Optical Limiting Properties of 3,5-Dithienylenevinylene BODIPY Dyes at 532 nm

Article abstract of DOI:10.1002/chem.201702503

The optical limiting properties of a series of near infrared absorbing 3,5-dithienylenevinylene BODIPY (boron-dipyrromethene) dyes (1–3) that contain donor and acceptor moieties in their π-conjugation systems were studied by using the z-scan technique at

Full text of DOI:10.1002/chem.201702503

A Journal of
Accepted Article
Title: Optical limiting properties of 3,5-dithienylenevinylene BODIPY
dyes at 532 nm
Authors: Jessica Harris, Lizhi Gai, Gugu Kubheka, John Mack, Tebello
Nyokong, and Zhen Shen
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To be cited as: Chem. Eur. J. 10.1002/chem.201702503
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Optical limiting properties of 3,5-dithienylenevinylene BODIPY
dyes at 532 nm
Jessica Harris,‡[a] Lizhi Gai,‡[b] Gugu Kubheka,[a] John Mack,*[a] Tebello Nyokong[a] and Zhen Shen*[b]
Abstract: The optical limiting properties of a series of near infrared
absorbing 3,5-dithienylenevinylene BODIPY dyes (1-3) that contain
donor and acceptor moieties in their -conjugation systems were
studied by using the z-scan technique at 532 nm in the nanosecond
pulse range. A strong reverse saturable absorption RSA response
was observed when the compounds are embedded into
poly(bisphenol carbonate A) polymer thin films, which demonstrates
that BODIPY dyes with this type of structure are suitable for use in
optical limiting applications.
electronic polarizabilities, and hence it is reasonable to expect
molecules of this type to possess the substantial second-order
hyperpolarizabilities that enhance their OL properties.[21,22]
Molecules with donor and acceptor moieties that are separated
by a -conjugation system (D--A) are also known to exhibit large
third order susceptibility values.[19] In this study, 3,5-
dithienylenevinylene BODIPY dyes (1-3) with electron donating 2-
thiophene rings have been studied to assess their potential for OL
applications (Scheme 1). To the best of our knowledge, the
properties of 3,5-dithienylenevinylene BODIPY dyes have not
been studied to any significant extent in the context of OL at 532
nm. BODIPY 3 is also substituted at the 2,6-positions with iodine
atoms, since the presence of heavy atoms promotes intersystem
crossing from the singlet to the triplet excited state by enhanced
Introduction
Optical limiting (OL) materials have been the focus of
considerable research interest in recent years, since they can
provide protection from intense incident laser beams.[1-3]
Preparing OL materials for the second harmonic of Nd:YAG lasers
at 532 nm has become particularly important in the context of
aviation safety where the irresponsible use of laser pens is
concerned and in the protection of other sensitive optical
devices.[4-7] High transmittance of low-intensity light is required
under ambient conditions, along with a significant attenuation of
an incident pulsed laser beam.[1-3] This has led to considerable
interest in the OL properties of porphyrins,[8,11] phthalocyanines,[8-
spin-orbit coupling and results in
fluorescence quantum yield.[23]
a
significantly lower
Scheme 1. The BODIPY dyes that were synthesized in this work for
NLO studies.
fullerenes,[1] and other organic chromophores,[12,13]
10]
nanoparticles,[14] metal nanowires,[15] and carbon nanotubes.[16]
The main mechanisms involved in achieving an OL response are
nonlinear absorption (NLA), nonlinear refraction (NLR) and
nonlinear scattering (NLS).[17,18] In this study, however, the main
focus is on the OL properties of molecular dyes that are caused
by NLA processes and result in a strong reverse saturable
Although the use of optically transparent organic solutions is
convenient for investigating the OL properties of dye molecules,
for the purpose of applications it is necessary for the OL materials
to be cast in the solid state, since incorporation into safety visors
or Perspex™ windshields is envisaged. In this work, BODIPYs
1−3 were embedded in poly(bisphenol carbonate A) (PBC)
polymer thin films,[24,25] since polycarbonates have previously
been used for making safety visors,[26] and in the manufacture of
eyewear, protective sportswear and other safety products. There
have been comparatively few studies on the use of BODIPY dyes
and their analogues as OL materials for 532 nm excitation
pulses[27-29] and those at other wavelengths.[30-32] This study
clearly demonstrates that near infrared absorbing BODIPY dyes
with extended D--A conjugation structures are potentially
suitable for OL applications.
absorption (RSA) response that leads to
a decrease in
transmittance at high incident light intensity levels.
