Tunable optical properties of push-pull chromophores: End group effect

Article abstract of DOI:10.1016/j.tetlet.2020.152205

A series of A-π-D-π-A type symmetrical push-pull chromophores with various end groups (e.g., trifluoroacetone, indanone, dicyano, isoxazolone and pyrazolinone) linked through a symmetric π-conjugated backbone (EDOT-phenylene vinylene-EDOT) was synthesized

Full text of DOI:10.1016/j.tetlet.2020.152205

Journal Pre-proofs
Tunable optical properties of push-pull chromophores: End group effect
Murat Tonga
PII:
S0040-4039(20)30670-5
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.152205
TETL 152205
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
5 May 2020
26 June 2020
29 June 2020
Please cite this article as: Tonga, M., Tunable optical properties of push-pull chromophores: End group effect,
Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.152205
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
©
2020 Elsevier Ltd. All rights reserved.

Tunable optical properties of push-pull chromophores: End group effect
Murat Tonga a,b
aDepartment of Chemistry, University of Massachusetts, Amherst, MA 01003, USA
bPresent Address: Polnox Corporation, 225 Stedman St Suite 23, Lowell, MA 01851, USA
e-mail: murattonga@gmail.com
Phone: 1-413-545-2291, Fax: 1-413-545-4490
ABSTRACT
A series of A-π-D-π-A type symmetrical push−pull chromophores with various end groups (e.g.,
trifluoroacetone, indanone, dicyano, isoxazolone and pyrazolinone) linked through a symmetric
π–conjugated backbone (EDOT-phenylene vinylene-EDOT) was synthesized. The effect of end
group tuning on optical properties was intensively investigated by UV-visible absorption,
fluorescence spectroscopy and DFT calculations. A broad range of chromophores showing
strong absorption was achieved with a fine alteration of the electron-accepting strength of the
terminal acceptors. The optical investigation demonstrated that their low optical band gap (1.8-
-1
-1
2
.2 eV) combined with outstanding molar absorptivity (45,000-101,500 M cm ) which would
provide strong light-capturing capability.
Keywords: Push-pull chromophores, donor-acceptor, end group, phenylene vinylene, EDOT,
ICT
INTRODUCTION
“
Donor−acceptor” or “push−pull” type structures are of increasing attention for the use in
organic electronic applications such as photovoltaic cells, light emitting diodes (LEDs),
1
nonlinear optical (NLO) devices and field-effect transistors (FETs). The term “donor-acceptor”
or “push-pull” has been used to define conjugated compounds that possess an electron donor
1

group (D) and an electron withdrawing (A) group connected to each other through π-conjugated
spacers where the alignment of the donor–acceptor compounds can be either symmetrical A-π-D-
2
π-A and D-π-A-π-D or asymmetrical D-π-A and D-π-A-π-A. Intramolecular charge transfer
(ICT) occurring from electron donor to electron acceptor through π-bridge allows controlling
3
absorption, electronic energy levels and carrier mobilities. The strength of ICT enables the
compounds to have narrow band gaps and strong light absorption via variations in the design and
choice of the donor and acceptor units.4
Among many donor−acceptor compounds, π–conjugated arylenevinylene oligomers have
5
attracted prominent attention. Specifically, oligo(phenylene vinylene)s (OPVs) have been used
in organic electronic applications due to large absorption bands, high quantum yields, and large
6
Stokes shifts. They can be an essential component for constructing organic electronic devices as
7
push-pull designs when coupled with electron acceptors. Eichen et al. showed a sequence-
8
independent synthesis of OPVs by employing bifunctional thiophene building units. Mayer et al.
synthesized various push-pull chromophores having electron-withdrawing units attached to a π-
9
conjugated backbone resulting from OPV. Krebs et al. has prepared oligo-phenylene vinylenes
1
0
for solar cell applications using a similar route. Nomura et al. demonstrated the synthesis of
1
1
well-defined OPVs with variations in repeat units and end groups. In our previous study, we
showed that D-A type structures composed of various π-conjugated units (e.g., aromatic and
vinylene) that are incorporated to viologen and pyridinium acceptors for extended absorption
1
2
13
maximum and strong molar absorptivity. Related studies are reported elsewhere.
Given our particular interest in the development of push−pull materials, the employment of end
group strategy into A-π-D-π-A compounds with tunable electronic and optical properties is
important for the development of novel organic electronic materials. Herein, this study reports
2

the synthesis, optical and electronic properties, and theoretical calculations of novel
chromophores which were developed with a variety of terminal acceptors including
trifluoroacetone, indanone, dicyano, isoxazolone and pyrazolinone to generate targets ADA-(1-
5
). The core donor unit D comprised 2,5-dihexyloxy-1,4-phenylene vinylene attached to an
electron-donating group 3,4-ethylenedioxythiophene (EDOT) through vinylene unit. EDOT has
gained attention as a building unit for conducting materials. A hybrid π-conjugated system
containing both EDOT and phenylene vinylene moieties was selected to increase absorption
cross sections for longer wavelength light, which enables a material to absorb very strongly.
Depending on the nature of the electron-accepting substituent, the newly synthesized
chromophores exhibit low to moderate luminescence and a strong absorption (300-700 nm)
-1
-1
coupled with excellent molar absorptivity (up to 101,500 M cm ).
RESULTS AND DISCUSSION
Synthesis
Knoevenagel (Friedel-Crafts reaction in the case of ADA-1) reaction furnished all A-π-D-π-A
conjugated molecules with the condensation reaction of a terminal aldehyde group in the donor
core (5) and an activated methylene group on the acceptors. Trifluoroacetone, indanone, dicyano,
isoxazolone and pyrazolinone moieties were used as electron-accepting moiety and 2,5-di(n-
hexyloxy)benzene vinylene-bis-EDOT as the electron-donating moiety. The synthetic strategy
for these chromophores starts with the synthesis of central π-conjugated donor (5).
3

