New meso-substituted corroles possessing pentafluorophenyl groups - Synthesis and spectroscopic characterization

Article abstract of DOI:10.1039/c4cp05648e

The investigation presented in this paper deals with new free-base corroles substituted with different peripheral groups. These aromatic macrocycles were efficiently synthesized by a [2+1] approach from dipyrromethanes. Moreover, the basic spectroscopic studies of the dyes in chloroform were conducted, and the UV-Vis absorption, fluorescence and ESR parameters were estimated. The experimental data were supported by quantum chemical calculations. The presence of monomeric dye structures is concentration independent (10^-6-10^-4 M), as expected for dyes in a solvent of low polarity, and rules out aggregate formation of corroles dissolved in chloroform. The excitation emission and fluorescence life-time values confirm the monomeric structure of the corroles. The spectra were compared with the time-dependent density functional theory (TD-DFT) results for the HOMO-LUMO states. The ESR examinations strongly show that for any type of studied fluorine corrole an unpaired electron is localized on the corrole macroring but not on the substituents both before and after light illumination. Laser illumination creates additional radicals, however with different effectiveness depending on the sample.

Full text of DOI:10.1039/c4cp05648e

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New meso-substituted corroles possessing
pentafluorophenyl groups – synthesis and
Cite this: Phys.Chem.Chem.Phys.,
spectroscopic characterization†
2
015, 17, 7411
a
b
b
c
Bartosz Bursa, Bolesław Barszcz, Waldemar Bednarski, Jan Paweł Lewtak,
c
c
c
a
Dominik Koszelewski, Olena Vakuliuk, Daniel T. Gryko* and Danuta Wrobel*
´
The investigation presented in this paper deals with new free-base corroles substituted with different
peripheral groups. These aromatic macrocycles were efficiently synthesized by a [2+1] approach from
dipyrromethanes. Moreover, the basic spectroscopic studies of the dyes in chloroform were conducted,
and the UV-Vis absorption, fluorescence and ESR parameters were estimated. The experimental data
were supported by quantum chemical calculations. The presence of monomeric dye structures is
ꢀ6
ꢀ4
concentration independent (10 –10 M), as expected for dyes in a solvent of low polarity, and rules
out aggregate formation of corroles dissolved in chloroform. The excitation emission and fluorescence
life-time values confirm the monomeric structure of the corroles. The spectra were compared with
the time-dependent density functional theory (TD-DFT) results for the HOMO–LUMO states. The ESR
examinations strongly show that for any type of studied fluorine corrole an unpaired electron is localized
on the corrole macroring but not on the substituents both before and after light illumination. Laser
illumination creates additional radicals, however with different effectiveness depending on the sample.
Received 4th December 2014,
Accepted 30th January 2015
DOI: 10.1039/c4cp05648e
www.rsc.org/pccp
1
9–21
Raman scattering and electron paramagnetic resonance.
Our experimental methods were supported by quantum
Corroles are synthetic aromatic porphyrin-analogue dyes, in chemical calculations. In this paper we wish to describe the
1
. Introduction
1
–8
which one meso carbon bridge is absent which leads to the synthesis and to present the spectroscopic characterization of
redistribution of electron density when one compares them to six new meso-substituted corroles possessing various groups of
9
porphyrins and in consequence this can result in changes of different electronic and steric character. In particular corroles
spectroscopic properties and make them promising candidates bearing naphthalene-1-yl substituents (and analogous ones) at
as photoactive agents. The similar but not the same molecular position 10 were studied. Thus, the general purpose of the
structure of corroles with respect to porphyrins, large delocalized presented paper is to investigate the fundamental electronic
p-electron conjugation, reasonable stability and very good properties by UV-vis spectroscopy (absorption, fluorescence,
matching of their absorption spectrum range to sunlight make and electron spin resonance (ESR)) supported by quantum-
them new excellent organic materials for light energy collection chemical calculations. Gaining in-depth knowledge of the
and conversion. Thus, in some laboratories corroles have attracted relationship between structure and optical properties is essen-
considerable interest because of their potential applications as tial for potential applications of corroles in optoelectronics and
photoconductors, in electronic devices, as gas sensors, solar cells related fields.
10–18
and in other photo-electroactive items.
Selected photophysical properties of some corroles have
been previously studied by us with the use of various spectro-
scopic methods: UV-Vis spectroscopy, infrared absorption,
2
. Materials and methods
2
.1. Synthesis
2,7-Dimethoxynaphthalene, 4,7-dimethoxy-1-naphthaldehyde,
,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), indium(III)
a
Faculty of Technical Physics, Institute of Physics, Poznan University of Technology,
6
0-965 Pozna n´ , Poland. E-mail: danuta.wrobel@put.poznan.pl
2
b
c
Institute of Molecular Physics, Polish Academy of Sciences, 60-179 Pozna n´ , Poland
Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warsaw,
Poland. E-mail: daniel@icho.edu.pl
chloride and pyrrole were purchased from Sigma-Aldrich. All
chemicals were used as received unless otherwise noted.
Reagent grade solvents (DCM, hexanes) were distilled prior to
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
1
c4cp05648e
use. All reported H NMR spectra were collected using a 400 or
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00 MHz spectrometer. Chemical shifts (d ppm) were deter-
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5
Method B. 2,7-Dimethoxy-1-naphthalenecarbaldehyde (108 mg,
mined with TMS as the internal reference; J values are given in 0.5 mmol) and 5-pentafluorophenyldipyrromethane (312 mg,
Hz. The UV-Vis absorption spectra were recorded in THF. The 1 mmol) were dissolved in a pre-prepared solution of TFA
absorption wavelengths are reported in nm. Flash column (10 mL) in DCM (10 mL). After 1 h at room temperature the
chromatography was performed on silica (200–400 mesh). reaction mixture was dissolved in DCM (800 mL), a solution of
The mass spectra were obtained by field desorption MS DDQ (300 mg, 1.3 mmol) in toluene (3 mL) was added, and the
(FD-MS) and electrospray ionisation (ESI-MS). The following reaction was stirred at room temperature for an additional 0.5 h.
compounds have been prepared according to literature proce- The reaction mixture was passed through a silica column (silica,
22
dures: 2,7-dimethoxy-1-naphthalenecarbaldehyde, 5-pentafluoro- DCM/hexanes, 1 : 3). All fractions containing corrole were com-
2
3
24
phenyldipyrromethane, 8-methoxy-4-quinolinecarboxaldehyde , bined and evaporated to dryness. Flash column chromatography
25
26
27
4
-formyl-7,8-dimethoxycoumarin, corrole 5 and corrole 6.
