Synthesis and optical properties of 1-naphthol rhodamine for deep red laser dyes

Article abstract of DOI:10.1016/j.tet.2020.131420

In this study, we synthesized two asymmetric rhodamine laser dyes based on 1-naphthol (Dye-1 and Dye-2) and investigated their photophysical and laser performances. It was found that the fluorescence emission wavelengths of the two dyes are successfully extended to the deep red region. Compared with Dye-1, the esterification product Dye-2 displays a redshift of ～8 nm in the maximum absorption wavelength (λ_abs) and fluorescence emission wavelength (λ_em). In aprotic solvents, both λ_abs and λ_em of Dye-2 red-shift with the increase of solvent polarity, while its fluorescence quantum yield always decreases with the increase of solvent polarity, no matter in protic solvents or aprotic solvents. The results of laser tests indicated that both Dye-1 and Dye-2 have wide laser tuning range and strong laser conversion efficiency in the red region. The laser conversion efficiency is closely relative to the dye concentration and linearly increases with the increase of pump laser energy.

Full text of DOI:10.1016/j.tet.2020.131420

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Synthesis and optical properties of 1-naphthol rhodamine for deep red laser dyes
Wei Ming, Fan Chen, Xiaojie Hu, Zhizhong Zhang, Shunzhou Chang, Risheng Chen,
Baozhu Tian, Jinlong Zhang
PII:
S0040-4020(20)30587-1
https://doi.org/10.1016/j.tet.2020.131420
TET 131420
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 23 April 2020
Revised Date: 13 July 2020
Accepted Date: 17 July 2020
Please cite this article as: Ming W, Chen F, Hu X, Zhang Z, Chang S, Chen R, Tian B, Zhang J,
Synthesis and optical properties of 1-naphthol rhodamine for deep red laser dyes, Tetrahedron (2020),
doi: https://doi.org/10.1016/j.tet.2020.131420.
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Synthesis and optical properties of 1-naphthol
rhodamine for deep red laser dyes
Leave this area blank for abstract info.
Wei Ming,a Fan Chen,a Xiaojie Hu,a Zhizhong Zhang,b
Shunzhou Chang,b Risheng Chen,b Baozhu Tian*a and Jinlong Zhang*a
a Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Institute of
Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science &
Technology, 130 Meilong Road, Shanghai 200237, PR China
b Research Institute of Physical and Chemical Engineering of Nuclear Industry, 168 JinTang Road, Tianjin 300180, PR
China.

Tetrahedron
journal homepage: www.elsevier.com
Synthesis and optical properties of 1-naphthol rhodamine for deep red laser dyes
Wei Ming,a Fan Chen,a Xiaojie Hu,a Zhizhong Zhang,b Shunzhou Chang,b Risheng Chen,b Baozhu Tian a*
and Jinlong Zhang a*
a Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Institute of Fine Chemicals, School of Chemistry and
Molecular Engineering, East China University of Science & Technology, 130 Meilong Road, Shanghai 200237, PR China
b Research Institute of Physical and Chemical Engineering of Nuclear Industry, 168 JinTang Road, Tianjin 300180, PR China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
In this study, we synthesized two asymmetric rhodamine laser dyes based on 1-naphthol (Dye-1
and Dye-2) and investigated their photophysical and laser performances. It was found that the
fluorescence emission wavelengths of the two dyes are successfully extended to the deep red
region. Compared with Dye-1, the esterification product Dye-2 displays a redshift of ~8 nm in
the maximum absorption wavelength (λabs) and fluorescence emission wavelength (λem). In
aprotic solvents, both λabs and λem of Dye-2 red-shift with the increase of solvent polarity, while
its fluorescence quantum yield always decreases with the increase of solvent polarity, no matter
in protic solvents or aprotic solvents. The results of laser tests indicated that both Dye-1 and
Dye-2 have wide laser tuning range and strong laser conversion efficiency in the red region. The
laser conversion efficiency is closely relative to the dye concentration and linearly increases
with the increase of pump laser energy.
Available online
Keywords:
Asymmetric rhodamine dye
Laser dyes
Optical properties
Laser properties
2009 Elsevier Ltd. All rights reserved.
Corresponding author.
Tel & Fax: +86-21-64252062. E-mail: baozhutian@ecust.edu.cn; jlzhang@ecust.edu.cn
1

sulfonic acid to get Dye-1. Finally, Dye-2 was obtained by the
esterification reaction between Dye-1 and methanol.
