308
R.C. Pivetta et al. / Journal of Photochemistry and Photobiology A: Chemistry 332 (2017) 306–315
mean-field approach to the Breit-Pauli operator, including one
electron terms, computing the Coulomb contribution with RI,
calculating the Exchange contribution via exact one center
integrals (including spin-other orbit interaction) and also includ-
ing local DFT correlation (SOCFlags 1,3,3,1 in the SOC module of
ORCA) [18].
J = 6.6 Hz, m-Mebpy), 8.11 (d, 1H, J = 5.4 Hz, m-bpy), 8.49 (d, 1H,
J = 7.2 Hz, o-Mebpy), 8.52 (s, 1H, m-Mebpy), 8.58 (d, 2H, J = 5.4 Hz,
b
-H 7,9), 8.72 (s, 4H,
2H, J = 6.0 Hz,
-H 6,8) and 9.23 (s, 1H, m-bpy). 19F NMR (CDCl3,
564.68 MHz): ꢂ161.70 to ꢂ161.68 (m, 2F, Fmeta); ꢂ152.59 (s, 1F,
para) and ꢂ137.73 to ꢂ137.90 (dd, 2F, J1 = 11.28 Hz and J2 = 62.04 Hz,
Fortho). 13C NMR (150.9 MHz, CDCl3):
= 29.88, 117.58, 122.58,
b-H 5), 9.06 (d, 1H, J = 6.6 Hz, o-bpy), 9.11 (d,
b
F
d
2.5. 1O2 generation and photostability assays
124.88, 126.17, 127.35, 129.43, 148.02, 148.29 and 149.12. HRMS-ESI
[M]+: m/z = 799.1756 (calcd for C42H20N6F10: 799.1663).
In a typical experiment of 1.3-diphenylisobenzofuran (DPBF)
photodegradation [24], 2.0 mL of 100
mM DPBF in DMSO was
3. Results
mixed with 0.4 mL (50 M) of corrole 2. The flask was completed
m
with DMSO until a final volume of 4.0 mL. In order to measure 1O2
generation, absorption spectra of the solutions (samples and
standard) were recorded for different exposure times by using a
660 nm diode laser positioned 1.0 cm from the sample (TheraLase
DMC, São Carlos, SP, Brazil) with an average power of 100 mW. The
singlet oxygen production quantum yield (FD) was calculated by
using Eq. (1):
3.1. Design and synthesis of corrole 2
Trans-A2B-corroles [16] that present
a bipyridyl moiety
attached at the 10-position of the corrole was studied. We focused
our investigation mainly on the relatively simple bipyridines that
present bidentade coordinating groups and can be used as a
platform of new peripheral complexes [14,15]. Two pentafluor-
ophenyl units were intended to be introduced at the position 5 and
15 of the macrocycle to warrantee good photo-stability of the
corrole core during photophysical characterization. Our strategy
was to synthesize a bipyridyl-aldehyde derivative which was
transformed into the corresponding corrole through the reaction
with 5 (pentafluorophenyl)dipyrromethane.
The reaction to obtain the functionalized bipyridyl-aldehyde
was based on the formylation reaction between 4,40-(dimethyl)
bipyridine (1.0 equivalent) and SeO2 (1.3 equivalents) described by
Busche and co-workers [27] (Scheme 1). After 24 h under reflux in
dry 1,4-dioxane the functionalized aldehyde 1 was isolated in large
scale (around 1–2 g; yield 35%). The access to bipyridyl-substituted
corrole 2 was performed, according to Gryko and collaborators
[16], and involves the condensation of 5-(pentafluorophenyl)
dipyrromethane and the adequate aldehyde 1 in a mixture of
MeOH/H2O (50:50; v/v) using HCl as catalyst (Scheme 1). The
reaction mixture was maintained under stirring for 1.5 h at room
temperature, and, after the usual work up and chromatographic
purification, we were able to isolate corrole 2 in 17% yield.
The structure of the corresponding free-base corrole 2 was
confirmed by mass spectrometry, NMR, electrochemistry, TD-DFT
calculations, UV–vis and fluorescence spectroscopy and their
photophysical properties were evaluated (vide infra).
