The effect of heavy atom to two photon absorption properties and intersystem crossing mechanism in aza-boron-dipyrromethene compounds

Article abstract of DOI:10.1016/j.dyepig.2015.07.002

Abstract New aza-boron-dipyrromethene compounds containing bromine atoms at various positions were designed and synthesized to enhance the triplet state population and two photon absorption properties for applications such as two-photon photodynamic therapy, triplet-triplet annihilation up-conversion. Steady state fluorescence and ultrafast pump probe spectroscopy techniques revealed that only 2, 6 positions of aza-boron-dipyrromethene core contribute to triplet state population significantly. Density function theory calculations showed that when bromine atoms introduced to 2, 6 position of aza-boron-dipyrromethene core, singlet and triplet energy levels get closer therefore probability of intersystem crossing increases. Z-scan experiments at 800 nm wavelengths revealed considerably large (610 GM) two photon absorption cross section value with respect to literature for compounds showing intersystem crossing mechanism. The efficient intersystem crossing and enhanced two-photon absorption properties make the investigated aza-boron-dipyrromethene compounds good candidates for two-photon photodynamic therapy application.

Full text of DOI:10.1016/j.dyepig.2015.07.002

Accepted Manuscript
The Effect of Heavy Atom to Two Photon Absorption Properties and Intersystem
Crossing Mechanism in Aza-Boron-Dipyrromethene Compounds
Ahmet Karatay, M. Ceren Miser, Xiaoneng Cui, Betül Küçüköz, Halil Yılmaz, Gökhan
Sevinç, Elif Akhüseyin, Xueyan Wu, Mustafa Hayvali, H. Gul Yaglioglu, Jianzhang
Zhao, Ayhan Elmali
PII:
S0143-7208(15)00270-3
10.1016/j.dyepig.2015.07.002
DYPI 4842
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 4 May 2015
Revised Date: 3 July 2015
Accepted Date: 5 July 2015
Please cite this article as: Karatay A, Miser MC, Cui X, Küçüköz B, Yılmaz H, Sevinç G, Akhüseyin E,
Wu X, Hayvali M, Yaglioglu HG, Zhao J, Elmali A, The Effect of Heavy Atom to Two Photon Absorption
Properties and Intersystem Crossing Mechanism in Aza-Boron-Dipyrromethene Compounds, Dyes and
Pigments (2015), doi: 10.1016/j.dyepig.2015.07.002.
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ACCEPTED MANUSCRIPT
The Effect of Heavy Atom to Two Photon
Absorption Properties and Intersystem Crossing
Mechanism in Aza-Boron-Dipyrromethene
Compounds
a
b
c
a
b
Ahmet Karatay, M. Ceren Miser, Xiaoneng Cui, Betül Küçüköz, Halil Yılmaz, Gökhan
b
a
c
*,b
*,a
Sevinç, Elif Akhüseyin, Xueyan Wu, Mustafa Hayvali, H. Gul Yaglioglu, Jianzhang
c
a
Zhao, Ayhan Elmali
a
Department of Engineering Physics, Faculty of Engineering, Ankara University, 06100
Beşevler, Ankara, Turkey
b
Department of Chemistry, Faculty of Science, Ankara University, 06100 Beşevler, Ankara,
Turkey
c
Dalian University of Technology,State Key Laboratory of Fine Chemicals, School of
Chemical Engineering, E-208 West Campus, 2 Ling-Gong Road, Dalian 116024, P. R. China

ACCEPTED MANUSCRIPT
ABSTRACT
New aza-boron-dipyrromethene compounds containing bromine atoms at various positions
were designed and synthesized to enhance the triplet state population and two photon
absorption properties for applications such as two-photon photodynamic therapy, triplet-
triplet annihilation up-conversion. Steady state fluorescence and ultrafast pump probe
spectroscopy techniques revealed that only 2, 6 positions of aza-boron-dipyrromethene core
contribute to triplet state population significantly. Density function theory calculations
showed that when bromine atoms introduced to 2, 6 position of aza-boron-dipyrromethene
core, singlet and triplet energy levels get closer therefore probability of intersystem crossing
increases. Z-scan experiments at 800 nm wavelengths revealed considerably large (610 GM)
two photon absorption cross section value with respect to literature for compounds showing
intersystem crossing mechanism. The efficient intersystem crossing and enhanced two-photon
absorption properties make the investigated aza-boron-dipyrromethene compounds good
candidates for two-photon photodynamic therapy application.
KEYWORDS Aza-boron-dipyrromethene, Heavy atom effect, Ultrafast pump probe
spectroscopy, Intersystem crossing, Two photon absorption, Z-scan technique
*
Corresponding authors. Tel./Fax: +90 (312) 2232395 (M. H.), Tel./Fax:+90 (312) 2127343 (H. G.
Y.).
E-mail addresses: yoglu@eng.ankara.edu.tr (H.G. Yaglioglu); hayvali@science.ankara.edu.tr
(M. Hayvali)

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1
. Introduction
There has been a great deal of interest on intersystem crossing (ISC) process of novel
materials due to their related applications in photochemical and photophysical processes, such
as photodynamic therapy (PDT) [1-5], photocatalytic organic reactions [6-11], triplet–triplet
annihilation (TTA), upconversion (UC), and singlet oxygen generation [12,13]. ISC process is
an efficient way to generate singlet oxygen especially for PDT application. The spin-orbit
perturbation of electronic states plays an important role on the photophysical properties of
organic molecules. Introducing heavy atoms to molecular systems increases ISC process and
therefore, changes photophysical properties, which is known as heavy atom effect [14].
Enhanced spin-orbit perturbations can be achieved by introducing a heavy atom directly onto
the absorbing core of the molecule (internal heavy atom effect) [15, 16] or by positioning
heavy atoms to the peripheral positions (external heavy atom effect) [13, 17, 18]. Internal
heavy atom effect is the most efficient way to enhance ISC process. Therefore, the effects of
heavy atom on the photoinduced electron transfer mechanism to the triplet state have been
extensively studied [1, 19].
On the other hand, organic molecules with large two photon absorption (TPA)
properties have attracted increasing attention due to a wide range of potential applications
including optical limiting [20,21], TPA imaging microscopy [22], three-dimensional
microfabrication [23,24], optical data storage [25,26], TPA upconversion lasing [27], and
especially for two-photon PDT [28]. Therefore, design and synthesis of molecules with large
TPA cross-sections (TPCS) become a popular research field [29, 30]. Two-photon PDT
application requires efficient ISC mechanism and high TPCS at near-IR region due to its low
energy, deep penetration and negligible damage to the normal biological tissue. However,
near-IR TPA photodynamic therapy is limited due to lack of TPA photosensitizer with high
intersystem crossing rate and large TPCS.

