Synthesis and photophysical properties of blue-emitting fluorescence dyes derived from naphthalimide derivatives containing a diacetylene linkage group

Article abstract of DOI:10.1016/j.dyepig.2018.05.065

Four naphthalimide-based dyes with a diacetylene linkage at the 3- or 4-position were synthesized to improve the thermal stability of the fluorescence dye as well as the efficiency of fluorescent emission at blue region. The absorption and fluorescence properties of the synthesized dyes were also investigated. The geometries and molecular orbitals of the dyes prepared were simulated using by density functional theory and time-dependent density functional theory using Gaussian 09. Furthermore, the suitability of the dyes for application in light-conversion films was examined. N-Phenyl groups were found to have a greater effect on the fluorescence of naphthalimide-based dyes than analogue containing an N-alkyl group. In addition, investigation of the effect of diacetylene linkages at the 3- or 4-positions of naphthalimide-based dyes showed that the fluorescence was influenced by the electron-donating effect of the diacetylene linkage which could afford more conjugation of π orbitals of the dyes. Four blue fluorescence dyes derived from 1,8-naphthalimide containing a diacetylene linkage were synthesized and then coated in PE film. The photophysical properties were analyzed using density functional theory (DFT) calculations, and excitations from the highest occupied molecular orbitals (HOMOs) to the lowest unoccupied molecular orbitals (LUMOs) of the dyes were simulated at the B3LYP/6-31G level of theory via the Gaussian 09 suite of programs. Using these methods, the influences of the position of the ethynyl linkages, alkyl groups, and phenyl groups on the electronic and fluorescence properties of the dyes were also clarified.

Full text of DOI:10.1016/j.dyepig.2018.05.065

Accepted Manuscript
Synthesis and photophysical properties of blue-emitting fluorescence dyes derived
from naphthalimide derivatives containing a diacetylene linkage group
Kyung-Won Kim, Geun-Hyeong Kim, Su-Hyeon Kwon, Hyo-In Yoon, Jung-Eek Son,
Jae-Hong Choi
PII:
S0143-7208(18)30605-3
10.1016/j.dyepig.2018.05.065
DYPI 6794
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 18 March 2018
Revised Date: 25 May 2018
Accepted Date: 25 May 2018
Please cite this article as: Kim K-W, Kim G-H, Kwon S-H, Yoon H-I, Son J-E, Choi J-H, Synthesis and
photophysical properties of blue-emitting fluorescence dyes derived from naphthalimide derivatives
containing a diacetylene linkage group, Dyes and Pigments (2018), doi: 10.1016/j.dyepig.2018.05.065.
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ACCEPTED MANUSCRIPT
Synthesis and photophysical properties of blue-emitting fluorescence dyes
derived from naphthalimide derivatives containing a diacetylene linkage
group
a
c
c
b
b
c*
Kyung-Won Kim , Geun-Hyeong Kim , Su-Hyeon Kwon , Hyo-In Yoon , Jung-Eek Son , Jae-Hong Choi
a
Advanced Organic Materials Science and Engineering, Kyungpook National University, Daegu 702-701,
Korea
b
Department of Plant Science, Seoul National University, Seoul 08826, Korea
c
Department of Textile System Engineering, Kyungpook National University, Daegu 702-701, Korea
*jaehong@knu.ac.kr
Keywords: naphthalimide, diacetylene linkage, blue fluorescence, light-conversion film, agricultural film
Abstract
Four naphthalimide-based dyes with a diacetylene linkage at the 3- or 4-position were synthesized to improve
the thermal stability of the fluorescence dye as well as the efficiency of fluorescent emission at blue region . The
absorption and fluorescence properties of the synthesized dyes were also investigated. The geometries and
molecular orbitals of the dyes prepared were simulated using by density functional theory and time-dependent
density functional theory using Gaussian 09. Furthermore, the suitability of the dyes for application in light-
conversion films was examined. N-Phenyl groups were found to have a greater effect on the fluorescence of
naphthalimide-based dyes than analogue containing an N-alkyl group. In addition, investigation of the effect of
diacetylene linkages at the 3- or 4-positions of naphthalimide-based dyes showed that the fluorescence was
influenced by the electron-donating effect of the diacetylene linkage which could afford more conjugation of π
orbitals of the dyes. Four blue fluorescence dyes derived from 1,8-naphthalimide containing a diacetylene
linkage were synthesized and then coated in PE film. The photophysical properties were analyzed using density

ACCEPTED MANUSCRIPT
functional theory (DFT) calculations, and excitations from the highest occupied molecular orbitals (HOMOs) to
the lowest unoccupied molecular orbitals (LUMOs) of the dyes were simulated at the B3LYP/6-31G level of
theory via the Gaussian 09 suite of programs. Using these methods, the influences of the position of the ethynyl
linkages, alkyl groups, and phenyl groups on the electronic and fluorescence properties of the dyes were also
clarified.
1
. Introduction
The main factors in plant growth are temperature, carbon dioxide, nutrients, and sunlight. Sunlight contains
ultraviolet (UV) light, photosynthetically active radiation (PAR), and near-infrared light (NIR). The effective
wavelength range for plant growth is 400-700 nm, called photosynthetically active radiation (PAR). Especially
in the blue and red regions (400-500 nm and 600-700 nm), most plants have maximum photosynthetic
sensitivity. In addition, UV regions, especially in UV-A (320-400 nm) which can lower photosynthetic
constants by more than 70 %, can inhibit the photosynthesis of many plants [1].
Chlorophyll b and carotenoids absorb blue light in the 400-500 nm regions promoting plant growth and
affecting initial growth such as flower formation and induction of flowering. In general, the light conversion
film for agriculture can be manufactured using by PE film which contains a fluorescent dye. The light
conversion film converts the incoming sunlight into the selective wavelengths of around 450 nm for blue
emission or 600 nm for red emission these are most effective for photosynthesis. Therefore, the productivity of
most of crops can be improved, and the cultivation period can be also shortened contributing for energy save [2].
Naphthalimide-based dyes generally show moderate thermal stabilities, excellent durability and large Stokes
shift owing to the planarity of their molecular structures. Moreover, naphthalimide-based dyes are easily
functionalized through the introduction of substituents at their terminal and N-positions, which enable the
modification of various characteristics, such as spectral properties and solubilities [3,4].
The introduction of diacetylene linkage can positively affect the optical performance and fluorescence of
these dyes. Although naphthalimide-based dyes have high solubilities and acceptable heat resistance, the
introduction of diacetylene linkage can be expected to improve further the heat resistance and quantum yield
comparing to fluorescence dyes containing an ethynyl linkage group [3,4].
In this study, diacetylene linkage was introduced at 3- or 4-position of 1,8-naphthalimidyl system starting
from 1,8-naphthalic anhydride, then the absorption and emission maxima of four blue fluorescence dyes

