Cyclometalated Ir(iii) complexes with styryl-BODIPY ligands showing near IR absorption/emission: Preparation, study of photophysical properties and application as photodynamic/luminescence imaging materials

Article abstract of DOI:10.1039/c4tb00284a

Heteroleptic C^N cyclometalated iridium(iii) complexes incorporating a monostyryl/distyryl BODIPY ligand via acetylide bonds of 2,2′-bipyridine (bpy) with both absorption (ca. ε = 8.96 × 10⁴ M ^-1 cm^-1, 9.89 × 10⁴

Full text of DOI:10.1039/c4tb00284a

Highlighting research from Prof. Jianzhang Zhao’s Laboratory
of Molecular Photochemistry & Photophysics, State Key
Laboratory of Fine Chemicals, Dalian University of
Technology, China.
As featured in:
Title: Cyclometalated Ir(III) complexes with styryl-BODIPY
ligands showing near IR absorption/emission: preparation,
study of photophysical properties and application as
photodynamic/luminescence imaging materials
Heteroleptic C^N cyclometalated iridium(III) complexes
incorporating a monostyryl/distyryl BODIPY ligand
showing strong near IR absorption were studied as
photodynamic/luminescence imaging materials.
See Jianzhang Zhao et al.,
J. Mater. Chem. B, 2014, 2, 2838.
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Cyclometalated Ir(III) complexes with styryl-
BODIPY ligands showing near IR absorption/
emission: preparation, study of photophysical
properties and application as photodynamic/
luminescence imaging materials†
Cite this: J. Mater. Chem. B, 2014, 2,
2838
Poulomi Majumdar,‡a Xiaolin Yuan,‡b Shengfu Li,b Boris Le Guennic,c Jie Ma,a
a
Caishun Zhang,a Denis Jacqueminde and Jianzhang Zhao
*
Heteroleptic C^N cyclometalated iridium(III) complexes incorporating a monostyryl/distyryl BODIPY ligand via
acetylide bonds of 2,20-bipyridine (bpy) with both absorption (ca. 3 ¼ 8.96 ꢀ 104 Mꢁ1 cmꢁ1, 9.89 ꢀ 104 Mꢁ1
cmꢁ1, and 7.89 ꢀ 104 Mꢁ1 cmꢁ1 at 664 nm, 644 nm, and 729 nm for Ir-2, Ir-3 and Ir-4, respectively) and
fluorescence emission bands (ca. 624–794 nm for Ir-1, Ir-2, Ir-3 and Ir-4) in the near infra-red region (NIR)
and exceptionally long-lived triplet excited states (s ¼ 156.5 ms for Ir-2) have been reported. Ir(ppy)3 (Ir-0;
ppy ¼ 2-phenylpyridine) was used as reference, which gives the typical weak absorption in visible range (3
¼ 1.51 ꢀ 104 Mꢁ1 cmꢁ1 Mꢁ1 cmꢁ1 at 385 nm). The nanosecond time-resolved transient absorption and DFT
calculations proposed that styryl BODIPY-localized long lived 3IL states were populated for Ir-1, Ir-2, Ir-3
and Ir-4 (sT ¼ 106.6 ms, 156.5 ms, 92.5 ms and 31.4 ms, respectively) upon photoexcitation. The complexes
were used as triplet photosensitizers for singlet oxygen (1O2) mediated photooxidation of 1,5-
dihydronaphthalene to produce juglone. The 1O2 quantum yields (FD) of Ir-1 (0.53) and Ir-2 (0.81) are ca.
9-fold of Ir-3 (0.06) and 40-fold of Ir-4 (0.02), respectively. Ir-2 has high molar absorption coefficient at
664 nm, moderate fluorescence in the NIR region, and high singlet oxygen quantum yield (FD ¼ 0.81),
exhibits predominate photocytotoxicity over dark cytotoxicity in LLC cells (lung cancer cells) upon
irradiation, making it potentially suitable for use in in vivo photodynamic therapy (PDT). Our results are
useful for preparation of transition metal complexes that show strong absorption of visible light in the NIR
region with long-lived triplet excited states and for the application of these complexes in photocatalysis
and theranostics such as simultaneous photodynamic therapy (PDT) and luminescent bioimaging.
Received 20th February 2014
Accepted 4th March 2014
DOI: 10.1039/c4tb00284a
www.rsc.org/MaterialsB
emerging interest for probing biochemical and biological
systems since cellular and tissue imaging in the NIR wave-
Introduction
lengths has better tissue penetration and less bioauto-
uorescence.1,2 On the other hand, cyclometalated Ir(III)
complexes are highly appealing because of their wide range of
applications in electroluminescence,3–12 luminescent molecular
probes,13–22 photodynamic therapy (PDT) for bioimaging,1 pho-
tocatalysis,23 and more recently triplet–triplet annihilation
(TTA) upconversion.24
In recent years, near-infrared (NIR) uorescent probes have
drawn considerable attention of chemists in view of their
aState Key Laboratory of Fine Chemical, School of Chemical Engineering, Dalian
University of Technology, Dalian, 116024, P.R. China. E-mail: zhaojzh@dlut.edu.cn;
Web: http://nechem.dlut.edu.cn/photochem; Fax: +86 411-8498-6236
bCenter Laboratory, Affiliated Zhongshan Hospital of Dalian University, Dalian
In general, cyclometalated Ir(III) complexes, with short
absorption wavelength, weak absorption of visible light and
short-lived triplet excited states (s, a few microseconds), are not
suitable for application in the newly developed areas, such as
photocatalysis,23a,25 luminescent molecular probes,15b,17,26
photodynamic therapy and TTA upconversion,24c for which
strong absorption of visible light and long-lived triplet excited
states are preferred.27
116001, P.R. China
c
´
Institut des Sciences Chimiques de Rennes, CNRS, Universite de Rennes 1, 1 Av. du
General Leclerc, 35042 Rennes Cedex, France
d
´
Laboratoire CEISAM, UMR CNR 6230, Universite de Nantes, 2 Rue de la Houssiniere,
BP 92208, 44322 Nantes Cedex 3, France
eInstitut Universitaire de France, 103, bd Saint-Michel, F-75005 Paris Cedex 05, France
† Electronic supplementary information (ESI) available: 1H, 13C, and HRMS
spectra of the compounds, and photophysical data of the ligands and
complexes and coordinates of the optimized geometries of the complexes. See
DOI: 10.1039/c4tb00284a
Concerning the theranostics application, one of the major
challenges is to develop new complexes that show strong
‡ These authors contribute equally to this work.
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uorescence as well as satisfactory intersystem crossing (ISC). be maximized and the excitation energy can be efficiently
These complexes can be used as multi-functional materials, funnelled to the triplet excited states thus enhancing the
such as photodynamic therapy and at the same time, for applicability of Ir(III) complexes in photocatalysis or PDT. More
luminescent bioimaging. The former application is based on importantly, the absorption as well as the emission wavelengths
efficient ISC to produce triplet excited states, whereas the latter can be extended to the NIR spectral region.
property is related to efficient radiative decay of singlet excited
Concerning this aspect, we have prepared four heteroleptic
states. However, for normal transition metal complexes, the ISC cyclometalated Ir(III) complexes (Ir-1, Ir-2, Ir-3 and Ir-4, Schemes 1
is efficient and the luminescence is phosphorescence, thus, the and 2) using BODIPY ligands to access strong absorption of NIR
luminescence is substantially dependent on molecular oxygen light through p-conjugation linkers to ensure ISC. Hence, the p-
(O2), which may cause interference for the bioimaging. Fine- extended styryl derivatives of uorophore, 4,40-diuoro-4-bora-
tuning the ISC to access balanced strong uorescence with 3a,4a-diaza-s-indacene (BODIPY), which exhibit remarkable
moderate ISC is difficult and very few transition metal wide-spread applications in biological labelling and cell imaging,
complexes were reported as uorescence emissive with as logic gates and ion sensors, and in dye-sensitized solar cells,29
moderate ISC efficiency.11b,18
were used for construction of the ligands. Previously it was found
In order to overcome the aforementioned challenge and to that extension of the ligand p-conjugation induces a strong red
develop methods to access transition metal complexes showing shi of the excitation/emission band compared to the unsub-
strong visible light absorption and long-lived triplet excited stituted complex.30 Herein, we introduced a bulky methoxyl/
states, herein we demonstrate that on attaching bulky organic methyl diamino mono/di styryl BODIPY ligand via acetylide
uorophores to the coordination center via a p-conjugation (–C^C–) bonds of 2,20-bipyridine (bpy) to access absorption/
linker (C^C triple bond),27a,28 the heavy atom effect of Ir(III) can uorescence in the NIR region, with reasonable ISC, as a result
Scheme 1 Synthesis of the ligands L1, L2, L3 and L4, the model complex Ir-0 and meso-tetraphenylporphyrin (TPP), methylene blue (MB) as
standard triplet photosensitizers and compound 7 used as the standard for the fluorescence quantum yields are also presented. Reagents and
conditions: (i) p-methoxybenzaldehyde (4 eq.), toluene, piperidine, AcOH, 120 ꢂC, reflux.; (ii) p-(N,N-dimethylamino)benzaldehyde (4 eq.),
toluene, piperidine, AcOH, 120 ꢂC, reflux.; (iii) 5-ethynyl-2, 20-bipyridine, TEA, THF, Pd(PPh3)4, CuI, Ar, 85 ꢂC, reflux., 12 h.