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There have been several studies about the application of aza-boron-dipyrromethene (aza-
BODIPY) compounds to one photon PDT in the literature [1, 31]. Our previous research on
aza-BODIPY compounds show that these compounds exhibit TPA properties [32, 33]. In this
work, we designed and synthesized new aza-BODIPY compounds possessing both ISC and
TPA properties for PDT applications.
In literature, heavy atom effect on photophysical properties of organic molecules and
complexes of various types of molecules such as meso-tetraaryl porphyrins for selenium
atoms [34, 35], poly halogenated meso-tetraaryl porphyrins and bacteriochlorins molecules
[
36, 37], BODIPY [38, 39], and aza-BODIPY [40-42] compounds were studied. Heavy atoms
introduced to 2,6 position of aza-BODIPY core are known to enhance the probability of ISC
due to internal heavy atom effect (i.e. spin orbit coupling) [14-16]. This effect was
investigated by monitoring fluorescence, phosphorescence and singlet oxygen quantum yields
[
1, 39, 43, 44]. It is known that number of heavy atoms introduced to BODIPY core other
than 2,6 positions do not affect ISC [43]. However, it is not clear, how do heavy atoms on the
peripheral positions effect ISC in the literature for aza-BODIPY compound. Therefore, our
designed and synthesized new aza-BODIPY compounds contain Br atoms at various
positions. Previous works investigating the heavy atom effects on the triplet population used
indirect methods such as singlet oxygen quantum yields. We investigated their triplet level
populations by using ultrafast pump probe spectroscopy technique. This technique is a very
sensitive tool to investigate directly the transition of triplet to levels with fs time resolution. In
order to clarify our experimental results and reveal the mechanism causing ISC, we performed
density functional theory (DFT) calculations for our investigated compounds.
2
. Result And Discussion
.1 Absorption and Fluorescence Measurement
2

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UV-Vis absorption and emission spectra of 4a-d and 5a-d are shown in Fig. 1 and Fig.
2
, respectively. Absorption spectrum of 4a compound reveals S →S transition with
0
1
maximum absorbance wavelength at 650 nm in Fig. 1. However, S →S transition of Br
0
1
containing compounds is between 645 nm and 667 nm. This spectral shift depends on the
position of Br atoms on aza-BODIPY core. Bathochromic shifts were observed when Br
atoms on the para positions of the phenyl ring on the any of 1,7 and 3,5 positions (4b-d, 5b-d)
as seen in Table 1. On the contrary, directly introducing of Br atoms to 2,6 position of aza-
BODIPY core leads to hypsochromic shifts (5a-d). Interestingly, the amounts of spectral shift
per binding position, whether it is bathochromic or hypsochromic are the same. Therefore,
these bathochromic or hypsochromic spectral shifts cancel each other for 4a, 5b and 5c
compounds and the absorption bands of these compounds are localized around 650 nm. In
addition, FWHM values for studied compounds increases with increasing the number of the
heavy atoms (Table 1).
On the other hand, another absorption band is observed at 320 nm which corresponds to
S →S transition of aza-BODIPY compounds without containing Br atoms at 2,6 position.
0
2
Upon introducing Br atoms at 2,6 position of aza-BODIPY, significant hypsochromic shift
about 20 nm) was observed for S →S transition.
(
0
2
It is known that aza-BODIPY compounds have high fluorescence quantum yields [45].
A single fluorescence signals were observed for 4a-d compounds as seen in Fig. 2. The
fluorescence intensity increases with increasing number of binding p-Br phenyl groups to
1
,7,3,5 positions of aza BODIPY core. Therefore, 4d compound containing p-Br phenyl at
,7,3,5 positions shows the highest fluorescence intensity while 4a compound has the lowest
1
fluorescence intensity among these compounds. On the other hand, it is well known that the
introducing Br atoms to 2,6 positions makes singlet-triplet transition easier [41]. Therefore, in

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our studied compounds, fluorescence signal drastically decrease for 5a-d compounds
containing Br atoms at 2,6 position of aza-BODIPY core due to the ISC process. This
decreased fluorescence signal may indicate that our low fluorescent compounds may have
efficient ISC due to heavy atom effect. In order to obtain more information about the effect of
heavy atom on aza-BODIPY compounds by changing position and number of heavy atoms,
we performed ultrafast pump probe spectroscopy experiments.
2.2 Ultrafast Pump Probe Spectroscopy
Ultrafast pump probe spectroscopy experiments were used to investigate the effect of
heavy atom and its position on ISC mechanism and decay processes of excited states of the
aza-BODIPY compounds. Femtosecond transient absorption spectra with 640 nm excitation
wavelength for 4a and 5a compounds in THF are given in Fig. 3a and 3b, respectively. The
results of experiments show different characteristics depending on the position and the
number of heavy atom. Transient absorption spectra of 4a have a great bleach signal at 650
nm and excited state absorption signal below 575 nm and above 750 nm as shown in Fig. 3a.
4
b-d compounds also show similar transient absorption spectra characteristics. However,
linear and transient absorption spectra of compound 5a have different characteristics. For
instance, vibration states appearing around 520 nm in linear absorption spectra get higher
absorption peak when Br atoms bond to 2,6 position of aza-BODIPY core. That causes an
extra bleach signal to appear around 520 nm in transient absorption spectra as seen in Fig. 3b.
In addition to that, an excited state absorption (ESA) signal appears in transient absorption
spectra at about 120 ps time delay and around 695 nm wavelength, which can be attributed to
T -T transition (Fig. 3b, Fig. 4). Similar spectral properties were also observed for other Br
1
n
compounds containing Br atoms at 2,6 position of aza-BODIPY core (5a-d). These
experimental data were given in supporting information.

