Configuration of white light emission by courmarin and naphthalimide

Article abstract of DOI:10.1080/15421406.2018.1452861

In this article, a dye with naphthalimide and coumarin was configured and was fully characterized. Its emission behavior was investigated in medium polar solvent. The emission behavior shows that there is no obvious energy transfer between naphthalimide and coumarin. Therefore, both the emission of naphthalimide and coumarin exhibit in the emission spectra, including blue and yellow part. The emission in film and solid shows different character. In film, single emission peak was observed. However, the solid emission covered a broad scope, including blue and yellow integrant. All the emission color was indicated by (Commission Internationale de L'Eclairage) CIE coordinates. The CIE coordinate of solid emission (0.29, 0.33) is approaching the ideal white light.

Full text of DOI:10.1080/15421406.2018.1452861

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Configuration of white light emission by courmarin
and naphthalimide
Xiaochuan Li, Yujie Han, Kyeongsu Min & Young-A Son
To cite this article: Xiaochuan Li, Yujie Han, Kyeongsu Min & Young-A Son (2018) Configuration
of white light emission by courmarin and naphthalimide, Molecular Crystals and Liquid Crystals,
660:1, 10-16, DOI: 10.1080/15421406.2018.1452861
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

https://doi.org/./..
Configuration of white light emission by courmarin and
naphthalimide
a
a
b
b
Xiaochuan Li , Yujie Han , Kyeongsu Min , and Young-A Son
aHenan Key Laboratory of Organic Functional Molecule and Drug Innovation, Collaborative Inovation Center of
Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and
Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University,
b
Xianxiang, Henan, P. R. China; BK, Department of Advanced Organic Materials Engineering, Chungnam
National University, Daejeon, South Korea
ABSTRACT
KEYWORDS
In this article, a dye with naphthalimide and coumarin was configured
and was fully characterized. Its emission behavior was investigated in
medium polar solvent. The emission behavior shows that there is no
obvious energy transfer between naphthalimide and coumarin. There-
fore, both the emission of naphthalimide and coumarin exhibit in the
emission spectra, including blue and yellow part. The emission in film
and solid shows different character. In film, single emission peak was
observed. However, the solid emission covered a broad scope, including
blue and yellow integrant. All the emission color was indicated by (Com-
mission Internationale de L’Eclairage) CIE coordinates. The CIE coordi-
nate of solid emission (0.29, 0.33) is approaching the ideal white light.
Coumarin; CIE; emission;
naphthalimide; white light
Introduction
Technology development significantly advances the quality of our life, which is based on the
development of various special function materials. Additionally, higher requirements have
been offered by the military service and special industry. Among various new types of materi-
als, emissive molecules fascinate the physicists and chemists. Intensive effort and tremendous
progress have been made toward this end and the spectra of fluorescent molecules overlap
almost the whole visible region from blue to deep-red. Currently, typical emission molecules,
such as coumarins, naphthalimide, bisindolylmalimide, perylenediimides, and rhodamine,
have been systematically engineered toward various purposes [1–11]. A direct application is
in signal translation and logic input/output. Therefore, robust fluorescent dyes with higher
are desired for chemists, physicists and biochemists [12–15]. In addition, the fluorescent dyes
are expected to have high quantum yield in solution and/or solid and structurally controllable