0-(4,7-Dimethoxynaphthalen-1-yl)-5,15-bis(pentafluorophenyl)- a dark solid. The resulting solid was suspended in hot MeOH,
corrole (1). 4,7-Dimethoxy-1-naphthaldehyde (108 mg, 0.5 mmol) cooled, and filtered to give pure corrole 2 (73 mg, 18%). R (DCM/
and 5-pentafluorophenyldipyrromethane (312 mg, 1 mmol) were hexanes, 1 : 1) = 0.60; H NMR (400 MHz, CDCl
dissolved in MeOH (50 mL). Subsequently, a solution of HClaq (ꢀ3)–(ꢀ1) (br s, 3H, NH), 2.87 (s, 3H, OCH ), 3.61 (s, 3H, OCH
36%, 2.5 mL) in H O (50 mL) was added, and the reaction was 6.20 (d, 1H, J = 2.5 Hz, naphtha.), 7.03 (dd, 1H, J = 2.5, J = 9 Hz,
stirred at room temperature for 1 h. The mixture was extracted naphtha.), 7.54 (d, 1H, J = 9.1 Hz, naphtha.), 7.94 (d, 1H, J = 9.1 Hz,
with CHCl
(2 ꢁ 50 mL), and the organic layer was washed twice naphtha.), 8.20 (d, 1H, J = 9.0 Hz, naphtha.), 8.41 (d, 2H, J = 4.6 Hz,
with H O, dried (Na SO ), filtered, and diluted to 250 mL with b-H), 8.53 (d, 2H, J = 3.2 Hz, b-H), 8.58 (d, 2H, J = 4.8 Hz, b-H), 9.07
(silica, DCM/hexanes, 1 : 9 - 1 : 4) afforded the title compound as
1
f
1
3
, Me
4
Si, ppm) d
3
3
),
(
2
1
2
3
2
2
4
+
CHCl . DDQ (300 mg, 1.3 mmol) was added, and the mixture was (d, 2H, J = 4.3 Hz, b-H); HRMS (FD): [M ] 816.1606 C H F N O
43 22 10 4 2
3
stirred for 0.5 h at room temperature. The reaction mixture was requires: 816.1583. Anal. calcd for C H F N O : C, 63.24; H,
43 22 10 4 2
concentrated to half the volume and was passed through a silica 2.72; F, 23.26, N, 6.86. Found: 63.01; H, 2.78; F, 23.18, N, 6.97.
column (silica, DCM/hexanes, 1 : 1). All fractions containing 10-(8-Methoxyquinolin-4-yl)-5,15-bis(pentafluorophenyl)-
corrole were combined and evaporated to dryness. Flash column corrole (3). 8-Methoxy-4-quinolinecarboxaldehyde (160 mg,
chromatography (silica, DCM/hexanes, 1 : 4) afforded the title 0.85 mmol) and 5-pentafluorophenyldipyrromethane (530 mg,
compound as a dark solid. The resulting solid was precipitated 1.7 mmol) were dissolved in DCM (55 mL). To the resulting
from hot DCM by adding cyclohexane. The crystals were filtered mixture TFA (200 mL) was added and the reaction mixture was
off and dried under vacuum to give 115 mg of pure corrole 1 stirred for 30 min. Subsequently Et N (400 mL) was added and,
3
1
(
28%). R (DCM/hexanes, 1 : 1) = 0.57; H NMR (400 MHz, CDCl , after diluting with DCM to 300 mL, a solution of DDQ (550 mg,
f
3
Me
4
Si, ppm) d (ꢀ2.5)–(ꢀ1) (br s, 3H, NH), 2.94 (s, 3H, OCH
3
), 2.38 mmol) in toluene (10 mL) was added, and the reaction was
3
4.24 (s, 3H, OCH ), 6.47 (d, 1H, J = 2.3 Hz, naphtha.), 7.08 (d, 1H, stirred at room temperature for a further 0.5 h. The reaction
J = 7.9 Hz, naphtha.), 7.15 (dd, 1H, J
.02 (d, 1H, J = 7.9 Hz, naphtha.), 8.46 (d, 1H, J = 9.3 Hz, 95 : 5). All fractions containing corrole were combined and
naphtha.), 8.50 (d, 2H, J = 4.6 Hz, b-H), 8.56 (br s, 2H, b-H), 8.60 evaporated to dryness. Flash column chromatography (silica,
d, 2H, J = 4.4 Hz, b-H), 9.10 (d, 2H, J = 4.0 Hz, b-H); HRMS (ESI): DCM/acetone, 95 : 5) afforded the title compound as a dark
1 2
= 2.5, J = 9.3 Hz, naphtha.), mixture was passed through a silica pad (silica, DCM/acetone,
8
(
[
+
MH ] 817.1678 C H F N O requires: 817.1655. Anal. calcd solid. The resulting solid was precipitated from hot DCM by
43 23 10 4 2
for C H F N O : C, 63.24; H, 2.72; N, 6.86. Found: 63.33; adding hexanes. The crystals were filtered off and dried under
4
3
22 10 4 2
H, 2.70; N, 6.71.