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Another evidence of ISC mechanism is clearly observed from the decay curves seen in
Fig. 5. The lifetime of the bleach signals show great differences whether including Br atoms
at 2,6 position of aza-BODIPY core or not. There is a long time component (with decay time
about µs range) for 5a-d compounds. This component can be attributed to lifetime of the
triplet states of the aza-BODIPY. These experimental results indicate that only Br atoms at
2
,6 positions enhance the ISC mechanism due to the internal heavy atom effect [7]. Enhanced
ISC mechanism also causes fluorescence signal reducing drastically as observed in the
fluorescence measurements in Fig. 2.
Moreover, different decay curves were recorded for 4a and 4d compounds as seen in
Fig. 6. The excited state lifetime of the 4d compound is longer than that of 4a compound. It
may be due to heavy atom effect since it contains more Br atoms.
In an attempt to clarify the reason why compounds 5a-d showing stronger ISC than 4a-
d compounds we performed DFT calculations for these compounds.
2.3 DFT Calculations on the Photophysical Properties of the Complexes
The ground state geometries of the compounds were optimized with the DFT theory.
The aza-BODIPY core takes a planar geometry. Interestingly, the four phenyl rings take a
nearly co-planar geometry orientation toward the aza-BODIPY core, even with a
perpendicular initial geometry for the DFT calculation. This result indicates that the coplanar
geometry is at least a local energy minimum. For example, the dihedral angle between the
phenyl ring (close to the BF complexation site) and the aza-BODIPY core is ca. 31°. For the
2
phenyl rings at the opposite position of the BF complexation, the dihedral angle is smaller
2
(24 °), probably due to the smaller steric hindrance. Similar results were found for all the
compounds 4b- 4c (see Supporting Information). The T triplet state energy of 4a was
1
calculated as 1378 nm (0.90 eV), which is close to a previously reported value (0.87 eV) [46].

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The excited state of compound 4a was calculated. The UV-Vis absorption maximum
is predicted at 605 nm, which is close, the experimental result of 650 nm. The deviation is
known for the calculation of BODIPY compounds with the DFT theory (Fig. 7). The frontier
molecular orbitals are delocalized on the aza-BODIPY core and the appended phenyl rings.
Similarly, the geometry of the ground state of the 2,6-dibromo aza-BODIPYs (5a-5d)
was also optimized. Interestingly, we found that the dihedral angles between the phenyl rings
and the aza-BODIPY core are increased, that is, the moieties in the molecules are less co-
planar. For example, the dihedral angle between the phenyl rings (close to the
BF complexation site) and the aza-BODIPY core is ca. 51°. For the phenyl rings on the
2
opposite to the BF complexation site, dihedral angle of ca. 41° was found. These angles are
2
much larger than that observed for the unbrominated compounds 4a-4d. These changes are
probably due to the steric hindrance of the bromine atoms at the 2,6 position of the aza-
BODIPY core.
The excited states of compound 5a were also studied with the DFT calculations
(
Table 2) (Fig. 8). Interestingly, shorter wavelength for UV-vis absorption band was found
for 5a as compared with that of 4a. For example, the first absorption band was predicted as
81 nm for 5a, as compared with that of 605 nm for 4a (Table 3). This blue-shifted
5
absorption of 5a as compared with 4a may be due to the poor planar geometry of the
molecule, as predicted by the DFT calculations on the ground state geometry.
The T state energy level of 5a was calculated as 0.98 eV (1267 nm). Thus 5a can be
1
1
used as triplet photosensitizer for photosensitizing of singlet oxygen ( O ). This theoretical
2
prediction is in agreement with the experimental results [1, 47].
The spin density surfaces of the compounds were studied with the optimized triplet
state geometry, so that the distribution of the triplet states of the compounds were unveiled
(Fig. 9) [48]. For compound 4a, the triplet state is delocalized over the entire molecule.

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Similar results were found for 4b-4d (see Supporting Information). For 5a, similar results
were observed. Note the bromine atoms contribute to the spin density surface, thus
intersystem crossing is expected for compound 5a.
DFT calculations revealed that singlet energy levels decreases and get closer to triplet
energy levels due to conformation transformation upon excitation for samples 5a-d (Fig.
S26). Decreasing singlet energy levels increase probability of ISC to triplet levels. This can be
attributed to spin-orbit coupling (heavy atom effect). Fluorescence quenching (Fig. 2) and
pump-probe experimental results (Fig. 3, 4) for these compounds support DFT calculations.
On the other hand heavy atoms that are not located at the core of aza-BODIPY (compounds
4
a-d) do not affect conformation transformation and therefore ISC probability is lower for
these molecules (Fig. 3, 4).
2.4 Two Photon Absorption Properties
It is known that TPA properties are improved upon increasing charge transfer for
BODIPY and aza-BODIPY compounds [49-51]. Therefore, in an attempt to find out whether
charge transfer to triplet state affect TPA properties, we investigated number and position
effects of Br atoms on TPA properties by OA Z-scan technique [49]. TPA coefficient (β) and
TPCS (σ ) were calculated from the following equations [51].
2
Nonlinear transmittance T is given in terms of laser intensityI0
,
1
(
T I
) = 1
(1)
0
+ I0 β l
where,
l
is optical path length. β value is obtained from the curve fitting the OA Z-scan data
-50
4
-1
to equation 1. TPCS value σ 2 (1 GM = 10 cm s photon ) is obtained by using β value in
the following equation,

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hv
β
σ 2
=
(2)
−3
N d ×10
A
0
where, NA is the Avogadro number and d0 is molar concentration of the solution.
2
OA Z-scan experimental results of 5a-d compounds as well as theoretical fits at 80 GW/cm
peak intensities are shown in Fig. 10. Calculated TPCS values are written in Table 1. TPA
properties depend on both position and the number of Br atoms introduced to the phenyl rings
at 1,3,5,7 positions. As seen from these results, when Br atoms are bound to 1,7 positions
(σ5c=444 GM) TPCS value is greater than that of bound to 3,5 positions (σ5b= 218 GM). This
result could be explained by considering our DFT calculation given in the previous section.
According to DFT calculations, dihedral angle for 1,7 positions are smaller than that of 3,5
positions. It is known that greater dihedral angle causes smaller the charge transfer due to the
non-planarity of the compound [52]. This explains why 1,7 position (compound 5c) is more
efficient for charge transfer than 3,5 positions (compound 5b) for the investigated
compounds.
Among 5a-d compounds, 5d has the highest TPCS value (610 GM). In the literature, there are
only a few studies about TPA properties of aza-BODIPY compounds [41, 50, 32]. The highest
TPCS value was measured about 30 GM at 800 nm wavelength [41]. Our TPCS value (610
GM) is about twenty times greater than this value.
3
. Conclusion
We synthesized and studied linear and nonlinear optical properties of aza-BODIPY
compounds containing heavy atom with different numbers and positions. The effect of heavy
atom on intersystem crossing mechanism of newly synthesized Br containing aza-BODIPY
compounds were investigated using fluorescence and ultrafast pump probe spectroscopy
experiments as well as density functional theory calculations. The fluorescence intensity