OL properties often depend on two-photon absorption (2PA),
which is a resonant third-order nonlinear optical (NLO) process in
which an excited state is formed by the simultaneous absorption
of two photons of half-energy, in an intense focused light beam
such as that generated by a laser source.[19,20] It has been
demonstrated that -conjugation systems possess large
[a]
[b]
‡
Dr. J. Mack, J. Harris, G. Kubheka, Prof. T. Nyokong
Department of Chemistry
Rhodes University
Grahamstown 6410 (South Africa)
E-mail: j.mack@ru.ac.za
Prof. Zhen Shen, L. Gai
State Key Laboratory of Coordination Chemistry
Nanjing National Laboratory of Microstructures
Nanjing University; Nanjing 210023 (P.R. China)
E-mail: zshen@nju.edu.cn
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
Results and Discussion
Synthesis and Characterization: BODIPYs are conventionally
prepared through an acid-catalyzed condensation reaction of a
pyrrole ring with an aromatic aldehyde.[33] 2,4-dimethylpyrrole is
usually preferred as a starting material, since the methyl-
substituents prevent the formation of porphyrins. The 1,3,5,7-
tetramethylBODIPYs that are formed in this manner can be
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R
B
R
B
R
S
CHO
TFA
DDQ
+
N
N
TEA
BF3Et2O
Piperidine
Acetic acid
Toluene
reflux
N
N
N
H
F
F
CHO
F
F
4 R=H
5 R=COOMe
S
S
1 R=H
2 R=COOMe
NIS
S
CHO
I
I
N
N
I
I
B
N
N
Piperidine
Acetic acid
Toluene
reflux
B
F
F
F
F
S
S
6
3
Scheme 2. The BODIPY dyes that were synthesized in this work for NLO studies.
readily iodinated at the 2,6-positions with N-iodosuccinimide (NIS).
The introduction of vinyl groups was achieved by reacting an
aromatic aldehyde with the appropriate 2,6-dibromoBODIPY to
form (Scheme 2).[34,35] The introduction of vinyl groups is one of
the most useful strategies for shifting the main spectral band of
the BODIPY chromophore to the red (Figure 1).[36] The protons
attached to the methyl groups are acidic enough to undergo
condensation reactions. Extension of the -conjugation and the
addition of functionality is most frequently accomplished through
the methyl groups at the 3,5-positions, since this generally
produces a greater red shift (ca. 50−100 nm) than is observed
upon extending the -conjugation through the 2,6-[26] or 1,7-
positions.[37] The main spectral bands of 1 and 2 lie at ca. 650 nm
(Table 1), while iodination results in a further red shift of the main
spectral band of 3 to 670 nm. The fluorescence quantum yield
(ΦF) and lifetime values (F) of 3 (Table 1) were found to be
significantly lower than those of BODIPYs 1 and 2 due to the
presence of iodine atoms at the 2,6-positions, which increases the
rate of ISC through a relaxation of the spin-selection rule.
The ground state absorption spectra of the thin films were
obtained in order to visualize the effect of a solid support. Figure
1 contains the absorption spectra of 1-3 in DMF and embedded
in poly(bisphenol A carbonate) (PBC) as thin films (1-PBC, 2-PBC,
and 3-PBC). The DMF spectra show the main absorption bands
of the BODIPYs are well defined and do not show signs of
aggregation. For BODIPY 1, the DMF spectrum is well-defined
but the 1-PBC spectrum shows significant aggregation. The thin
film spectra of 2 and 3 are slightly red-shifted but show that the
BODIPYs maintain their electronic character.
