Synthesis and properties of seminaphthorhodafluor red laser dyes

Article abstract of DOI:10.1007/s11164-019-04076-9

In the present work, we synthesized two seminaphthorhodafluor red laser dyes SNARF-X1 and SNARF-X2 and investigated their photo-physical properties in different solvents and the laser properties in ethanol. It was found that the wavelengths of absorption and fluorescence emission spectra are not very sensitive to the solvent polarity, while the fluorescence intensities decrease with the increase in solvent polarity. SNARF-X1 and SNARF-X2 not only emit tunable red laser (590–670?nm for SNARF-X1 and 600–680?nm for SNARF-X2) but also show high laser conversion efficiency. The above two dyes also show high photo-stability under 532?nm ND:YAG laser irradiation. In this regard, the half-lives of laser efficiency for SNARF-X1 and SNARF-X2 are 7?h and 6?h, respectively.

Full text of DOI:10.1007/s11164-019-04076-9

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-04076-9
Synthesis and properties of seminaphthorhodaꢀuor red
laser dyes
1
1
2
2
Wei Ming · Xiaojie Hu · Zhizhong Zhang · Shunzhou Chang ·
2
1
1
Risheng Chen · Baozhu Tian · Jinlong Zhang
Received: 26 November 2019 / Accepted: 30 December 2019
©
Springer Nature B.V. 2020
Abstract
In the present work, we synthesized two seminaphthorhodafuor red laser dyes
SNARF-X1 and SNARF-X2 and investigated their photo-physical properties in diꢀ-
ꢀ
erent solvents and the laser properties in ethanol. It was ꢀound that the wavelengths
oꢀ absorption and fuorescence emission spectra are not very sensitive to the sol-
vent polarity, while the fuorescence intensities decrease with the increase in solvent
polarity. SNARF-X1 and SNARF-X2 not only emit tunable red laser (590–670 nm
ꢀor SNARF-X1 and 600–680 nm ꢀor SNARF-X2) but also show high laser conver-
sion eꢁciency. The above two dyes also show high photo-stability under 532 nm
ND:YAG laser irradiation. In this regard, the halꢀ-lives oꢀ laser eꢁciency ꢀor
SNARF-X1 and SNARF-X2 are 7 h and 6 h, respectively.
Keywords Seminaphthorhodafuor · Laser dye · Photo-physical properties · Laser
properties
Electronic supplementary material The online version oꢀ this article (https://doi.org/10.1007/s1116
4
-019-04076-9) contains supplementary material, which is available to authorized users.
*
*
Baozhu Tian
baozhutian@ecust.edu.cn
Jinlong Zhang
jlzhang@ecust.edu.cn
1
2
Key Laboratory ꢀor Advanced Materials and Feringa Nobel Prize Scientist Joint Research
Center, Institute oꢀ Fine Chemicals, School oꢀ Chemistry and Molecular Engineering, East
China University oꢀ Science and Technology, 130 Meilong Road, Shanghai 200237, China
Research Institute oꢀ Physical and Chemical Engineering oꢀ Nuclear Industry, 168 JinTang
Road, Tianjin 300180, People’s Republic oꢀ China
Vol.:(012
1
3456789)
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W. Ming et al.
Introduction
Dye laser can emit laser by pulse ꢀorm, continuous wave, and other modes. It can be
pumped by a variety oꢀ excitation sources and possesses the inherent ability to pro-
duce high pulse energy and high average power [1]. As the essential material oꢀ dye
laser, the organic fuorescence dyes play the key role in the laser emission process
owing to their wide spectrum tunability, high fuorescence quantum yield, and broad
spectral bandwidth. In 1960s, chloroaluminum phthalocyanine was reported ꢀor the
ꢂrst time as a laser dye. So ꢀar, the commercial laser dyes mainly include coumarins
[
2, 3], rhodamines [4–6], and BODIPY [7–13], which also can be applied in indus-
try, medicine, basic physics research, spectral analysis, and other ꢂelds [14–20].