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Scheme 2 Synthesis of the complexes Ir-1, Ir-2, Ir-3 and Ir-4. The complexes are cationic, and the counter anion [PF6]ꢁ has been omitted for
clarity. (i) [Ir(ppy)2]Cl2, CH2Cl2–MeOH (2 : 1, v/v), argon, 45 ꢂC, reflux., 6 h.
the complexes show reasonably high uorescence quantum IrCl3$3H2O was purchased from Xian Catalyst Chemical Co.,
yields and satisfactory ISC. Thus, the complexes can be used as Ltd (P. R. China). 5-Ethynyl-2,20-bipyridine,33 cyclometalated
theranostic reagents for simultaneous luminescent imaging and Ir(III) chloro-bridge dimers [Ir-(ppy)2]2Cl2,34 and complex Ir-0,35
the photodynamic therapy effect. These properties are exclusive were synthesized according to literature methods. For the
for the normal transition metal complexes.
preparation of compounds 5 and 6, L1, L2, L3 and L4, please
To date only a few styryl aryl cyclometalated Ir(III) complexes refer to ESI materials.†
have been reported, application of the triplet excited states and
photocatalysis have not been studied,30,31 although, a BODIPY-
containing a tridentate N^N^N Pt(II) styryl terpyridine complex
was reported but with a short luminescence lifetime of 3–4 ns
and low uorescence quantum yield.32
Synthesis of 3 and 4
Method A. To a solution of 2 (250 mg, 0.555 mmol) and p-
methoxybenzaldehyde (0.27 mL, 2.22 mmol) in dry toluene,
acetic acid (1.5 mL) and piperidine (1.5 mL) were added under a
N2 atmosphere. The reaction mixture was heated at 120 ꢂC
under reux with a Dean Stark trap to remove the water
generated by the condensation. The reaction was monitored by
Herein, for the rst time we have reported the Ir(III)
complexes (Ir-2, Ir-3 and Ir-4) exhibiting both excitation and
emission bands in the NIR region. The photophysical properties
have been studied with a steady state and time-resolved spec-
troscopy, and DFT calculations. Strong absorption in the NIR
region (ca. 3 is up to 7.89 ꢀ 104 Mꢁ1 cmꢁ1 at 729 nm) and a long-
lived triplet excited state (s ¼ 156.5 ms) were observed, which are
unprecedented for Ir(III) complexes. Furthermore, the
complexes show strong uorescence (FF is up to 39.9%), as well
as moderate ISC property (singlet oxygen quantum yield is up to
FD ¼ 81%). We also nd that these properties are variable for
the complexes. The Ir(III) complexes were used as triplet
photosensitizers for singlet oxygen (1O2) mediated photooxida-
tion and to investigate the PDT effect in LLC cells (lung cancer
cells). These results are useful for designing Ir(III) complexes
that show strong absorption of visible light in the NIR region
and long-lived triplet excited states, and for the application of
these complexes in photocatalysis, theranostics such as PDT/
uorescence bioimaging and non-linear optics.
TLC (CH2Cl2–petroleum ether
¼
1 : 2 as eluent). Aer
consumption of all the starting materials, the reaction mixture
was cooled to room temperature (rt) and the majority of the
solvent was evaporated under reduced pressure. Water (150 mL)
was added to the residue and the product was extracted from
CH2Cl2 (3 ꢀ 100 mL). The organic phase was dried over Na2SO4,
the solvent was evaporated under reduced pressure, and the
crude products thus obtained were puried by column chro-
matography (silica gel, CH2Cl2–petroleum ether ¼ 1 : 2, v/v).
The rst band was collected to obtain a carmine solid as
compound 3. Yield: 186 mg, 59%. mp 223–225 ꢂC. 1H NMR (400
MHz, CDCl3): d 7.57–7.50 (m, 6H), 7.30–7.28 (m, 3H), 6.92 (d,
2H, J ¼ 12 Hz), 6.64 (s, 1H), 3.85 (s, 3H), 2.67 (s, 3H), 1.43 (s, 3H),
1.39 (s, 3H). 13C NMR (100 MHz, CDCl3): d 161.03, 155.08,
153.24, 144.80, 142.24, 139.85, 137.90, 134.88, 133.32, 129.25,
129.19, 129.16, 128.95, 128.22, 118.34, 116.28, 114.37, 83.72,
55.38, 29.67, 16.36, 14.59. TOF MALDI-HRMS: calcd
([C27H24BF2IN2O]+), m/z ¼ 568.0994, found, m/z ¼ 568.0970. The
second band, from the silica gel column chromatography of the
Experimental section
Materials and reagents
All the chemicals are analytically pure and were used as same reaction mixture was isolated as a bluish green solid as
received. Solvents were dried and distilled prior to synthesis. compound 4. Yield: 126 mg, 33%. mp 209–211 ꢂC. 1H NMR
2840 | J. Mater. Chem. B, 2014, 2, 2838–2854
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(400 MHz, CDCl3): d 8.06 (d, 1H, J ¼ 16 Hz), 7.64–7.58 (m, 6H), ([C39H31BF2N4O + H]+), m/z ¼ 621.2637, found, m/z ¼ 621.2622;
7.52–7.50 (m, 3H), 7.32–7.30 (m, 3H), 6.95 (t, 4H, J ¼ 8 Hz), 6.67 calcd ([C39H31BF2N4O]+), m/z
(s, 1H), 3.87–3.86 (m, 6H), 1.44–1.43 (m, 6H). 13C NMR (100 620.2589.
MHz, CDCl3): d 160.88, 160.37, 155.34, 148.14, 144.07, 142.99,
¼
620.2559, found, m/z
¼
138.12, 137.14, 135.27, 134.00, 132.15, 129.99, 129.46, 129.22,
129.19, 128.95, 128.50, 118.89, 117.20, 116.84, 114.38, 114.26,
Synthesis of Ir-1
81.01, 55.41, 53.45, 17.04, 14.86. TOF MALDI-HRMS: calcd A solution of L1 (55.8 mg, 0.09 mmol) and [Ir(ppy)2]Cl2 (40.7
([C35H30BF2IN2O2]+), m/z ¼ 686.1413, found, m/z ¼ 686.1682.
mg, 0.038 mmol) in CH2Cl2–MeOH (15 mL, 1 : 2, v/v) was
Method B. To a solution of 2 (250 mg, 0.555 mmol) and p- reuxed for 6 h at 45 ꢂC under an Ar atmosphere. Then the
methoxybenzaldehyde (0.27 mL, 2.22 mmol) in dry toluene, reaction mixture was cooled to rt and a 10-fold excess of
acetic acid (1.5 mL) and piperidine (1.5 mL) were added under a NH4[PF6] was added. The suspension was stirred for 15 min
N2 atmosphere. The reaction mixture was heated at 120 ꢂC and then ltered to remove the insoluble inorganic salts. The
under reux by using a Dean Stark trap and the reaction was solution was evaporated to dryness under reduced pressure.
monitored by TLC (CH2Cl2–petroleum ether ¼ 1 : 2 as eluent). The crude product was puried by column chromatography
The moment compound 4 was found to be formed on the TLC (silica gel, CH2Cl2–MeOH ¼ 20 : 1, v/v) to give a carmine solid
plate, the reaction mixture was cooled to rt and the majority of Ir-1 (the solid was washed with hexane to remove the grease).
the solvent was evaporated under reduced pressure. Water (150 Yield: 72.0 mg, 71.4%. mp 234–236 ꢂC. 1H NMR (400 MHz,
mL) was added to the residue and the product was extracted CD2Cl2): d 8.36 (dd, 2H, J ¼ 8 Hz, 4 Hz), 8.02 (t, 1H, J ¼ 8 Hz),
from CH2Cl2 (3 ꢀ 100 mL). The organic phase was dried over 7.96–7.92 (m, 2H), 7.87 (d, 2H, J ¼ 8 Hz), 7.83 (s, 1H), 7.70 (t,
Na2SO4, evaporated under reduced pressure, and the crude 2H, J ¼ 8 Hz), 7.64 (dd, 2H, J ¼ 12 Hz, 8 Hz), 7.50–7.40 (m, 8H),
product thus obtained was puried by column chromatography 7.36–7.30 (m, 2H), 7.26–7.22 (m, 2H), 6.99 (t, 1H, J ¼ 8 Hz),
(silica gel, CH2Cl2–petroleum ether ¼ 1 : 2, v/v). The carmine 6.94–6.91 (m, 3H), 6.88–6.81 (m, 4H), 6.64 (s, 1H), 6.24 (dd, 2H,
solid was obtained as compound 3. Yield: 227 mg, 72%.
J ¼ 8 Hz, 4 Hz), 3.76 (s, 3H), 2.46 (s, 3H), 1.39 (s, 3H), 1.30 (s,
Following the similar synthesis procedure, the above reaction 3H). 13C NMR (100 MHz, CD2Cl2): d 168.01, 165.99, 165.20,
mixture was reuxed for 12 h until most of compound 3 was 161.66, 159.89, 157.10, 155.60, 155.54, 155.08, 153.54, 152.64,
converted to compound 4, as visualized from TLC (CH2Cl2– 150.95, 150.06, 148.91, 146.05, 144.00, 141.53, 140.77, 139.75,
petroleum ether ¼ 1 : 2 as eluent). Aer that the reaction 138.60, 135.07, 134.71, 132.35, 132.24, 131.95, 131.06, 130.50,
mixture was cooled to room temperature, the solvent was evap- 129.67, 129.05, 128.46, 126.09, 125.27, 125.03, 124.45, 123.73,
orated, water (150 mL) was added and was extracted from 123.69, 123.16, 123.08, 120.34, 120.19, 119.48, 116.29, 114.79,
CH2Cl2 (3 ꢀ 100 mL). The crude product thus obtained on 112.46, 92.52, 91.23, 86.29, 55.78, 29.85, 14.79, 12.92. TOF
evaporating the organic phase, was puried by silica gel column MALDI-HRMS: calcd ([C61H47BF2IrN6O]+), m/z ¼ 1121.3502,
chromatography (CH2Cl2–petroleum ether ¼ 1 : 2, v/v as eluent). found, m/z ¼ 1121.3568. Anal. calcd for [C61H47BF8IrN6OP +
The bluish green solid was obtained as compound 4. Yield: 267 2CH3OH + C6H14]: C, 58.51; H, 4.91; N, 5.93. Found: C, 58.35;
mg, 70%. The spectral data of compound 3/4 obtained by H, 4.82; N, 5.61.