FsDtdk I
kstd
.
std
FD
¼
:
ð1Þ
I
ꢀ
ꢁ ꢀ
ꢁ
in which, Istd=I ¼ 1 ꢂ 10A = 1 ꢂ 10A
,
FsDtd is the singlet oxygen
std
quantum yield of standard sample (in our case, Zinc Phthalocya-
nine (ZnPc) dissolved in DMSO, FsDtd ¼ 0:67 [25]), k and kstd are the
photodegradation kinetic constants for corrole
2 and ZnPc
(standard), respectively, and Astd and A are the absorbances for
ZnPc and corrole 2, respectively. The photostability of corrole 2 was
also monitored by absorption measurements for different expo-
sure times with the same pump diode laser with 100 mW of
average power. All experiments were performed in duplicate and
independently.
2.6. Aggregation study
The self-aggregation of porphyrin macrocycles is a natural
tendency due to the strong attractive interactions between
p
-systems of the polyaromatic compounds [26]. It is already
known that the aggregation degree increases with concentration.
In order to investigate possible aggregation of corrole 2, UV–vis
spectra were measured as a function of the concentration using
dichloromethane as solvent. Changes in the lmax from the bands in
UV–vis spectra were monitored.
3.2. Mass spectrometry and NMR analysis of corrole 2
Considering the characterization of corrole 2, its high resolution
(HRMS-ESI) mass spectrum (ESIy, Fig. S1) shows only one ion peak
at m/z 799 ([M]+), in agreement with the meso-mono(4-methyl-
bipyridyl)-substituted corrole 2. When the ESI-MS/MS fragmenta-
tion processes of 2 are analyzed, we observed a systematic HF loss
in the pentafluorophenyl group (ESIy, Fig. S2). In general, the 1H
NMR spectrum of corrole 2 showed the expected profile for trans-
2.7. Synthesis of 10-(4-methyl-bipyridyl)-bis-5,10-
(pentafluorophenyl)corrole (2)
5-(pentafluorophenyl)dipyrromethane (0.319 g; 1.025 mmol)
and the aldehyde 1 (0.108 g; 0.55 mmol) were dissolved in
50 mL MeOH. Subsequently, a solution of HClaq (37%; 2.5 mL) in
H2O (50 mL) was added and the reaction was stirred at room
temperature for 1.5 h. The mixture was extracted with CHCl3, and
the organic layer was washed twice with H2O, dried (Na2SO4),
filtered, and diluted to 250 mL with CHCl3. A solution of DDQ
(0.231 g; 1.025 mmols) in toluene/dichloromethane mixture (1:3;
8 mL) was added, and the mixture was stirred for 20 min. The
reaction mixture was concentrated to half of this volume and it was
purified first on a silica-gel chromatography column (DCM/n-
hexane, 1:2, v/v). Then, the resulting residue was purified by
preparative silica-gel TLC plates using a mixture of DCM/MeOH
(95:5, v/v) to obtain pure dark greenish corrole 2.
A2B-corroles molecules. For instance, the signals at
8.58 ppm correspond to the resonances of the -pyrrolic protons
H-6,8, H-5 and H-7,9 respectively. As expected, the singlet at
8.52 ppm and doublets at 8.49 and 7.19 ppm with coupling
d 9.11, 8.72 and
b
d
d
constants (J) of 6.6 and 7.2 Hz were identified as the resonances of
the ortho and meta Me-bpy protons. The signals due to the meta
and ortho protons of the bipyridyl ring between corrole macrocycle
and Me-bpy fragment appear at
respectively. The signal corresponding to the inner protons of
corrole 2 appear at 2.54,
ꢂ2.87 and the CH3 protons (singlet) at
d 9.23, 9.06 and 8.11 ppm,
d
d
respectively (ESIy, Fig. S3).
The 19F NMR spectrum of compound 2 showed a similar profile
as that of 5,10,15-tris(pentafluorophenyl)corroles. For example, the
corrole 2 19F NMR spectrum shows the resonances of the fluorine
Spectroscopic data for corrole 2: Yield 0.079 g; 0.098 mmol
(17%). M.p. > 300 ꢃC (decomp.). 1H NMR (600 MHz, CDCl3):
d
= ꢂ2.87 (bs, 3H, inner NH), 2.54 (s, 3H, CH3), 7.19 (d, 1H,