emission wavelength. However, electronic excitation energy transfer (EET) is the unavoid ele-
ment in configuration of multichromophoric systems [16–20]. Distance dependent is the typi-
cal character of EET mechanism; include Förster-type “Coulombic” interactions, Dexter-type
CONTACT Prof. Young-A Son
National University,  Daehakro, Yuseong, Daejeon , South Korea; Prof. Xiaochuan Li
yason@cnu.ac.kr
Department of Advanced Organic Materials Engineering, Chungnam
lixiaochuan@htu.cn School
of Chemistry and Chemical Engineering, Henan Normal University, East Jianshe Rd. , Xinxiang, Henan , China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©
 Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
exchange interactions, and other contributions to short-range coupling due to orbital overlap
effects [21]. Fluorescence resonance energy transfer (FRET) is one of the typical EET models,
which has succeeded applied in bio-sensors. In FRET cassette, spectral overlap between the
donor emission and the acceptor absorptions is the key factor to efficiency of ET, which also
set a threshold for the selection of emitters [22]. However, another ET mechanism (through-
bond energy transfer, TBET) avoids the requirement of spectral overlap as that of the FRET. It
affords the possibility of configuring multi-fluorescence-emitting single molecules by choos-
ing suitable dye pairs [23, 24].
In this contribution, naphthalimide, green-yellow emitters, and coumarin, blue emitters
were incorporated together. The two chromophores were linked by an N-containing bridge,
which, to an extent, influence the energy transfer between naphthalimide and coumarin. By
introduction alkyl substitution to the molecular framework, a mixed blue and yellow fluores-
cence could emit from this single molecule and obtain the white-light source. Compared to
the multicomponent white-light sources, direct white light from a single component entity
may be expected to avoid the drawbacks of combined emitters, thus giving rise to white light
of higher quality. Therefore, configuring new molecular system that can emit white light is
clearly of interest and importance.
Experimental
General procedures and materials
The solvents used in the reaction were carefully dried according to the standard procedure
˚
and stored over 4 A molecular sieve. All the reagent-grade chemicals were purchased from
Sigma-Aldrich CO. LLC. (South Korea) and used without further purification. Melting points
were determined on a Mel-Temp IA9200 digital melting point apparatus in a glass capillary
®
and were uncorrected. All synthesized compounds were routinely characterized by TLC and
H NMR. TLC was performed on aluminum-backed silica gel plates (Merck DC. Alufolien
1
Kieselgel 60 F254).
NMR spectroscopy and high resolution mass spectra (HRMS)
Nuclear magnetic resonance (NMR) spectra were recorded on a Brucker AM-400 spectrom-
eter operating at frequencies of 400 MHz for proton in CDCl . Proton chemical shifts (δ)
3
are relative to tetramethylsilane (TMS, δ = 0) as internal standard and expressed in parts per
million. Spin multiplicities are given as s (singlet), d (doublet), t (triplet), and m (multiplet)
as well as b (broad). Coupling constants (J) are given in Hertz. The mass spectra measured
on a LC-MS (Waters UPLC-TQD) mass spectrometer. High resolution mass spectra (HRMS)
were measured on a Brucker micrOTOF II Focus instrument.
UV-Vis and emission spectra
The absorption spectra were measured with a PERSEE TU-1900 and an Agilent 8453 spec-
trophotometer. Emission spectra were measured with Shimadzu RF-5301PC fluorescence
spectrophotometer. The solvents used in photochemical measurement were spectroscopic
grade and were purified by distillation. The stock solution of compounds (2 × 10−3 M) was