0-(2,7-Dimethoxynaphthalen-1-yl)-5,15-bis(pentafluorophenyl)- 99 : 1) = 0.50; H NMR (500 MHz, CDCl
corrole (2) ), 6.52 (d, 1H, J = 2.8 Hz,
(ꢀ1) (br s, 3H, NH), 3.00 (s, 3H, OCH
Method A. 2,7-Dimethoxy-1-naphthalenecarbaldehyde (108 mg, quin.), 7.42 (dd, 1H, J = 2.8, J = 9.4 Hz, quin.), 8.04 (d, 1H, J =
.5 mmol) and 5-pentafluorophenyldipyrromethane (312 mg, 4.2 Hz, quin.), 8.24 (d, 1H, J = 9.4Hz, quin.), 8.41 (d, 2H, J =
mmol) were dissolved in MeOH (50 mL). Subsequently, a 4.8 Hz, b-H), 8.59 (d, 2H, J = 4.1 Hz, b-H), 8.65 (d, 2H, J = 4.6 Hz,
vacuum to give 121 mg of corrole 3 (18%). R
f
(DCM/MeOH
1
1
3 4
, Me
Si, ppm) d (ꢀ3)–
3
1
2
0
1
solution of HClaq (36%, 2.5 mL) in H O (50 mL) was added, and b-H), 9.07 (d, 1H, J = 4.2 Hz, quin.), 9.14 (d, 2H, J = 4.3 Hz, b-H);
2
+
the reaction was stirred at room temperature for 1 h. The mixture HRMS (TOF MS FD): [M ]: 787.1457 C H N OF requires:
4
1
19
5
10
was extracted with CHCl
washed twice with H O, dried (Na
50 mL with CHCl . DDQ (300 mg, 1.3 mmol) was added, and the corrole (4). 4-Formyl-7,8-dimethoxycoumarin (47 mg, 0.20 mmol)
3
(2 ꢁ 50 mL), and the organic layer was 787.1430. UV-vis (THF) l 328, 412, 566, 609 nm.
2
2
SO ), filtered, and diluted to 10-(7,8-Dimethoxycoumarin-4-yl)-5,15-bis(pentafluorophenyl)-
4
2
3
mixture was stirred overnight at room temperature. The reaction and 5-pentafluorophenyldipyrromethane (125 mg, 0.4 mmol)
mixture was concentrated to half the volume and was passed were dissolved in a pre-prepared solution of TFA (20 mL) in
through a column (silica, DCM/hexanes, 1 : 3). All fractions DCM (10 mL). After 20 min at room temperature the reaction
containing corrole were combined and evaporated to dryness. mixture was diluted with DCM (50 mL) and a solution of DDQ
Flash column chromatography (silica, DCM/hexanes, 1 : 9 - 1:4) (118 mg, 0.52 mmol) in toluene (2 mL) was added, and the
afforded the title compound as a dark solid. The resulting solid reaction was stirred at room temperature for an additional
was suspended in hot MeOH, cooled, and filtered to give pure 0.5 h. The reaction mixture was passed through a silica pad
corrole 2 (19 mg, 4.7%).
(silica, DCM/acetone, 95 : 5). All fractions containing corrole
7
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were combined and evaporated to dryness. Flash column chromato- 2.4. Photophysical parameters
graphy (silica, DCM/acetone, 95 : 5) afforded the title compound as a
dark solid. The resulting solid was precipitated from hot DCM by
adding hexanes. The crystals were filtered off and dried under
Fluorescence quantum yield (F
parative method according to eqn (1)
F
) is determined by the com-
31,32
2
vacuum to give 121 mg of corrole 4 (16%). R (DCM/acetone 98 : 2)
F ꢂ ARef ꢂ n
f
FF ¼ FRef
(1)
1
2
Ref
=
0.58; H NMR (400 MHz, CDCl
3
, Me
), 4.20 (s, 3H, OCH
.99 (s, 1H, coumar.), 8.57 (br s, 2H, b-H), 8.72–8.75 (m, 4H, b-H),
4
Si, ppm) d (ꢀ3)–(ꢀ2) (br s, 3H,
FRef ꢂ A ꢂ n
NH), 3.83 (s, 3H, OCH
3
3
), 6.49 (s, 2H, coumar.),
where F and FRef are the areas under the fluorescence emission
curves of samples 1–6 and the references, respectively; A and
6
9
+
.13 (br s, 2H, b-H); HRMS (TOF MS ESI): [MH ]: 835.1397 C42
H
21
ARef are the relative absorbance of the sample and the refer-
10 4 4
F N O
requires: 835.1364; UV-vis (THF) l 413, 422, 566, 607 nm.
ences at the excitation wavelength; n and nRef are the refractive
2
.2. Spectroscopic investigations
indices of the solvents and the references. As a reference
chlorophyll a in methanol was used (FRef = 0.32 ). The samples
and the reference were excited at the same wavelength
3
3
UV-Vis spectra of the samples 1–6 in chloroform (e = 4.80) were
recorded with the use of a Cary 4000 UV-Vis spectrometer in the
range 300–800 nm, and fluorescence emission (lexc = 405 nm)
and excitation spectra (lem = 700 nm) were recorded with the
use of a Hitachi 4500 Fluorometer. Absorption and fluores-
(405 nm).
3
. Results and discussion
ꢀ
4
ꢀ5
cence spectra in solution were recorded for 10 , 10 and
ꢀ6
3.1. Design and synthesis
10
M concentrations. Fluorescence kinetics were determined
with the use of a PTI instrument. The values of the life-time Six carefully designed corroles were synthesized for this study.
were evaluated with the use of the Launch EasyLife V program. meso-substituted trans-A B-corroles possessing two pentafluoro-
2
Continuous wave X-band ESR experiments were carried out phenyl substituents at positions 5 and 15 were chosen as a key
1
2,27
using a Bruker ELEXSYS 500 EPR spectrometer equipped with motif due to their stability
which is crucial in advanced
a Super High Sensitivity Probehead resonator and a helium photophysical studies. Structural diversity has been achieved by
gas-flow cryostat (ESR900, Oxford Instruments). Dark and light attaching substituents differing in steric and electronic effects at
spectra were recorded at 250 K for a chloroform solution with position 10. We selected the following substituents: 4-nitrophenyl
ꢀ
5
a 10 M fluorine corrole concentration. Light spectra were (strongly electron-withdrawing, lack of steric hindrance), 2,7-
ꢀ2
recorded immediately after solution illumination (30 mW cm
,
dimethoxynaphthalen-1-yl and 4,7-dimethoxynaphthalen-1-yl
1
min) which was performed directly in the resonator with 405 nm (electron-donating, steric hindrance), 4-methoxyquinoliny-1-yl
semiconductor laser light. The number of radicals was obtained (basic nitrogen atom, steric hindrance) and 5,6-dimethoxy-
after double integration of the EPR spectra and comparison with a coumarin-1-yl (strongly polarized, steric hindrance). 5,10,15-
DPPH standard. The concentration of free radicals was calculated Tris(pentafluorophenyl)corrole (5) has also been studied as a
in relation to the number of corrole molecules.
