Mizobe Y, Ito H, Hisaki I, Miyata M, Hasegawa Y, Tohnai N. A novel strategy for
fluorescence enhancement in the solid-state: affording rigidity to fluorophores packing.
Chem Commun 2006;2126–8.
[23] Ooyama Y, Yoshikawa S, Watanabe S, Yoshida K. Molecular design of novel non-
planar heteropolycyclic fluorophores with bulky substituents: convenient synthesis and
solid-state fluorescence characterization. Org Biomol Chem 2006;4:3406–9.
[24] Thomas R, Varghese S, Kulkarni GU. The influence of crystal packing on the solid
state fluorescence behavior of alkyloxy substituted phenyleneethynylenes. J Mater
Chem 2009;19:4401–6.
[25] Mei J, Leung NLC, Kwok RTK, Lam JWY, Tang BZ. Aggregation-induced
emission: together we shine, united we soar!. Chem Rev 2015;115:11718–940.
[26] Matsui M, Ooiwa K, Okada A, Kubota Y, Funabiki K, Sato H. Solid-state
fluorescence of pyridinium styryl dyes. Dyes Pigm 2013;99:916–23.
[27] Würthner F, Kaiser TE, Möller CRS. J-aggregates: from serendipitous discovery to
supramolecular engineering of functional dye materials. Angew Chem Int Ed
2011;50:3376–410.
[28] Kobayashi T. J-aggregates. World Scientific; 2012.
[29] Nakahara H, Fukuda K, Moebius D, Kuhn H. Two-dimensional arrangement of
chromophores in J-aggregates of long-chain merocyanines and its effect on energy
transfer in monolayer systems. J Phys Chem 1986;90:6144–8.
[30] Kim BS, Kashibuchi D, Son YA, Kim SH, Matsumoto S. Effect of phenyl ring
21

ACCEPTED MANUSCRIPT
substitution on J-aggregate formation ability of novel bisazomethine dyes in vapour-
deposited films. Dyes Pigm 2011;90:56–64.
[31] Kinashi K, Lee KP, Matsumoto S, Ishida K, Ueda Y. Alkyl substituent effects on J-
or H-aggregate formation of bisazomethine dyes. Dyes Pigm 2012;92:783–8.
[32] Miguel Gd, Ziol M, Zitnan M, Organero JA, Pandey SS, Hayase S, Douhal A.
Photophysics of H- and J-aggregates of indole-based squaraines in solid state. J Phys
Chem C 2012;116:9379–89.
[33] Matsumoto S, Shirai K, Kobayashi K, Wada T, Shiro M. J-aggregate structures in
crystals of three bisazomethine dyes. Z Kristallogr 2004;219:239–43.
[34] Kim BS, Jindo T, Eto R, Shinohara Y, Son YA, Kim SH, Matsumoto S. Effects of
alkoxy substitution on the crystal structure of 2,3-bis[(E)-4-(diethylamino)-2-
alkoxybenzylideneamino]fumaronitrile derivatives. CrystEngComm 2011;13:5374–83.
[35] Kubota Y, Kasatani K, Takai H, Funabiki K, Matsui M. Strategy to enhance solid-
state fluorescence and aggregation-induced emission enhancement effect in pyrimidine
boron complexes. Dalton Trans 2015;44:3326–41.
[36] Dong J, Solntsev KM, Tolbert LM. Activation and tuning of green fluorescent
protein chromophore emission by alkyl substituent-mediated crystal packing. J Am
Chem Soc 2009;131:662–70.
[37] Shen X, Huang G, Li K, Zhang G, Zhang D. Tuning the solid-state emission of the
analogous GFP chromophore by varying alkyl chains in the imidazolinone ring. Sci
China Chem 2013;56:1197–203.
[38] Koren AB, Curtis MD, Francis AH, Kampf JW. Intermolecular interactions in π-
stacked conjugated molecules. Synthesis, structure, and spectral characterization of
alkyl bithiazole oligomers. J Am Chem Soc 2003;125:5040–50.
22

ACCEPTED MANUSCRIPT
[39] Mei J, Hong Y, Lam JWY, Qin A, Tang Y, Tang BZ. Aggregation-induced emission:
the whole is more brilliant than the parts. Adv Mater 2014;26:5429–79.
[40] Rohatgi-Mukherjee KK. Fundamentals of photochemistry. New Age International;
2013.
[41] He J, Xu B, Chen F, Xia H, Li K, Ye L, Tian W. Aggregation-induced emission in
the crystals of 9,10-distyrylanthracene derivatives: the essential role of restricted
intramolecular torsion. J Phys Chem C 2009;113:9892–9.
[42] Kittredge KW, Fox MA, Whitesell JK. Effect of alkyl chain length on the
fluorescence of 9-alkylfluorenyl thiols as self-assembled monolayers on gold. J Phys
Chem B 2001;105:10594–9.
[43] Ghosh S, Li XQ, Stepanenko V, Würthner F, Control of H- and J-type π- stacking
by peripheral alkyl chains and self-sorting phenomena in perylene bisimide homo- and
heteroaggregates. Chem Eur J 2008;14:11343–57.
[44] Matsumoto S, Kobayashi T, Aoyama T, Wada T, J-aggregates in vapor deposited
films of a bisazomethine dye. Chem Commun 2003;1910–1.
[45] Tanaka T, Matsumoto S, Kobayashi T, Satoh M, Aoyama T. Highly oriented J-
aggregates of bisazomethine dye on aligned poly(tetrafluoroethylene) surfaces. J Phys
Chem C 2011;115:19598–605.
[46] Matsumoto S, Shirai K, Kobayashi K, Wada T, Shiro M. J-aggregate structures in
crystals of bisazomethine dyes. Z Kristallogr 2004;219: 239–43.
[47] Kobayashi T, Matsumoto S, Tanaka T, Kunugita H, Ema K, Aoyama T, Wada T.
Photoluminescence properties of vapor deposited films of a bisazomethine dye. Phys
Chem Chem Phys 2005;7:1726–31.
[48] Kobayashi T, Matsumoto S, Aoyama T, Wada T. Optical nonlinearity of J-
23