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prepared were measured. To evaluate the effect of florescence dye onto photosynthesis, its rate of lettuce grown
under fluorescent film was examined comparing with that under transparent PE film.
2
. Experimental
2
.1. Materials and instrumentation
1
,8-Naphthalimide (99%), bromine (98%), 2-methyl-3-butyn-2-ol (99%), copper iodide (99.5%), and
bis(triphenylphosphine)palladium(II) dichloride (98%) were purchased from Sigma-Aldrich. n-Butylamine
(
(
99%) and aniline (99%) were purchased from TCI. Triphenylphosphine (99%), copper(II) acetate monohydrate
99%), copper(I) chloride (99%), and silver sulfate (98.5%) were purchased from Alfa-Aesar. Potassium
hydroxide, triethylamine, tetrahydrofuran, ethanol, methanol, n-hexane, ethyl acetate, methyl chloride, and other
solvents were purchased from Duksan Pure Chemical. All chemicals were used without any additional
purification.
The fluorescence dyes and intermediates were analyzed by HPLC (Acme 9000, Young Lin, Korea), gas
chromatography/mass spectrometry (GC-MS; 7890A-5975C GC/MSD, Agilent, USA), liquid
1
chromatography/tandem mass spectrometry (LC-MS; Agilent, USA), H-NMR (in DMSO-d or CDCl , Advance
6
3
Digital 400, Bruker, Germany), and elemental analysis (Flash 200, Thermo Fisher, Italy). For UV-Visible
spectroscopic analysis, the dyes were dissolved in N,N-dimethylformamide, and absorbance spectra were
collected using a UV-Visible spectrophotometer (Thermo Scientific, Evolution 300). Fluorescence intensities
and fluorescence spectra were collected using a fluorescence spectrophotometer (Scinco, Fluoro Mate FS-2) by
-5
dissolving the dyes in methylene chloride at a concentration of 5.0×10 mol/L. The fluorescence intensity was
measured at a PMT voltage of 500 V, and the quantum yields were calculated using anthracene (Ф=0.27 in
ethanol) as a reference. Thermal stability measurements were conducted from 30 to 500 °C at a heating rate of
1
0 °C/min under nitrogen conditions using a thermal analyzer system (Q600, TA Instruments, Japan).
The transmittance of each film (transparent PE film, fluorescent PE film) was measured at room
temperature using a spectroradiometer (BLUE-Wave spectrometer, Stellar Net Inc., Tampa, FL, USA) with
integrating sphere (IC-2, Stellar Net Inc., Tampa, FL, USA). The light source was UV-Vis mixed light
consisting of UV-A (FL20SBLB, Sankyo Denki Co., Ltd., Hiratsuka, Japan), UV-B (GL20SE, Sankyo Denki

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Co., Ltd., Hiratsuka, Japan) and tungsten-halogen (SL-FILTER Tungsten Halogen, Stellar Net Inc., Tampa, FL,
USA).
2
.2. Syntheses of dyes
The synthetic procedures for the intermediates and dyes are outlined in Scheme 1 (Intermediates 1–6) and
Scheme 2 (Intermediates 7–14 and Fluorescence dye 1–4), respectively.
O
N
O
O
O
1
O
Br
Br
3
O
N
O
Br
4
O
O
O
Bromination
Aminolysis
O
N
O
1
,8-Naphthalic anhydride
Br
O
O
O
5
O
N
O
Br
2
Br
6
Scheme 1. Synthetic routes of the designed dyes.
2
.2.1. 3-Bromo-1,8-naphthalic anhydride (Intermediate 1): Bromination
1
,8-Naphthalic anhydride (10 mmol, 1.98 g) and silver(I) sulfate (5 mmol, 1.56 g) were added to sulfuric acid
(
40 mL) under stirring. The reaction mixture was cooled in an ice-bath and bromine (13 mmol, 6.3 mL) was
slowly added. Subsequently, the mixture was heated to 65 °C and stirred for 12 h. When the reaction was
complete, the reaction mixture was cooled to room temperature and then poured into water to obtain crystals.
The crystals were recovered by vacuum filtration and recrystallized from ethyl acetate and methanol. The
product was further purified by column chromatography (adsorbent: silica gel, eluent: ethyl acetate/hexane
1
(
1:5)).Yield: 78.7%; H-NMR (400MHz, DMSO-d ), δ: 8.09(m, 1H, ArH),8.75(d, 1H, ArH), 8.81(d, 1H, ArH),
6
+
8
.94(d, 1H, ArH), 9.22(d, 1H, ArH); GC-MS: 277(M ); Elemental analysis: Found: C, 52.21; H, 1.89; O, 17.04;
calculated for C H BrO : C, 52.02; H, 1.82; O, 17.32.
1
2
5
3