2
reference point. The synthesis of all the trans-A B-corroles was
performed according to the well-known [2+1] condensation
2
.3. Computational details
34
of dipyrromethanes with aldehydes under either classical
2
7
35
In order to interpret the experimental UV-Vis spectra we per- TFA–DCM or in the H O–MeOH–HCl system (Scheme 1).
2
formed calculations of the transition energies by means of The corresponding aldehydes were prepared following litera-
2
2,24,25
time-dependent density functional theory (TD-DFT). The calcu- ture procedures.
lations were performed using the B3LYP hybrid functional depends both on the conditions and on the electronic character
Becke 3-parameter exchange functional combined with Lee– of the aldehyde. In the case of 4,7-dimethoxynaphthaldehyde,
Interestingly the yield of corroles 1–4
(
Yang–Parr correlational functional) and the standard 6-31G the condensation in polar solvents afforded corrole 1 in high
basis set. The choice of the functional was made taking into yield (Scheme 1). On the other hand, the analogous reaction
account the results published in ref. 28, in which a few involving 2,7-dimethoxynaphthaldehyde led to the corre-
functionals were applied to the TD-DFT calculations of corroles. sponding corrole 2 in 5% yield only. This can be partly
It was concluded that to reproduce the energetic relations rationalized based on the lipophilic character of that aldehyde,
between the electronic transitions, the use of hybrid func- which is not compatible with the H
tionals like B3LYP is most reasonable. The calculations were same reaction performed in CH Cl
2
O–MeOH–HCl system. The
afforded corrole 2 in 18%
2
2
run on the equilibrium geometries of isolated molecules yield. The same conditions were also used for formyl-coumarin
obtained from the optimization procedure performed earlier to give corrole 4 in 16% yield. meso-substituted corroles, bearing a
4
5
for all the investigated corroles (DFT, B3LYP/6-31G). The coumarin moiety attached to a corrole core by various linkers
2
9
37,38
Gaussian 03 program package was used for that purpose.
have been prepared before.
It is worth noting that the yield
The first 200 transitions have been calculated. To convolute the of corrole 4 was significantly higher than the efficiency of the
resulting transition energies and oscillator strengths into the condensation of 5-pentafluorophenyldipyrromenthane with other
3
0
absorption spectra the GaussSum program was used. The formyl-coumarins leading to previously described coumarin-
3
7,38
spectra were generated assuming a FWHM (full width at half corroles (B5–8%).
maximum) parameter equal to 3000 cm for all transitions.
This can be rationalized by the much
ꢀ1
weaker polarization of 4-formyl-7,8-dimethoxycoumarin compared
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Scheme 1 Synthesis and molecular structures of the investigated corroles.
to previously employed formyl-coumarins, which leads to a lower samples 2 and 6 to that of sample 1, and the shapes of samples
number of side-reactions. For the condensation of 4-formyl-8- 3 and 4 to that of sample 5, are shown. The location of the bands
methoxyquinoline, the conditions previously optimized for alde- and the full widths at half maximum (FWHM) are almost inde-
36
hydes bearing basic nitrogen atoms were utilized, giving corrole 3 pendent of the dye concentration; this indicates the presence (or
in 18% yield (Scheme 1). Corroles 5 and 6 were prepared following high predominance) of monomeric dye structures in the whole
2
6,27
known procedures.
range of dye concentrations. This conclusion is in agreement with
Ziegler et al.; they ruled out the presence of aggregates in corroles
dissolved in non-polar chloroform.
39
3
.2. Electronic absorption spectra
Experimental. The electronic absorption spectra of corroles
–6 in chloroform at three concentrations (10 , 10 and 10 M) 410 and 427 nm indicates the presence of at least two electronic
The two-structural band in the Soret region with maxima at
ꢀ6
ꢀ5
ꢀ4
1
have been measured. In Fig. 1 we present representative spectra of transitions. Also the band in Fig. 1 observed at 562 nm is broad
the corroles 1 and 5. The spectra are normalized to unity at the and split into two bands at 556 and 573 nm. Additionally, the
highest Soret band. The second derivative spectra of 1 and 5 are long wavelength band (638 nm) is also present. Table 1A
also shown as an example. For the remaining dyes one does not gathers the band intensity ratios as well as the values of the
ꢀ
6
observe any influence of concentration on the spectra shape, as FWHM (of the dyes at a concentration of 10 M).
3
7,38
expected for dyes in solvent of low polarity. The spectra of the dyes
The previously described coumarin-corroles
usually
are slightly different in their shapes. Similarities of the shapes of contained either p-expanded coumarins or strongly polarized
7
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ꢀ4
ꢀ6
Fig. 1 Representative absorption spectra and derivative spectra of corroles 1 (A, B) and 5 (C, D) in chloroform; concentration 10 –10 M; normalized
to unity at the highest Soret band. The remaining dyes show concentration independence. B and D show the range 450–700 nm with notation of the
transition assignments.
coumarins bearing an electron-donating group at position 7. In denoted as T1 and T2 (Table 1B). Five of them belong to the
spite of these differences both the absorption and emission
spectra of corrole 4 (Fig. 5–7) bear a strong resemblance to groups – samples 1–4 and 6) and one corrole is the A
previous dyads with a very visible shoulder on the Soret band positions are substituted with the same groups – sample 5). We
and two distinct Q-bands (560–570 nm and 610–620 nm). conducted our absorption experiments at room temperature, thus
The origin of the absorption bands is discussed on the basis it should be expected that a thermodynamic equilibrium with a
2
A B-type corroles (two meso-positions are occupied with different
3
-type (meso-
40
of Gouterman’s four orbital model and our TD-DFT calculations balance of the two tautomers T1 and T2 in coexistence would be
presented in this paper. The corroles are much less symmetric obtained. The results of the experimental data, supported by
(
D
their symmetry is C2v) whereas porphyrins are characterized by means of the derivative absorption Gaussian analysis and by the
41,42
2h or D4h symmetry.