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drastically decreased when compounds include heavy atoms at 2,6 position of the aza-
BODIPY core as observed in the literature. Ultrafast pump probe experimental results
explained observed fluorescence quenching by showing triplet state population when Br
atoms are introduced to the 2,6 positions of aza-BODIPY core. Further, density functional
theory calculations supported these findings by revealing that singlet and triplet levels get
closer to each other when Br atoms are at 2,6 position of aza-BODIPY core. Our experimental
and theoretical investigations showed that introducing Br atoms on peripheral positions of
aza-BODIPY compounds does not affect the triplet state populations. Open aperture Z-scan
experiments at 800 nm wavelengths revealed considerably large (610 GM) two photon
absorption cross section values for investigated compounds showing intersystem crossing
mechanism. This value at 800 nm wavelengths is much greater than that of aza-BODIPY
compounds in the literature at this wavelength, which is important for photodynamic therapy
application. Experimental findings also revealed that binding of phenyl rings affect two
photon absorption properties considerably. Our studied compounds with high intersystem
crossing mechanism and enhanced two photon absorption properties at 800 nm wavelengths
may be good candidates for two-photon photodynamic therapy applications. On the other
hand, observed weak fluorescence signal and high two-photon absorption cross section value
may be useful for fluorescence and two-photon fluorescence imaging applications. Therefore,
we believe this work gives valuable contribution to design new compounds for two photon
absorption applications.
4
. Experimental Section
4.1 Syntheses of Studied Compounds
4
.1.1 General

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All solvents and reagents were purchased from Sigma-Aldrich Chemical Company and used
as received without further purification. Reactions were monitored by thin layer
chromatography using fluorescent coated aluminum sheets (Merck 60 PF-254). Compounds
1
a-d, 2a-d, 3a-d, 4a-c, 5a were prepared according to the literature [1,53,54].
4
.1.2 Characterization
Melting points were determined on a Gallenkamp melting point platform. Flash column
chromatography was carried out using silica columns on Combi Flash Rf 200 (Teledyne-Isco,
Lincoln, NE) instruments unless otherwise mentioned. The IR spectra were recorded using
Shimadzu Infinity model FTIR spectrometer equipped three reflections ATR attachment.
Mass spectral analyses were performed with a Waters 2695 Alliance MicromassZQ
1
LC/MSspectrometer. H NMR spectra were recorded with a VARIAN Mercury 400 MHz
1
spectrometer. H NMR chemical shifts (δ) are given in ppm downfield from Me Si,
4
1
3
determined by chloroform (δ = 7.26 ppm). C NMR spectra were recorded with a VARIAN
1
3
Mercury 100 MHz spectrometer. C NMR chemical shifts (δ) are reported in ppm with the
internal CDCl at δ 77.0 ppm as standard.
3
4
.1.2 Syntheses of Compounds
Synthesis Compound 4d: A solution of compound 3d (0.23 g, 0.30 mmol) in dry
CH Cl (100 mL) was treated with diisopropylethylamine (0.52 mL, 3.00 mmol) and the
2
2
mixture was stirred for 10 min at room temperature. Then, boron trifluoridediethyletherate
0.55 mL, 4.50 mmol) was added and the reaction mixture was stirred at room temperature for
4 h. The mixture was washed with water, and the organic layer dried over sodium sulfate.
(
2
Removal of solvent gave a residue, which was purified by flash chromatography on silica
eluting with hex/EtOAc (2:1) resulting the product as a dark blue solid (0.20 g, 83%), mp
1
2
70-273 °C. HNMR (400 MHz, CDCl ) δ 7.89 (d, J = 8.4 Hz, 6H), 7.64-7.60 (m, 10H), 7.00
3

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1
3
(
s, 2H), C NMR (100 MHz, CDCl ) δ 132.3, 132.1, 131.8, 131.5, 131.4, 129.4, 128.9, 128.0,
3
-1
1
26.5, 125.1; IR (cm ): 1581.6, 1292.3, 1232.5; Anal. Calcd. for C H BBr F N : C, 47.28;
32 18 4 2 3
H, 2.23; N, 5.17. Found: C, 47.06; H, 2.14; N, 5.23;ES/MS calculated for 812.9, found 813.7.
Synthesis Compound 5b: A solution of compound 4b (0.21 g, 0.32 mmol) in dry
CH Cl (60 mL) was added to N-bromosuccinimide (NBS) (0.12g, 0.68 mmol), and the
2
2
mixture was stirred at room temperature for 24 h. After the reaction was completed, the
solvent was evaporated under reduced pressure. The residue was washed with water and dried
over sodium sulfate. The residual was purified by flash chromatography on silica eluting with
hex/EtOAc (2:1) which gave the product as a dark blue solid (0.20 g, 76%), mp 283 °C.
1
13
HNMR (400 MHz, CDCl ) δ 7.87-7.85 (m, 4H), 7.62 (s, 8H), 7.47-7.45 (m, 6H), C NMR
3
(
100 MHz, CDCl ) δ 157.3, 144.4, 143.3, 131.9, 131.5, 130.7, 130.3, 130.1, 129.9, 128.7,
3
-1
1
28.1, 126.0; IR (cm ): 1587.4, 1313.5, 1296.2; Anal. Calcd. for C H BBr F N : C, 47.28;
32 18 4 2 3
H, 2.23; N, 5.17. Found: C, 46.83; H, 2.32; N, 5.09; ES/MS calculated for 812.9 found 813.0.
Synthesis Compound 5c: A solution of compound 4c (0.20 g, 0.31 mmol) in dry
CH Cl (60 mL) was added to N-bromosuccinimide (NBS) (0.12 g, 0.68 mmol), and the
2
2
mixture was stirred at room temperature for 24 h. After the reaction was completed, the
solvent was evaporated under reduced pressure. The residue was washed with water, and
dried over sodium sulfate. The residual was purified by flash chromatography on silica eluting
with hex/EtOAc (2:1) which gave the product as a dark blue solid (0.14 g, 56%), mp 245 °C.
1
HNMR (400 MHz, CDCl ) δ 7.74 (d, J = 8.4 Hz, 4H), 7.71 (d, J = 8.0 Hz, 4H), 7.60 (d,
3
1
3
J=8.4 Hz, 4H), 7.50-7.47(m, 6H), C NMR (100 MHz, CDCl ) δ 159.0, 144.3, 141.9, 146.0,
3
-
1
1
1
2
32.3, 131.7, 131.3, 130.5, 129.6, 129.3, 128.3, 124.9, 110.8; IR (cm ): 1587.4, 1274.9,
222.9; Anal. Calcd. for C H BBr F N : C, 47.28; H, 2.23; N, 5.17. Found: C, 46.92; H,
3
2
18
4
2
3
.28; N, 5.11; ES/MS calculated for 812.9 found 813.1.