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2
.2.2. 4-Bromo-1,8-naphthalic anhydride (Intermediate 2): Bromination
1
,8-Naphthalic anhydride (10 mmol, 1.98 g) was dissolved in a 4M KOH solution (12 mL) under vigorous
stirring. The reaction mixture was cooled in an ice-bath and bromine (1 mmol, 6.3 mL) was slowly added.
Subsequently, the mixture was heated to 65 °C and stirred for 12 h. When the reaction was complete, the
reaction mixture was cooled in an ice-bath and sulfuric acid (10 mL) was slowly added. The resulting solution
was allowed to reflux for 1 h. Cool to room temperature and add crystals. The crystals were recovered by
vacuum filtration and recrystallized from methanol. The product was further purified by column
1
chromatography (adsorbent: silica gel, eluent: ethyl acetate/hexane (1:5)).Yield: 64.2%; H-NMR (400MHz,
DMSO-d ), δ: 8.20(d, 1H, ArH), 8.47(d, 1H, ArH), 9.15(d, 1H, ArH), 9.20(d, 1H, ArH), 9.35(d, 1H, ArH); GC-
6
+
MS: 277(M ); Elemental analysis: Found: C, 51.83; H, 1.80; O, 17.53; calculated for C H BrO : C, 52.02; H,
1
2
5
3
1
2
.82; O, 17.32.
.2.3. 5-Bromo-2-butyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 3): Aminolysis
A mixture of intermediate 1 (5 mmol, 1.66 g) and n-butylamine (7.5 mmol, 0.74 mL) was added to ethanol
15 mL) and the resulting solution was refluxed for 10 h. When the reaction was complete, the reaction mixture
(
was cooled to room temperature and the resulting crystals were recovered by vacuum filtration. The obtained
reaction product was recrystallized from methanol. The product was further purified by column chromatography
1
(
adsorbent: silica gel, eluent: ethyl acetate/hexane (1:5)).Yield: 77.2%; H-NMR (400MHz, DMSO-d ), δ:
6
0
8
.89(m,3H, CH ),1.31(m,2H, CH ), 1.55(m,2H, CH ), 3.12(t,2H, CH ), 7.88(m,1H, ArH), 8.23(d,1H, ArH),
3 2 2 2
.36(m,1H, ArH), 8.46(m,2H, ArH);GC-MS: 331(M-1); Elemental analysis: Found: C, 57.91; H, 4.27;N, 4.25;
O, 9.54; calculated for C H BrNO : C, 57.85; H, 4.25; N, 4.22;O, 9.63.
1
6
14
2
2
.2.4. 6-Bromo-2-butyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 5): Aminolysis
Intermediate 5 was synthesized according to the procedure used for intermediate 3, except intermediate 2 was
1
used instead of intermediate 1. Yield: 62.8%; H-NMR (400MHz, DMSO-d ), δ: 0.90 (m, 3H, CH ), 1.31(m, 2H,
6
3
CH ), 1.56(m, 2H, CH ), 3.24(t, 2H, CH ), 7.88(m, 1H, ArH), 8.22 (d, 1H, ArH), 8.23(d, 1H, ArH), 8.52(d, 1H,
2
2
2
ArH), 8.85(d,1H, ArH); GC-MS: 331(M-1); Elemental analysis: Found: C, 57.88; H, 4.14; N, 4.36; O, 9.77;
calculated for C H BrNO : C, 57.85; H, 4.25; N, 4.22; O, 9.63.
1
6
14
2
2
.2.5. 5-Bromo-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 4): Aminolysis

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A mixture of intermediate 1 (5 mmol, 1.66 g) and aniline (10 mmol, 0.93 g) was added to ethanol (15 mL)
and the resulting solution was refluxed for 10 h. When the reaction was complete, the reaction mixture was
cooled to room temperature and the resulting crystals were recovered by vacuum filtration. The obtained
reaction product was recrystallized using methanol. The product was further purified by column
1
chromatography (adsorbent: silica gel, eluent: ethyl acetate/hexane (1:5)). Yield: 64.8%; H-NMR (400MHz,
DMSO-d ), δ: 7.17(m, 1H, ArH), 7.41(d, 4H, ArH), 8.23(m, 1H, ArH), 8.34(m, 1H, ArH), 8.50(d, 1H, ArH),
6
8
.84(d, 1H, ArH); GC-MS: 350(M-1); Elemental analysis: Found: C, 61.38; H, 2.87; N, 3.95; O, 9.12;
calculated for C H BrNO : C, 61.39; H, 2.86; N, 3.98; O, 9.09.
1
8
10
2
2
.2.6. 6-Bromo-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 6): Aminolysis
Intermediate 6 was synthesized according to the procedure used for intermediate 4, except intermediate 2 was
1
used instead of intermediate 1. Yield: 61.8%; H-NMR (400MHz,DMSO-d ), δ: 7.19(m, 1H, ArH), 7.43(s, 4H,
6
ArH), 7.86(m, 1H, ArH), 8.13(d, 1H, ArH), 8.46(d, 2H, ArH); GC-MS: 350(M-1); Elemental analysis: Found: C,
6
1.35; H, 2.90; N, 3.99; O, 9.08; calculated for C H BrNO : C, 61.39; H, 2.86; N, 3.98; O, 9.09.
18 10 2
Scheme 2. Synthetic schemes of the four fluorescence dyes 1-4.