Nevertheless, the four-orbital model Gouterman model of the electronic transitions of the two tautomers
43,44
refers also to corrole systems.
affects the absorption properties.
The reduced symmetry strongly T1 and T2, are gathered in Table 1B. The four-orbital model
43,44
The absorption bands of predicts the presence of four electronic transitions. On the basis
corroles contain intense Soret bands and weaker Q bands. In our of Table 1B the following electronic transitions can be identified
absorption experiments two sets of bands are well recognized, in as belonging to the tautomers T1 and T2. The S (0–0) transitions
1
the region of 400–450 nm and of 500–700 nm. In the decomposi- can be assigned to T1 and T2 in the ranges of 635–638 nm and
tion of the Soret and Q bands it is useful to analyze the spectra 605–613 nm, respectively. The S
2
(0–0) transitions are observed in
(0–1), S (0–1) and
2
S (0–2) are also identified. At this point of our discussion it is
and assign the bands of the tautomer electronic transitions as the range of 568–577 nm. Some overtones S
1
2
28
proposed by Beenken et al. Two different types of tautomers of
the studied corroles are expected and can be identified – they are worth noting that in one of our papers we have also presented
45
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Table 1 (A) Selected absorption and fluorescence parameters; the data of the absorption maxima were evaluated on the basis of the Gaussian
a
decomposition. (B) Band analysis of the absorption spectra of the studied corroles at room temperature by means of fourth derivative minima, and the
b 40
band assignment to the transitions of the tautomers T1 and T2 in the Q-band range by means of the Gouterman model
(A)
ꢀ1
2
2
Dye
F
F
Band intensity ratio
Absorption maximum [nm]
FHWM [cm
]
R
t [ns]
w
1
2
3
4
5
6
0.31
0.30
0.27
0.25
0.21
0.07
410/427
407/423
408/425
410/425
407/424
407/427
1.05
0.98
1.12
1.15
1.22
1.06
374
371
380
380
379
374
394
391
392
390
392
390
410
407
408
410
407
407
427
423
425
425
424
427
722
626
477
667
637
755
750
766
477
534
475
562
580
522
580
486
545
723
636
700
617
644
568
0.9990
0.9977
0.9894
0.9955
0.9925
0.9932
3.96 ꢃ 0.09
4.27 ꢃ 0.11
4.30 ꢃ 0.14
4.37 ꢃ 0.15
4.95 ꢃ 0.41
1.26 ꢃ 0.09
1.51
0.95
1.45
1.27
1.38
0.86
1045
(B)
Experimental maximum position
Assignment
T1
ꢀ1
Dye
1
Corrole type
nm
cm
Gouterman model
T2
A
2
A
2
A
2
A
2
A
3
B
B
B
B
638
15 674
16 313
16 949
17 331
18 018
15 740
16 695
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
S
S
1
1
(0–0)
(0–1)
613
590
577
555
548
545
533
517
510
492
480
S
1
(0–0)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
18 762
19 342
19 608
20 325
20 833
S
S
2
(0–1)
(0–2)?
1
S
S
S
S
2
2
1
1
(0–1)
(0–2)?
(0–0)
(0–1)
S
2
(0–2)
2
3
4
5
638
15 674
16 340
17 007
17 391
18 051
15 740
16 695
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
612
588
575
554
548
545
530
518
512
495
483
S
1
(0–0)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
18 868
19 305
19 531
20 202
20 704
S
S
2
(0–1)
(0–2)?
1
S
S
S
S
2
2
1
1
(0–1)
(0–2)?
(0–0)
(0–1)
S
2
(0–2)
638
15 674
16 420
17 153
17 545
18 083
15 740
16 695
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
609
583
573
553
548
545
529
514
507
491
478
S
1
(0–0)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
18 904
19 455
19 724
20 367
20 921
S
S
2
(0–1)
(0–2)?
1
S
S
S
S
2
2
1
1
(0–1)
(0–2)?
(0–0)
(0–1)
S
2
(0–2)
636
15 724
16 447
17 153
17 513
18 083
15 740
16 695
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
608
583
571
553
548
545
528
515
509
492
483
S
1
(0–0)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
18 939
19 417
19 646
20 325
20 704
S
S
2
(0–1)
(0–2)?
1
S
S
S
2
2
1
(0–1)
(0–2)?
(0–0)
S
2
(0–2)
634
05
15 773
16 529
15 740
16 695
6
S
1
(0–0)
7
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Table 1 (continued)
(B)
Experimental maximum position
Assignment
T1
ꢀ1
Dye
Corrole type
nm
cm
Gouterman model
T2
5
5
5
5
5
5
5
5
4
4
82
68
51
48
45
26
14
08
95
80
17 182
17 606
18 149
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
S
1
(0–1)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
19 011
19 455
19 685
20 202
20 833
S
S
2
(0–1)
(0–2)?
1
S
S
S
S
2
2
1
1
(0–1)
(0–2)?
(0–0)
(0–1)
S
2
(0–2)
6
A
2
B
640
15 625
16 393
17 036
17 452
18 018
15 740
16 695
17 040
17 570
17 995
18 250
18 340
18 870
19 295
19 550
20 170
20 850
610
587
573
555
548
545
531
517
510
496
480
S
1
(0–0)
S
S
2
(0–0)
(0–1)
1
S
S
2
1
(0–0)
(0–2)?
18 832
19 342
19 608
20 161
20 833
S
S
2
(0–1)
(0–2)?