ACCEPTED MANUSCRIPT
aggregates in vapor deposited films of a bisazomethine dye. Thin Solid Films
2006;509:145–8.
[49] Tanaka T, Satoh M, Ishitobi M, Aoyama T, Matsumoto S, Highly dichroic
bisazomethine dye films on friction-transferred poly(tetrafluoroethylene) layers. Chem
Lett 2011;40:1170–2.
[50] Ribierre JC, Satoh M, Ishizuka A, Tanaka T, Watanabe S, Matsumoto M,
Matsumoto S, Uchiyama M, Aoyama T. Organic field-effect transistors based on J-
aggregate thin films of a bisazomethine dye. Org Electron 2012;13:999–1003.
[51] Ribierre JC, Yokota Y, Satoh M, Ishizuka A, Tanaka T, Watanabe S, Matsumoto M,
Muranaka A, Matsumoto S, Uchiyama M, Aoyama T, Influence of the grain orientation
on the charge transport properties of organic field-effect transistors. RSC Adv
2014;4:36729–37.
[52] Dong XZ, Cai C, Huagong J 2003;20:761.
[53] Takakura H, Sasakura K, Ueno T, Urano Y, Terai T, Hanaoka K, Tsuboi T, Nagano
T. Development of luciferin analogues bearing an amino group and their application as
BRET donors. Chem Asian J 2010;5:2053–61.
[54] Burla MC, Caliandro R, Camalli M, Carrozzini B, Cascarano GL, Giacovazzo C,
Mallamo M, Mazzone A, Polidori G, Spagna R. SIR2011: a new package for crystal
structure determination and refinement. J Appl Cryst 2012;45:357–61.
[55] CrystalStructure 4.2.1: Crystal structure analysis package, rigaku corporation
(2000-2016). Tokyo 196-8666, Japan.
[56] Macrae CF, Edgington PR, McCabe P, Pidcock E, Shields GP, Taylor R, Towler M,
Streek Jvd. Mercury: visualization and analysis of crystal structures. J Appl Cryst
2006;39:453–7.
24

ACCEPTED MANUSCRIPT
[57] Kim SH, Yoon SH, Kim SH, Han EM. Red electroluminescent azomethine dyes
derived from diaminomaleonitrile. Dyes Pigm 2004;64:45–8.
[58] Elliott RJ. Intensity of optical absorption by excitons. Phys Rev 1957;108:1384–9.
25

ACCEPTED MANUSCRIPT
Figure captions
Fig. 1 The synthetic route and chemical structures of novel bisazomethine dyes.
Fig. 2 Normalised (a) absorption and (b) fluorescence spectra for DP1b–DP20b in
chloroform solution; the concentrations of 1.0×10-5 M for each derivative.
Fig. 3 Normalised (a) absorption and (b) fluorescence spectra for DP1b–DP20b in the
crystalline state.
Fig. 4 Crystal structure of DP4b viewed from three directions: (a) top view, (b) side
view along the long molecular axis, and (c) side view along the short molecular axis.
Fig. 5 Crystal structure of DP5b viewed from three directions: (a) top view, (b) side
view along the long molecular axis, and (c) side view along the short molecular axis.
Fig. 6 Crystal structure of DP6b viewed from three directions: (a) top view, (b) side
view along the long molecular axis, and (c) side view along the short molecular axis.
Fig. 7 Crystal structure of DP16b viewed from three directions: (a) top view, (b) side
view along the long molecular axis, and (c) side view along the short molecular axis.
Fig. 8 Crystal structure of DP3b solvate viewed from three directions: (a) top view, (b)
side view along the long molecular axis, and (c) side view along the short molecular
axis.
Table captions
Table 1 Absorption and fluorescence properties in chloroform solution and in the
crystalline state.
Table 2 Summary of crystallographic data.
26