Among various laser dyes, rhodamine dye has received much research attention
due to its high laser conversion eꢁciency and laser stability [2]. However, the emis-
sion wavelength oꢀ traditional rhodamine dyes generally does not exceed 600 nm
[21], limiting their applications in red region. The dyes that emit in less than 600 nm
always have some disadvantages. For instance, in the ꢂeld oꢀ biomedical science,
the laser with wavelength less than 600 nm has higher energy and easily causes
the damage oꢀ biological tissues. In addition, the short-wavelength laser always
displays shallower tissue penetration depth, which is unꢀavorable to the detection
and treatment oꢀ deep tissues. To obtain the red or near-inꢀrared rhodamine laser
dyes, it is necessary to modiꢀy the molecular structure oꢀ traditional rhodamine dye.
For example, it is a ꢀeasible choice to increase their conjugate structure. Seminaph-
thorhodafuor (SNARF) is a type oꢀ rhodamine dye and has two existent ꢀorms in
solution, namely carboxylic acid and inner ester (Fig. 1). It has been used as a vari-
ety oꢀ red fuorescent probes because its fuorescence emission can reach the red
region and the independent hydroxyl in the molecule can be connected with a vari-
ety oꢀ detection groups [22–26]. However, the application oꢀ SNARF as a laser dye
has not reported.
Herein, a SNARF dye (SNARF-X1) was synthesized by the dehydration and
condensation oꢀ 1,6-naphthol, 8-Hydroxyjulolidine, and phthalic anhydride. And
its methyl ester (SNARF-X2) was ꢀurther prepared by the esteriꢂcation reaction
between SNARF-X1 and methyl alcohol. On the basis oꢀ absorption and fuores-
cence spectrum tests, we ꢀurther investigated the infuences oꢀ diꢃerent solvents on
the spectral properties oꢀ SNARF-X1 and SNARF-X2. Using a 532 nm ND:YAG
Fig. 1 Two existence ꢀorms oꢀ SNARF
1
3

Synthesis and properties of seminaphthorhodaꢀuor red laser…
pulsed laser as light source, the laser emission spectra and stability oꢀ SNARF-X1
and SNARF-X2 were studied. Moreover, we also explored the infuence oꢀ dye con-
centration on the laser conversion eꢁciency oꢀ the above two dyes.
Experimental section
Synthesis of the dyes
Figure 2 illustrates the synthetic route oꢀ SNARF-X1 and SNARF-X2, which
includes the syntheses oꢀ compound M-1, M-2, SNARF-X1, and SNARF-X2.
Synthesis of compound M‑1
Under nitrogen atmosphere, 1.09 g (10 mmol) 3-aminophenol was dissolved in
8
mL 1-chloro-3-bromopropane, ꢀollowed by addition oꢀ 2.7 g anhydrous potassium
carbonate. Under constant stirring, the mixture was refuxed ꢀor 24 h under 150 °C.
Then, the excess potassium carbonate was ꢂltered and the crude product was
obtained by concentrating the ꢂlter liquor under vacuum. Finally, the crude product
was puriꢂed by column chromatography using petroleum/ethyl acetate=1/1 (v/v)
1
as the eluent to give a gray–white product (M-1) (0.82 g, 58%). H NMR (400 MHz,
d6-DMSO): δ=7.26 (s, 1H), 6.45 (m, 1H), 4.54 (s, 1H), 4.42 (m, 4H), 2.69 (m, 4H),
2
.00 (m, 4H) (Fig. S1).
Synthesis of compound M‑2
1
.89 g (10 mmol) 8-hydroxyjulolidine (M-1) and 1.60 g (10.8 mmol) phthalic
anhydride were added into 100 mL toluene. Then, the mixture was refuxed under
Fig. 2 Synthetic route oꢀ SNARF-X1 and SNARF-X2
1
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W. Ming et al.