1. Introduction
Organic fluorescent dyes are considered to the most
competent laser medium materials, due to their wide tunable
spectrum, high fluorescence quantum yield and wide frequency
band. In 1966, for the first time phthalocyanine dye was used as a
laser dye [1]. Later, rhodamine 6G dye was successfully applied
in the dye laser and realized the output of dye laser [2]. Up to
now, hundreds of laser dyes including coumarin [3, 4],
rhodamine [5-7], BODIPY [8-14], and cyanine dyes [15-19],
have been developed. Since the output wavelength range of these
laser dyes can cover the waveband from ultraviolet region of 300
nm to the near infrared region of 1200 nm, they also have a
promising prospect in the applications of biology, medicine,
physics and spectral analysis [20-27].
2.2. Absorption and fluorescence emission spectra
Figure 1. (a) Normalized absorption and (b) fluorescence
emission spectra of Dye-1 and Dye-2 in ethanol solution (1 ×
10‒5 mol/L). The fluorescence emission spectra were measured
by using the 530 nm line of Xenon lamp as the excitation source
(λex = 530 nm).
As a type of laser dyes, rhodamine laser dye has received
much attention owing to their high laser conversion efficiency
and laser stability. However, the absorption wavelengths of
traditional rhodamine laser dyes are generally shorter than 580
nm, and the fluorescence emission wavelengths are no longer
than 600 nm [28]. In some special cases, it is necessary to use the
red laser dyes with emission wavelengths longer than 600 nm.
For instance, in the medicine field, the short wavelength laser
with higher energy not only easily damages the biological tissue
but also cannot reach the deep tissue. Therefore, it is very
necessary to develop some rhodamine laser dyes in red (or deep
red) region. One way of obtaining red (or deep red) laser dyes is
to modify the structure of traditional rhodamine dyes. For
example, a useful strategy to obtain red (or deep red) laser dyes is
to increase the conjugated structure of rhodamine molecules.
Figure 1 shows the absorption and fluorescence emission
spectra of Dye-1 and Dye-2 in ethanol solution with a
concentration of 1.0 × 10−5 mol/L. As shown in Figure 1a, both
Dye-1 and Dye-2 have two absorption peaks in the range of
450‒600 nm, ascribed to the S0-S1 electron transition and
vibrational transition, respectively [29, 30]. In addition, both of
the two dyes possess another peak at 400 nm, which is from the
S0-S2 electron transition [29, 30]. The maximum absorption
wavelengths (λabs) of Dye-1 and Dye-2 in ethanol solution are
519 nm and 527 nm, respectively, while their maximum
fluorescence emission wavelength (λem) are 593 nm and 602 nm,
respectively (Figure 1b). As the dye was esterified from
carboxylic acid Dye-1 to methyl Dye-2, its λabs and λem are
red-shifted by 8 nm and 9 nm, respectively. Additionally, Dye-1
and Dye-2 display two strong fluorescence emission peaks at 646
nm and 655 nm, respectively.
Herein, two asymmetric rhodamine laser dyes Dye-1 and
Dye-2 containing only one nitrogen atom were synthesized by
replacing the aniline structure at one end of rhodamine molecule
with naphthalene ring. The results showed that both Dye-1 and
Dye-2 exhibited two fluorescence emission peaks, one of which
appeared in the deep red region (646 nm for Dye-1 and 655 nm
for Dye-2). On this basis, we further tested the laser emission
spectra and photo-stability of Dye-1 and Dye-2, and investigated
the effects of solvent type, concentration and pump power on
their laser performances.
2.3. Effect of solvents on the absorption and fluorescence spectra
2. Results/Discussion
2.1. Synthesis of Dye-1 and Dye-2
Figure 2. (a) Absorption and (b) fluorescence emission spectra of
Dye-2 in different solvents (1.0 × 10−5 mol/L). For all the
fluorescence measurements, λex is 530 nm.
Table 1. Absorption and fluorescence characteristics of Dye-2 in
different solvents.