Method B is superimposable with those of Method A.
Synthesis of L2
Synthesis of L1
To a deaerated solution of 4 (137 mg, 0.20 mmol) and 5-
To a deaerated solution of compound 3 (114 mg, 0.20 mmol) ethynyl-2,20-bipyridine (36 mg, 0.20 mmol) in the mixed
and 5-ethynyl-2,20-bipyridine (36 mg, 0.20 mmol) in the mixed solvent of triethylamine (5 mL) and THF (10 mL), Pd(PPh3)4
solvent of triethylamine (5 mL) and THF (10 mL), Pd(PPh3)4 (11.6 mg, 0.01 mmol, 5 mol%) and CuI (3.8 mg, 0.02 mmol, 10
(11.6 mg, 0.01 mmol, 5 mol%) and CuI (3.8 mg, 0.02 mmol, 10 mol%) were added under an Ar atmosphere. The reaction
mol%) were added under an Ar atmosphere. The reaction mixture was reuxed for 12 h at 85 ꢂC. Thereaer the synthetic
mixture was reuxed for 12 h at 85 ꢂC. Then the reaction procedure is similar to that of L1; a bluish green solid L2 was
mixture was cooled to rt and the solvent was removed under obtained. Yield: 74.2 mg, 50.2%. mp 298–300 ꢂC. 1H NMR (400
reduced pressure. The crude product thus obtained, was puri- MHz, CD2Cl2): d 8.31 (d, 1H, J ¼ 20 Hz), 7.91 (d, 1H, J ¼ 8 Hz),
ed by column chromatography (silica gel, CH2Cl2–MeOH ¼ 7.85 (t, 1H, J ¼ 8 Hz), 7.69–7.60 (m, 6H), 7.57–7.52 (m, 5H),
100 : 1, v/v) to give a carmine solid L1. Yield: 59.6 mg, 48%. mp 7.48–7.44 (m, 1H), 7.37–7.31 (m, 4H), 6.98–6.94 (m, 5H), 6.71
306–308 ꢂC. 1H NMR (400 MHz, CD2Cl2): d 8.71 (s, 1H), 8.65 (d, (s, 1H), 3.85–3.86 (m, 6H), 1.58 (s, 3H), 1.47 (s, 3H). 13C NMR
1H, J ¼ 4 Hz), 8.41–8.38 (m, 2H), 7.84 (dd, 2H, J ¼ 20 Hz, 8 Hz), (100 MHz, CD2Cl2): d 161.47, 161.09, 155.68, 150.75, 150.57,
7.58–7.49 (m, 6H), 7.35–7.29 (m, 4H), 6.93 (d, 2H, J ¼ 8 Hz), 6.68 144.71, 143.65, 138.59, 137.41, 135.14, 135.05, 132.33, 132.24,
(s, 1H), 3.83 (s, 3H), 2.71 (s, 3H), 1.54 (s, 3H), 1.46 (s, 3H). 13C 131.81, 130.09, 129.72, 129.59, 129.41, 129.31, 128.83, 124.29,
NMR (100 MHz, CD2Cl2): d 161.09, 155.56, 155.14, 151.10, 124.40, 121.06, 119.08, 117.01, 116.79, 114.78, 111.72, 107.67,
149.18, 144.79, 141.58, 140.49, 138.73, 138.18, 136.96, 134.65, 106.87, 70.85, 55.77, 14.99, 13.09. TOF MALDI-HRMS: calcd
134.18, 130.39, 129.25, 129.18, 128.92, 128.22, 123.90, 121.02, ([C47H37BF2N4O2 + H]+), m/z ¼ 739.3056, found, m/z ¼
120.12, 118.47, 116.25, 114.40, 114.00, 92.78, 86.70, 70.43, 739.3011; calcd ([C47H37BF2N4O2]+), m/z ¼ 738.2978, found, m/
55.39, 29.67, 14.59, 12.87. TOF MALDI-HRMS: calcd z ¼ 738.2966.
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1
hexane to remove the grease). Yield: 74.7 mg, 65.6%. H NMR
Synthesis of Ir-2
(400 MHz, CD2Cl2): d 8.71 (dd, 2H, J ¼ 12 Hz, 8 Hz), 8.14 (t, 1H, J
¼ 8 Hz), 8.08 (d, 1H, J ¼ 8 Hz), 7.98–7.89 (m, 5H), 7.85–7.80 (m,
1H), 7.75 (dd, 3H, J ¼ 16 Hz, 8 Hz), 7.60 (t, 2H, J ¼ 8 Hz), 7.55–
7.52 (m, 5H), 7.48–7.39 (m, 6H), 7.36–7.32 (m, 3H), 7.05 (dd, 2H,
J ¼ 16 Hz, 8 Hz), 7.00–6.97 (m, 1H), 6.92 (t, 1H, J ¼ 8 Hz), 6.88–
6.84 (m, 1H), 6.74–6.70 (m, 5H), 6.27 (dd, 2H, J ¼ 16 Hz, 8 Hz),
3.04–3.03 (m, 12H), 1.46 (s, 3H), 1.32 (s, 3H). 13C NMR (100
MHz, CD2Cl2): d 167.78, 162.03, 156.76, 155.37, 153.37, 152.00,
151.76, 151.28, 151.12, 150.59, 149.73, 149.58, 148.58, 148.49,
144.37, 143.60, 143.51, 142.12, 140.37, 139.57, 138.20, 138.12,
137.29, 136.57, 134.98, 131.60, 131.53, 131.01, 130.75, 129.71,
129.12, 128.80, 128.75, 128.02, 127.76, 125.88, 125.79, 125.30,
124.90, 124.76, 124.68, 124.01, 123.31, 122.77, 122.71, 119.96,
119.84, 119.17, 113.92, 113.31, 112.08, 111.95, 94.55, 92.15,
70.49, 40.03, 39.93, 29.66, 14.65, 12.41. TOF MALDI-HRMS:
calcd ([C71H59BF2IrN8]+), m/z ¼ 1265.4553, found, m/z ¼
1265.4539. Anal. calcd for [C71H59BF8IrN8P + 2CH3OH + C6H14]:
C, 60.80; H, 5.23; N, 7.18. Found: C, 60.61; H, 5.02; N, 7.08.
A solution of L2 (66.5 mg, 0.09 mmol) and [Ir(ppy)2]Cl2 (40.7 mg,
0.038 mmol) in CH2Cl2–MeOH (15 mL, 1 : 2, v/v) was reuxed
for 6 h at 45 ꢂC under an Ar atmosphere. Thereaer the
synthetic procedure is similar to that of Ir-1. Ir-2 was obtained
as a purple solid (the solid was washed with hexane to remove
the grease). Yield: 80.8 mg, 72.5%. mp 296–298 ꢂC. 1H NMR (400
MHz, CD2Cl2): d 8.50 (d, 2H, J ¼ 8 Hz), 8.09 (dd, 2H, J ¼ 16 Hz, 8
Hz), 7.99–7.89 (m, 5H), 7.81–7.72 (m, 3H), 7.61–7.53 (m, 9H),
7.51–7.47 (m, 3H), 7.44–7.38 (m, 2H), 7.34–7.31 (m, 2H), 7.08–
6.84 (m, 10H), 6.74 (s, 1H), 6.29–6.23 (m, 2H), 3.85–3.84 (m, 6H),
1.48 (s, 3H), 1.35 (s, 3H). 13C NMR (100 MHz, CD2Cl2): d 167.74,
167.71, 161.36, 160.83, 156.53, 155.21, 153.53, 152.06, 150.71,
149.57, 149.52, 148.57, 148.52, 145.24, 143.58, 143.53, 143.33,
139.72, 139.47, 139.36, 138.86, 138.26, 138.21, 136.77, 135.15,
134.57, 131.58, 131.50, 131.23, 130.87, 130.74, 129.71, 129.53,
129.47, 129.30, 128.84, 128.41, 128.16, 125.67, 124.92, 124.89,
124.31, 123.37, 123.33, 122.77, 119.96, 119.89, 119.30, 116.46,
116.15, 114.40, 93.69, 92.33, 68.00, 55.43, 14.70, 12.52. TOF
MALDI-HRMS: calcd ([C69H53BF2IrN6O2]+), m/z ¼ 1239.3920,
found, m/z ¼ 1239.3990. Anal. calcd for [C69H53BF8IrN6O2P +
2CH3OH + C6H14]: C, 60.27; H, 4.93; N, 5.48. Found: C, 60.45; H,
4.95; N, 5.24.
Analytical measurements
1H and 13C NMR spectra were recorded on a Bruker 400 and
100 MHz spectrophotometer, respectively (CDCl3 or CD2Cl2 as
solvent, TMS as standard, d ¼ 0.00 ppm). High resolution mass
spectra (HRMS) were determined on a MALDI TOF micro MX
spectrometer. Elemental analysis was carried out with a VarioEL
III Element analyzer (Elementar, Germany) and was in agree-
ment with the calculated values within ꢃ0.4%. Fluorescence
spectra were measured on a RF-5301PC spectrouorometer
(Shimadzu). Fluorescence quantum yields were measured with
compound 7 as standard (FF ¼ 9.3% in toluene).36 Phospho-
rescence quantum yields were measured with Ru(dmb)3[PF6]2
as standard (FP ¼ 7.3% in deaerated CH3CN, dmb ¼ 4,40-
Synthesis of Ir-3
A solution of L3 (57 mg, 0.09 mmol) and [Ir(ppy)2]Cl2 (40.7 mg,
0.038 mmol) in CH2Cl2–MeOH (15 mL, 1 : 2, v/v) was reuxed
for 6 h at 45 ꢂC under an Ar atmosphere. Thereaer the
synthetic procedure is similar to that of Ir-1; Ir-3 was obtained
as a purple solid (the solid was washed with hexane to remove
the grease). Yield: 74.7 mg, 73.2%. mp 254–256 ꢂC. 1H NMR (400
MHz, CD2Cl2): d 8.42 (dd, 2H, J ¼ 16 Hz, 8 Hz), 8.10 (t, 1H, J ¼ 8
Hz), 8.02–8.00 (m, 2H), 7.95 (d, 2H, J ¼ 8 Hz), 7.91 (s, 1H), 7.80–
7.76 (m, 2H), 7.72 (dd, 2H, J ¼ 12 Hz, 8 Hz), 7.56–7.51 (m, 7H),
7.44–7.38 (m, 3H), 7.31 (t, 2H, J ¼ 4 Hz), 7.07 (t, 1H, J ¼ 8 Hz),
7.04–6.99 (m, 3H), 6.96–6.90 (m, 2H), 6.73–6.71 (m, 3H), 6.33–
6.30 (m, 2H), 3.05 (s, 6H), 2.53 (s, 3H), 1.46 (s, 3H), 1.36 (s, 3H).