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2
.2.7. 2-Butyl-5-(3-hydroxy-3-methylbut-1-ynyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 7):
Sonogashira coupling
A mixture of intermediate 3 (1 mmol, 330 mg), 2-methyl-but-3-yn-2-ol (3 mmol, 252 mg), cuprous iodide
(
15.9 mg, 0.05 mmol), triphenylphosphine (13.1 mg,0.05 mmol), and tetrakis(triphenylphosphine)-
palladium(II)dichloride (115 mg, 0.1 mmol) was carefully degassed and charged with nitrogen. Anhydrous
tetrahydrofuran (10 mL) and trimethylamine (15 mL) were then added. The reaction mixture was refluxed for 24
h under a nitrogen atmosphere. The reaction was terminated with ammonia water (10 mL), then extracted with
methyl chloride (10 mL), washed with water (10 mL), dried over anhydrous magnesium sulfate, and evaporated
to obtain the crude product. The crude product was purified by column chromatography (adsorbent: silica gel,
1
eluent: ethyl acetate/hexane(1:5)).Yield: 79.8%; H-NMR (400MHz, DMSO-d ), δ: 1.01(m,3H, CH ),1.24(t,2H,
6
3
CH ), 1.41 (t,2H, CH ), 1.46(s,6H, CH ), 3.24(t,2H,CH ), 5.59(s,1H, OH), 7.69(s,1H, ArH), 7.80(s,1H, ArH),
2
2
3
2
+
8
6
.27(d,1H, ArH), 8.35(d,1H, ArH), 8.40(d,1H, ArH);GC-MS: 335(M );Elemental analysis: Found: C, 75.25; H,
.31; N, 4.13; O, 14.31;calculated for C H BrNO : C, 75.20; H, 6.31; N, 4.18; O, 14.31.
1
8
10
2
2
.2.8. 2-Butyl-6-(3-hydroxy-3-methylbut-1-ynyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 9):
Sonogashira coupling
Intermediate 9 was synthesized according to the procedure used for intermediate 7, except intermediate 5 was
1
used instead of intermediate 3. Yield: 69.8%; H-NMR (400MHz, DMSO-d ), δ: 0.91(m,3H, CH ),1.28(m,2H,
6
3
CH ), 1.55(t,2H, CH ), 1.56 (s,6H, CH ), 3.16(t,2H,CH ), 5.49(s,1H, OH), 7.75(s,1H, ArH), 8.36(s,1H, ArH),
2
2
3
2
+
8
6
.40 (s,1H, ArH), 8.41(s,1H, ArH), 8.45(s,1H, ArH);GC-MS: 335(M );Elemental analysis: Found: C, 75.23; H,
.28; N, 4.17; O, 14.32;calculated for C H BrNO : C, 75.20; H, 6.31; N, 4.18; O, 14.31.
1
8
10
2
2
.2.9. 5-(3-Hydroxy-3-methylbut-1-ynyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 8):
Sonogashira coupling
Intermediate 8 was synthesized according to the procedure used for intermediate 7, except intermediate 4 was
1
used instead of intermediate 3. Yield: 65.5%; H-NMR (400MHz, DMSO-d ), δ: 1.26(s, 6H, CH ), 5.49(s, 1H,
6
3
OH), 7.09(m, 1H, ArH), 7.41(m, 4H, ArH), 7.70 (s, 1H, ArH), 7.85(s, 1H, ArH), 8.39(d, 1H, ArH), 8.57(d, 1H,
+
ArH), 8.69(d, 1H, ArH); GC-MS: 355(M ); Elemental analysis: Found: C, 77.70; H, 4.85; N, 3.96; O, 13.13;
calculated for C H NO : C, 77.73; H, 4.82; N, 3.94; O, 13.15.
2
3
17
3

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2
.2.10. 6-(3-Hydroxy-3-methylbut-1-ynyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 10):
Sonogashira coupling
Intermediate 10 was synthesized according to the procedure used for intermediate 7, except intermediate 6 for
1
used instead of intermediate 3. Yield: 66.7%; H-NMR (400MHz, DMSO-d ), δ: 1.44(s, 6H, CH ), 5.49(s, 1H,
6
3
OH), 7.23(m, 4H, ArH), 7.39 (m, 1H, ArH), 7.66(m, 1H, ArH), 8.13(d, 1H, ArH), 8.56(d, 2H, ArH); GC-MS:
+
3
55(M ); Elemental analysis: Found: C, 77.71; H, 4.84; N, 3.91; O, 13.18; calculated for C H NO : C, 77.73;
23
17
3
H, 4.82; N, 3.94; O, 13.15.
2
.2.11. 2-Butyl-5-ethynyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 11): Hydrolysis
Intermediate 7 (1 mmol) and potassium hydroxide (3 mmol, 168 mg) were added to anhydrous toluene (3
mL). The mixture was refluxed for 6 h under a nitrogen atmosphere and then filtered. The filtrate was
evaporated to obtain the crude product, which was purified by column chromatography (adsorbent: silica gel,
1
eluent: ethyl acetate/hexane (1:5)). Yield: 83.7%; H-NMR (400MHz, DMSO-d ), δ: 0.92(m, 3H, CH ), 1.25(t,
6
3
2
H, CH ), 1.49(t, 2H, CH ), 3.44(t, 2H, CH ), 4.71(s, 1H, CH), 7.80(s, 1H, ArH), 8.39(d, 1H, ArH), 8.50(d, 1H,
2 2 2
+
ArH), 8.51(d, 1H, ArH),8.54 (d, 1H, ArH); GC-MS: 277(M ); Elemental analysis: Found: C, 77.95; H, 5.46; N,
5
2
.02; O, 11.57; calculated for C H NO : C, 77.96; H, 5.45; N, 5.05; O, 11.54.
18 15 2
.2.12. 2-Butyl-6-ethynyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 13): Hydrolysis
Intermediate 13 was synthesized according to the procedure used for intermediate 11, except intermediate 9
1
was used instead of intermediate 7. Yield: 84.7%; H-NMR (400MHz, DMSO-d ), δ: 1.02(m, 3H, CH ), 1.16(t,
6
3
2
H, CH ), 1.41(t, 2H, CH ), 3.66(t, 2H, CH ), 4.93(s, 1H, CH), 7.70(s, 1H, ArH), 7.88 (s, 1H, ArH), 8.39(d, 1H,
2 2 2
+
ArH), 8.50(d, 1H ArH), 8.51(d, 1H, ArH); GC-MS: 277(M ); Elemental analysis: Found: C, 77.99; H, 5.42; N,
5
2
.01; O, 11.50; calculated for C H NO : C, 77.96; H, 5.45; N, 5.05; O, 11.54.
18 15 2
.2.13. 5-Ethynyl-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 12): Hydrolysis
Intermediate 12 was synthesized according to the procedure used for intermediate 11, except intermediate 8
1
was used instead of intermediate 7. Yield: 78.7%; H-NMR (400MHz, DMSO-d ), δ: 4.05(s, 6H, CH), 7.19(m,
6
+
1
H, ArH), 7.43(m, 4H, ArH), 7.86 (m, 1H, ArH), 8.13(d, 1H, ArH), 8.46(d, 2H, ArH); GC-MS: 297 (M );
Elemental analysis: Found C, 79.78; H, 3.68; N, 4.64; O, 10.52; calculated for C H NO : C, 79.87; H, 3.73; N,
20
11
2
4
.71; O, 10.76.