Solvent
CH2Cl2
CHCl3
CH3CN
DMSO
C2H5OH
CH3OH
H2O
λabs
(nm)
526
εmax
(× 104 M‒1 cm‒1
1.58
λem
(nm)
599
a
Polarity
3.40
ΦF
)
0.52
0.36
0.22
0.10
0.49
0.41
0.19
4.40
6.20
7.20
4.30
6.60
10.20
528
529
532
527
527
527
1.18
0.85
0.35
1.48
1.34
0.70
601
612
619
606
605
610
Scheme1. Synthetic routes of Dye-1 and Dye-2
Scheme1 illustrates the synthetic routes of Dye-1 and Dye-2:
Firstly, the intermediate M2 was synthesized by the
Friedel-Crafts reaction between 8-hydroxyjulolidine (M-1) and
phthalic anhydride. Then, it reacted with 1-naphthol in methane
2

a
The values of fluorescence quantum yields (ΦF) were
redshifts from 600 nm to 611 nm. The variation of fluorescence
emission wavelength is probably relative to its existence state in
solvent: At high concentration, the dye molecules would
assemble into J-aggregates, leading to the red-shift of absorption
and fluorescence wavelengths [34, 35].
determined by using rhodamine 101 as standard (ΦF of
rhodamine 101 in ethanol is 0.96).
Figure 2 displays the absorption and fluorescence emission
spectra of Dye-2 in different solvents. Table 1 lists the solvent
polarity, λabs, molar extinction coefficient (εmax), λem, and
fluorescence quantum yield (ΦF). From Figure 2 and table 1, it
Table 2. The relationship between the maximum fluorescence
wavelengths (λem) of Dye-2 and its concentrations.
can be seen that in aprotic solvents (CH2Cl2, CHCl3, CH3CN and
DMSO), both λabs and λem of Dye-2 red-shift with the increase of
solvent polarity. However, both λabs and λem have no evident
Concentration
0.1
600
---
1.0
2.5
5.0
7.5
10.0
611
654
25
50
75
100
613
664
×10‒5 mol/L
difference in protic solvents (C2H5OH, CH3OH and H2O). No
Peak 1 (nm)
604
649
605
652
607
652
608
652
612
655
612
659
613
662
matter in protic solvents or aprotic solvents, all of the molar
extinction coefficient (εmax), fluorescence intensity, and
fluorescence quantum yield (ΦF) of Dye-2 gradually decrease
with the increase of solvent polarity. This is because the strong
interaction between the excited state molecule and the polar
solvent would increase the probability of non-radiative transition
[31].
Peak 2 (nm)
2.5. Laser performances
2.4. Effect of dye concentration on fluorescence characteristics
Figure 4. (a) Laser emission spectra of Dye-1 and Dye-2 in
ethanol (0.56×10‒3 mol/L). (b) Laser efficiencies of the second
peak of Dye-1 and Dye-2 in different concentrations of ethanol
solutions. The output energy of pump laser for the above tests
was fixed at 13 mJ.
Figure 4 a shows the laser emission spectra of Dye-1 and
Dye-2 in ethanol solution, in which X-axis is the detection
wavelength and the Y-axis is the corresponding laser conversion
efficiency. As can be seen, the laser tuning range of Dye-1 is
from 594 nm to 680 nm, and it has two peaks at 608 nm and 654
nm, corresponding to the maximum laser conversion efficiencies
of 11.6% and 12.4%, respectively. The laser tuning range of
Dye-2 is in the range of 600‒670 nm, and the maximum laser
efficiencies at 608 nm and 654 nm are 11.8% and 14.4%,
respectively. By comparing the fluorescence and laser emission
spectra of Dye-2, it can be found that the maximun laser emission
wavelength of Dye-2 is consistent with its maximun fluorescence
emission wavelength.
Figure 3. Fluorescence spectra of Dye-2 with different
concentrations in ethanol solution. The dye concentration is
C×10‒5 mol/L (C is the value of the inset). For all the
fluorescence measurements, λex is 530 nm.