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Synthesis Compound 5d: A solution of compound 4d (0.10 g, 0.13 mmol) in dry
CH Cl (20 mL) was added to N-bromosuccinimide (NBS) (0.05g, 0.28 mmol), and the
2
2
mixture was stirred at room temperature for 24 h. After the reaction was completed, the
solvent was evaporated under reduced pressure. The residue was washed with water, and
dried over sodium sulfate. The residual was purified by flash chromatography on silica eluting
with hex/EtOAc (2:1) which gave the product as a dark blue solid (0.05 g, 38%), mp>300 °C.
1
13
HNMR (400 MHz, CDCl ) δ 7.72 (d, J = 8.8 Hz, 4H), 7.64-7.58 (m, 12H), C NMR (100
3
-1
MHz, CDCl ) δ 144.3, 142.1, 132.0, 131.8, 131.5, 129.2, 127.8, 126.2, 124.9; IR (cm ):
3
1
587.4, 1311.6, 1296.2; Anal. Calcd. for C H BBr F N : C, 39.59; H, 1.66; N, 4.33. Found:
32 16 6 2 3
C, 39.83; H, 1.41; N, 4.49. ES/MS calculated for 970.7 found 971.8.
4.2 Optical Measurements
The UV-Vis absorption spectra of aza-BODIPY derivatives were recorded using a scanning
spectrophotometer (Shimadzu UV- 1800). The fluorescence measurements were obtained
with a Perkin Elmer model LS 55 fluorescence spectrometer. All fluorescence spectra were
-5
obtained at 1x10 M concentration in THF solution by using 10 mm quartz cell.
Ultrafast pump probe spectroscopy measurements were performed using Ti:Sapphire
laser amplifier, optical parametric amplifier system with 45 fs pulse duration and 1 kHz
repetition rate (Spectra Physics, Spitfire Pro XP, TOPAS). In order to investigate effect of the
heavy atom on ISC mechanisms and excited state lifetime, commercial pump probe
experimental setup (Spectra Physics, Helios) with white light continuum probe was used. The
pump wavelength was chosen for ultrafast pump probe spectroscopy experiments according to
maximum absorption wavelength of the investigated samples. Pulse duration was measured as
1
20 fs inside the pump probe setup.
Nonlinear optical absorption properties of aza-BODIPY derivatives were investigated
by using open aperture (OA) Z-scan technique [55]. Laser source is mode-locked Ti:Sapphire

ACCEPTED MANUSCRIPT
laser amplifier system with 800 nm wavelength, 1 ps pulse duration and 1 kHz repetition rate
(Spectra Physics, Spitfire Pro XP, TOPAS). Laser beam was focused on solution in 1 mm
thick cell by a lens with 20 cm focal length. Concentrations of the solutions for two photon
absorption measurements were 0.005 M. 4a-d compounds have linear absorption at 800 nm
wavelength for 0.005 M. Therefore, OA Z-scan experiments were not performed for these
compounds. TPA properties of compounds 5a-d were investigated and compared with each
other.
4
.3 DFT Calculation
The DFT calculations were used for optimization of both singlet states and triplet states. The
UV−Vis absorption and the energy level of the T1 state were calculated with the time
dependent DFT (TDDFT), based on the optimized singlet ground state geometries (S state).
0
The spin density surface of the complexes was calculated based on the optimized triplet state.
All the calculations were performed at the B3LYP/GENECP/LANL2DZ level with Gaussian
0
9W [56].
REFERENCES
[
1] Gorman A, Killoran J, O’Shea C, Kenna T, Gallagher WM, O’Shea DF. In Vitro Demonstration of the
Heavy-Atom Effect for Photodynamic Therapy. J. Am. Chem. Soc 2004; 126:10619 10631.
2] McDonnell SO, Hall MJ, Allen LT, Byrne A, Gallagher WM, O’Shea DF. Supramolecular Photonic
Therapeutic Agents. J. Am. Chem. Soc 2005; 127:16360–16361.
3] Kamkaew A, Lim SH, Lee HB, Kiew LV, Chung LY, Burgess K. BODIPY Dyes in Photodynamic Therapy.
Chem. Soc. Rev 2013; 42:77 88.
4] Cakmak Y, Kolemen S, Duman S, Dede Y, Dolen Y, Kilic B, Kostereli Z, Yildirim LT, Dogan AL, Guc D,
Akkaya EU. Designing Excited States: Theory-Guided Access to Efficient Photosensitizers for Photodynamic
Action. Angew. Chem. Int. Ed 2011; 123:12143 12147.
–
[
[
–
[
–

ACCEPTED MANUSCRIPT
[
5] O’Connor AE, Gallagher WM, Byrne AT. Porphyrin and Nonporphyrin Photosensitizers in Oncology:
Preclinical and Clinical Advances in Photodynamic Therapy. Photochem. Photobiol 2009; 85:1053
–
1074.
6838.
7] Shi L, Xia W. Photoredox Functionalization of C–H Bonds Adjacent to a Nitrogen Atom. Chem. Soc. Rev
012; 41:7687–7697.
[
[
6] Xuan J, Xiao WJ. Visible-Light Photoredox Catalysis. Angew. Chem. Int. Ed 2012; 51:6828–
2
[
[
8] Ravelli D, Fagnoni M, Albini A. Photoorganocatalysis. What for?. Chem. Soc. Rev 2013; 42:97–113.
9] Maity S, Zhu M, Shinabery RS, Zheng N. Intermolecular [3+2] Cycloaddition of Cyclopropylamines with
Olefins by Visible-Light Photocatalysis. Angew. Chem. Int. Ed 2012; 51:222
10] Neumann M, Füldner S, König B, Zeitler K. Metal-Free, Cooperative Asymmetric Organophotoredox
Catalysis with Visible Light. Angew. Chem. Int. Ed 2011; 50:951 954.
11] Zou YQ, Lu LQ, Fu L, Chang NJ, Rong J, Chen JR, Xiao WJ. Visible-Light-Induced Oxidation/[3+2]
Cycloaddition/Oxidative Aromatization Sequence: A Photocatalytic Strategy to Construct Pyrrolo[2,1-
a]isoquinolines. Angew. Chem. Int. Ed 2011; 50:7171 7175.
12] Schweitzer C, Schmidt R. Physical Mechanisms of Generation and Deactivation of Singlet Oxygen. Chem.
Rev 2003; 103:1685–1757.
–226.
[
–
[
–
[
[
[
13] Koziar JC, Cowan DO. Photochemical Heavy-Atom Effects. Acc. Chem. Res 1978; 11:334–341.
14] Sauerwein B, Schuster GB. External Iodine Atoms Influence Over the Intersystem Crossing Rate of
Cyanine Iodide Ion Pair in Benzene Solution. J. Phys. Chem 1991; 95:1903–1906.
15] Yuster P, Weissman SI. Effects of Perturbations on Phosphorescence: Luminescence of Metal Organic
Complexes. J. Chem. Phys 1949; 17:1182 1188.
16] McClure DS. Triplet‐Singlet Transitions in Organic Molecules. Lifetime Measurements of the Triplet State.
J. Chem. Phys 1949; 17:905–913.
17] McGlynn SP, Reynolds MJ, Daigre GW, Christodoyleas NDJ. The External Heavy-Atom Spin-Orbital
[
–
[
[
1,2
Coupling Effect. III. Phosphorescence Spectra and Lifetimes of Externally Perturbed Naphthalenes . J. Phys.
Chem 1962; 66:2499–2505.
[
18] Kasha MJ. Collisional Perturbation of Spin‐Orbital Coupling and the Mechanism of Fluorescence
Quenching. A Visual Demonstration of the Perturbation. J. Chem. Phys 1952; 20:71–74.
19] (a) Zhang X, Xiao Y, Qi J, Qu J, Kim B, Yue X, Belfield KD. Long-Wavelength, Photostable, Two-Photon
Excitable BODIPY Fluorophores Readily Modifiable for Molecular Probes. J. Org. Chem 2013; 78: 9153−9160;
[