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2
.2.14. 6-Ethynyl-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Intermediate 14): Hydrolysis
Intermediate 14 was synthesized according to the procedure used for intermediate 11, except intermediate 10
1
was used instead of intermediate 7. Yield: 79.5%; H-NMR (400MHz, DMSO-d ), δ: 4.05(s, 6H, CH), 7.19(m,
6
1
1
H, ArH), 7.43(m, 4H, ArH), 7.89(s, 1H, ArH), 7.90(s, 1H, ArH), 8.49(d, 1H, ArH), 8.60(d, 1H, ArH), 8.71(d,
+
H, ArH); GC-MS: 297(M ); Elemental analysis: Found: C, 79.57; H, 3.63; N, 4.65; O, 10.79; calculated for
C H NO : C, 80.80; H, 3.73; N, 4.71; O, 10.76.
2
0
11
2
2
.2.15. Synthesis of blue fluorescence dye 1: C–C bond formation
A mixture of intermediate 11 (1 mmol, 332 mg), copper(I) chloride (8.1 mmol, 0.75 mg), and copper(II)
acetate (7.5 mmol, 1.5 mg) was added to pyridine (30 mL). The mixture was stirred for 1 h and then heat to
0 °C and stirred for another 3 h. When the reaction was complete, water was added to the reaction mixture.
4
Precipitated crystals were sufficiently washed with water through a reduced pressure filter. The crystals were
dissolved in methyl chloride and impurities were removed by filtration. The filtrate was evaporated to obtain
fluorescence dye 1. The product was further purified by column chromatography (adsorbent: silica gel, eluent:
1
ethyl acetate/hexane (1:5)). Yield: 78.5%; H-NMR (400MHz, DMSO-d ), δ: 0.92(m, 6H, CH ), 1.29(m, 4H,
6
3
CH ), 1.53(m, 4H, CH ), 3.14(t, 4H, CH ), 7.80(t, 2H, ArH), 8.12(m, 2H, ArH), 8.17(m, 2H, ArH), 8.36(m, 2H,
2
2
2
+
ArH), 8.42(m, 2H, ArH); LC-MS: 552(M ); Elemental analysis: Found: C, 78.21; H, 5.14; N, 5.05; O, 11.60;
calculated for C H N O : C, 78.24; H, 5.11; N, 5.07; O, 11.58.
3
6
28
2
4
2
.2.16. Synthesis of blue fluorescence dye 2: C–C bond formation
Fluorescence dye 2 was synthesized according to the procedure used for Fluorescence 1, except intermediate
1
1
1
8
2 was used instead of intermediate 11. Yield: 77.5%; H-NMR (400MHz, DMSO-d ), δ: 0.91(t, 6H, CH ),
6
3
.30(m, 4H, CH ), 1.55(m, 4H, CH ), 3.13(t, 4H, CH ), 7.73(m, 2H, ArH), 7.81(m, 2H, ArH), 8.28(m, 2H, ArH),
2
2
2
+
.34(m, 2H, ArH), 8.40(d, 2H, ArH); LC-MS: 552(M ); Elemental analysis: Found: C, 78.21; H, 5.14; N, 5.04;
O, 11.61; calculated for C H N O : C, 78.24; H, 5.11; N, 5.07; O, 11.58.
3
6
28
2
4
2
.2.17. Synthesis of blue fluorescence dye 3: C–C bond formation
Fluorescence dye 3 was synthesized according to the procedure used for Fluorescence 1, except intermediate
1
1
3 was used instead of intermediate 11. Yield: 65.5%; H-NMR (400MHz, DMSO-d ), δ: 7.14(m, 2H, ArH),
6
7
.41(m, 8H, ArH), 7.78(m, 2H, ArH), 8.09(d, 2H, ArH), 8.33(m, 2H, ArH), 8.34(d, 2H, ArH), 8.40(d, 2H, ArH);