To ivestigate the effect of dye concentration on its
fluorescence characteristics, we measured the fluorescence
emission spectra of Dye-2 in different concentrations of ethanol
solution (1.0×10‒6‒1.0×10‒3 mol/L). As shown in Figure 3, when
the dye concentration is 1.0×10‒6 mol/L, the fluorescence
spectrum of Dye-2 consists of a strong peak at 600 nm and a
weak shoulder peak at ~ 650 nm. With the increase of dye
concentration, the intensity of the second peak in the range of
648‒665 nm increases gradually at the beginning, and then
reaches a maximum when the dye concentration is 7.5 ×10‒6
mol/L. According to the previous reports [32, 33], the intensity
increase of the second peak should be ascribed to the increase of
stacked dye aggregates. When the dye concentration is higher
than 7.5 ×10‒6 mol/L, the intensity of the second peak begins to
decrease with further increasing the dye concentration, which is
because the high dye concentration would result in
fluorescence quenching. When the concentration of dye reaches
1.0×10-3 mol/L, the fluorescence seems to be completely
quenched. We further analyzed the influence of dye
concentration on its maximum fluorescence wavelength (λem). As
summarized in table 2, the maximum fluorescence wavelengths
of peak 1 and peak 2 gradually red-shift with increasing the dye
concentration. For instance, as the dye concentration increases
from1.0×10‒6 mol/L to 1.0×10‒4 mol/L, the corresponding λem
Since the laser conversion efficiency of a laser dye is closely
relative to its concentration in solvent [9, 36], here we measured
the laser conversion efficiencies of Dye-1 and Dye-2 at 654 nm
and 660 nm, respectively. As shown in Figure 4 b, when the dye
concentration is less than 0.2×10-3 mol/L, no laser is generated,
due to the self-absorption of dye to light. When the dye
concentration is increased to 0.56×10‒3 mol/L, Dye-1 and Dye-2
have the maximum laser conversion efficiencies of 11.8% and
14.4%, respectively. However, when the dye concentration is
higher than 0.56×10‒3 mol/L, the laser conversion efficiency
begins to decrease with the increase of dye concentration, which
is due to the reabsorption/reemission processes as well as the
generation of non-fluorescent aggregates [37, 38].
To study the influence of pump laser energy on the laser
conversion efficiency, we tested the laser conversion efficiencies
of Dye-2 at 660 nm by tuning the pump laser energy from 1 mJ
to 20 mJ. When the pump laser energy is lower than 4 mJ, no
laser emission can be detected, indicating that the threshold of
Dye-2 for laser emission is about 4 mJ. According to the
3

principle of laser [38], during laser production, energy gain and
loss take place simultaneously in the optical cavity. The threshold
of laser refers to the condition when the gain energy is equal to
the loss energy. Only when the energy of pump laser is higher
than the threshold, can the laser emit. As shown in Figure 5, the
laser conversion efficiency increases linearly with the increase of
pump laser energy. The laser conversion efficiency (Y) can be
estimated by the equation Y = 0.3209x + 0.1097 (x is pump laser
energy).
Since the photo-stability of laser dye is very important to a
laser dye for its practical application, here we investigated the
variation of output laser efficiency as a function of pump laser
irradiation time. As can be seen in Figure 6, the decline rate of
the output laser efficiency of Dye-2 is much slower than that of
Dye-1. The half-lives of output laser efficiency for Dye-1 and
Dye-2 are 120 min and 320 min, respectively. The above results
mean that the photo-stability of Dye-2 is much higher than that of
Dye-1. The huge difference of Dye-1 and Dye-2 in
photo-stability can be interpreted by their difference in
electrophilicity index (ω). As a kind of global reactivity
descriptor similar to the chemical hardness and chemical
potential, ω has been used to evaluate the the photostability of
some fluorescent dyes [39]. As the increase of ω, the molecule
would become more stable, leading to better light fastness and
photo-stability [40, 41]. The electrophilicity index (ω) of two
dyes were calculated by Eq. (1):
ω = μ2/2η
(1)
Where chemical potential (μ) and chemical hardness (η) were
determined using the energies of frontier molecular orbitals
E
HOMO , ELUMO and given by Eqs. (2-3):
μ = -1/2 (EHOMO + ELUMO
η = 1/2 (ELUMO - EHOMO
)
(2)
(3)
)
Figure 5. Variation of Dye-2 laser efficiency as a function of
laser pumped energy. The dye concentration in ethanol is 0.56 ×
10‒3 mol/L and the detection wavelength is 660 nm.
The electrophilicity indexes of Dye-1 and Dye-2 in different
solvents (dichloromethane, DMSO, propanol, ethanol and
methanol) were calculated at B3LYP/6-311G(d) level. As shown
in Table 3, the ω values of Dye-2 in different solvents are higher
than those of Dye-1, implying that Dye-2 has higher
photo-stability than Dye-1.