1
20 °C ꢀor 24 h. Aꢀter the mixture was cooled to room temperature, the precipi-
tate was ꢂltered and washed with water. Finally, the crude product was puriꢂed by
column chromatography using dichloromethane/methanol=100/2 (v/v) as the elu-
1
ent to give a yellow crystal (M-2) (2.35 g, 69.7%). H NMR (400 MHz, CDCl ,
3
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
1
3
(
t, J=6.4 Hz, 2H), 2.47 (t, J=6.1 Hz, 2H), 1.95 (m, 2H), 1.85 (m, 2H) (Fig. S2). C
NMR (400 MHz, CDCl , ppm): δ=197.77, 170.56, 160.75, 149.34, 141.42, 132.56,
3
1
2
31.11, 130.32, 128.96, 128.26, 127.88, 112.79, 109.02, 105.54, 50.17, 49.79,
7.27, 21.63, 20.66, 19.89 (Fig. S3).
Synthesis of compound SNARF‑X1
3
37 mg (1.0 mmol) compound M-2 and 160 mg (1.0 mmol) 1,6-naphthalene diphe-
nol were added to 10 mL methyl sulꢀonic acid. Aꢀter stirred at 65 °C ꢀor 12 h,
the mixture was poured into a saturated NaClO aqueous solution at 80 °C and
4
the obtained precipitate was ꢂltered and dried under vacuum. Finally, the crude
product was puriꢂed by SiO column chromatography using dichloromethane/
2
methanol=100/4 (v/v) as the eluent to obtain the dark brown product SNARF-X1
1
(
367 mg, yield: 79.6%). H NMR(400 MHz, DMSO-d6): δ=10.14 (s, 1H), 8.35 (d,
J=9.0 Hz, 1H), 8.03 (d, J=7.4 Hz, 1H), 7.81 – 7.67 (m, 2H), 7.35 (d, J=8.8 Hz,
1
H), 7.31 – 7.22 (m, 2H), 7.15 (d, J=2.3 Hz, 1H), 6.56 (d, J=8.8 Hz, 1H), 6.14 (s,
H), 3.2 (m, 2H), 3.14 (m, 2H), 3.07 (t, J=6.5 Hz, 2H), 2.60–2.41 (m, 2H), 2.00
1
1
3
(
m, 2H), 1.80 (m, 2H) (Fig. S4). C NMR (400 MHz, DMSO): δ=165.04, 160.77,
1
1
1
56.79, 153.41, 152.00, 151.37, 138.46, 133.81, 133.48, 130.93, 130.53, 129.14,
28.47, 125.83, 125.50, 125.12, 122.74, 120.33, 116.85, 115.72, 115.38, 110.77,
05.32, 52.38, 51.20, 50.74, 26.74, 19.64, 19.07, 18.72 (Fig. S5). HRMS (ESI):
−
calcd. For [C H NO −H] 460.1549; ꢀound 460.1551 (Fig. S6).
3
0
23
4
Synthesis of compound SNARF‑X2
1
.00 g (2.17 mmol) SNARF-X1, 100 mL dried methanol, and 3 mL sulꢀuric acid
were added into a 250-mL three-necked fask and refuxed at 60 °C ꢀor 36 h. When
the temperature oꢀ the reaction solution was cooled to room temperature, the mixed
solution was dropped into 10% NaClO solution to obtain precipitate. Finally, the
4
target compound SNARF-X2 was isolated by SiO column chromatography using
2
the mixed solution oꢀ dichloromethane and methanol with a volume ratio oꢀ 100:6
1
and recrystallized in ethanol. Yield: 730 mg, 70.9%. H NMR (400 MHz, DMSO-
d6): δ=8.63 (d, J=9.1 Hz, 1H), 8.32 (d, J=7.9 Hz, 1H), 7.96 (d, J=7.5 Hz,
1
H), 7.89 (d, J=7.7 Hz, 1H), 7.67 (d, J=9.0 Hz, 1H), 7.52 (d, J=7.5 Hz, 1H),
.40 (d, J=9.1 Hz, 1H), 7.32 (s, 1H), 6.90 (d, J=9.0 Hz, 1H), 6.87 (s, 1H), 3.70
7
(
t, J=5.3 Hz, 2H), 3.65 (t, J=5.4 Hz, 2H), 3.57 (s, 3H), 3.16 (t, J=6.3 Hz, 2H),
1
3
2
.75(m, 2H), 2.09 (m, 2H), 1.92 (d, J=1.8 Hz, 2H) (Fig. S7). C NMR (400 MHz,
DMSO): δ=165.02, 160.75, 156.71, 153.36, 151.95, 151.31, 138.42, 133.79,
1
33.49, 130.91, 130.53, 129.12, 128.44, 125.80, 125.43, 125.11, 122.71, 120.30,
1
3

Synthesis and properties of seminaphthorhodaꢀuor red laser…
1
1
4
16.83, 115.67, 115.34, 110.70, 105.28, 52.76, 52.38, 51.19, 50.71, 26.74, 19.62,
+
9.03, 18.70 (Fig. S8). HRMS (ESI): calcd. For [C H NO +H] 476.1817; ꢀound
3
1
25
4
76.1807 (Fig. S9).