Figure 1. Ground state absorption spectra for BODIPYs 1-3 in DMF (blue) and
embedded in PBC thin films (red).
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2P0Leff
w20
2P0Leff
z0
Table 1. Photophysical data for 3,5-dithienylenevinylene BODIPYs 1-3 in DMF.
Q0 =
=
(7)
log 
5.00
5.05
4.73

abs [nm]

exc [nm]a

em [nm]a
F
F [ns]
1
2
3
651
656
670
651
656
670
663
671
695
0.33
0.40
0.11
2.89
2.87
1.62
Equation 5 gives a Gaussian plot with Q0 as the maximum value
at the beam waist (z = 0). The peak value and the FWHM of the
plot give values of Q0 and z0 respectively. The value of  may then
be calculated using Equation 8.[39]
[a] Excitation and emission spectra are provided in Figure S1, Supplementary
Information.
z0Q0
NLO properties: The measured quantity in an open-aperture z-
scan experiment is the normalized transmittance, given by
Equation 1 for a Gaussian pulse.[38,39]
 =
(8)
2P0Leff
The imaginary component of the third order susceptibility, Im[(3)],
is directly proportional to , as seen in Equation 9:
2
q (z) ꢀ∞
1
T(z) =
ln[1 + q0(z)e- ]d
(1)
-∞
√
0
20c
ꢁ ꢂ
3
Imꢏ ꢐ =
(9)
2
Where q0(z) is a parameter characterizing the strength of the
nonlinearity and is given by Equation 2 when using a circular
Gaussian beam.[38,39]
where  and c are the linear refractive index and speed of light,
respectively, and 0 is the permittivity of free space. The third-
order nonlinear optical susceptibility is used to describe ultrafast
responses,[40] with nonlinear absorption being described by the
imaginary component, while the real component is representative
of the nonlinear refraction of the material. The optimal range for
Im[(3)] is 10−9−10−11 esu. While Im[(3)] describes the speed of the
NLA response of the material, the behavior at a molecular level
may be described using hyperpolarizability (), which describes
the nonlinear absorption per mole of the OL compound, and is
useful when comparing efficiencies of different optical limiters.
The correlation between Im[(3)] and  is shown in Equation 10:
2P0Leff
w(z)2
ꢁ ꢂ
q0 z =
(2)
where  is the nonlinear absorption coefficient of the material, P0
is the peak power of the pulses and Leff is the effective path length
in the sample, given by Equation 3:
1-e-L
Leff
=
(3)

where  is the linear absorption coefficient. For applications of
these materials,  should always be measured at the intended
wavelength:[19] in this case, 532 nm. In Equation 2, w(z) is the
beam width as a function of the sample position, and is given
by:[19]
Im[(3)
]
 =
(10)
f4CmolNA
where NA is Avogadro’s constant, Cmol is the concentration of the
active species in the excited state per mole, and f is the Lorentz
2
z
ꢃ
w(z) = w0 1+ ꢄz ꢅ
(4)
local field factor, f = (2+2)/3.[41] Optimal values of  lie in the 10−29
-
0
10−34 esu range.