Figure 7. (a) Laser conversion efficiency and (b) Laser stability
of Dye-1 and Dye-2 in different solvents (0.56×10‒3 mol/L). The
detection wavelengths for Dye-1 and Dye-2 are 645 nm and 660
nm, respectively. The output power of pump laser is 13 mJ.
The laser properties of a laser dye is relative to not only its
structure but also the property of the used solvent. Herein, we
further investigated the influences of different solvents
(dichloromethane, DMSO, propanol, ethanol, methanol and
Figure 6. Photo-stability of Dye-1 and Dye-2 measured in
ethanol solution (0.56×10‒3 mol/L) under pump laser irradiation.
The output energy of pump laser was fixed at 13 mJ.
Table3. The electrophilicity indexes (ω) of Dye-1 and Dye-2 in different solvents.
Dye-1
μ
Dye-2
solvents
ELUMO
(eV)
EHOMO
(eV)
η
ω
ELUMO
(eV)
EHOMO
(eV)
μ
η
ω
(eV)
(eV)
(eV)
(eV)
(eV)
(eV)
CH2Cl2
DMSO
PrOH
-3.4450
-3.2436
-3.3062
-3.2871
-3.2654
-6.3022
-6.0845
-6.1498
-6.1307
-6.1062
4.8736
4.6641
4.7280
4.7089
4.6858
1.4286
1.4205
1.4218
1.4218
1.4204
8.3130
7.6572
7.8612
7.7978
7.7291
-3.4695
-3.2545
-3.3198
-3.2980
-3.2763
-6.3103
-6.0899
-6.1579
-6.1362
-6.1144
4.8899
4.6722
4.7389
4.7171
4.6954
1.4204
1.4177
1.4191
1.4191
1.4191
8.4170
7.6989
7.9126
7.8398
7.7680
C2H5OH
CH3OH
4

water) on the laser conversion efficiency and laser stability of
Dye-1 and Dye-2. From Figure 7 a, it can be seen that the laser
conversion efficiencies of Dye-2 are very different in the above
solvents. For instance, the laser conversion efficiencies of Dye-1
and Dye-2 in dichloromethane are 11.8% and 15.0%,
respectively, but they are less than 10% in DMSO. Strangely,
both Dye-1 and Dye-2 almost have no laser emission in water,
which is probably due to their very low solubility in water.
Figure 7 b shows the laser stability of Dye-1 and Dye-2 in
different solvents. In a same solvent, the laser stability of Dye-2
is higher than that of Dye-1. The laser stability of Dye-1 and
Dye-2 varies in different solvents, which may be relative to the
difference of solvent characteristics such as polarity, viscosity,
oxygen content, dissolving ability to dye, and so on [42].
The laser performances of Dye-1 and Dye-2 were measured
by a home-made laser testing system, in which a 532 nm
Nd:YAG pulsed laser with a frequency of 10 Hz and pulse
duration time of 8 ns was employed as the excitation light source.
Before the measurements, the solid-state laser was lightened for
30 min to make the outputted laser become stable. For each
measurement, 1.5 mL dye solution was injected into the cuvette
fixed in the light path and excited by the Nd:YAG pulsed laser.
At different output wavelengths, the output powers of dye
solution were measured with an optical power meter and the
output powers were recorded at the intervals of 2 nm.
4.3. Calculation details
The optimization and frequency calculations of Dye 1 and Dye
2
were performed by using the DFT-B3LYP method
We further tested the laser performances of the commercial
dye rhodamine B (Figure S9 and Figure S10) and compared them
with those of Dye 1 and Dye 2 (Table S1). It can been that the
laser emission wavelength and laser tuning range of these two
dyes are larger than rhodamine B, but their laser conversion
efficiency and laser stability is lower that of rhodamine B.
implemented with the 6-31G(d) basis set. The results confirm
that there is no imaginary frequency in the optimized geometry,
thus, the molecules are in the minimum energy state. The
calculations of the frontier molecular orbitals (HOMO: highest
occupied molecular orbital and LUMO: lowest unoccupied
molecular orbital) were fulfilled at DFT-B3LYP/6-311G(d) level.
The chemical potential (μ), chemical hardness (η) were
calculated using the energies of frontier molecular orbitals, which
are further used for the calculation of electrophilicity index (ω) of
the two dyes. In addition, the polarizable continuum model
(PCM) was adopted as a solvation model as implemented in
Gaussian 09 software to simulate the solvent effects. All of the
calculations have been carried out with Gaussian 09.