1
S
S
2
2
(0–1)
S
2
(0–2)
(0–2)?
a
2
FWHM – full width at half maximum (calculated with the Gaussian component program), R – coefficient of determination, F
F
– fluorescence
2
b
quantum yield, t – fluorescence life-time, w – chi square. Bands expected by the model but not found in the analysis of the experimental
spectrum are given in bold. Questionable assignments are marked by ‘‘?’’, precision ꢃ 0.5 nm.
the results of some vibrational bands and also the combination (oscillator strengths versus wavelength) calculated by the TD-DFT
bands with the use of very sensitive infrared photoacoustic method for all investigated corroles are presented in Fig. 2. In all
examinations. However, a few bands predicted in the Gouterman cases the Soret band (about 400 nm) consists of 3–4 intense
1 2
model are not seen (e.g. S (0–2) and S (0–0)).
transitions. However, the spectral distance between the transitions
Quantum chemical calculations. Our supposition as to is quite small and they appear in the resulting spectra as single
the spectral behavior of the corrole dyes was confirmed by bands. In the experimental spectra the Soret band is observed also
quantum-chemical calculations. The electronic transitions as a single band (with some components visible), so there is an
Fig. 2 Electronic transitions (oscillator strengths versus wavelength) calculated by the TD-DFT method for all the investigated corroles.
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agreement between the calculated and experimental spectra. In (highest occupied molecular orbital) and LUMO (lowest unoccu-
the Q band spectral region, two bands are observed in all the pied molecular orbital). Of course other orbitals also take part but
experimental spectra (614 and 638 nm). In the calculated spectra, the dominant contribution arises from the HOMO - LUMO
the band is not separated but can be seen in Fig. 2; there are two transition. The main transitions with appropriate descriptions
(
or more) intense transitions in this region. A similar result has are collected in Table 3. The HOMO and LUMO energies and
46
been obtained in calculations done by Salvatori et al. for a set the HOMO–LUMO energy gap values calculated for the investi-
of free-base and copper corroles. The electronic transition related gated corroles are collected in Table 2 and Fig. 3 while the contour
to the appearance of the Q band involves mainly the HOMO plots of the mentioned orbitals are gathered in Fig. 4.
Table 2 HOMO and LUMO energies and the HOMO–LUMO energy gap values calculated for the investigated corroles (eV). The values calculated for
similar free base corroles by Salvatori and Beenken are provided for comparison
1
2
3
4
5
6
Ref. 46
Ref. 28
E
total (hartree)
ꢀ3018.805
ꢀ5.20
ꢀ3018.802
ꢀ5.14
ꢀ2920.335
ꢀ5.39
ꢀ3129.867
ꢀ5.58
ꢀ3132.251
ꢀ5.63
ꢀ2840.650
ꢀ5.58
HOMO
LUMO
D
ꢀ4.76
ꢀ2.30
2.46
ꢀ5.244
ꢀ2.595
2.649
ꢀ2.75
ꢀ2.69
ꢀ2.91
ꢀ3.05
ꢀ3.10
ꢀ3.16
H–L
2.45
2.45
2.48
2.53
2.53
2.42
Table 3 Selected electronic transitions calculated for the investigated corroles using the TD-DFT (B3LYP/6-31G) method. The major contributions of
the involved orbitals are also given. The table is limited to the transitions with wavelength > 350 nm and oscillator strengths > 0.1
Wavelength (nm)
Oscillator strength
Major contribution
1
5
3
3
3
3
62.1
94.3
85.5
72.4
51.1
0.1918
0.5418
0.3818
0.554
H ꢀ 2 - LUMO (15%), HOMO - LUMO (63%)
H ꢀ 1 - L + 1 (13%), HOMO - L + 1 (26%)
H ꢀ 4 - LUMO (40%), H ꢀ 2 - L + 1 (16%), H ꢀ 1 - L + 1 (12%)
H ꢀ 4 - LUMO (45%), H ꢀ 1 - L + 1 (17%)
HOMO - L + 2 (68%)
0.1907
2
5
5
3
3
3
3
53.5
36.4
96.8
87.0
74.1
51.6
0.1816
0.1418
0.5368
0.3744
0.5476
0.1501
H ꢀ 1 - LUMO (22%), H ꢀ 1 - L + 1 (14%), HOMO - LUMO (43%), HOMO - L + 1 (15%)
H ꢀ 1 - LUMO (40%), HOMO - LUMO (24%), HOMO - L + 1 (21%)
H ꢀ 1 - LUMO (14%), HOMO - L + 1 (38%)
H ꢀ 4 - LUMO (42%), H ꢀ 1 - L + 1 (23%)
H ꢀ 4 - LUMO (45%), H ꢀ 1 - L + 1 (23%)
HOMO - L + 2 (56%), HOMO - L + 3 (14%)
3
5
5
3
3
3
49.3
34.6
92.3
83.1
70.0
0.1476
0.1521
0.6197
0.3415
0.6289
H ꢀ 1 - LUMO (28%), H ꢀ 1 - L + 1 (12%), HOMO - LUMO (36%), HOMO - L + 1 (19%)
H ꢀ 1 - LUMO (34%), H ꢀ 1 - L + 1 (10%), HOMO - LUMO (30%), HOMO - L + 1 (19%)
H ꢀ 1 - LUMO (14%), HOMO - L + 1 (35%)
H ꢀ 4 - LUMO (42%), H ꢀ 2 - L + 1 (13%), H ꢀ 1 - L + 1 (14%)
H ꢀ 4 - LUMO (39%), H ꢀ 1 - L + 1 (21%)
4
5
5
3
3
3
3
47.2
31.9
94.1
89.2
85.9
64.3
0.1142
0.1582
0.3133
0.3133
0.5257
0.5745
H ꢀ 1 - LUMO (32%), H ꢀ 1 - L + 1 (11%), HOMO - LUMO (31%), HOMO - L + 1 (22%)
H ꢀ 1 - LUMO (28%), H ꢀ 1 - L + 1 (13%), HOMO - LUMO (35%), HOMO - L + 1 (17%)
H ꢀ 1 - L + 1 (26%), H ꢀ 1 - L + 2 (30%)
H ꢀ 1 - L + 2 (47%), HOMO - L + 1 (15%)
H ꢀ 2 - L + 1 (15%), H ꢀ 1 - L + 1 (14%), H ꢀ 1 - L + 2 (14%), HOMO - L + 1 (16%)
H ꢀ 4 - LUMO (18%), H ꢀ 2 - L + 1 (41%), H ꢀ 1 - L + 1 (13%)
5
5
3
3
3
34.2
95.7
86.8
69.7
0.1511
0.7181
0.7593
0.3045
H ꢀ 1 - LUMO (21%), H ꢀ 1 - L + 1 (16%), HOMO - LUMO (40%), HOMO - L + 1 (15%)
H ꢀ 1 - LUMO (18%), HOMO - L + 1 (33%)
H ꢀ 2 - LUMO (16%), H ꢀ 1 - L + 1 (37%)
H ꢀ 2 - LUMO (74%), H ꢀ 1 - L + 1 (10%)
6
5
5
4
3
3
3
3
60.3
14.6
94.7
91.3
81.8
68.9
60.8
0.1808
0.1576
0.1214
0.6029
0.4419
0.505
H ꢀ 1 - LUMO (19%), H ꢀ 1 - L + 2 (10%), HOMO - LUMO (46%)
H ꢀ 1 - LUMO (22%), H ꢀ 1 - L + 1 (14%), HOMO - L + 1 (24%), HOMO - L + 2 (33%)
H ꢀ 1 - LUMO (13%), H ꢀ 1 - L + 1 (60%), H ꢀ 1 - L + 2 (11%)