Characterization
1
13
HNMR and CNMR spectra were recorded on a Bruker AM400 NMR spectrom-
eter with TMS as the internal standard. High-resolution mass spectra (HRMS) were
tested on a Waters LCT Premier XE spectrometer. UV–Vis absorption spectra were
measured with a SHIMADZU UV-2450 spectrophotometer at room temperature.
The fuorescence spectra were tested on a SHIMADZU RF-5301PC fuorescence
spectrophotometer. The fuorescence quantum yields were determined on an Edin-
burgh Instruments FLS980 fuorescence spectrophotometer.
Laser property measurement
The laser properties oꢀ SNARF-X1 and SNARF-X2 were measured by a homemade
laser testing system, in which a 532 nm ND:YAG pulsed laser with a ꢀrequency oꢀ
1
0 Hz and pulse duration time oꢀ 8 ns was employed as the excitation light source.
Beꢀore the measurement, the solid-state laser was lightened ꢀor 30 min to make the
outputted laser become stable. For each measurement, 1.5 mL dye solution was
injected into the cuvette ꢂxed in the light path and excited by the ND:YAG pulsed
laser. At diꢃerent output wavelengths, the output powers oꢀ dye solution were meas-
ured with an optical power meter. For the laser stability tests, 25 μL dye solution
was taken out and its UV–Vis absorption spectrum was measured aꢀter being diluted
by ten times.
Result and discussion
Absorption and ꢀuorescence emission spectra
Figure 3 shows the normalized absorption and fuorescence emission spectra oꢀ
SNARF-X1 and SNARF-X2 in ethanol solution. As shown in Fig. 3a, SNARF-X1
exhibits a maximum absorption peak at 555 nm, a shoulder peak at 522 nm, and a
weak peak in the range oꢀ 355–435 nm. According to the previous report [11, 27],
they should be attributed to the S –S transition, S –S vibrational transition, and
0
1
0
1
S –S transition, respectively. Similarly, SNARF-X2 also presents three absorption
0
2
peaks around 568 nm, 530 nm, and 400 nm. Interestingly, the maximum absorption
wavelength (λ ) oꢀ the shoulder peak is very near to the emission wavelength oꢀ the
abs
ND:YAG pulsed laser (532 nm), implying that this dye can eꢃectively respond to
the ND:YAG pulsed laser.
In Fig. 3b, the maximum fuorescence emission wavelengths (λ ) oꢀ SNARF-X1
em
and SNARF-X2 in ethanol are located at 588 nm and 599 nm, respectively. By com-
paring their λ and λ values, it can be seen that the λ and λ oꢀ SNARF-X2
abs
em
abs
em
1
3

W. Ming et al.
Fig. 3 Normalized absorption (a) and fuorescence emission (b) spectra oꢀ SNARF-X1 and SNARF-X2
1.0×10− mol/L) in ethanol. For all oꢀ the fuorescence tests, the excitation wavelength (λ ) is 555 nm
5
(
ex
redshiꢀt about 12 nm were compared with those oꢀ SNARF-X1. The redshiꢀts oꢀ λ
abs
and λ can be ascribed to the contribution oꢀ methyl esteriꢂcation. Beꢀore ester-
em
iꢂcation, the carboxyl group in the benzene ring can rotate ꢀreely. Moreover, the
benzene ring also can pivot to a certain degree. Aꢀter esteriꢂcation, the rotation oꢀ
benzene ring and carboxyl group would be restrained due to the increase in steric
hindrance. Consequently, the energy oꢀ the whole molecule is reduced, leading
to the redshiꢀts oꢀ λ and λ . Interestingly, both oꢀ SNARF-X1 and SNARF-X2
abs
em
exhibit another weak emission peak around 650 nm, which is relative to the conju-
gation with naphthol.