13C NMR (100 MHz, CD2Cl2): d 168.02, 158.50, 155.63, 153.42,
153.21, 152.65, 152.20, 151.83, 151.06, 149.99, 148.95, 148.88,
146.03, 143.98, 141.74, 141.41, 139.71, 139.59, 139.44, 138.73,
138.58, 138.33, 135.46, 134.97, 131.96, 131.84, 131.05, 130.18,
130.12, 129.55, 128.72, 128.38, 126.34, 125.26, 124.89, 124.35,
124.00, 123.67, 123.19, 123.08, 122.94, 121.72, 120.36, 120.18,
119.75, 113.13, 112.28, 111.60, 93.30, 90.98, 40.31, 30.03, 15.11,
12.83. TOF MALDI-HRMS: calcd ([C62H50BF2IrN7]+), m/z ¼
dimethyl-2,20-bipyridine).
Fluorescence
lifetimes
were
measured with an OB920 luminescence lifetime spectrometer
(Edinburgh, UK). Absorption spectra were recorded on an Agi-
lent 8453A UV/Vis spectrophotometer. The nanosecond time-
resolved transient difference absorption spectra were recorded
on a LP 920 laser ash photolysis spectrometer (Edinburgh
Instruments, Livingston, UK). The sample solutions were
purged with N2 for 15 min before measurement. The samples
were excited with a 355 or 532 nm nanosecond pulsed laser, and
the transient signals were recorded on a Tektronix TDS 3012B
oscilloscope. The lifetime values (by monitoring the decay
traces of the transients) were obtained with the LP920 soware.
1134.3818, found, m/z
[C62H50BF8IrN7P + 2CH3OH]: C, 57.23; H, 4.35; N, 7.30. Found:
C, 57.39; H, 4.59; N, 6.99.
¼
1134.3732. Anal. calcd for
DFT calculations
The density functional theory (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
Synthesis of Ir-4
A solution of L4 (68.8 mg, 0.09 mmol) and [Ir(ppy)2]Cl2 (40.7 mg, with the time dependent DFT (TDDFT), based on the optimized
0.038 mmol) in CH2Cl2–MeOH (15 mL, 1 : 2, v/v) was reuxed singlet ground state geometries (S0 state). The spin density
for 6 h at 45 ꢂC under an argon atmosphere. Thereaer the surfaces of the complexes were calculated based on the opti-
synthetic procedure is similar to that of Ir-1; a greyish green mized triplet states. All the calculations were performed at the
solid compound Ir-4 was obtained (the solid was washed with B3LYP/GENECP/LANL2DZ or M062X/GENECP/LANL2DZ level
2842 | J. Mater. Chem. B, 2014, 2, 2838–2854
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with Gaussian 09W.37 Toluene was used as the solvent for the Memorial Institute (RPMI)-1640 Medium supplemented with
calculations (CPCM model).
Foetal Bovine Serum (FBS) (10%) and penicillin (100 U mLꢁ1
culture medium), streptomycin (100 mg mLꢁ1 culture medium),
NaHCO3 (2 g Lꢁ1), and 1% antibiotics (penicillin–streptomycin,
100 U mLꢁ1). Cultures were grown in a humidied incubator at
37 ꢂC, 5% CO2, and 95% relative humidity. Similarly, 1121 cells
were cultured.
Photooxidation
10 mL CH2Cl2–MeOH (9/1, v/v) solution containing 1,5-dihy-
dronaphthalene (DHN, 2.0 ꢀ 10ꢁ4 M) and a photosensitizer (2.0
ꢀ 10ꢁ5 M) was placed in a round-bottom ask and was irradi-
ated by a 35 W xenon lamp through a 0.72 M NaNO2 solution to
cut off the light with a wavelength shorter than 385 nm. At
intervals of 2–5 min, 2 mL of the mixture was sampled for the
UV/Vis absorption measurement and was put back immediately
aer recording the absorption spectra, and UV/Vis absorption
spectra were recorded using the Agilent 8453 UV/Vis spectro-
photometer. The power density was tuned to 20 mW cmꢁ2 and
was measured with a solar power meter. The DHN consumption
was monitored by a decrease in the absorption at 301 nm, the
concentration of DHN was calculated by using its molar
absorption coefficient (3 ¼ 7664 Mꢁ1 cmꢁ1) at 301 nm. The
juglone production was monitored by an increase in the
absorption at 427 nm, the concentration of juglone was calcu-
lated by using its molar absorption coefficient (3 ¼ 3811 Mꢁ1
cmꢁ1), and the yield of juglone was obtained by dividing the
concentration of juglone with the initial concentration of DHN.
For trypan blue staining, exponentially growing, LLC cells
were seeded at a density of 1.0 ꢀ 106 cells per well, in triplicate,
and 24 h later they were treated with different concentrations
(1 mM, 10 mM and 20 mM) of Ir(III) complexes in DMSO as indi-
vidual entities, at 37 ꢂC in a humidied 5% CO2 atmosphere for
the below mentioned time periods. Then, cells were kept either
in the dark or were illuminated with a 635 nm LED for a period
of 4 h at 37 ꢂC in a humidied incubator containing 5% CO2. To
evaluate the cell viability of the dye, wells that had been irra-
diated for 4 h were incubated in the dark for a further 24 h.
Untreated LLC cells were used as controls. As controls, plates
kept in the dark for 4 h were also incubated for an additional 24
h. Aer the appropriate incubation period, the medium was
removed and the cells were washed with PBS for three times,
prior to cell imaging. Confocal uorescence imaging studies
were performed on a Nikon ECLIPSE-Ti confocal laser scanning
microscope.
To study the cell death induced by Ir(III) complexes upon PDT
treatment on LLC cells, aer the appropriate incubation period,
the medium of each well was collected, rinsed with PBS for three
times, and trypsinized followed by centrifugation. The cells
were re-suspended, collected and mixed with the same volume
of 0.4% trypan blue solution. Cells were allowed to stand from 5
to 15 min. The viable (unstained) and dead (stained) cells was
visualised with a light microscope. All compounds used were
prepared as a stock in DMSO, immediately before use.
Singlet oxygen (1O2) quantum yields (FD)
FD values of the triplet photosensitizers were measured
according to a modied literature method,38 with MB (FD ¼ 0.57
in dichloromethane) as standard.39 Quantum yields for singlet
oxygen generation in CH2Cl2 were determined by monitoring
the photooxidation of 1,3-diphenylisobenzofuran (DPBF)
sensitized by the iridium complexes. 1,3-Diphenylisobenzo-
furan (DPBF) was used as the 1O2 scavenger, due to its fast
reaction with 1O2. The absorbance of DPBF was adjusted to
around 1.0 at 414 nm in air saturated CH2Cl2. Then, the
photosensitizer was added to cuvette and photosensitizer's
absorbance was adjusted to around 0.2–0.3. Then, the cuvette
was exposed to monochromatic light at the specic wavelength
for 10 seconds depending on the efficiency of the triplet
photosensitizers. The photosensitizer and MB were irradiated
with the same wavelength. Absorbance was measured six times
aer each irradiation. Then, the slopes of the curves of absor-
bance maxima of DPBF at 414 nm versus irradiation time for
each photosensitizer were calculated. Singlet oxygen quantum
yields (FD) were calculated according to the equation (eqn (1)):
Results and discussion
Design and synthesis of the complexes
Our strategy for the formation of heteroleptic Ir(III) centred
complexes containing 2,20-bipyridine based ligands has been
rationalized on the fact to maximize the heavy atom effect
exerted by Ir(III) on the styryl BODIPY ligand. A p-conjugation
linker was used, a typical strategy to access strong visible light-
absorption, long-lived triplet excited states and efficient ISC in
transition metal complexes.40,41 The styryl BODIPY and its
respective bulky ligand have been introduced to extend the UV-
Vis absorption wavelength and uorescence emission to the
NIR region, respectively.30 Initially, the Knoevenagel condensa-
tion reaction of 2-iodo BODIPY with p-methoxybenzaldehyde
was carried out, which regioselectively at the 5-position of the
BODIPY moiety led to the formation of 5-monostyryl BODIPY
derivative 3 as the major product along with 3,5-distyryl BODIPY
derivative 4 as the minor product (Scheme 1). The molecular
structure of both the derivatives 3 and 4, thus isolated by
column chromatography were conrmed by 1H NMR and 2D
COSY NMR, in particular by the shi in the peak due to the b-
ꢀ
ꢁꢀ
ꢁ
msam
mstd
Fstd
FDsam ¼ FDstd
(1)
Fsam
where “sam” and “std” designate the “Ir(III) photosensitizers”
and “MB”, respectively. “m” is the slope of difference in change
in absorbance of DPBF (at 414 nm) with the irradiation time, “F”
is the absorption correction factor, which is given by F ¼ 1 ꢁ
10ꢁOD (OD is the absorbance at the irradiation wavelength).