where w0 is the beam waist at the focus (z = 0), defined as the
distance from the beam centre to the point where the intensity
reduces to 1/e2 of its axis value; while z and z0 are the translation
distance of the sample relative to the focus, and Rayleigh length,
respectively. The Rayleigh length is defined as πꢆꢇꢈ/ꢉ where  is
the wavelength of the laser. Equations 1-4 are used to determine
the nonlinear absorption coefficient () from experimentally
measured normalized transmittance. Tsigaridas et al.[39] have
produced an analytical formula given by Equation 5:
The limiting intensity (Ilim) is the threshold fluence value at which
the transmittance is 50% of the linear transmittance. It is possible
to approximate the value of Ilim experimentally, using a plot of
output fluence (Iout) vs input fluence (Iin). While there is currently
no defined optimal range for Ilim values, it makes sense that a
good optical limiter would be those compounds exhibiting lower
Ilim values, as this means that the limiting would occur at a lower
intensity, allowing for more cautious protection of sensors. As a
guideline on limits of exposure to radiation, the International
Commission on Non-Ionizing Radiation Protection has published
a guideline[42] giving insight into exposure limits for a variety of
lasers. This work deals with 10 ns pulses of light at 532 nm
derived from an Nd:YAG laser through the use of a second
harmonic generation crystal and, as such, its exposure limit can
be determined from Equation 11, which gives the exposure limit
as a function of time.
ꢁ ꢂ
2ꢁ ꢂ
3ꢁ ꢂ
ꢁ ꢂ
a0+a1T z +a2T z +a3T z for T z ≤ 0.75
ꢁ ꢂ
q0 z = ꢊ
(5)
ꢋ
ꢌc
2
c0+c1 T(z) for T(z) ≥ 0.75
where the coefficients a0, a1, a2, a3, c0, c1 and c2 for Gaussian
pulses are given as 15.66, −37.45, 30.76, −8.97, −2.301, 2.156
and −1.563 respectively.[39] Equation 5 provides values of q0(z)
directly from the normalized transmittance T(z). Substituting
Equation 4 into Equation 2 gives q0(z) as follows:
2.7CAt0.75 Jcm-2
(11)
CA is a correction factor (= 1 for lasers with wavelengths of 400-
700 nm). For this work, the exposure limit (t) was determined to
be 0.95 Jcm−2 assuming a 0.25 s exposure time. This exposure
time was selected because it is the average human response time
(blink reflex) to a sudden flux of light into the eye.[43] Irradiance
Q0
q0(z) =
(6)
2
ꢎ
1 + ꢍzz0
where
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Figure 2. Z-scan (a) and nonlinear fit (q0(z)) curves (b) for BODIPYs 1-3 in DMF solution and when embedded in thin films. Detailed NLO parameters are provided
in Table 2. Red lines are used to show the response curves that were calculated using Equation 5.
has units of Wcm−2, with the maximum value occurring at the
focus (z = 0), determined by Equation 12.
by finding the product of Iin(z) and the transmittance
corresponding to each z position (T(z)) (Equation 16).
E
w20
ꢁ ꢂ
ꢁ ꢂ
Iout z = Iin z T(z)
(16)
I00
=
(12)
The open aperture z-scan method was used to characterize the
OL properties of the series of 3,5-divinyl-BODIPY dyes selected
for this study. The  value is an important parameter for assessing
the suitability of materials for optical limiting, since it measures the
degree of nonlinear absorptivity and depends on the population
of molecules in the excited state. Generally, this parameter
depends on two-photon absorption processes.[17,44] Since
nanosecond pulses are used excited state absorption (ESA) can
also happen on this timescale. When the ESA is more intense
than the absorption in the ground state, ESA from a two-photon
pumped state can also provide the RSA response that is required
for optical limiting. These OL mechanisms result in positive
nonlinear absorption coefficients, and a decrease in transmittance
as the material approaches the zero position of the z-scan
instrument at high-intensity levels.[45]
where E is maximum laser energy (J),  is the length of the laser
pulse (s) and ꢆꢇ is beam waist (cm). Since 1 Js−1 = 1 W, the
maximum irradiance has units of Wcm−2. For any given z-scan
experiment, the laser energy remains constant and hence, the
overall laser power also remains constant. However, the
irradiance varies with z, as the beam width depends on the
distance from the focus. The cross-sectional area of the beam is
circular and hence equal to w(z)2. Multiplying the irradiance by
the corresponding beam area gives the laser power, P. At the
focus (z = 0), P is given by Equation 13.
P = I00w20
(13)
At any other z position, P is given by Equation 14.