GaussView05 was used for visualization of the results from the
output file.
3. Conclusion
In this work, for the first time we synthesized two asymmetric
rhodamine laser dyes based on 1-naphthol (Dye-1 and Dye-2)
and systematically investigated their light absorption,
fluorescence emission, and laser performances. It was found that
the fluorescence emission wavelengths of Dye-1 and Dye-2 were
successfully extended to the deep red region (646 nm for Dye-1
and 655 nm for Dye-2). Due to the effect of esterification, the
absorption and fluorescence emission wavelengths of Dye-2
red-shift ~8 nm compared with those of Dye-1. In aprotic
solvents, both λabs and λem of Dye-2 red-shift with the increase of
solvent polarity, but they have no evident difference in protic
solvents. No matter in protic solvents or aprotic solvents, the
fluorescence quantum yield of Dye-2 gradually decreases with
the increase of solvent polarity. The results of laser tests indicate
that both Dye-1 and Dye-2 have a wide laser tuning range and a
strong laser conversion efficiency in the red region. The laser
conversion efficiency is closely relative to the dye concentration
and the optimized concentration of Dye-1 and Dye-2 in ethanol is
0.56×10‒3 mol/L. The laser conversion efficiency increases
linearly with the increase of pump laser energy. Since the effect
of esterification, Dye-2 exhibits much higher laser stability than
Dye-1. Moreover, it was found that the solvents have a vital
influence on both the laser conversion efficiency and laser
stability. We believe that this study provides a reference for the
synthesis and application of deep red laser with high efficiency
and photo-stability.
2-[(2,3,6,7-tetrahydro-10-hydroxy-1H,5H-benzo[ij]quinolizin-
9-yl)carbonyl] (M-2)
Under argon protection, 1.89 g (10 mmol) 8-hydroxyjulolidine
(M-1) and 1.60 g (10.8 mmol) phthalic anhydride were added to
100 mL toluene. Then, the mixture was refluxed under 120 °C
for 24 h. After the mixture was cooled to room temperature, the
precipitate was filtered and washed with water. Finally, the crude
product was purified by column chromatography using
dichloromethane/methanol = 100/2 (v/v) as the eluent to give a
yellow crystal (M-2) (2.35g, 69.7%). 1H NMR (400 MHz,
CDCl3, ppm): δ = 12.83 (s, 1H), 8.09 (d, J = 8.8 Hz, 1H), 7.60 (t,
J = 7.5 Hz, 1H), 7.50 (t, J = 7.5 Hz, 1H), 7.33 (d, J = 7.6 Hz, 1H),
6.45 (s, 1H), 3.24 (q, J = 7.2 Hz, 4H), 2.74 (t, J = 6.4 Hz, 2H),
2.47 (t, J = 6.1 Hz, 2H), 1.95 (m, 2H), 1.85 (m, 2H).(Figure S1)
13C NMR (400 MHz, CDCl3, ppm): δ = 197.77, 170.56, 160.75,
149.34, 141.42, 132.56, 131.11, 130.32, 128.96, 128.26, 127.88,
112.79, 109.02, 105.54, 50.17, 49.79, 27.27, 21.63, 20.66, 19.89.
(Figure S2)
4. Experimental section
Synthesis of Dye-1
4.1. Instruments and test methods
Under argon protection, 337 mg (1.0 mmol) M-2 and 144 mg
(1.0mmol) 1-naphthol were added into a 100 mL round-bottom
flask containing 10 mL methane sulfonic acid. After stirred
overnight at 70°C, the reaction mixture was poured into a
saturated sodium perchlorate solution and stirred at 80°C for 1 h.
Then, the resulting precipitate was filtered, dried in vacuum, and
purified by column chromatography. Finally, the product was
recrystallized in ethanol to give a dark brown product Dye-1.
Yield: 380 mg, 70.0%. 1H NMR (400 MHz, DMSO-d6): δ = 8.72
(d, J = 7.9 Hz, 1H), 8.31 (d, J = 7.6 Hz, 1H), 8.12 (d, J = 7.0 Hz,
1H), 7.90 (d, J = 15.4, 7.6 Hz, 5H), 7.49 (d, J = 7.2 Hz, 1H), 7.04
(d, J = 8.8 Hz, 1H), 6.91 (s, 1H), 3.68 (d, J = 16.6 Hz, 4H), 3.17
(t, J = 6.0 Hz, 2H), 2.78 (m, 2H), 2.10 (m, 2H), 1.93 (m, 2H).