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+
LC-MS: 592(M ); Elemental analysis: Found: C, 81.05; H, 3.42; N, 4.75; O, 10.78; calculated for C H N O :
40
20
2
4
C, 81.07; H, 3.40; N, 4.73; O, 10.80.
2
.2.18. Synthesis of blue fluorescence dye 4: C–C bond formation
Fluorescence dye 4 was synthesized according to the procedure used for Fluorescence 1, except intermediate
1
1
4 was used instead of intermediate 11. Yield: 64.7%; H-NMR (400MHz, DMSO-d ), δ: 7.16(m, 2H, ArH),
6
7
.45(m, 8H, ArH), 7.71(m, 2H, ArH), 7.78(m, 2H, ArH), 8.36(m, 2H, ArH), 8.39(d, 2H, ArH), 8.40(d, 2H, ArH);
+
LC-MS: 592(M ); Elemental analysis: Found: C, 81.08; H, 3.42; N, 4.71; O, 10.79; calculated for C H N O :
40
20
2
4
C, 81.07; H, 3.40; N, 4.73; O, 10.80.
2
.3. Geometry optimization of dyes
DFT and TD-DFT calculations were carried out with the Gaussian09 program package. The 6-31G Pople
basis set was used for all elements with the conventional B3LYP exchange-correlation function. The
intermolecular interactions were analyzed by examining the core twist angles and the size of the substituents.
The dihedral angles of the naphthalimide main body were calculated by measuring the distortion angle of the
ethynyl linkage in the center of the naphthalimide main body. The lengths of the substituents were calculated as
the longest linear distance between atoms in the substituents. The displacement of the substituents from the
plane of naphthalimide backbone was assessed by measuring the angle between the substituents and the plane
[
5,6].
2
.4. Photosynthesis test
Lettuce (Lactuca sativa L.) was transplanted one month after seeding. The plants were covered with
transparent or fluorescent film in a greenhouse. The photosynthetic rate of the leaves was measured by a
CO /H O gas analyzer (LI-6400, LI-COR, Lincoln, NE, USA) at 21 days after transplanting. The conditions
2
2
inside the leaf chamber were held constant at a leaf temperature of 25℃, a CO concentration of 400 ppm and a
2
relative humidity of 60±5 %. The photosynthetic rate was the value of three plants per treatment and measured
in real time during the day under natural sunlight. Based on photosynthetic rate measurements, photosynthetic

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response to light intensity (PPFD, photosynthetic photon flux density) is represented by a rectangular hyperbola
equation.
2
.5. Thermal stability test
To investigate the thermal stability of Fluorescence dyes l-4, thermogravimetric analysis (TGA) were performed. All
samples were heated at a rate of 10 °C/min, under flowing nitrogen upto 600 °C.
2
.6. Solubility test
The solubility measurements were carried out according to KS M ISO 7579 [5].
3
. Results and discussion
3
.1. Design concept of dye molecule and syntheses of dyes
The reaction steps of the synthesized dyes 1-4 including 14 intermediates are shown in Schemes 1 and 2. All
fluorescence dyes were designed to have a diacetylene linkage group starting from 1,8-naphthalic anhydride via
bromination, aminolysis, Sonogashira coupling, hydrolysis and final coupling reaction in sequence. Two
positional isomeric products between dyes 1 & 3, and dyes 2 & 4 were selectively prepared from corresponding
bromo analogues (intermediate 1 and 2). The fluorescence dyes containing an ethynyl linkage group derived
from 1,8-naphthalimide exert generally moderate heat stability and quantum yield, as reported in previous
literatures [3,4]. Therefore, in this study, the extended ethynyl linkage group (diacetylene group) was introduced
by replacing an ethynyl group to improve properties of the heat stability and quantum yield as well.
3
.2. Geometry optimization of synthesized dyes
The geometry-optimized structures of the synthesized dyes were obtained by DFT calculations using
Gaussian09 are shown in Fig. 1 where the planarity of the naphthalimide system can be visualized. In particular,

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the size of the dye molecule and their substituents mainly affect the distance between molecules, intermolecular
interactions, and fluorescence properties [7-9].
Fig. 1. Geometry-optimized structures of the synthesized dyes.
The calculated lengths of the diacetylene linkage introduced into naphthalimidyl moiety are listed in Table 1.
The angle of naphthalimide and N-substituent was calculated as α value, and the angle of naphthalimide and
diacetylene linkage was calculated as β value, respectively. According to the DFT simulation, as shown in
Figure 1, all π-orbital systems including naphthalimidyl rings and diacetylene group retain its planarity which is
in accordance with the same angle in both α and β values. Therefore, it can be expected that the planarity of
fluorescence dyes 1-4 can contribute to improved thermal stability and fluorescence behaviors exerted by
extended π-interactions [10-15].

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Table 1
Dihedral angles of the synthesized dyes.
Theoretically calculated dihedral angles (°)
Dye No.
α
γ
-
δ
-
β
Fluorescence dye 1
Fluorescence dye 2
Fluorescence dye 3
Fluorescence dye 4
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
-
-
0.34
0.37
0.34
0.37
α(°)=N –ethynyl bond dihedral angle, β(°)=N –ethynyl bond dihedral angle, γ(°)=R –N dihedral angle, δ(°)=R –N dihedral angle.
1
2
1
1
2
2
3
.3. Absorption properties of synthesized dyes
The absorption spectra of the synthesized dyes 1-4 are shown in Fig. 2 and Table 2. In terms of the absorption
maxima of the synthesized dyes, it was clearly observed that isomeric dyes 4-substituted of 1,8-naphthalimide
by a diacetylene group absorbed bathochromically by 58 and 60 nm in comparison of corresponding 3-
analogues for N-butyl group and N-phenyl group, respectively. This red shift can be explained by the
conjugation of the π orbitals increased by interactions of 4-posion of naphthalimidyl systems with diacetylene
group. For the effect of N-substituent onto absorption maxima, N-phenyl group provided a bathochromic shift
compared to N-butyl analogues irrespective of the position of diacetylene group, however the shifts were
comparatively smaller as 12 nm (for 3-position) and 14 nm (for 4-posistion). In case of N-butyl group, its
electron donating effect may cause the shorter absorption maxima.
The molar extinction coefficients of the four fluorescence dyes (26,000–28,000) were very similar regardless
of the type of N-substituent or the position of the diacetylene group that can suggest all four dyes 1-4 retain
similar planarity of the π-conjugation systems throughout dye molecule.