P = Iin(z)w(z)2
(14)
Figures 2-4 show the representative open-aperture z-scans at
532 nm using 10 ns pulses for 1-3 in DMF solution and in thin
films. The main OL parameters that were calculated on this basis
are provided in Table 2. The measurements demonstrate that
there is strong nonlinear absorption behavior in both samples,
with the shapes of the z-scan profile exhibiting RSA signatures.[46]
Analyses of the z-scan results to obtain eff values were carried
out by fitting the data to the 2PA-assisted ESA function described
above.
As P remains constant throughout any given z-scan run,
Equations 13 and 14 can be combined and simplified as shown in
Equation 15:
2
Iin z = I00 ꢄww(z)ꢅ
(15)
0
ꢁ ꢂ
As the transmittance gives the percentage of light that passes
through a material, the output fluence (Iout(z)) may be calculated
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Table 2. Optical limiting properties of 1-3 in DMF and in thin films.
Concentration × 10−5 [M]a
 [cm−1
]

eff × 10−9 [mW−1
]
Im[(3)] × 10−10 [esu]
 [esu]
Ilim [Jcm−2
]
Iout % at 50% Iin
Film-thickness [µm]b
1
2
3
9.73a
8.56a
18.10a
21b
0.63
0.82
0.88
103
56
1.40
1.35
1.62
21.1
13.0
11.5
0.46
0.44
0.53
6.89
4.24
3.76
1.20 × 10−30
1.31 × 10−30
7.58 × 10−31
7.8 × 10−29
4.2 × 10−29
2.5 × 10−28
---
---
1.63
0.61
0.40
0.96
80
78
71
39
25
38
1-PBC
2-PBC
3-PBC
21b
17b
12
[a] Concentration in DMF solution. [b] Average thickness of BODIPY-embedded PBC films.
longer lived S1 excited state.[27] The z-scan plots for BODIPYs 1-
3 in solution are shown in Figure 2. The z-scan plots show a
typical nonlinear absorption behavior, with RSA profiles.
Equations 1-4 were used to determine the eff values for each
sample, and the results are summarized in Table 2. The
experimental eff values for BODIPYs 1-3 in DMF solution were
found to be 1.40 × 10−9, 1.35 × 10−9, and 1.62 × 10−9 mW−1,
respectively. The magnitude of the eff values for BODIPYs 1-3 lie
within the range of values previously reported for other organic
compounds with promising OL properties.[24]
BODIPYs 1-3 were embedded in PBC as thin films and their 
values measured. Z-scan plots for the thin films are shown in
Figure 2. The eff values of the 1-PBC, 2-PBC and 3-PBC thin
films were found to be 21.1 × 10−9, 13.0 × 10−9, and 11.5 × 10−9
mW−1, respectively. The eff values of 1-3 were significantly
improved in this context, which has previously been attributed to
aggregation of the molecule.[46] The effects of aggregation are
noticeable in the spectrum of 1-PBC (Figure 1), which has
significantly higher absorption at 532 nm and more noticeable
broadening of the main spectral band in the NIR region, but
appear to be relatively minor in the spectra of the 2-PBC and 3-
PBC thin films.
Table 2 summarizes the third-order nonlinear susceptibility
(Im[(3)]) and second-order hyperpolarizability values of BODIPYs
1-3 in solution and as thin films. The  value (Table 2) provides a
measure of the interaction of an incident photon with the
permanent dipole moment of the BODIPY dyes at a molecular
level, while the Im[(3)] value provides a measure of the ultra-fast
response of an NLO material. Since the  values describe the
nonlinear absorption per mole of the OL compound, it is useful
when comparing the efficiencies of different optical limiters. Both
the Im[(3)] and  values are required to be sufficiently large for a
material to be considered promising for OL applications; reported
values for Im[(3)] and  are typically in the range of 10−9−10−15 and
10−29−10−34 esu, respectively.[47] The concentrations of BODIPYs
1-3 in solution were determined to be in the order of 10−4 M (Table
2), while the thicknesses of the films were determined to be 21
µm for 1-PBC and 2-PBC, and 17 µm for 3-PBC by using scanning
electron microscopy (see Figure S2, Supplementary Information).