Cell culture
LLC cells (lung cancer cells) were maintained at a density of pyrrolic proton at the 6-position of the BODIPY from d 6.0 to ca.
1.0 ꢀ 106 cells per mL for confocal imaging in Roswell Park 6.6 ppm, due to the formation of the styryl group at the
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5-substitution position. The data were consistent with those of intramolecular charge transfer (ICT) effect due to the large
previously reported mono42–45 and distyryl BODIPY dyes.29c,46 extended p conjugation in distyryl in comparison to mono-
Similarly, 5-monostyryl BODIPY derivative 5 and 3,5-distyryl styryl. Approximately, 38 nm and 65 nm of red shis for the
BODIPY derivative 6 were synthesized and characterized absorption of ligands and complexes were observed in the case
(Scheme 1).
of methoxy monostyryl BODIPY compared to amino dimethyl
Pd(0)-catalyzed Sonogashira coupling reactions of 2-iodo monostyryl BODIPY. Similar changes were observed for
styryl BODIPY derivatives and 5-ethynyl-2,20-bipyridine were methoxy distyryl BODIPY vs. amino dimethyl distyryl BODIPY.
carried out to form bulky p-extended styryl BODIPY ligands This red shi is due to the more signicant intramolecular
(Scheme 1) to enhance UV-Visible absorption wavelength and charge transfer (ICT) in styryl BODIPY ligands and complexes
uorescence emission of the Ir(III) centred complexes. Ir(III) with a dimethyl amino group. The characteristic absorption
complexes were synthesized from the bis(pyridylphenyl)-iridiu- spectrum together with the excitation and emission spectra of
m(III) dichloride intermediate (Scheme 2).59 Ir-0 was prepared as complexes Ir-1, Ir-2, Ir-3 and Ir-4 are shown in Fig. 2.
the model complex for photophysical studies. All the complexes
were obtained with moderate to satisfactory yields.
The luminescence spectra of the compounds
The photoluminescence of the compounds was studied (Fig. 3).
The ligands L1, L2, L3 and L4 give strong uorescence in the
UV-Vis absorption spectra of the complexes
NIR region at 625 nm (FF ¼ 68.6%), 684 nm (FF ¼ 35.6%), 674
The UV-Vis absorption of the styryl BODIPY ligands and Ir(III)
complexes were studied (Fig. 1). Styryl BODIPY based ligands
nm (FF ¼ 24.5%) and 758 nm (FF ¼ 10.3%), respectively (Fig. 3a
and Fig S43†). The dual emission was observed for L2 at 684 nm
L1, L2, L3 and L4 exhibited intense absorption maxima at
605 nm (3 ¼ 1.03 ꢀ 105 Mꢁ1 cmꢁ1), 666 nm (3 ¼ 1.13 ꢀ 105 Mꢁ1
cmꢁ1), 639 nm (3 ¼ 1.23 ꢀ 105 Mꢁ1 cmꢁ1) and 723 nm (3 ¼ 6.89
ꢀ 104 Mꢁ1 cmꢁ1), respectively in UV-Vis absorption (Fig. 1a).
UV-Vis absorption spectra of the model complex Ir-0 showed
maxima for the typical cyclometalated Ir(III) complex in the UV
range (3 ¼ 4.98 ꢀ 104 Mꢁ1 cmꢁ1 at 284 nm) and a very weak
absorption in the visible-light range (3 ¼ 1.51 ꢀ 104 Mꢁ1 cmꢁ1 at
385 nm) (Fig. 1b).15,47
In contrast, styryl BODIPY based heteroleptic cyclo-
metalated Ir(III) complexes displayed strong absorption
maxima at 606 nm (3 ¼ 1.14 ꢀ 105 Mꢁ1 cmꢁ1) for Ir-1, and in
the NIR region at 664 nm (3 ¼ 8.96 ꢀ 104 Mꢁ1 cmꢁ1), 644 nm (3
¼ 9.89 ꢀ 104 Mꢁ1 cmꢁ1) and 729 nm (3 ¼ 7.89 ꢀ 104 Mꢁ1 cmꢁ1
)
for Ir-2, Ir-3 and Ir-4, respectively (Fig. 1b). No signicant
wavelength shi upon complexation with Ir(III) was observed.
This demonstrates that the molecular orbitals of the ligands
remained unaltered to a large extent on complexation. From
the absorption of the ligands and complexes, it was observed
that distyryl BODIPY induced ca. 58 nm (for methoxy substit-
uent) and ca. 85 nm (for dimethyl amino substituent) of red
shis for the respective ligands and complexes as compared to
Fig.
2 Normalized absorption spectra (black) and fluorescence
spectra (red) (c ¼ 1.0 ꢀ 10ꢁ5 M in toluene): (a) Ir-1, (b) Ir-2, (c) Ir-3 and
(d) Ir-4.
the respective monostyryl BODIPY, owing to
a more
Fig. 1 UV-Vis absorption spectra of the (a) ligands L1, L2, L3 and L4 Fig. 3 (a) Fluorescence spectra of ligands L1 and L3 and (b) normalized
and (b) complexes Ir-1, Ir-2, Ir-3, Ir-4 and Ir-0. c ¼ 1.0 ꢀ 10ꢁ5 M in fluorescence spectra of complexes Ir-1, Ir-2, Ir-3, Ir-4 and Ir-0. (lex
¼
toluene. 20 ꢂC.
580 nm, c ¼ 1.0 ꢀ 10ꢁ5 M in toluene). 20 ꢂC.
2844 | J. Mater. Chem. B, 2014, 2, 2838–2854
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Journal of Materials Chemistry B
and 619 nm and for L4 at 758 nm and 659 nm. A similar trend
was observed for the complexes with uorescence quantum
yields (FF) of 39.9%, 13.2%, 32.6% and 1.0% for Ir-1, Ir-2, Ir-3
and Ir-4, respectively (Fig. 3b and Table 3). The appearance of
two emission peaks can be attributed to the S2 emission of the
chromophores, presumably due to a Franck Condon barrier for
the internal conversion of S2 / S1. Another possible origin for
the minor emission shoulder at higher energy side of the
emission band is due to the vibrational structure of the lumi-
nescence. Both the peaks exhibit similar behaviour on
increasing the concentration (see ESI, Fig. S49b and S49d†) and
on varying the excitation wavelength (Fig. S50b and S50d†)
suggesting that the two emission peaks are from the same
species.
Fig. 4 Comparison of the emission intensities of the complexes: (a) Ir-
1 and Ir-3, lex ¼ 496 nm and (b) Ir-2 and Ir-4, lex ¼ 546 nm. c ¼ 1 ꢀ
10ꢁ5 M in toluene. 20 ꢂC.
Intramolecular charge transfer was proved by the concen-
tration-dependent and excitation-energy dependence behaviour
of emission spectra of Ir-2 and Ir-4. Due to the large ICT effect in
the distyryl group and styryl BODIPY with an amino substituent,
the emission was red shied for distyryl and dimethyl amino
styryl BODIPY ligands and complexes as compared to that of
monostyryl and styryl BODIPY with a methoxy group, respec-
tively (Fig. 4 and S43†).
In contrast to ligands, the complexes show weaker uores-
cence (Fig. 5). The uorescence emission of the ligands was
remarkably quenched in the complexes which indicated effi-
cient intersystem crossing (ISC) from the singlet excited states
to the triplet excited states of the complexes upon visible light
photoexcitation.35 ISC is weaker in Ir-2. Such a result is rarely
observed for cyclometalated Ir(III) complexes, e.g. in an Ir(III)
coordination center with a BODIPY uorophore, the uores-
cence emission of the BODIPY could not be completely
quenched rather, the phosphorescence of the Ir(III) coordina-
tion center was quenched instead.48 Thus, the ISC in Ir-1 to Ir-4
may have been arouse due to the direct association of the p-core
of the styryl BODIPY uorophore to the Ir(III) coordination
centres, which was not the case for some of the previous Ir(III)
complexes that contained a bulky organic chromophore.11b,35,48
Ir-1, Ir-2, Ir-3 and Ir-4 were not sensitive to O2, thus exhibits no
phosphorescence (see ESI, Fig. S42†). The model complex Ir-
0 gave a structureless intense emission band at 507 nm and the
Fig. 5 Comparison of the emission intensities of the ligands and
complexes: (a) L1 and Ir-1, lex ¼ 580 nm; (b) L2 and Ir-2, lex ¼ 580 nm.
(c) L3 and Ir-3, lex ¼ 580 and (d) L4 and Ir-4, lex ¼ 580 nm. c ¼ 1 ꢀ
10ꢁ5 M in toluene. 20 ꢂC.
emission can be signicantly quenched by O2. The structureless
3
intense emission indicates that the emission is from a MLCT
excited state.
Table 1 Electronic excitation energies (eV) and corresponding oscillator strengths (f), main configurations and CI coefficients of the low-lying
electronic excited states of complex Ir-1 calculated by TDDFT//B3LYP/LANL2DZ based on the DFT//B3LYP/LANL2DZ optimized ground state
geometries
TDDFT//B3LYP/GENECP
Electronic transition
Energya [eV nmꢁ1
]
f b
Compositionc
CId
Character
Singlet
S0 / S1
S0 / S2
S0 / S5
S0 / S7
S0 / S17
S0 / T1
1.93/643
2.28/544
2.77/448
2.98/417
3.29/376
1.23/1012
1.2242
0.8532
0.3269
0.1228
0.1407
0.0000e
H / L
0.7019
0.6895
0.5733
0.4248
0.6329
0.5304
0.4475
ILCT
ILCT
MLCT/LLCT
MLCT/LLCT
ILCT
H / L+1
Hꢁ2 / L
Hꢁ1 / L+1
Hꢁ4 / L+1
H / L+1
H / L
Triplet
ILCT
ILCT
a
Only the selected low-lying excited states are presented. b Oscillator strengths. c Only the main congurations are presented. d The CI coefficients
are in absolute values. e No spin–orbital coupling effect was considered, thus the f values are zero.