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Table 1 Absorption and fluorescence properties in chloroform solution and in the crystalline state.
In chloroform solution
λmax (nm) εmax×10-5 Fmax (nm)a ΦF (%)b SS (nm)c
In crystalline state
λmax (nm) Fmax (nm)d ΦF (%)e SS (nm)f
Dye
∆λ (nm)g ∆F (nm)h
558
558
558
558
558
558
558
558
558
558
558
1.11
1.12
1.12
1.11
1.11
1.12
1.11
1.12
1.12
1.12
1.12
611
610
609
611
611
610
612
612
610
610
611
3.1
3.4
4.7
4.8
4.3
4.0
4.3
3.1
4.3
3.9
3.0
53
52
51
53
53
52
54
54
52
52
53
608
607
609
610
609
609
608
609
610
610
609
702
697
696
694
688
687
680
679
687
689
682
4.1
12.9
5.3
94
90
87
84
79
78
72
70
77
79
72
50
49
51
52
51
51
50
51
52
52
51
91
87
87
83
77
77
68
67
77
79
71
DP1b
DP2b
DP3b
DP4b
DP5b
DP6b
DP7b
DP8b
DP12b
DP16b
DP20b
5.0
13.7
20.1
17.1
16.6
13.7
12.8
11.9
aFmax (solution) excited at 558 nm.
eΦF : Fluorescence quantum yield in a crystalline state.
fSS : Stokes shift, Fmax - λmax in a crystalline state.
g∆λ (nm) : λmax (the crystalline state) - λmax (solution).
h∆F (nm) : Fmax (the crystalline state) - Fmax (solution).
bΦF : Fluorescence quantum yield in solution.
cSS : Stokes shift, Fmax - λmax in chloroform solution.
dFmax (the crystalline state) excited at 610 nm.

ACCEPTED MANUSCRIPT
Table 2 Summary of crystallographic data.
Crystal data
Formula
Formula weight
Crystal system
Space group
Temperature, K
a, Å
DP2b
DP3b
DP4b
DP5b
DP6b
DP7b
DP8b
DP12b
DP16b
DP20b
C34H46N6O2 C37H51N6O2Cl3 C38H54N6O2 C40H58N6O2 C42H62N6O2 C45H67N6O2Cl3 C46H70N6O2 C54H86N6O2 C62H102N6O2 C70H118N6O2
570.78
P-1
trclinic
296
8.6273(2)
9.0502(2)
13.3357(3)
73.833(1)
86.587(1)
75.355(1)
1
718.21
P-1
trclinic
223.2
8.843(2)
13.289(3)
17.726(4)
73.521(5)
77.317(8)
88.466(8)
2
626.88
P-1
trclinic
223.2
8.550(7)
9.149(9)
12.90(1)
87.48(4)
72.02(4)
74.27(4)
1
654.94
P21/c
monoclinic
296
8.7836(2)
25.0075(6)
9.0627(2)
90
103.622(1)
90
682.99
P-1
trclinic
223.2
8.794(9)
8.879(8)
13.32(1)
79.54(6)
85.63(4)
78.57(5)
1
830.42
P-1
trclinic
93
10.756(3)
13.803(3)
16.943(4)
101.927(5)
91.835(3)
91.153(4)
2
739.10
P-1
trclinic
296
8.4180(2)
9.4288(2)
15.4182(4)
95.911(1)
97.431(1)
105.153(1)
1
851.31
P-1
trclinic
93
8.538(7)
8.996(8)
17.08(2)
76.91(4)
77.83(5)
75.35(6)
1
963.53
P-1
trclinic
223.2
8.343(2)
11.267(3)
17.408(6)
83.234(9)
84.48(1)
70.471(9)
1
1075.74
P-1
trclinic
223.2
8.339(5)
11.259(6)
19.91(1)
76.83(2)
87.47(3)
70.16(2)
1
b, Å
c, Å
α, deg
β , deg
γ, deg
Z
2
V, Å3
967.51(4)
0.980
308.00
0.490
1947.3(8)
1.225
764.00
0.274
923.0(2)
1.128
340.00
0.071
1934.68(8)
1.124
712.00
0.546
1001.0(2)
1.132
372.00
0.070
2459.0(1)
1.121
892.00
0.225
1159.27(5)
1.059
404.00
1220.0(2)
1.159
468.00
0.070
1528.7(8)
1.047
532.00
0.063
1711.0(2)
1.044
596.00
0.062
dcalc, g/cm3
F(000)
ꢀ, mm-1
0.503
No. of reflns
measured
No. of unique
reflns
No. of
parameters
8231
3290
190
16992
10133
437
5899
3170
208
17158
3503
217
1039
337
16120
8524
505
10750
3957
239
1234
413
9946
5276
316
10784
5599
352
226
299
0.0866/
0.1972
1.000
0.0805/
0.1753
1.000
0.0792/
0.2385
1.000
0.0892/
0.2052
1.000
0.0806/
0.1630
1.000
0.0665/
0.1327
1.000
0.0694/
0.1465
1.000
0.1033/
0.2246
1.000
0.0779/
0.1573
1.000
0.0880/
0.1671
1.000
R1/ wR2
GOF
CCDC
1485364
1485365
1485366
1485371
1485372
1485373
1485374
1485375
1485376
1485377