The Im[(3)] values obtained for both solutions and thin films lie in
the 10−9−10−15 range, while the  values of the 1-PBC and 2-PBC
thin films also fall within the literature range. The  value of the
2,6-halogenated BODIPY in the 3-PBC thin film was even more
favorable. In general, the Im[(3)] and  values are much larger in
thin films compared to the corresponding solution (Table 2). 1,
which showed a particularly high eff value in the context of the 1-
PBC thin film, also has a high value for Im[(3)] (Table 2), as the
two quantities are directly proportional.
Figure 3. Output fluence (Iout) versus input fluence (Iin) curves for 1-3 in DMF
(A) and in thin films (B). Detailed NLO parameters are provided in Table 2.
In molecules where the linear absorption at the laser wavelength
of 532 nm is zero, all the observed absorption at that wavelength
must be due to multi-photon absorption. However, when
nanosecond pulses are used as is the case in this study it may
also be due to sequential 2PA and ESA,[27] so the intrinsic value
for  that is associated only with 2PA cannot be determined, and
an effective value (eff) is determined instead. Additionally,
thiophene-substituted BODIPYs 1-3 have a small amount of linear
absorbance occurring at 532 nm, which means that the S1 state
can be populated through the absorption of a single photon as
well as through 2PA. Thus, there are multiple processes that
could be contributing to the OL properties of these compounds.
Recently, a styryl-substituted BODIPY,[27] has reportedly shown
strong RSA behavior consistent with 2PA-assisted ESA from its
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Figure 4. (LEFT) Normalised transmittance vs input fluence curves BODIPYs 1-3 in DMF (a) and embedded in PBC as thin films (b). Grey dashed lines indicate
50% transmittance and are used to identify the Ilim values. (RIGHT) Logarithmic plot of Iout versus Iin for BODIPYs 1-3 measured in DMF solutions (a) and embedded
in PBC as thin films (b). Detailed NLO parameters are provided in Table 2.
The limiting threshold intensity or fluence value, Ilim, is defined as
the input fluence at which the nonlinear transmittance is 50% of
the linear transmittance. The value of Ilim can be determined using
plots of input fluence vs. output fluence (Figure 3), and
transmittance vs. input fluence (Figure 4). The Ilim values of 1 and
2 in solution could not be estimated, since the transmittance did
not drop below 50% (Figure 4 and Table 2), while that of 3 is 1.63
Jcm−2. The values for the thin films were 0.61, 0.40 and 0.96
Jcm−2 for 1-3, respectively. The values for 1-PBC and 2-PBC,
which contain non-iodinated BODIPYs fall well below the damage
threshold of 0.95 Jcm−2, which suggests that the introduction of
heavy atoms at the 2,6-positions of the BODIPY core provides no
significant advantage in this regard. A logarithmic plot of Iout
versus Iin can also provide a rough comparison of the OL
properties of different optical limiting materials. Figure 4 shows
the logarithmic plot of Iout versus Iin for BODIPYs 1-3 in DMF and
as films. The Iout percentage values suggest that the responses of
BODIPYs 1 and 2 are very similar (80% and 78%, respectively),
while that of BODIPY 3, which contains iodine atoms at the 2,6-
positions, is even better (at 71%). However, 2-PBC shows a
significantly better response of 25%, while 1-PBC and 3-PBC
have Iout percentage values of 40%, and 38%, respectively.
wavelength of 532 nm making dyes of this type potentially suitable
for optical limiting applications where the second harmonic of
Nd:YAG lasers is concerned. The Ilim values for PBC films
embedded with 1-3 are significantly below the threshold value that
has been reported for damage to the human eye of 0.95 Jcm−2.