Eꢁect of solvents on the absorption and ꢀuorescence spectra
The infuences oꢀ solvent properties on the light absorption and fuorescence emis-
sion spectra oꢀ SNARF-X1 and SNARF-X2 were investigated by analyzing their
absorption and fuorescence emission spectra in diꢃerent solvents. As shown in
Fig. 4a, SNARF-X1 almost has no absorption in the aprotic solvents (CHCl ,
3
CH Cl , acetone, and CH CN), while it displays stronger absorption in the protic
2
2
3
solvents (propanol, ethanol, methanol and water). It is well known that the visible
light absorption oꢀ rhodamine dyes arises ꢀrom the conjugated structure oꢀ xanthene.
In the aprotic solvents, SNARF-X1 exists mainly in the ꢀorm oꢀ lactone, which has
no absorption in the visible light region due to the disappearance oꢀ conjugated dou-
ble bond in xanthene structure (Fig. 1). In the protic solvents, the carboxyl group
oꢀ SNARF-X1 can ꢀorm hydrogen bond with the hydrogen oꢀ the protic solvents,
restraining the ꢀormation oꢀ SNARF-X1 lactone. Consequently, SNARF-X1 exhibits
strong visible light absorption in the protic solvents. In contrast, neither in protic
solvents nor in aprotic solvents, SNARF-X2 always displays stronger absorption in
the visible light region (Fig. 4b). This is because the ꢀormation oꢀ ester can strain the
ꢀormation oꢀ lactone structure.
Table 1 summarizes the light absorption and fuorescence characteristics oꢀ
SNARF-X1 and SNARF-X2 as shown in Fig. 4a–d. In both the aprotic solvents
(
CH Cl , CHCl , acetone, and CH CN) and protic solvents (C H OH, C H OH,
2 2 3 3 3 7 2 5
1
3

Synthesis and properties of seminaphthorhodaꢀuor red laser…
Fig. 4 Absorption and fuorescence emission spectra oꢀ SNARF-X1 and SNARF-X2 in diꢃerent solvents
−
5
(
1.0×10 mol/L): absorption spectra oꢀ a SNARF-X1 and b SNARF-X2; fuorescence emission spectra
oꢀ c SNARF-X1 and d SNARF-X2. For all oꢀ the fuorescence tests, λ is 555 nm
ex
Table 1 Absorption and fuorescence characteristics oꢀ SNARF-X1 and SNARF-X2
Solvent
Polarity
SNARF-X1
SNARF-X2
a
a
ꢀF
λabs (nm)
λem (nm)
ꢀF
λabs (nm)
λem (nm)
Aprotic solvents
CH Cl
CHCl3
3.4
4.4
5.4
6.2
–
–
–
–
585
585
588
589
0.16
0.10
0.07
0.05
569
574
567
566
596
596
598
597
0.58
0.50
0.33
0.28
2
2
Acetone
CH CN
3
Protic solvents
C H OH
4.0
4.3
6.6
10.2
554
555
556
564
588
588
590
594
0.44
0.40
0.32
0.20
568
568
567
568
598
599
596
600
0.46
0.44
0.38
0.24
3
7
C H OH
2
5
CH OH
3
H O
2
a
The values oꢀ fuorescence quantum yields (Φ ) were determined by using rhodamine 101 as the stand-
F
ard (Φ in ethanol is 0.96)
F
1
3

W. Ming et al.
CH OH, and H O), λ and λ oꢀ SNARF-X1 show a slight bathochromic shiꢀt
3
2
abs
em
with the increase in solvent polarity, while those oꢀ SNARF-X2 always have no evi-
dent variation. This result indicates that SNARF-X1 is more sensitive to the polarity
oꢀ solvents. In the case oꢀ fuorescence intensity, both SNARF-X1 and SNARF-X2
display evident decrease with increasing the polarity oꢀ solvents ꢀor both protic and
aprotic solvents. This phenomenon can be interrupted as ꢀollows: With the increase
in solvent polarity, the electrostatic attraction among diꢃerent dye molecules also
enhances and the probability oꢀ molecular collision also increases, leading to the
increase in non-radiative transition [28–30]. Consequently, the fuorescence inten-
sity decreases with the increase in solvent polarity.