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Fig. 2. Absorption spectra of the synthesized dyes in chloroform (100 ppm).
3
.4. Fluorescence properties of synthesized dyes
All fluorescence properties except quantum yield were measured at the excitation wavelength corresponding
to the maximum absorption wavelength. The quantum efficiency was measured at the excitation wavelength of
3
20 nm, and the reference was calculated based on anthracene (Φ = 0.27 in ethanol).
Four fluorescence dyes showed high quantum yields ranged in 0.77 and 0.83 where dye 1 emitted at highest
quantum yield, as shown in Table 2. This high quantum yields can be attributed to the fact that fluorescence
dyes incorporating diacetylene linkage grope is planar, therefore led to the increased ICT effect.
In the four fluorescence dyes 1-4, the longest maximum emission wavelength was observed by dye 4 at 440
nm, whereas the dye 1 emitted at shortest wavelength of 414 nm, as shown in Table 2. Assuming from the
fluorescence emission maxima, all dyes 1-4 can be effective to the enhancement of photosynthesis as a blue
light.
To realize photoelectric exchange, self-quenching of the fluorescence should be minimized so that an
appropriate Stokes shift can be obtained. The four synthesized dyes have Stokes shifts of 54–100 nm and
fluorescence dyes 1 and 2, substituted with diacetylene linkage group at the 3-position of 1,8-naphthalimide,
exerted comparatively higher Stokes shifts, however the influence by N-substituent to the Stokes shift is to be
negligible [16-18]. Therefore, it can be concluded that the energy difference between absorbed photon and
emitted photon of 4-substituted dyes 1 and 2 was larger than that of corresponding analogues 3 and 4 resulted by
a vibrational relaxation.
The Results of fluorescence spectra of the synthesized dyes are shown in Fig. 3, and the results of
fluorescence emission maxima and Stokes shift are also summarized in Table 2.

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Fig. 3. Fluorescence spectra of the synthesized dyes in chloroform (100 ppm).
Table 2
Absorption and fluorescence properties of the synthesized dyes.
a
b
Dye No.
λmax (nm)
λem (nm)
Stokes shift (nm)
εmax
Φ
Fluorescence dye 1
Fluorescence dye 2
Fluorescence dye 3
Fluorescence dye 4
314
326
372
386
414
421
432
440
100
95
28,000
26,000
27,000
26,000
0.83
0.79
0.81
0.77
60
54
−5
a: λem- maximum emission wavelength (nm), b: Φ - quantum yield (10 mol/L in methylene chloride, excited at 320 nm).
Optical images of the synthesized dyes in chloroform solution are shown in Fig. 4. The images were
photographed under UV light of 365 nm.
Fig. 4. Optical images of the synthesized dyes in chloroform solution (100 ppm) under UV light of 365 nm.
3
.5. Molecular orbital modeling of synthesized dyes

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Table 3 shows the HOMO and LUMO diagrams of the TD-DFT simulation of excitation energy of LUMO in
the HOMO of the synthesized fluorescence dyes 1-4 [12-14,19-25].
This result shows that the n-butyl and phenyl group at N-substituent of naphthalimdyl ring was structurally
distorted and the electrons are localized. The largest band gap between HOMO and LUMO was observed by dye
1
that was 3.65 eV, whereas dye 2 was calculated to be smallest in four fluorescence dyes 1-4, as shown in
Table 3.
Fig. 5. Molecular orbital models of the HOMOs and LUMOs of the synthesized dyes.
Table 3
TD-DFT results for excitation from the HOMO to the LUMO of the synthesized dyes.
Electronic properties
Dye No.
HOMO(eV)
LUMO(eV)
Band gap(eV)
Fluorescence dye 1
-6.35
-2.70
3.65

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Fluorescence dye 2
Fluorescence dye 3
Fluorescence dye 4
-6.38
-6.27
-6.33
-3.38
-2.72
-3.01
3.00
3.55
3.32
3
1
.6. Thermal stability test
In the previous studies [3,4], fluorescence dyes A and B containing an ethynyl linkage group derived from
,8-naphthalimde decomposed readily at 282 ℃ and 265 ℃, respectively. As it was expected, in this study, the
extended ethynyl group (diacetylene group) for dye 1 resulted in extremely improved thermal stability, thus the
decomposition temperature was greatly increased to 398 ℃ which was higher than 133 ℃ and 106 ℃
compared to that of dye A and B, respectively. In addition, weight reduction was also not occurred at 200 ℃.
Therefore it can be concluded that the presence of a diacetylene linkage group provided readily significant
thermal stability due to its increased π orbital conjugation throughout the dye molecule.
The results of thermal stability for three fluorescence dyes were summarized in Table 4.
Table 4
Comparison of thermal stability between fluorescence dyes containing a diacetylene group (dye 1) and an
ethynyl group (dye A and B) [3,4].
Thermal stability (TGA)
Dye No.
Weight reduction (%, 200 ℃)
Decomposition temp. (℃)
Fluorescence dye A
Fluorescence dye B
Fluorescence dye 1
1.12
2.85
265
282
398
0
O
O
4 9
C H
O
N
O
4 9
C H
N
N
O
N
O
O
O
Fluorescence dye A [3]
Fluorescence dye B [4]

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3
.7. Solubility test
To produce excellent light-converting agricultural films, the synthesized fluorescence dyes must have good
solubility. There is a correlation with the light transmittance of agricultural films, which also require excellent
fluorescence. Both fluorescence dye 1 and dye 3 appeared to be higher solubility in four fluorescence dyes 1-4
which also satisfied the minimum solubility of 1.0 g/L in methyl ethyl ketone (MEK) required for agricultural
photocatalytic films. However, all dyes exerted very similar solubility ranged in 2.2 ~ 2.5 g/L in MEK (Table 5)
due to their similarity in structure.
Table 5
Results of the solubility of fluorescence dyes 1–4.
Dye No.
Solubility (g/L)
Fluorescence dye 1
Fluorescence dye 2
Fluorescence dye 3
Fluorescence dye 4
2.5
2.3
2.5
2.2
*Measured in MEK.
3
.8. PE Film test
All the properties of the synthesized fluorescence dyes 1-4 were to be suitable for the application to light-
conversion PE film. As fluorescence dye 1 exhibited narrow absorption and fluorescence spectra and greater
Stokes shift compared to other three dyes 2-4 which can contribute to a minimal self-quenching property
resulting in higher fluorescent efficiency. Therefore fluorescence dye 1 was applied to PE film after solubilizing
in MEK.
In general, most of agricultural films using inorganic dyes exhibit poor dispersibility and are opaque, resulting
in diminished light-conversion effects. However, the surface of PE film by applying the fluorescence dye 1, as
shown in Fig. 6, was not observed any aggregations and thus it was transparent.