1
2
X. LI ET AL.
Scheme . Synthesis of BNC.
prepared and a fixed amount of these concentrated solutions were added to each experimental
solution. All the experiments were done repeatedly, and reproducible results were obtained.
Prior to the spectroscopic measurements, solutions were deoxygenated by bubbling nitrogen
through them.
Synthesis
The total synthesis of C -alkyl substituted naphthalimide-coumarin (BNC) is shown in
4
Scheme 1. The synthesis started from 4-Br-1,8-naphthalimide (1) and N, N-diethyl salicy-
laldehyde (4), which are commercially available. 1 can be easily imidication when treated
with n-octyl amine in refluxed ethanol [25, 26]. Subsequent substitution by nitrogen atom of
hydrazine hydrate yielded N-allkyl-4-hydrazinyl-1,8-naphthalimide (3) [26]. Then it was con-
densed with 3-acetyl-7-diethylamino-coumarin (5), which was synthesized as described by
known procedure, yielding the target C -alkyl substituted naphthalimide-coumarin (BNC),
4
a bright powder.
C4-alkyl substituted naphthalimide-coumarin (BNC)
N-allkyl-4-hydrazinyl-1,8-naphthalimide (3, 169.5 mg, 0.50 mmol) was charged into a dry
flask with anhydrous ethanol (80 mL). Then, 3-acetyl-7-diethylamino-coumarin (5, 149.6 mg,
0
.50 mmol) was added. The mixture was heated to reflux for 10 h. After the starting materials
were fully reacted, as confirmed by TLC, the solvent was evaporated in vacuum. The residue
was loaded to the column (silica gel 200–300 mesh) and eluted by mixed dichloromethane
and ethyl acetate (50:1). Bright orange powder was obtained (226 mg, 84%).
Mp: 213–216°C; 1H NMR (400 MHz, CDCl ): δ 8.68 (s, 1H), 8.58 (d, J = 7.2 Hz, 1H), 8.51
3
(
7
4
d, J = 8.4 Hz, 1H), 8.22 (d, J = 8.0 Hz, 1H), 8.05 (s, 1H), 7.77 (d, J = 8.4 Hz, 1H), 7.68 (t, J =
.8 Hz, 1H), 7.38 (d, J = 8.8 Hz, 1H), 6.65 (d, J = 8.0 Hz, 1H), 6.50 (s, 1H), 3.36 (q, J = 5.6 Hz,
H), 3.13 (t, J = 7.2 Hz, 2H), 2.13 (s, 3H), 1.53–1.61 (2H, m), 1.31–1.35 (2H, m), 0.93 (3H,
1
3
t, J = 6.8 Hz). C NMR (100 MHz, CDCl ): δ 165.3, 162.8, 160.4, 156.0, 144.6, 135.0, 131.6,
3
1
1
31.4, 130.5, 129.9, 126.9, 125.8, 123.7, 119.8, 117.6, 113.1, 108.4, 96.1, 44.3, 41.4, 26.0, 14.7,
2.9. HRMS (ESI): Calcd. for C H N O [M+H ] 524.2424, found 524.2430.
+
31
32
4
4

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
13
0
0
0
0
0
.8
.6
.4
.2
.0
toluene
chloroform
dioxane
THF
3
00 350 400 450 500 550 600 650
Wavelength (nm)
Figure . Absorption spectra of BNC in selected solvents (. × − M).
Result and discussion
The absorption behavior of BNC was investigated in selected organic solvents, such as toluene,
chloroform, dioxane, and THF, because influence of the polar environment is more approach
to the practical environment. The butyl substitution at naphthalimide provides appropriate
solubility in most organic solvents. In contrast to its analogues, BNC also shows robust stabil-
ity toward natural light, which was demonstrated by exposure to room light for several months
with no color fading. Figure 1 shows the absorption contour of BNC in the selected solvents.
In the selected medium polarity solvents, the absorption spectra are of similar shape with each
other, indicating less solvatochromism. Obviously, the longest absorption band were located
around 350–500 nm, with absorption peak around 450 nm and shoulder peak 400 nm. The
maximum absorption at longer wavelength side could be ascribe to S →S transition with
0
1
the bands on the high- and low-energy side corresponding to 0–1 and 0–0 vibration transi-
tion, respectively. According to the absorption range, it can be matched with the commer-
cially available blue OLED (organic light-emitting diode) chip. BNC could absorb the UV
light emitted by blue OLED chip with better efficiency.
The emission behavior is also investigated in the above selected solvents. Without the
influence of strong polar environment, the emission band of BNC exhibits broad emission
character, which includes blue (465 nm) and yellow (550 nm) two emission colors (Fig. 2). The
mixture of blue and yellowish color could give an approximately white light. The two emission
bands correspond to the typical emission region of coumarin (460 nm) and naphthalimide
(548 nm). It is likely that the two fluorophores are simply mixed together, which indicates the
800
600
400
200
0
Chloroform
dioxane
THF
Toluene
450
500
550
600
650
700
Wavelength / nm
Figure . Emission spectra of BNC in selected solvents (. × − M).