Laser properties
Figure 5 shows the laser spectra oꢀ SNARF-X1 and SNARF-X2 in ethanol solution.
Herein, the lasing eꢁciency is denoted as the ratio between the output energy oꢀ
dye laser and the incident energy oꢀ pump laser. As shown in Fig. 5, both SNARF-
X1 and SNARF-X2 give two laser emission peaks in the range oꢀ 590–680 nm, in
which the laser peaks at 604 nm ꢀor SNARF-X1 and 610 nm ꢀor SNARF-X2 should
correspond to their fuorescence emission peaks at 587 nm and 600 nm, respec-
tively. Interestingly, the laser emission peaks at 654 nm (SNARF-X1) and 660 nm
(
SNARF-X2) become much stronger than their fuorescence emission peaks at
6
6
50 nm. The maximum laser eꢁciencies oꢀ SNARF-X2 at 610 nm (17.2%) and
60 nm (11.0%) are, respectively, higher than those oꢀ SNARF-X2 at 604 nm
(
15.4%) and 654 nm (10.6%). Interestingly, the maximum laser emission wave-
lengths oꢀ SNARF-X1 and SNARF-X2 exhibit a redshiꢀt compared to their corre-
sponding maximum fuorescence emission wavelengths. To explore the ꢀactor that
results in this diꢃerence, we investigated the infuence oꢀ SNARF-X2 concentration
on its maximum fuorescence wavelength. From Table 2, we can see that the λ oꢀ
em
SNARF-X2 gradually increases with increasing its concentration. When the concen-
tration oꢀ SNARF-X2 is 4.0×10− mol/L, the maximum fuorescence wavelengths
4
Fig. 5 Laser emission spectra
oꢀ SNARF-X1 and SNARF-
X2 in ethanol solution
4.0×10− mol/L)
4
(
1
3

Synthesis and properties of seminaphthorhodaꢀuor red laser…
Table 2 Relationship between the maximum fuorescence wavelengths oꢀ SNARF-X2 and its concentra-
tions
1
0−4 mol/L
0.2
0.6
1.0
1.4
1.8
2.0
3.0
4.0
6.0
8.0
10.0
Peak 1 (nm)
Peak 2 (nm)
597
650
599
650
601
652
605
655
608
657
609
658
610
659
611
660
612
662
614
663
615
665
oꢀ the two peaks are located at 611 nm and 660 nm, respectively, consistent with its
maximum laser emission wavelengths. The above results imply that the laser and
fuorescence emission wavelengths oꢀ SNARF-X1 and SNARF-X2 can be tuned in a
certain range by adjusting their concentration.
Herein, we ꢀurther analyzed the eꢃect oꢀ dye concentration on the laser conver-
sion eꢁciencies oꢀ SNARF-X1 and SNARF-X2. As shown in Fig. 6, at the begin-
ning, the laser eꢁciencies oꢀ SNARF-X1 at 654 nm and SNARF-X2 at 660 nm
increase gradually with the increase in dye concentration and then display a down-
trend with ꢀurther increasing their concentrations. The optimal dye concentration ꢀor
−
4
obtaining the maximum laser conversion eꢁciency is 4.0×10 mol/L. This result
is relative to the eꢃect oꢀ reabsorption/reemission oꢀ photos, because the dye mol-
ecule in this solution can absorb the photon emitted by another molecule beꢀore,
which is aꢃected by the dye concentration [31, 32].