ACCEPTED MANUSCRIPT
(
b) Solovyov KN, Borisevich EA. Intramolecular heavy-atom effect in the photophysics of organic molecules.
Physics – Uspekhi 2005; 48:231 – 253; (c) Zhao J, Wu W, Sun J, Guo S. Triplet photosensitizers: from
molecular design to applications. Chem. Soc. Rev 2013; 42:5323-5351.
[
20] He GS, Xu GC, Prasad PN, Reinhardt BA, Bhatt JC, Dillard AG. Two- photon absorption and optical-
limiting properties of novel organic compounds. Opt. Lett 1995; 20:435- 437.
21] Ehrlich JE, Wu XL, Lee IYS, Hu ZY, Röckel H, Marder SR, Perry JW. Two-photon absorption and
broadband optical limiting with bis-donor stilbenes. Opt. Lett 1997; 22:1843- 1845.
22] Kasischke KA, Wishwasrao HD, Fisher PJ, Zipfel WR., Webb WW. Neutral activity triggers neuronal
oxidative metabolism followed by astrocytic glycolysis. Science 2004; 305: 99-103.
23] Kawata S, Sun HB, Tanaka T, Takada K. Finer feartures for functional microdevices. Nature 2001;
12:697- 698.
24] Zhou W, Kuebler SM, Braun KL, Yu T, Cammack JK, Ober CK, Perry JW, Marder SR. An efficient two-
photon-generated photoacid applied to positive-tone 3D microfabrication. Science 2002; 296:1106-1109.
25] Cumpston BH, Ananthavel SP, Barlow S, Dyer DL, Ehrlich JE, Erskine LL, Heikal AA, Kuebler SM, Lee
[
[
[
4
[
[
IYS, McCord-Maughon D, Qin JG, Röckel H, Rumi M, Wu XL, Marder SR, Perry JW. Two-photon
polymerization initiator for three-dimensional optical data storage and microfabrication. Nature 1999; 398: 51-
5
4.
26] Parthenopoulos DA, Rentzepis PM. Three-dimensional optical storage memory. Science 1989; 245: 843-
45.
27] Bhawalkar JD, He GS, Park CK, Zhao CF, Ruland G, Prasad PN. Efficient, two-photon pumped green
upconverted cavity lasing in a new dye. Opt. Commun 1996; 124: 33-37.
28] Bhawalkar JD, Kumar ND, Zhao CF, Prasad PN. Two-photon photodynamic therapy. J. Clin. Laser Med.
Surg 1997; 15:201- 204.
29] Albota M, Beljonne D, Bredas JL, Ehrlich JE, Fu JY, Heikal AA, Hess SE, Kogej T, Levin MD, Marder
[
8
[
[
[
SR, McCord-Maughon D, Perry JW, Rockel H, Rumi M, Subramaniam G, Webb WW, Wu XL, Xu C. Design
of organic molecules with large two-photon absorption cross sections. Science 1998; 281:1653–1656.
[
30] Kogej T, Beljonne D, Meyers F, Perry JW, Marder SR, Bredas JL. Mechanism for enhancement of two-
photon absorption in donor–acceptor conjugated chromophores. Chem. Phys. Lett 1998; 298:1–6.

ACCEPTED MANUSCRIPT
[
31] Killoran J, Allen L, Gallagher JF, Gallagher WM, O′Shea DF. Synthesis of BF2 chelates of
tetraarylazadipyrromethenes and evidence for their photodynamic therapeutic behavior. Chem. Commun 2002;
7:1862-1863.
32] Küçüköz B, Hayvalı M, Yılmaz H, Uğuz B, Kürüm U, Yaglioglu HG, Elmali A. Synthesis, optical
1
[
properties and ultrafast dynamics of aza-boron-dipyrromethene compounds containing methoxy and hydroxy
groups and two-photon absorption cross-section. J. Photochem. Photobio.A: Chem 2012; 247:24-29.
[
33] Tekin S, Küçüköz B, Yılmaz H, Sevinç G, Hayvalı M, Yaglioglu HG, Elmali A. Enhancement of two
photon absorption properties by charge transfer in newly synthesized aza-boron-dipyrromethene compounds
containing triphenylamine, 4-ethynyl-N,N-dimethylaniline and methoxy moieties. J. Photochem. Photobio.A:
Chem 2013; 256:23– 28.
[
34] You Y, Gibson SL, Hilf R, Davies SR, Oseroff AR, Roy I, Ohulchanskyy TY, Bergey EJ, Detty MR. Water
Soluble, Core-Modified Porphyrins. 3. Synthesis, Photophysical Properties, and in Vitro Studies of
Photosensitization, Uptake, and Localization with Carboxylic Acid-Substituted Derivatives. J. Med. Chem 2003;
4
6:3734
–3747.
[
35] Hilmey DG, Abe M, Nelen MI, Stilts CE, Baker GA, Baker SN, Bright FV, Davies SR, Gollnick SO,
Oseroff AR, Gibson SL, Hilf R, Detty MR. Water-Soluble, Core-Modified Porphyrins as Novel, Longer-
Wavelength-Absorbing Sensitizers for Photodynamic Therapy. II. Effects of Core Heteroatoms and Meso-
Substituents on Biological Activity. J. Med. Chem 2002; 45:449–461.
[
36] Pineiro M, Rocha Gonsalves AMd’A, Pereira MM, Formosinho SJ, Arnaut LG. New Halogenated
Phenylbacteriochlorins and Their Efficiency in Singlet-Oxygen Sensitization. J. Phy. Chem. A 2002; 106:3787
795.
37] Azenha EG, Serra AC, Pineiro M, Pereira MM, de Melo JS, Arnaut LG, Formosinho SJ, Rocha Gonsalves
AMd’A. Heavy-Atom Effects on Metalloporphyrins and Polyhalogenated Porphyrins. Chem. Phy 2002;
80:177–190.
38] Jiao L, Pang W, Zhou J, Wei Y, Mu X, Bai G, Hao E. Regioselective Stepwise Bromination of Boron
Dipyrromethene (BODIPY) Dyes. J. Org. Chem 2011; 76:9988−9996.
39] Awuah SG, Polreis J, Biradar V, You Y. Singlet Oxygen Generation by Novel NIR BODIPY Dyes. Org.
Lett 2011; 13:3884-3887.
40] Guennic BL, Maurya O, Jacquemin D. aza-boron-dipyrromethene Dyes: TD-DFT Benchmarks, Spectral
Analysis and Design of Original Near-IR Structures. Phys. Chem. Chem. Phys 2012; 14:157–164.
–
3
[
2
[
[
[