H ꢀ 1 - LUMO (12%), HOMO - L + 2 (38%)
H ꢀ 2 - LUMO (32%), H ꢀ 2 - L + 1 (11%), H ꢀ 1 - L + 2 (29%)
H ꢀ 2 - LUMO (55%), H ꢀ 1 - L + 2 (22%)
0.1345
H ꢀ 2 - L + 1 (76%)
7
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substituent. Selected electronic transitions calculated for the
investigated corroles using the TD-DFT (B3LYP/6-31G) method
are shown in Table 3. The major contributions of the involved
orbitals are also given. The table is limited to the transitions with
wavelengths > 350 nm and oscillator strengths > 0.1.
3.3. Fluorescence studies
The studied corroles exhibit strong fluorescence; Fig. 5 shows
the results for all the dyes in chloroform when excited at
405 nm. The character of the fluorescence spectra is typical
for the porphyrin-like corroles. As seen, the spectra are depen-
dent on the samples and differ from each other in shapes and
Fig. 3 HOMO–LUMO energy gap values calculated for the investigated location of the maxima. The bands of samples 1 and 6 are
corroles.
located at about 651 nm and the bands of 2–5 at about 642 nm;
weak bands in the range 700–750 nm are also seen. Moreover,
the fluorescence of the samples is characterized by small humps
observed in the shorter wavelength range (600–625 nm), which
are very well seen in the spectra of samples 2–6 and much less in
that of sample 1. The differences in the shapes of the fluores-
cence spectra can be compared with our TD-DFT results and the
tautomer T1 and T2 absorption band analysis by means of the
Gouterman model. Thus, the predominant fluorescence is seen
in the long wavelength region and can be assigned to the
emission of the tautomer T1; the less intense shorter wavelength
2
8,47
humps can have their origin in the fluorescence of T2.
The
differences in the sample fluorescence behavior come from the
presence of the various substituents attached to the main corrole
1
3
core. Similar fluorescence behavior was shown by Kruk et al.
for other NH meso-(dichloropyrimidinyl)corrole tautomers,
although the T2 tautomer emission in their work was much
more intense than that of our samples.
The higher intensity of T2 seems to be influenced strongly
by the electron-withdrawing character of the substituents at
position 10. Both C
electron-deficient. The same holds true for the nitro group
corrole 6), but the nitro group quenches emission so its effect
on the T1/T2 ratio is more complex.
6 5
F (corrole 5) and pyranone (corrole 4) are
(
Fig. 4 Contour plots of the corrole molecular orbitals.
It is easy to notice some differences in the HOMO and
LUMO energy values. The greatest differences are between the
HOMO levels of 5 and 2 (0.49 eV) and the LUMO levels of 6 and
2
(0.47 eV). Despite that, the energy gap between the HOMO
and LUMO is very similar for all the investigated corroles – the
greatest difference is between that of 6 and those of 4/5
(
0.11 eV). The energy gap and the HOMO–LUMO energy values
46
28
are also similar to the ones calculated by Salvatori and Beenken
for similar free-base corroles (see Table 2 for comparison).
In the investigated molecules both the HOMO and the LUMO
are localized on the corrole ring and not on the substituents. The
only exception is the LUMO of 6 which is localized on the corrole
macroring and on one of the substituents. The reason for this
is the presence of the electron-withdrawing nitro group in the Fig. 5 Fluorescence spectra of the dyes in chloroform; excitation at 405 nm.
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Fig. 6 Excitation emission spectra of the corroles observed at 700 nm.
The shapes of the excitation emission spectra observed noticeable difference among the samples is the ESR line
at 700 nm correspond to those of the absorption spectra in amplitude, which is proportional to the number of radicals
the range 350–680 nm (Fig. 6). However, the exception is the created. Because after illumination the shape of the ESR
slightly split band in the Soret region, which confirms the spectrum does not change and one can observe only increased
presence of the T1 and T2 tautomers.
line amplitude in comparison to the dark samples, we conclude
The fluorescence decays of two selected dyes (1 and 6) in that light creates some additional radicals of the same type as
chloroform are shown in Fig. 7. On the basis of the fluorescence those of the samples before illumination.
kinetics the life-time values are evaluated and the results are
shown in Table 1A. The life-time values of 1.26–4.95 ns the light-induced sample 2. Approximations indicate that
depending on the dye) are characteristic of porphyrin-like dyes any spectrum consists of two Gaussian lines. These two lines
Fig. 9 presents an example of ESR signal deconvolution for
(
1
st
and confirm monomeric corrole emission. The results of the are characterized by different line widths, DBpp = 6 Gs and
deconvolution procedure give the typical monoexponential DB
2
nd
1st
2nd
= 8 Gs, and g-factors, g = 2.0030 and g
= 2.0032. The
pp
decay; however we are not able to recognize the life-times of two components of the ESR spectrum result from the partial
tautomers T1 and T2 in our experiment. In Table 1A the values charge separation in the fluorine corrole molecules and the
of the fluorescence quantum yields are also collected.
creation of cationic and anionic radicals.