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supported by the increased uorescence quantum yield and life
time with increasing solvent polarity for Ir-1 and Ir-2 whereas
these were decreased in the case of Ir-3 and Ir-4. For Ir-0 no
considerable effect was observed towards solvent polarity.
The absorption and emission spectra of Ir-1, Ir-2, Ir-3 and Ir-
4 are shown in (Fig. 2) and Stokes shis are tabulated in Table 3.
Stokes shis (Dst) were found to be higher for Ir-3 and Ir-4
compared to Ir-1 and Ir-2, respectively.
Solvent-dependency of the UV-Vis absorption and the
luminescence spectra of the complexes
The study of the solvent dependency of the complexes was
carried out with the intention to study the properties of the
emissive excited state of the complexes. The UV-Vis absorption
of Ir-1, Ir-2, Ir-3, and Ir-4 (Fig. 6 & S45†) along with the respective
ligands (Fig. S44 & S45†) does not show signicant solvent
dependency, indicating that the ground states were not affected
by the solvent polarity or hydrogen bonding. We noted that
the complexes are soluble in aqueous solution (MeOH–H2O, Nanosecond time-resolved transient difference absorption
8 : 2, v/v).
On comparison, the emissions of the complexes are more
spectroscopy
The nanosecond time-resolved transient difference absorption
spectra of the complexes were studied so as to investigate the
triplet excited states of the complexes (Fig. 8, see ESI Fig. S51–
S53†). Upon 532 nm pulsed laser excitation, positive transient
absorption (TA) bands at 374 and 665 nm were observed for Ir-1
(Fig. 8a) along with the bleaching bands at 429 nm and 600 nm
due to the UV-Vis absorption (Fig. 1b). Based on these results,
we conclude that the triplet excited state of Ir-1 is localized on
the styryl BODIPY ligand, not on the Ir(III) coordination center.
The transient signal was quenched in aerated solution, which
proves the triplet feature of the transients. The lifetime of the
triplet excited state was determined to be 106.6 ms.
Similarly, upon 532 nm photoexcitation, the bleaching band
at 662 nm was observed for Ir-2 (Fig. 8c) which is also consistent
with the UV-Vis absorption spectra (Fig. 1b). This implies that
the triplet excited state of Ir-2 is also localized on the styryl
BODIPY ligand and not on the Ir(III) coordination center. The
lifetime of the triplet excited state was determined to be 156.5 ms
for Ir-2 which was also found to be quenched in aerated solu-
tion. The transient absorption spectrum of Ir-3 (see ESI,
Fig. S51†) was found to be similar to that of Ir-1, with a slightly
blue-shied bleaching band at 632 nm and positive transient
absorption bands at about 408 nm and 760 nm. The lifetime of
sensitive to the polarity of the solvents (Fig. 7 and S48†). For Ir-1
and Ir-2, the emission intensity is slightly increased in solvents
with high polarity and displayed hypsochromic shi with
increasing solvent polarity. This distinctive property for Ir-1 and
Ir-2 may be attributed to the decreased energy gap between
ground and excited states with increased possibility of transi-
tion on increasing the polarity. In contrast, bathochromic shi
was observed in the case of amino dimethyl substituted
complexes Ir-3 and Ir-4 and the respective emission intensity is
completely quenched in high polar solvents, thus suggesting
the activation of the non-emissive decay channel in high polar
solvents. Energy gap law may also play a role in this change of
the uorescence quantum yield. Based on these results, we
propose that the emission of the complexes is inuenced by the
polarity of the solvents and amino dimethyl styryl BODIPY Ir(III)
complexes have more signicant ICT than the methoxyl styryl
BODIPY in high polar solvents. These results were further
Fig.
6 Solvent-polarity-dependence of the absorption of the
complexes (a) Ir-1 and (b) Ir-3. c ¼ 1.0 ꢀ 10ꢁ5 M. 20 ꢂC.
Fig. 7 Solvent-polarity-dependence of the emission of the complexes Fig. 8 Nanosecond time-resolved transient difference absorption
(c ¼ 1.0 ꢀ 10ꢁ5 M): (a) Ir-1, lex ¼ 570 nm and (b) Ir-3, lex ¼ 595 nm. spectra after pulsed excitation: (a) Ir-1 and (c) Ir-2 and decay traces of
20 ꢂC.
(b) Ir-1 and (d) Ir-2. lex ¼ 532 nm, c ¼ 1.0 ꢀ 10ꢁ5 M in toluene. 20 ꢂC.
2846 | J. Mater. Chem. B, 2014, 2, 2838–2854
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the transient was determined to be 92.5 ms. To the best of our
knowledge, these values are the longest triplet state lifetimes
observed for the styryl BODIPY group in transition metal
complexes.32 The lifetime of the triplet excited state for Ir-4 was
found to be 31.4 ms. These 3IL state lifetime values are close to
those of Styryl BODIPY-C60 Dyads (105.6 ms/123.2 ms)49 but much
longer than that observed for the iodo-styryl BODIPY (4 ms).36
Previously the triplet excited state lifetimes of the BODIPY-
containing Ir(III) complexes were reported as 87.2 ms.28b
In disagreement to Ir-1, Ir-2, Ir-3 and Ir-4, a notably different
transient prole was observed for Ir-0 with a transient absorp-
tion band at 320 nm along with a bleaching band at 525 nm due
to the strong phosphorescence emission (see ESI Fig. S51d†).
The lifetime of the triplet excited state for Ir-0 was found to be
3
1.34 ms. Thus, Ir-0 was distinguished in the MLCT state.
DFT calculations: assignment of the excited states
From a theoretical perspective, the photophysical properties of
transition metal complexes were studied by density functional
theory (DFT) calculations.27a,41i,50 In order to study the lowest-
lying triplet excited states of the complexes, the localization of
spin density surfaces of the complexes were studied.24d,27a,28a,41i,51
The spin density surfaces of complexes Ir-1–Ir-4 are exclusively
localized on the styryl BODIPY moieties (Fig. 9), the Ir(III)
centres made no contribution suggesting that the triplet states
are in the 3IL state of the respective complexes, which is in full
agreement with the nanosecond time-resolved transient
absorption of the complexes.24d,28,50e,52 However, the spin density
surface of Ir-0 is distributed on the ppy ligand as well as on the
Ir(III) coordination center. Thus, this result was in agreement
with the LLCT/MLCT assignment of Ir-0.
The ground state geometries of the complexes were opti-
mized. Slightly distorted conformations were observed for styryl
BODIPY moieties (Fig. 10, 11, and S54†). The deviation from the
coplanar geometry is more signicant for Ir-4 (Fig. S55†).
The UV-Vis absorption of the complexes was calculated
based on the optimized ground state geometry (Franck–Condon
principle).53,54 The calculated UV-Vis absorption band of Ir-1 is
at 643 nm (1.93 eV), which is close to the experimental result at
606 nm (2.05 eV. Fig. 1b). The main transition for this
Fig. 10 Electron density maps of the frontier molecular orbital of
complex Ir-1, based on the ground state optimized geometry by the
DFT calculations at the B3LYP/LANL2DZ level with Gaussian 09W.
absorption band is HOMO / LUMO. Based on the molecular
orbitals in the low-lying singlet excited states of this transition,
it is clear that this transition is styryl BODIPY ligand localized
transition (Fig. 10), which is in agreement with the experimental
results. The energy gap between the ground state (S0) and the
triplet excited states (T1) of Ir-1 calculated by the TDDFT is
predicted as 1.23 eV. The molecular orbitals involved in the
transitions of T1 states are mainly localized styryl BODIPY
ligands (Fig. 10 and Table 1). Therefore, the T1 state can be
3
identied as the IL state, which is in agreement with the spin
density analysis and the transient absorption studies.27a
Similar calculations were carried out for Ir-2. The calculated
absorption band is at 738 nm (1.68 eV), which is longer than the
experimental results (1.87 eV, 664 nm, Fig. 1b). Molecular
orbitals of HOMO / LUMO are involved in this S0 / S1 tran-
sition (Fig. 11 and Table 2). These molecular orbitals are also
styryl BODIPY ligand localized, which is in agreement with the
UV-Vis absorption spectra (Fig. 1b). The S0 / T1 energy gap was
estimated with the TDDFT method as 1.10 eV. Since the major
component of the S0 / T1 state is HOMO / LUMO+1, the T1
state can be identied as the 3IL state since the molecular
orbitals are localized on the styryl BODIPY ligand. This result is
also in agreement with the spin density analysis and the tran-
sient absorption spectroscopy (Fig. 11 and Table 1). For Ir-3 (see
ESI, Fig. S54 and Table S2†) and Ir-4 (see ESI, Fig. S55 and Table
S3†) also, analogous calculations were carried out; the results
are similar to those of Ir-1 and Ir-2. The S0 / T1 energy gaps,
calculated with the TDDFT method were found to be 1.14 eV
and 1.02 eV for Ir-3 and Ir-4, respectively. For both the
complexes Ir-3 and Ir-4 3IL states were also identied for T1
states.
The excitations of Ir-0 were also studied by TDDFT calcula-
tions. The calculated UV-Vis absorption band was at 387 nm
which is in agreement with the experimental results (385 nm).
Fig. 9 Isosurfaces of the spin density of the complexes at the opti-
mized triplet state geometry calculated at the B3LYP/LANL2DZ level
with Gaussian 09W.