ACCEPTED MANUSCRIPT
[
41] Batat P, Cantuel M, Jonusauskas G, Scarpantonio L, Palma A, O’Shea DF, McClenaghan ND. BF2-
azadipyrromethenes: Probing the Excited-State Dynamics of a NIR Fluorophore and Photodynamic Therapy
Agent. J. Phys. Chem. A 2011; 115:14034–14039.
[
42] Adarsh N, Avirah RR, Ramaiah D. Tuning Photosensitized Singlet Oxygen Generation Efficiency of Novel
aza-BODIPY Dyes. Org. Lett 2010; 12:5720-5723.
43] Ortiz MJ, Agarrabeitia AR, Duran-Sampedro G, Banuelos Prieto J, Lopez TA, Massad WA, Montejano HA,
[
Garcia NA, Lopez AI. Synthesis and functionalization of new polyhalogenated BODIPY dyes. Study of their
photophysical properties and singlet oxygen generation. Tetrahedron 2012; 68:1153–1162.
[
44] Yogo T, Urano Y, Ishitsuka Y, Maniwa F, Nagano T. Highly Efficient and Photostable Photosensitizer
Based on BODIPY Chromophore. J. Am.Chem. Soc 2005; 127:12162–12163.
45] Loudet A, Burgess K. BODIPY Dyes and Their Derivatives: Syntheses and Spectroscopic Properties.
Chem. Rev 2007; 107:4891−4932.
46] Quartarolo AD, Russo N, Sicilia E. Structures and Electronic Absorption Spectra of a Recently Synthesised
Class of Photodynamic Therapy Agents. Chem. Eur. J 2006; 12:6797 – 6803.
47] Adarsh N, Shanmugasundaram M, Avirah RR, Ramaiah D. aza-BODIPY Derivatives: Enhanced Quantum
[
[
[
Yields of Triplet Excited States and the Generation of Singlet Oxygen and their Role as Facile Sustainable
Photooxygenation Catalysts. Chem. Eur. J 2012; 18:12655 – 12662.
[
48] (a) Hanson K, Tamayo A, Diev VV, Whited MT, Djurovich PI, Thompson ME. Efficient Dipyrrin-Centered
Phosphorescence at Room Temperature from Bis-Cyclometalated Iridium(III) Dipyrrinato Complexes. Inorg.
Chem 2010; 49:6077–6084; (b) Wu W, Zhao J, Sun J, Guo S. Light- Harvesting Fullerene Dyads as Organic
Triplet Photosensitizers for Triplet–Triplet Annihilation Upconversions. J. Org. Chem 2012; 77:5305−5312.
[
49] Wang Y, Zhang D, Zhou H, Ding, JC, Xiao Y, Qian S. Nonlinear optical properties and ultrafast dynamics
of three novel boradiazaindacene derivatives. J. Appl. Phys 2010; 108:033520.
50] Bouit PA, Kamada K, Feneyrou P, Berginc G, Toupet L, Maury O, Andraud C. Two-photon absorption-
[
related properties of functionalized BODIPY dyes in the infrared range up to telecommunication wavelengths.
Adv. Mater 2009; 21:1151.
[
51] Zheng Q, He GS, Prasad PN. A novel near IR two-photon absorbing chromophore: optical limiting and
stabilization performances at an optical communication wavelength. Chem. Phys. Lett 2009; 475: 250-255.

ACCEPTED MANUSCRIPT
[
52] Knyukshto VN, Sagun EI, Shul’ga AM, Bachilo SM, Starukhin DA, Zen’kevich ÉI. Manifestation of
Nonplanarity Effects and Charge-Transfer Interactions in Spectral and Kinetic Properties of Triplet States of
Sterically Strained Octaethylporphyrins. Optics And Spectroscopy 2001; 90:67-77.
[
53] Bellier Q, Pegaz S, Aronica C, Le Guennic B, Andraud C, Maury O. Near-Infrared Nitrofluorene Substitued
aza-Boron-dipyrromethenes Dyes. Org. Lett 2011; 13:22-25.
54] Gao L, Deligonul N, Gray GT. Gold (I) Complexes of Brominated azadipyrromethene Ligands. Inorg.
Chem 2012; 51:7682−7688.
55] Sheik- Bahae M, Said AA, Wei TH, Hagan DJ, Stryland WV. Sensitive measurement of optical
nonlinearities using a single beam. IEEE Journal of Quantum Electronics 1990; 26:760-769.
56] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, Scalmani G, Barone V,
[
[
[
Mennucci B, Petersson GA, Nakatsuji H, Caricato M, Li X, Hratchian HP, Izmaylov AF, Bloino J, Zheng G,
Sonnenberg JL, Hada M, Ehara M, Toyota K, Fukuda R, Hasegawa J, Ishida M, Nakajima T, Honda Y, Kitao O,
Nakai H, Vreven T, Montgomery JAJr, Peralta JE, Ogliaro F, Bearpark M, Heyd JJ, Brothers E, Kudin KN,
Staroverov VN, Kobayashi R, Normand J, Raghavachari K, Rendell A, Burant JC, Iyengar SS, Tomasi J, Cossi
M, Rega N, Millam JM, Klene M, Knox JE, Cross JB, Bakken V, Adamo C, Jaramillo J, Gomperts R, Stratmann
RE, Yazyev O, Austin AJ, Cammi R, Pomelli C, Ochterski JW, Martin RL, Morokuma K, Zakrzewski VG, Voth
GA, Salvador P, Dannenberg JJ, Dapprich S, Daniels AD, Farkas Ö, Foresman JB, Ortiz JV, Cioslowski J, Fox
DJ. Gaussian 09W (Revision A.1), Gaussian Inc.: Wallingford, CT, 2009.