The increase in the number of radicals (proportional to the
ESR signal amplitude) under laser illumination and the decrease
3.4. ESR spectroscopy
Fig. 8 presents the qualitative changes in the ESR spectra after the discontinuation of illumination due to partial ionic
recorded for samples 1–6 before and after illumination. Each radical recombination can be described by the exponential
fluorine corrole solution shows an almost symmetrical ESR line function, with characteristic times of growth and decay of the
characterized by the parameters: line width DBpp = 6.5 (ꢃ 0.1) order of a few minutes and a few hours, respectively. The
Gs, g-factor g = 2.0030 (ꢃ 0.0002). The lack of differences in the concentrations of radicals in the solutions of the different
ESR parameter values strongly suggests that for any of the fluorine corroles before and after 1 minute of illumination
studied fluorine corroles, an unpaired electron is localized are presented in Fig. 10. It is worth mentioning that the ESR
on the corrole macroring but not on the substituents. The only results also show radicals in the powdered samples, but their
7
420 | Phys. Chem. Chem. Phys., 2015, 17, 7411--7423
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Fig. 10 Concentrations of radicals in corrole solutions before and after
ꢀ2
Fig. 7 Fluorescence kinetics of corroles 1 and 6 in chloroform.
laser illumination: 30 mW cm , 1 min, 405 nm.
concentration is much smaller and does not exceed 0.02% (at
least about one order of magnitude less in comparison to those
in solution). The creation of radicals most probably results
from an activation process. In the case of solution samples
the activation energy of radical creation is lowered and leads
to an increase of radical concentration. As presented in Fig. 10,
samples 1 and 2 show the highest concentrations of radicals
(above 1.50%) before laser illumination. Samples 5 and 6 have
the lowest concentrations under the same conditions, i.e. 0.27%
and 0.18%, respectively. One minute of laser illumination
creates additional radicals in all of the samples. This process
is most effective in sample 3 (0.70% additional radicals) and the
least efficient in sample 5 (0.13%).
4
. Conclusions
ꢀ5
Fig. 8 ESR spectra of corroles 1–6 in chloroform (10 M), recorded at
50 K before and after laser illumination.
In summary we can conclude the following:
1) The free-base corroles possessing partly polarized struc-
tures due to the presence of two strongly electron-withdrawing
groups, in chloroform show a monomeric structure even
2
(
6 5
C F
in solutions of high concentrations. This is confirmed by the
absorption and excitation emission as well as the fluorescence
experiments (intensity ratio, FWHM parameters and fluores-
cence life-time). The multi-structural character of the bands in
the Soret and in the Q-band regions (410–427 nm, 500–650 nm)
indicate the presence of more than one electronic transition
assigned to the tautomers T1 and T2. The emission spectra
evidently show the predominance of the T1 tautomer fluores-
cence in the room temperature spectra.
(2) The experimental data are supported by quantum
chemical calculations (TD-DFT) of the HOMO and LUMO,
and the agreement between the experimental and simulated
results is evident. In the investigated molecules (samples 1–5)
both the HOMO and the LUMO are localized on the corrole ring
and not on the substituents. The only exception is the LUMO of
6
which is localized on the corrole macroring and on the nitro
Fig. 9 Experimental and approximated ESR spectra of the light-induced
sample 2.
substituent.
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(
3) The ESR experiments strongly show that an unpaired 17 J. M. Barbe, G. Canard, S. Brand ´e s and R. Guilard, Angew.
electron is localized on the corrole macroring but not on the
Chem., Int. Ed., 2005, 117, 3163.
substituents both before and after light illumination – laser 18 S.-L. Lai, L. Wang, C. Yang, M.-Y. Chan, X. Guan, C.-C. Kwok
illumination creates additional radicals, however with different
effectiveness depending on the sample.
and C.-M. Che, Adv. Funct. Mater., 2014, 24, 4655.
19 K. Lewandowska, B. Barszcz, J. Wolak, A. Graja,
M. Grzybowski and D. T. Gryko, Dyes Pigm., 2013, 96, 249.
2
0 K. Lewandowska, B. Barszcz, A. Graja, B. Bursa, A. Biadasz,
D. Wr ´o bel, W. Bednarski, S. Waplak, M. Grzybowski and
D. T. Gryko, Synth. Met., 2013, 166, 70.
Abbreviations
UV-vis Ultraviolet–visible
2
1 B. Bursa, D. Wr ´o bel, K. Lewandowska, A. Graja,
M. Grzybowski and D. T. Gryko, Synth. Met., 2013, 176,
ESR
Electron spin resonance
FWHM Full width at half maximum
TD-DFT Time-dependent density functional theory
1
8–25.
2
2
2
2 T. Mizutani, T. Murakami, T. Kurahashi and H. Ogoshi,
J. Org. Chem., 1996, 61, 539.
3 A. Osuka, G. Noya, S. Taniguchi, T. Okada, Y. Nishimura,
I. Yamazaki and N. Mataga, Chem. – Eur. J., 2000, 6, 33.
4 J.-P. Liou, C.-Y. Nien, C.-Y. Chang, J.-Y. Chang, Y.-C. Chen,
C.-C. Kuo, H.-P. Hsieh, J.-S. Wu, S.-Y. Wu and J.-Y. Chang,
J. Med. Chem., 2010, 53, 2309.
5 K. Bohra, B. Kumar, V. S. Parmar, A. K. Prasad, D. Sharma
and C. E. Olsen, J. Indian Chem. Soc., 2013, 90, 1885.
6 D. T. Gryko and B. Koszarna, Org. Biomol. Chem., 2003,
Acknowledgements
The paper was supported by the Poznan University of
Technology (grant 06/62/DSPB/0215; B.B1, B.B2, D.W.) and by
EuroSolarFuels grant.
2
2
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