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photocatalysis as a singlet oxygen (1O2) photosensitizer. Herein,
the 1O2 photosensitizing ability of the complexes as triplet
photosensitizers were studied with visible light photooxidation
using DHN as the 1O2 scavenger to follow the kinetics of the 1O2
production of the triplet photosensitizers. The photooxidation
product juglone thus formed can be used for preparation of
anti-cancer compounds.55 The conventional triplet photosensi-
tizers meso-tetraphenylporphyrin (TPP) and methylene blue
(MB) were studied for comparison. The consumption of DHN
can be monitored by the decrease in its absorption at 301 nm
1
signifying the progress of O2 photosensitizing with Ir(III).49,56
The UV-Vis absorption spectra of the mixture were moni-
tored (Fig. 12 and S57†). The more efficient changes were found
for Ir-2 than other complexes. However, for Ir-1, the decrease of
the DHN absorption at 301 nm occurs at a much lesser extent
than that of Ir-2. The absorption of all the complexes in the
visible region did not change upon continuous irradiation,
therefore the photostability of the complexes is good. Signi-
cant changes were found for TPP and MB (Fig. S57b and S57c†).
The photooxidation velocities with Ir(III) complexes as the
triplet photosensitizers were compared with MB and TPP by
plotting the ln(Ct/C0) against the irradiation time (Fig. 13a). The
1
larger the slope of the plot, the more efficient the O2 photo-
sensitizing ability. Ir-2 is more efficient than MB (FD ¼ 65%).57
Fig. 11 Electron density maps of the frontier molecular orbitals of
complex Ir-2. Based on the ground state optimized geometry by the
DFT calculations at the B3LYP/LANL2DZ level with Gaussian 09W.
Ir-3 and Ir-0 show much weaker 1O2 photosensitizing ability. Ir-
1
0 shows weaker O2 photosensitizing ability due to the lack of
visible light-harvesting. Ir-4 is the photosensitizer that gives the
poorest performance. The parameters related to photooxidation
of DHN using the Ir(III) complexes, MB and TPP are summarized
in Table 4. Ir-1 and Ir-2 show FD values of 53% and 81%,
The Ir(III) atom and ppy ligands contributed to the transitions,
could be assigned as MLCT or LLCT transitions (see ESI,
Fig. S56 and Table S4†). The S0 / T1 energy gap was found to be
2.64 eV (470 nm, 2.64 eV), which was in good agreement with
the observed RT phosphorescence emission at 507 nm (2.45 eV)
indicating that the T1 state could be assigned as LLCT or MLCT
(see ESI, Fig. S56 and Table S4†). These parameters are
comparable to the experimental results of the complexes
(Table 3).
1
respectively, thus these complexes are efficient O2 photosen-
sitizers. The absorption of Ir-2 in the visible region is much
stronger than that of Ir-1, therefore the 1O2 photosensitizing
ability of Ir-2 is much more efficient than Ir-1. Ir-3 and Ir-4 show
a very low yield of 6% and 2%, respectively, which may be
responsible for the poor 1O2 photoxidation ability of Ir-3 and Ir-
4. Ir-2 as a photosensitizer on photoirradiation for 40 min,
yielded 91% of juglone, which is higher than the other Ir(III)
complexes and MB (Fig. 13a and Table 4). Ir-4 yielded only 41%
of juglone due to low singlet oxygen quantum yield (FD). It
should be pointed out that the photooxidation of the complexes
are dependent on the intrinsic properties of the triplet
Photosensitization of singlet oxygen (1O2): photoxidation with
the complexes as a triplet photosensitizer
As the complexes show strong absorption of visible light and
long-lived triplet excited states (Table 3), these are applicable in
Table 2 Electronic excitation energies (eV) and corresponding oscillator strengths (f), main configurations and CI coefficients of the low-lying
electronic excited states of complex Ir-2 calculated by TDDFT//B3LYP/LANL2DZ based on the DFT//B3LYP/LANL2DZ optimized ground state
geometries
TDDFT//B3LYP/GENECP
Electronic transition
Energya [eV nmꢁ1
]
f b
Compositionc
CId
Character
Singlet
S0 / S1
S0 / S2
S0 / S7
S0 / S17
S0 / T1
1.68/738
1.96/633
2.68/462
3.22/385
1.10/1130
0.7719
0.8263
0.6249
0.1178
0.0000e
H / L
0.7027
0.7041
0.5402
0.6348
0.5852
ILCT
ILCT
ILCT
LLCT/MLCT
ILCT
H / L+1
Hꢁ1 / L+1
H / L+6
H / L+1
Triplet
a
Only the selected low-lying excited states are presented. b Oscillator strengths. c Only the main congurations are presented. d The CI coefficients
are in absolute values. e No spin–orbital coupling effect was considered, thus the f values are zero.
2848 | J. Mater. Chem. B, 2014, 2, 2838–2854
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Journal of Materials Chemistry B
Table 3 Photophysical properties of ligands and cyclometalated Ir(III) complexesa
3b
lem/nm
FFc/%
sFd/ns
Dst
sT
i
j
labs/nm
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
L1
L2
L3
L4
605/564e
601/556f
593/550g
593/550h
666/612e
659/608f
650/601g
650/604h
639/590e
636/590f
627g
1.030/0.324e
1.060/0.345f
1.036/0.346g
1.029/0.348h
1.132/0.339e
1.039/0.353f
1.015/0.355g
0.948/0.345h
1.225/0.466e
1.137/0.487f
1.078g
625e
624f
68.6e
6.1f
4.00e
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3.85f
615g
616h
684e
682f
36.2g
34.4h
35.6e
13.5f
12.1g
18.4h
24.5e
16.0f
2.1g
3.70g
3.65h
4.48e
4.49f
676g
678h
674e
699f
4.21g
4.76h
3.72e
3.52f
710g
714h
758/679e
0.61g
628h
1.035h
1.3h
0.69h
723e
0.689e
10.3e
3.64 (lem ¼ 758)e
3.10 (lem ¼ 679)e
2.87 (lem ¼ 779)f
2.60 (lem ¼ 674)f
1.14g
k
k
720f
0.586f
779/674f
3.4f
—
—
k
k
k
k
k
k
k
k
709g
0.542g
782g
792h
507e
511f
0.9g
1.0h
—
—
—
—
—
—
—
—
712h
0.558h
1.47h
k
Ir-0
Ir-1
Ir-2
284/385e
282/382f
280/378g
280/375h
606/563e
602/561f
594/554g
593/552h
664/610e
0.498/0.151e
0.770/0.207f
0.478/0.133g
0.948/0.249h
1.138/0.375e
1.176/0.439f
1.189/0.434g
1.133/0.420h
0.896/0.346e
—
54.63e
1.34e
k
k
—
104.74f
—
k
k
513g
515h
624e
624f
—
55.28g
—
k
72.6h
39.9e
4.7f
57.08h
—
2.21e
18e
22f
21g
23h
27e
106.6e
k
0.55f
—
615g
616h
691/621e
6.9g
0.54g
113.2g
21.0h
11.7h
13.2e
0.83h
3.86 (lem ¼ 691)e
2.47 (lem ¼ 621)
2.03 (lem ¼ 691)f
0.77 (lem ¼ 613
3.04 (lem ¼ 691)g
0.96 (lem ¼ 609)
3.64 (lem ¼ 691)h
1.33 (lem ¼ 611)
3.33e
156.5e
653/601f
647/596g
646/596h
0.982/0.419f
0.979/0.411g
0.896/0.394h
678/613f
673/609g
674/611h
6.0f
25f
26g
28h
—
k
10.4g
13.8h
90.8g
103.7h
92.5e
Ir-3
644/596e
645f
0.989/0.438e
0.949f
683e
32.6e
1.3f
39e
71f
k
716f
0.73f
—
633g
0.882g
718g
0.6g
0.4h
1.0e
0.35g
85g
104h
65e
37.5g
61.6h
31.4e
632h
0.895h
736h
0.45h
Ir-4
729/286e
0.789/1.211e
794/684e
2.10 (lem ¼ 794)e
2.54 (lem ¼ 684)e
0.89f
720f
710g
714h
0.847f
0.843g
0.788h
777f
787g
800h
0.2f
57f
77g
86h
—
k
0.23g
0.18h
0.71g
54.4g
91.0h
0.76h
a
b
c
c ¼ 1.0 ꢀ 10ꢁ5 M. Molar extinction coefficient at the absorption maxima. 3: 105 Mꢁ1 cmꢁ1
.
Fluorescence quantum yields with complex
d
Ru(dmb)3[PF6]2 (Fp ¼ 7.3% in MeCN) and BODIPY derivative 7 (FF ¼ 9.3% in toluene) as the standard. Fluorescence lifetimes under an air
atmosphere. In toluene. f In dichloromethane. In methanol. h In acetonitrile. Stokes shi (in nm). Triplet excited state lifetimes, measured
e
g
i
j
by nanosecond time-resolved transient absorptions under the N2 atmosphere (c ¼ 1.0 ꢀ 10ꢁ5 M). Not determined.
k
photosensitizers (such as the light-harvesting ability and the of the complexes are directly related to the light-absorbing and
triplet state lifetimes), but it is also strongly dependent on the the triplet excited state lives of the triplet photosensitizers.
match between the absorption spectra of the photosensitizers
and the emission spectra of the excitation lamp. The compar-
ison of the absorption spectra of photosensitizers and the
Fluorescent imaging and intracellular PDT studies
emission of excitation lamp was carried out (see ESI, The complexes show uorescence and intersystem crossing. As
Fig. S57d†). The excitation lamp gives broad emission spectra a result, the luminescence is independent of oxygen (O2), and
(not monochromatic light), and there is a good agreement singlet oxygen (1O2) can be produced upon photoexcitation.
between the absorption spectra of the triplet photosensitizers Therefore, these complexes can be used as multi-functional
and the emission spectra. Therefore, the comparison of the materials. Since, the singlet oxygen quantum yield of Ir-2 is
photooxidation of the Ir-1, Ir-2, Ir-3, Ir-4 and the model triplet high, we have explored the cytotoxicity of Ir(III) complexes in
photosensitizers is reliable: the relative photooxidation ability LLC cells (lung cancer cells) both in the presence and in the
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Table
4
Pseudo-first-order kinetics parameters, 1O2 generation
quantum efficiencies and yields of juglone for the photooxidation of
DHN using complexes Ir-1, Ir-2, Ir-3, Ir-4, MB and TPP as triplet
photosensitizers
Yieldi [%]
a
b
d
sT [ms]
kobs
vic
FD
Ir-1
Ir-2
Ir-3
Ir-4
Ir-0
MB
TPP
106.6
156.5
92.5
31.4
1.34
83.3
82.5
51.1
48.4
9.1
0
5.2
1.022
0.968
0.182
0
0.104
0.982
1.378
0.53e
0.81f
0.06g
0.02h
—
72.3
91.2
58.4
41.0
48.7
86.2
99.9
49.1
68.9
0.57
0.65
a
Triplet excited state lifetimes, meꢁa5sured by nanosecond time-resolved
transient absorptions (c ¼ 1.0 ꢀ 10 M in toluene). b Pseudo-rst-order
rate constant, ln(Ct/C0) ¼ ꢁkobst. In 10ꢁ3 minꢁ1
.