These results demonstrate that BODIPY dyes with D--A
structures are potentially suitable for use in OL applications, such
as use in thin films to enhance aviation safety and protect
sensitive optical devices. Further studies are already in progress
to determine how the structures of BODIPY dyes can be modified
to further enhance the OL properties.
Experimental Section
General: All air and moisture-sensitive reactions were carried out under a
nitrogen atmosphere. Poly(bisphenol A carbonate) was obtained from
Fluka Analytical (MW ~ 28,200, d: 1.2 g ml−1 at 298 K). All other reagents
were obtained from commercial suppliers and used without further
purification unless otherwise indicated. Dichloromethane was distilled over
calcium hydride. Triethylamine was obtained by simple distillation. Ether
and THF were distilled over sodium. 1H and 13C NMR spectra were
measured by using a Bruker DRX600 spectrometer and referenced to the
residual proton signals of the solvent. Mass spectral data were obtained
on a Bruker Daltonics AutoflexII™ MALDI-TOF spectrometer. Elemental
analyses were carried out using a Vario-Elementar Microcube ELIII Series
CHNS analyzer.
Conclusions
Nanosecond timescale open aperture z-scan studies
demonstrate near infrared absorbing BODIPY dyes with D--A
structures, such as the 3,5-dithienylenevinylene BODIPY dyes in
this study, have relatively strong OL properties and relatively
weak absorbance under ambient light conditions at an excitation
Equipment: Electronic absorption spectra were measured on a Shimadzu
UV-2550 spectrophotometer. Fluorescence emission spectra were
recorded on a Varian Eclipse spectrofluorimeter, while fluorescence
lifetimes were measured using a time-correlated single photon counting
(TCSPC) spectrometer (FluoTime 200, Picoquant GmbH). A frequency-
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10.1002/chem.201702503
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doubled Quanta-Ray Nd:YAG laser was used as an excitation source for
the z-scan measurements in a near-Gaussian transverse mode at 532 nm,
and the input and output energies were determined with Coherent J5-09
detectors. A low pulse repetition rate of 10 Hz was used to avoid the
occurrence of cumulative thermal nonlinearities. The beam was filtered
spatially so that higher order modes can be eliminated before being
focussed with a lens (focal length = 15 cm). A 2 mm quartz cuvette was
used during the z-scan measurements in DMF solution. The PBC thin film
National Natural Science Foundation of China (No. 21371090),
and Natural Science Foundation of Jiangsu Province
(BK20130054) grants to ZS, and a Pearson Young Memorial
Scholarship to JH. Photophysical measurements were made
possible by the Laser Rental Pool Programme of the Council for
Scientific and Industrial Research (CSIR) of South Africa. The
authors thank Marcel Louzada for help with the z-scan
calculations.
thicknesses were determined using
a TESCAN Vega TS 5136LM
scanning electron microscopy instrument.
Keywords: Dyes/Pigments • BODIPYs • nonlinear optics •
Synthesis: BODIPYs 3-6 (Scheme 1) were prepared in a similar manner
according to the literature procedures.[48-51]
optical limiting • z-scan
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512.45; found: 511.96 [M]+; elemental analysis calcd (%) for
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N 5.43, S 12.68.
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Acknowledgements
This study was made possible by support from a China-South
Africa joint research program (CS08-L07 and uid: 95421) to ZS
and JM, a Competitive Support for Unrated Researchers grant
from the National Research Foundation of South Africa (uid:
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Entry for the Table of Contents
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BODIPYs as optical limiters: The
Jessica Harris, Lizhi Gai, Gugu
optical limiting properties of a series of
Kubheka, John Mack,* Tebello
Nyokong and Zhen Shen*
3,5-dithienylenevinylene
BODIPY
dyes with D--A type structures were
studied by using the z-scan technique
at 532 nm in the nanosecond pulse
range. An unusually strong reverse
saturable absorption RSA response
was observed when the compounds
are embedded in poly(bisphenol
carbonate A) polymer thin films.
Page No. – Page No.
Optical limiting properties of 3,5-
dithienylenevinylene BODIPY dyes at
532 nm
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