14
X. LI ET AL.
Figure . CIE chromaticity diagram of the emissions of BNC in solutions.
energy transfer in the excited state is not sufficient. Therefore, appropriate molecular struc-
ture, together with the controllable intramolecular energy transfer, could realize the double
emission as we designed for white light or approximate white light. The emission quantum
yield in the selected solvents are determined to be 0.40 (chloroform), 0.41 (dioxane), 0.36
(
THF), and 0.35 (toluene) with reference to quinine sulfate (ꢀ = 0.55, 0.1N H SO ) as a
2
4
standard. The detailed emission color of BNC was demonstrated by CIE coordinates (Fig. 3).
Obviously, CIE coordinates of the emission color do not distribute closely to the ideal white
light coordinate (0.33, 0.33). It indicates that the proportion of blue part accounts higher
in contrast to the yellow part. All the coordinates are corresponding to their emission in
solution.
Due to the alkyl substitution to naphthalimide, it inhibits the molecules to form tight
packing modes, avoiding the nonradiation energy loss. Therefore, BNC exhibits highly emis-
sive character in film and solid state (Fig. 4). In film state, a single emission character was
observed, which is different to the solution state. The CIE coordinate in film state also moves
to the yellow-green region, indicating the naphthalimide emission character. It may relate
with the polar environment of the polymer matrix. In addition, the polymer matrix could
efficiently isolate the dye molecules in polymer lattices. It is similar to that in solution that the
dye molecules were excited by absorbing energy via UV irradiation and transfer part of the
Figure . Emission spectra of BNC in film at  wt.% in polycarbonate. Inset: CIE coordinates of BNC in film.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
15
Figure . Emission spectra of BNC in film at  wt.% in polycarbonate. Inset: CIE coordinates of BNC in solid.
energy to environment (solution or polymer). Obviously, the energy loss from dye molecules
to polymer is higher than that from dye molecules to solvent molecules. Figure 5 shows the
emission and CIE coordinate of BNC in solid state. In solid state, the effects of C -alkyl sub-
4
stitution, together with other unknown factor, inhibited the forming of over-tight packing
efficiently between molecules and maintain the highly emissive character in solid powder. It
is different from the energy loss of excited dye molecules in film (amorphous state) that the
interaction between dye molecules were enhanced, which also enhanced the energy loss of
excited dye molecules to lower energy state. Particularly, there is no efficient energy transfer
between coumarin and naphthalimide and the emission band range from blue (420 nm) to
red (650 nm). Among the emission region, the blue (460 nm) part and yellow part (560 nm)
configuring the white light. However, the main emission of BNC in solid contains two emis-
sion peak 425 and 528 nm. It varies slightly away from the idea white light integrant (460 and
5
60 nm). Therefore, the emission of BNC in solid was not ideal white light. The CIE coordi-
nate (0.29, 0.33) accurately shows that the emission should be a blue-white emission definitely.
Also, it leaves a scope in structure modification for configuring ideal white light.
Conclusions
In summary, a newly designed dye molecule with two fluorophores was synthesized by incor-
porating coumarin and naphthalimide. It was fully characterized. The emission behavior
shows there is no significant energy transfer between coumarin and naphthalimide. Therefore,
BNC exhibits broad emission scope covering the blue and yellow region. The emission color
in solution is approaching the ideal white light. In film state, the emission behavior is largely
different from that of the solution, showing naphthalimide single emission character. In solid
state, the C -alkyl substitution inhibits the over-tight packing and maintains its highly solid
4
emissive character. The CIE coordinate of solid emission shows blue-white color character.
Further structural modification based on BNC is still underway toward idea white light.
Funding
This work was supported by the National Natural Science Foundation of China (21772034), and
the Program for Innovative Research Team in University of Henan Province (15IRTSTHN003). This
study was supported by the Basic Science Research Pro-gram through the National Research Founda-
tion of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant No. NRF-
2
017R1E1A1A01074266).

1
6
X. LI ET AL.
ORCID
Xiaochuan Li http://orcid.org/0000-0002-6903-9574
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