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Table 1. Optical Properties of Studied Compounds in THF.
Stokes
Shift
-
1
-
c
a
b
ε (M cm
d
FWHM
σ
2
Sample
λ
max(nm)
λ
emis(nm)
Φfluo
1
)
(nm)
(
GM
)
(nm)
4
a
650
659
658
667
645
651
651
657
682
693
690
699
685
685
685
685
84600
77800
66000
60700
75500
45900
59300
39100
0.019
0.028
0.032
0.043
<0.001
0.002
0.001
0.002
32
48
51
49
53
51
55
52
59
-
4
b
34
32
32
40
34
34
28
-
4
c
-
4
d
-
5
a
347
218
444
610
5
b
5
c
5
d
a
The peak wavelength of absorption spectra
b
c
d
The peak wavelength of one-photon fluorescence with excitation wavelength λabs
TPA cross section at wavelength of 800 nm
Rodamine was used as a standard for fluorescence quantum yields

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Table 2. Selected parameters for the vertical excitation (UV-Vis absorption and fluorescence
emission) of the compounds. Electronic excitation energies (eV) and oscillator strengths (f),
configurations of the low-lying excited states of 5a and its fluorescent precursors. THF was
employed as solvent in the calculation. Calculated by B3LYP/6-31G(d)/ LANL2DZ, based
on the optimized ground state geometries.
Electronic
TDDFT/B3LYP/6-31G(d)
b
c
d
Excitation energy
2.13eV (581 nm)
f
Composition
H→L
CI
Absorption
Triplet
S0
S0
S0
→
S1
0.7053
0.2551
0.3739
0.8445
0.7047
0.6525
2.50eV (495 nm)
H−2→L
H→L+1
→S3
→S15
4.48eV (277 nm)
0.98eV (1267 nm)
e
0.0000
0.0000
0.0000
H→L
0.7153
0.6896
0.6884
S0
S0
S0
→
→
→
T1
T2
T3
1
2
.98eV (627 nm)
.07eV (599 nm)
H−1→L
H−2→L+1
a
Only selected excited states were considered. The numbers in parentheses are the excitation energy
b
c
in wavelength. Oscillator strength. H stands for HOMO and L stands for LUMO. Only the main
d
configurations are presented. Coefficient of the wave function for each excitations. The CI
e
coefficients are in absolute values. No spin-orbital coupling effect was considered, thus the f values
are zero.

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Table 3. Electronic Excitation Energies (eV), Corresponding Oscillator Strengths (f), Main
Configurations and CI Coefficients of the Low-Lying Electronic Excited States of the 4a. Calculated
by TDDFT//B3LYP/6-31G(D)/LanL2DZ Based on the Optimized Ground State Geometries
TDDFT//B3LYP/6-31G(d)
a
b
c
d
Electronic
transition
Energy (eV/nm) f
Composition
CI
S0→S1
2.05 / 605
0.8462
H→L
0.7082
S0→S2
S0→S3
S0→S8
2.51 / 493
2.61 / 474
3.32 / 374
0.0098
0.3454
0.1977
H−1→L
H−2→L
H−7→L
H−5→L
H→L+1
H−18→L
0.6996
0.7027
0.6791
0.1299
0.1171
0.1519
S0→S23
3.79 / 327
0.1301
H−16→L
H−13→L
0.4603
0.1567
H−3→L+1
H→L+1
H→L+3
H−12→L
H−2→L+2
H−1→L+1
H−1→L+3
H→L
0.4788
0.5444
0.4282
0.1165
0.1865
0.6218
0.2173
0.7205
0.6879
S0→S14
S0→S21
4.26 / 291
5.08 / 244
0.7034
0.2227
e
e
e
T0→T1
T0→T2
T0→T3
0.90 / 1378
2.06 / 602
2.14 / 580
0.0000
0.0000
0.0000
H−1→L
H−2→L
0.6850
a
b
c
Only the selected low-lying excited states are presented. Oscillator strength. Only the main
d
e
configurations are presented. The CI coefficients are inabsolute values. No spin-orbital coupling
effect was considered, thus the f values are zero.

ACCEPTED MANUSCRIPT
Figure Captions
-5
Figure 1. Normalized absorption spectra of studied compounds in THF (1×10 M). The inset shows
the shifts of maximum absorption wavelengths.
-5
Figure 2. Fluorescence spectra of studied compounds in THF (1×10 M).
Figure 3. Femtosecond transient absorption spectra of (a) 4a (b) 5a compounds in THF.
Figure 4. Transient absorption spectra with different time delays for (a) 4a (b) 5a compounds. The
excitation wavelengths are peak maximums of absorption spectrums.
Figure 5. (a) The position effect of heavy atom on transient absorption spectra at 650 nm probe
wavelength. The figure inset indicates molecular structure of compounds. Femtosecond transient
absorption spectra as a function of time of (b) 4a and (c) 5a.
Figure 6. Effects of different number of heavy atoms on transient absorption spectra which are probed
at bleach wavelength. The figure inset indicates molecular structure of compounds.
Figure 7. Electron density maps of the frontier molecular orbitals of compound 4a based on the
optimized ground state geometry. The solvent THF was considered in the calculations (PCM model).
Calculated at the B3LYP/6-31G(d)/ LanL2DZ level with Gaussian 09W.
Figure 8. Selected frontier molecular orbitals involved in the excitation, emission and triplet excited
states of 5a. ISC stands for intersystem crossing. The calculations are at the B3LYP/6-31G(d)/
LANL2DZ level using Gaussian 09W.
Figure 9. Spin density of the compounds 4a and 5a. Calculated based on the optimized triplet state by
DFT at theB3LYP/6-31G(d)/LanL2DZ level using Gaussian 09W.
Figure 10.Experimental results (symbols) and theoretical fits (solid line) of open aperture Z-scan
2
experiments for 5a-d compounds at 80 GW/cm input intensity in THF, using 800 nm femtosecond
pulses.

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Fig. 1

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Fig.2

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Fig. 3

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Fig. 4

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Fig. 5