(Figure S3) 13C NMR (101 MHz, DMSO): δ = 166.40, 160.23,
1HNMR and 13CNMR spectra were recorded on a Bruker
AM400 NMR spectrometer, using TMS as the internal standard.
The mass spectra of the samples were determined by an Agilent
G2577A electron bombardment mass spectrometer. UV‒Vis
absorption spectra were measured with a Shimadzu UV-2450
spectrophotometer at room temperature. The fluorescence spectra
and fluorescence quantum yield were determined on an
Edinburgh Instruments FLS 980 fluorescence spectrophotometer
and the 530 nm line of Xenon lamp was used as the excitation
source (λex = 530 nm).
4.2. Laser performance measurement
5

[8] J. J. Banuelos, BODIPY dye, the most versatile fluorophore ever, Chem.
Record.16 (2016) 335‒348.
149.95, 139.23, 135.36, 133.19, 130.88, 130.47, 130.00, 128.41,
125.98, 125.86, 122.67, 122.55, 122.22, 119.99, 117.99, 117.16,
114.45, 105.57, 105.28, 100.51, 98.94, 97.16, 51.33, 50.83,
26.75, 19.69, 19.12, 18.78. (Figure S4) HRMS (ESI): Calcd. For
[C30H24NO3]+ 446.1751; found 446.1761. (Figure S5)
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Synthesis of Dye-2
1.00 g (2.17 mmol) Dye-1, 3 mL concentrated sulfuric acid,
and 100 mL absolute methanol were added into a 250 mL round
bottom bottle with condensing tube and drying tube.
Subsequently, the mixture solution was refluxed for 36 h. When
the reaction solution was cooled to room temperature, it was
dropped into a 10% NaClO4 solution to obtain precipitation.
Then, the crude product was purified by SiO2 column
chromatography using the mixed solution of dichloromethane
and methanol with a volume ratio of 100/4. Finally, the product
was recrystallized in ethanol to obtain the target product Dye-2.
Yield: 940 mg, 92.2%. 1H NMR (400 MHz, DMSO-d6); δ = 8.77
(m, 1H), 8.35 (d, J = 7.9 Hz, 1H), 8.14 (d, J = 6.8 Hz, 1H), 8.00
(d, J = 7.5 Hz, 1H), 7.97 (s, 1H), 7.92 (s, 1H), 7.91 (d, J = 3.9 Hz,
2H), 7.88 (s, 1H), 7.55 (d, J = 7.5 Hz, 1H), 7.03 (d, J = 8.9 Hz,
1H), 6.94 (s, 1H), 3.75 (t, J = 5.3 Hz, 2H), 3.70 (t, J = 5.4 Hz,
2H), 3.57 (s, 3H), 3.22 (t, J = 6.1 Hz, 2H), 2.78 (m, 2H), 2.11
(dd, J = 11.2, 5.3 Hz, 2H), 1.92 (m, 2H). (Figure S6) 13C NMR
(101 MHz, DMSO): δ = 165.04, 156.14, 154.05, 152.12, 150.24,
135.50, 133.67, 133.58, 131.14, 130.99, 130.65, 130.59, 129.57,
129.14, 128.54, 128.50, 126.10, 125.98, 122.79, 122.32, 122.16,
118.27, 117.30, 105.57, 52.40, 51.48, 51.02, 26.72, 19.58, 19.03,
18.66. (Figure S7) HRMS (ESI): Calcd. For [C31H26NO3]+
460.1907; found 460.1919. (Figure S8)
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Acknowledgment
This work has been supported by the Research Fund of
Science and Technology on Particle Transport and Separation
Laboratory, the Shanghai Municipal Science and Technology
Major Project (2018SHZDZX03), and the Program of
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Supplementary data (Figures S1-S10 and Table S1) to this article
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Highlights
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Two rhodamine laser dyes based on 1-naphthol were synthesized for the first time.
Both of the two dyes display a wide laser tuning range.
Both of the two dyes exhibit a strong laser conversion efficiency in the deep red region.
Solvents have a vital influence on both the laser conversion efficiency and laser stability.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Jinlong Zhang