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Fig. 6. Light-conversion film containing fluorescence dye 1.
Total transmittance and reflectance were measured in the ultraviolet region (300–400 nm), the photosynthetic
effective wavelength range (400–700 nm), and the near infrared region (NIR, 700–800 nm) can be expressed as
a minus value. Fig. 7 shows a comparison of the relative transmittance between florescent PE film coated by
blue fluorescence dye 1 and transparent PE film. The transmittance of the dye-coated film in the UV region was
1
5
7.3 % lower than that of the PE transparent film. In contrast, the transmittance of the dye-coated film at 400–
00 nm, which is most effective wavelength range for photosynthesis, observed by 142.8 % which was 46.8%
higher than that of the transparent film (96.0 %).
Fig. 7. Spectral transmittance of transparent PE film and fluorescent film (Fluorescence dye 1) measured by
using spectroradiometer under UV-Vis mixed light.
Table 6 shows the results of analyzing the PPFD increase or decrease ratio in the ultraviolet ray (300-400 nm)
and the photosynthetic effective wavelength (400-700 nm) of the light conversion film. PPFD in the ultraviolet
region was reduced by 20.5 % compared to the transparent PE film, however it was increased by 9.0 % in the
blue light region (400-500 nm) which was mainly due to the presence of blue fluorescence emitting dye.
Table 6
Results of PPFD of fluorescent film by light wavelength range compared to transparent PE film without a dye.

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UV
300-400 nm)
Blue
(400-500 nm)
Green
(500-600 nm)
Red
(600-700 nm)
dye
(
Fluorescence dye 1
-20.5 %
9.0 %
2.9 %
2.4 %
The rate of photosynthetic rate of photosynthetic rate of photosynthetic rate of lettuce in photoprotective film
and transparent PE film with blue fluorescent dye, Fluorescence dye 1, under sunlight condition was measured
and compared.
Fig. 8. Photosynthetic rate of lettuce grown under transparent PE film and fluorescent film (Fluorescence dye 1)
at 21 days after transplanting.
As it is shown in Fig. 8, photosynthetic rate of lettuce grown under fluorescent film was higher than that
under transparent film without a fluorescence dye. In fluorescent film treatment, photosynthetic rate at PPFD
-2
-1
4
75 mol·m ·s was 18.7 % higher than that in transparent film. The increase in photosynthetic rate can be
integrated throughout the day and accumulate carbohydrates, which can improve growth soon. Actually, growth
results were not shown in the paper but were good. In particular, fresh weight, dry weight and leaf area of
lettuce were significantly increased after three weeks of cultivation.
4
. Conclusions
In this study, the effects of diacetylene linkage on the fluorescence properties of naphthalimide-based dyes
were examined by designing dyes bearing alkyl and phenyl groups substituted at the N-position.

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The introduced a diacetylene linkage was found to retain a planarity by linking two naphthalimidyl rings
which was calculated by TD-DFT method where the electron density was mainly increased on the diacetylene
group in state of LUMO of the fluorescence dyes which indicated the extension of π-conjugations.
It was clearly observed that 4-substituted of 1,8-naphthalimide by a diacetylene group absorbed
bathochromically by 58 and 60 nm in comparison of corresponding 3-analogues due to the extended π orbitals.
In contrast, the molar extinction coefficients of the four fluorescence dyes were very similar regardless of the
type of N-substituent or the position of the diacetylene group.
Four fluorescence dyes showed high quantum yields ranged in 0.77 and 0.83 where dye 1 emitted at highest
quantum yield. The longest maximum emission wavelength was observed by dye 4 at 440 nm, whereas the dye
1
emitted at shortest wavelength of 414 nm. The Stokes shifts ranged in 54–100 nm where fluorescence dyes 1
and 2, substituted with diacetylene linkage group at the 3-position of 1,8-naphthalimide, exerted comparatively
higher Stokes shifts. Therefore all dyes 1-4 can be effective to the enhancement of photosynthesis as a blue light.
As it was expected, the extended ethynyl group (diacetylene group) for dye 1 resulted in extremely improved
thermal stability, thus the decomposition temperature was greatly increased to 398 ℃ which was higher than
1
33 ℃ and 106 ℃ compared to that of dye A and B those contain an ethynyl linkage group, respectively.
The transmittance of the dye-coated PE film using dye 1 at 400–500 nm was observed by 46.8% higher than
that of the transparent film which was in accordance with PPFD increase in 9.0 % in the blue light region (400-
00 nm) which was mainly due to the presence of blue fluorescence emitting dye. By using PE film coated by
5
dye 1, therefore, fresh weight, dry weight and leaf area of lettuce were significantly increased after three weeks
of cultivation.
Acknowledgements
This work was supported by the Technology Innovation Program funded by the Ministry of Trade, Industry
and Energy(KOREA).

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Highlights
ò
ò
ò
ò
Blue fluorescence dye emitting in the range of blue light region (400-450 nm)
Dye for enhancing the efficiency of the photo-synthesis when it is coated on PE film
Dyes containing a diacetylene linkage group between two naphthalimdyl rings
The quantum yield for synthesized dyes exerted 0.77 ~ 0.83 which can be very efficient to emit
a blue fluorescence