Since the laser stability oꢀ dyes is very important ꢀor its practical application, we
tested the laser stability oꢀ SNARF-X2 dye in ethanol. As displayed in Fig. 7a, the
laser conversion eꢁciency oꢀ dye SNARF-X2 decreases gradually and its halꢀ-liꢀe is
3
60 min. To disclose the reason that results in the decline oꢀ laser conversion eꢁ-
ciency, we tested the absorption spectra oꢀ SNARF-X2 solution at diꢃerent intervals
oꢀ laser irradiation. From Fig. 7b and its inset, we can see that the dye concentration
also decreases with the continuation oꢀ laser irradiation time and the variation in
its absorbance intensity at 567 nm is very consistent with that oꢀ the laser conver-
sion eꢁciency. This result revealed that the decline oꢀ laser conversion eꢁciency is
attributed to the decomposition oꢀ SNARF-X2 dye.
Fig. 6 Laser eꢁciencies oꢀ
SNARF-X1 and SNARF-X2 as
a ꢀunction oꢀ dye concentration
in ethanol solution
1
3

W. Ming et al.
Fig. 7 a Laser stability oꢀ SNARF-X2 in ethanol solution evaluated by its laser eꢁciency variation as
a ꢀunction oꢀ laser irradiation time. b Absorption curves oꢀ SNARF-X2 in ethanol solution at diꢃer-
ent laser irradiation times. The inset oꢀ Fig. 2b is the corresponding absorbance variation at maximum
absorption wavelength (568 nm)
We ꢀurther compared the laser stability oꢀ SNARF-X1 and SNARF-X2 in
ethanol. As shown in Fig. 8, the laser stability oꢀ SNARF-X1 is better than that
oꢀ SNARF-X2, and the halꢀ-lives oꢀ SNARF-X1 and SNARF-X2 are 420 min
and 360 min, respectively. The higher laser stability oꢀ SNARF-X1 is probably
relative to the ꢀormation oꢀ hydrogen bond between two SNARF-X1 molecules.
Lacking oꢀ intermolecular hydrogen bond, SNARF-X2 exhibits lower stability
under laser irradiation.
Fig. 8 Laser stability oꢀ
SNARF-X1 and SNARF-X2
in ethanol. The inset illustrates
the ꢀormation oꢀ intermolecular
hydrogen bond between two
SNARF-X1 molecules
1
3

Synthesis and properties of seminaphthorhodaꢀuor red laser…
Conclusion
With the aim oꢀ extending the laser emission wavelength oꢀ rhodamine dyes, herein,
we synthesized two red dyes SNARF-X1 and SNARF-X2. Due to the eꢃect oꢀ ester-
iꢂcation, the fuorescence emission wavelengths oꢀ SNARF-X2 redshiꢀt~12 nm
were compared with that oꢀ SNARF-X1. It was ꢀound that the wavelengths oꢀ
absorption and fuorescence emission spectra are not very sensitive to the solvent
polarity, while the fuorescence intensities decrease with the increase in solvent
polarity. Both oꢀ the dyes can emit red laser, and the tunable ranges oꢀ SNARF-
X1 and SNARF-X2 are 590–670 nm and 600–680 nm, respectively. The maximum
laser conversion eꢁciencies oꢀ SNARF-X2 at 610 nm (17.2%) and 660 nm (11.0%)
are higher than those oꢀ SNARF-X2 at 604 nm (15.4%) and 654 nm (10.6%). The
halꢀ-lives oꢀ laser eꢁciency ꢀor SNARF-X1 and SNARF-X2 reach 7 h and 6 h,
respectively. Moreover, we investigated the infuence oꢀ dye concentration on the
laser conversion eꢁciencies oꢀ SNARF-X1 and SNARF-X2 and ꢀound the optimal
−
4
dye concentration ꢀor attaining the highest laser eꢁciency is 4.0×10 mol/L. We
believe that this study provides a reꢀerence ꢀor the synthesis and application oꢀ red
laser with high eꢁciency and photo-stability.
Acknowledgements This work has been supported by the Research Fund oꢀ Science and Technology on
Particle Transport and Separation Laboratory, the Shanghai Municipal Science and Technology Major
Project (2018SHZDZX03), and the Programme oꢀ Introducing Talents oꢀ Discipline to Universities
(
B16017).
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