Initial consumption
c
rate of DHN, vi ¼ kobs[DHN]. In 10ꢁ5 minꢁ1
.
Singlet oxygen (1O2)
d
generation quantum yield measured using methylene blue (FD ¼ 0.57
e
f
g
in CH2Cl2) as a reference. lex ¼ 611 nm. lex ¼ 652 nm. lex ¼ 642
nm. h lex ¼ 664 nm. i Yield of juglone aer photoreaction for 40 min.
Fig. 12 UV-Vis absorption spectral change for DHN using complex (a) signal (lex ¼ 543 nm). The overlay of uorescence and bright
Ir-1, (b) Ir-2, (c) Ir-4, and (d) Ir-0 as photosensitizers. Irradiated with a
eld images, conrm the good cellular permeability of the
35 W xenon lamp (20 mW cmꢁ2 in the photoreactor; the UV light with
photosensitizers. In contrast, cellular uptake of Ir-4 was poor in
the absence of light. As a control the cells were incubated in the
absence of light and also in the absence of sensitizers. No
a wavelength shorter than 385 nm was blocked by 0.72 M NaNO2
solution). In CH2Cl2–CH3OH (9 : 1, v/v); c [DHN] ¼ 2.0 ꢀ 10ꢁ4 M; c
[photosensitizer] ¼ 2.0 ꢀ 10ꢁ5M; 20 ꢂC.
Fig. 13 (a) Plots of ln(Ct/C0) vs. irradiation time (t) for the photooxi-
dation of DHN using Ir(III) complexes; (b) plots of chemical yields of
juglone vs. irradiation time for the photooxidation of DHN. Irradiated
with a 35 W xenon lamp (20 mW cmꢁ2 in the photoreactor; the UV
light with a wavelength shorter than 385 nm was blocked by 0.72 M
NaNO2 solution). In CH2Cl2–CH3OH (9 : 1, v/v); c [DHN] ¼ 2.0 ꢀ 10ꢁ4
M; c [photosensitizer] ¼ 2.0 ꢀ 10ꢁ5M; 20 ꢂC.
absence of light to investigate the photodynamic therapy (PDT)
effect of the complexes. PDT being an non-invasive and attrac-
tive protocol in the treatment of a variety of cancer cells by the
combined use of near IR or visible light with a photosensitizing
drug, has been used to form intracellular reactive oxygen
species (ROS) to kill cells and to stimulate the immune
response. No IR absorbing Ir(III) complexes have been reported
for application in PDT studies.59,60
Fig. 14 Confocal fluorescence images in LLC cells. (a) Cells in control
on incubation in the dark for 24 h; (b) cells in control on irradiation for
4 hours by a 635 nm LED followed by further incubation in the dark for
24 h; (c) Ir-2 (10 mM) treated cells in the dark for 24 h and (d) Ir-2 (10
The cells were treated with 10 mM Ir(III) complexes and were
kept either in the dark or were illuminated with a 635 nm LED.
To ascertain the cellular uptake of the photosensitizers, incu-
bated cells were imaged using a confocal uorescence micro-
scope (Fig. 14, S58–S60†). Ir-1–Ir-3 exhibits a red uorescence
mM) treated cells on irradiation for 4 hours by a 635 nm LED followed
by further incubation in the dark for 24 h.
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Table 5 IC50 values of Ir-1 and Ir-2 (mM)a
Ir-1
In dark On photoirradiation In dark On photoirradiation
Ir-2
Cell
1121 9.81
2.58
6.18
16.70
15.63
7.68
9.80
LLC
8.16
Fig. 15 Trypan blue staining images of LLC cells treated (a) in the
absence of LED and photosensitizers, (b) in the absence of LED but in
the presence of Ir-2 (10 mM) and (c) on illumination of LED and Ir-2
(10 mM).
a
IC50, the concentration of compound that inhibits the proliferation
rate by 50% compared with control untreated cells. Irradiated by a
635 nm LED.
of Ir-1 and Ir-2 for different concentrations of 0, 1, 2, 4, 8, 16,
and 25 mM in cells were investigated both in the absence and in
the presence of light for 36 h using the MTT assay.62 Cells were
incubated with different concentrations 0, 1, 2, 4, 8, 16, and 25
mM of Ir-1 and Ir-2 for 36 h. IC50 values for Ir-1 on photo-
irradiation and in the dark were found to be 2.58 and 9.81 mM,
respectively for 1121 cell lines. For LLC cell lines the respective
values were 6.18 and 8.16 mM. Similarly, IC50 values for Ir-2 on
photoirradiation and in the absence of photoirradiation were
found to be 7.68 and 16.70 mM, respectively for 1121 cell lines
and for LLC cell lines the values were 9.80 and 15.63 mM,
respectively.
uorescence was observed in the respective controls (Fig. 14a
and b).
The effect of Ir(III) complexes for cell viability was investi-
gated both in the presence and in the absence of light using
trypan blue staining (Fig. 15 and Fig. S61–S64†).58 Trypan blue is
one of the dye exclusion procedures for viable cell counting.
This method is based on the principle that live (viable) cells do
not take up certain dyes, whereas dead (nonviable) cells do.
Since cells are very selective to the compound that penetrates
through the cell membrane in a viable cell, trypan blue is not
absorbed and hence, live cells with undamaged cell membranes
are not colored. However, it traverses the membrane of the dead
cell and binds to several intracellular proteins, staining the cell
blue. Therefore, dead cells are shown to be a distinctive blue
color or dark black at the center of the cell as per the back-
ground of the image under a light microscope, and living cells
are excluded from staining.
Phototoxicity with different concentrations of the Ir-
complexes (1 mM, 10 mM, 20 mM), and different optical doses (1
h, 3 h) was studied. The results show that with increasing the
complexes concentration or optical doses, the PDT effect
become more signicant, especially with increasing the
complex concentration (see ESI, Fig. 14, S58, and S59 for
detail†).
The PDT effect of TPP (tetraphenylporphyrin) under the
same condition was studied.61 The trypan blue staining experi-
ments show that the PDT effect of our Ir-complexes is more
signicant than TPP (see ESI Fig. S61–S63 and S66 for detail†).
The reason may be due to the stronger absorption of the Ir-
complexes in the visible spectral region as compared with that
of TPP. Note that the absorption of porphyrins in the visible
spectral region is actually weak (the most intense absorption of
porphyrin is at ca. 400 nm).
Conclusions
In conclusion, we prepared four styryl-BODIPY-containing het-
eroleptic C^N Ir(III) complexes which show strong NIR absorp-
tion (644–729 nm), strong NIR uorescence (700–800 nm), and
long-lived triplet excited states (92.5–156.5 ms). In these
complexes the p-conjugation framework of the ligands were
connected to the Ir(III) coordination center via the C^C bond,
with the aim to induce efficient ISC. The photophysical prop-
erties of the complexes and the NIR light-harvesting ligands
were studied with the steady state and time-resolved absorp-
tion/emission spectroscopy, as well as DFT calculations. We
found that the complexes are strongly uorescent, although the
p-conjugation is present between the BODIPY ligands and the
Ir(III) coordination center. Moderate intersystem crossing (ISC)
was observed for the complexes, proved by the population of the
long-lived intraligand triplet excited state (3IL) and the 1O2
photosensitizing property. Based on the property of NIR
absorption/uorescence and the reasonable 1O2 quantum yield,
the complexes were used as multi-functional materials as
luminescent bioimaging reagents and in intracellular photo-
dynamic studies. Our results are useful for preparation of NIR-
absorbing cyclometalated Ir(III) complexes, and the relevant
application of these complexes as multi-functional materials
such as a luminescent bioimaging reagent, in PDT and photo-
catalysis, etc.
The 1O2 production of the complexes in aqueous solution
was studied (see ESI Table S1†). Aqueous solvent MeOH–H2O
(4 : 1, v/v) and protic solvent MeOH were used. Ir-1 and Ir-2
show FD values of 70% and 35%, respectively. However, Ir-3 and
1
Ir-4 show no O2 production (see ESI Table S1†). These results
are in agreement with the PDT studies as discussed above. The
1
failure of Ir-3 and Ir-4 to produce O2 in aqueous solution may
be due to the quenching of the triplet states of Ir-3 and Ir-4 by
the intramolecular charge transfer (ICT).
Acknowledgements
IC50 values of the complexes in the absence of LED illumi- We thank the NSFC (21073028, 21273028 and 51202207), the
nation were studied (Table 5). 1121 and LLC cell lines were Royal Society (UK) and NSFC (China-UK Cost-Share
cultured as described in the main manuscript. The IC50 values Science Networks, 21011130154), Ministry of Education
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(SRFDP-20120041130005) and the Fundamental Research
Funds for the Central Universities (DUT14ZD226) for nancial
support.
M. Schaferling and E. Holder, Eur. J. Inorg. Chem., 2010,
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