Scheme 1. Synthetic route to the chromophores.
4

The central donor molecule was prepared in five steps starting from p-hydroquinone according to
1
2
our previous report. Initially, 1,4-di-n-hexyloxybenzene (1) was synthesized in 63% yield from
p-hydroquinone and 1-bromodecane in the presence of K CO . The presence of six carbons is
2
3
sufficient for testing and processability of target chromophores. Subsequent bromomethylation
of 1 with glacial acetic acid solution with paraformaldehyde and hydrogen bromide readily
afforded intermediate molecule 2 in 84% yield. Arbuzov reaction with triethylphosphite
converted molecule 2 to 2,5-di-n-hexyloxy-1,4-xylenediethylphosphonate ester (3) with a high
yield of 99%. An EDOT unit was employed to extend π-conjugation. Horner-Wadsworth-
Emmons (HWE) procedure gave intermediate 4 in good yield of 68% by reacting molecule 3
with a mono-aldehyde substituted EDOT which was readily obtained with Vilsmeier-Haack
reaction from EDOT. In a similar manner, a subsequent Vilsmeier-Haack formylation provided
molecule 5 having terminal aldehyde groups in the core donor moiety which are the key building
blocks for end-group functionalization with an acceptor molecule.
As regards the acceptors, isoxazolone and pyrazolinone derivatives were synthesized from ethyl
acetoacetate while commercially available acceptors including 1-indanone, malononitrile and
trifluoroacetic anhydride were used as is. Phenyl hydrazine was condensed with ethyl
acetoacetate to obtain 3-methyl-1-phenyl-2-pyrazoline-5-one as in the reported procedure.14
Similarly, isoxazolone derivative, 3-methyl-5(4H)-isoxazolone, was readily obtained by
1
5
refluxing ethyl acetoacetate with hydroxylamine hydrochloride. Knoevenagel condensation of
aldehydes of molecule 5 with 1-indanone, malononitrile, 3-methyl-5(4H)-isoxazolone and 3-
methyl-1-phenyl-2-pyrazoline-5-one in refluxing ethanol in the presence of a base catalyst
(
piperidine, NH OAc or NaOH) afforded the chromophores ADA-(2-5) in moderate-to-good
4
yields (75-90%) (Details are given in the Supporting Information). Friedel-Crafts reaction of
5

molecule 4 with trifluoroacetic anhydride directly gave ADA-1 by refluxing in 1,2-
dichloroethane. Notably, all chromophores showed good solubility in most of the organic
solvents such as dichloromethane, chloroform, acetone and acetonitrile. The resulting products
were thoroughly characterized by 1H NMR and high-resolution mass spectrometry (HRMS).
Optical Properties
In order to investigate their photophysical properties, the UV−vis absorption and
photoluminescence (PL) spectra of the chromophores were studied at solution state in
dichloromethane (DCM). The solution absorption spectroscopy of the push–pull chromophores
provides insight about their excited state behavior, particularly ICT character and variation as a
function of the acceptor strengths. The absorption spectra of the chromophores showed a similar
shape, which can be ascribed to their structure analogues. The spectra demonstrated a broad
absorption at 300-700 nm. The absorption bands in the high-energy regions (300-425 nm) are
ascribed to the π–π* electronic transition of the conjugated molecular backbone whereas the low
energy region of 425-700 nm is due to ICT transitions from donor to acceptor. In DCM, the
ADA-(1–5) peak maxima are seen at progressively longer wavelengths following the trend of
increasing electron-withdrawing ability: trifluoroacetone < indanone < dicyano < isoxazolone <
pyrazolinone (Figure 1, left). The largest λmax red shifts of ~100 nm relative to ADA-1 were
obtained using pyrazolinone end group in ADA-5. The larger red shift in ADA-5 is most likely
because of its stronger ICT nature compared to ADA-1. Only a 4 nm λmax red shift compared to
ADA-4 was observed with a pyrazolinone acceptor in ADA-5, which can be ascribed to similar
electron-withdrawing strengths. The chromophores ADA-1 and ADA-2 showed the highest
energy onset at 525 nm and 556 nm, respectively. In comparison with ADA-1, ADA-2 showed a
red shift of 35 nm for absorption, induced by the stronger electron-accepting property of
6

indanone group. Replacement of indanone in ADA-2 by the strong electron acceptor dicyano in
ADA-3 leads to a red shift as large as 66 nm. The spectral onsets provided the same trends as
was observed for their absorbance maxima. The chromophores absorb strongly through much of
the visible spectrum with band onsets at 550–700 nm.
Figure 1. Normalized UV–vis absorption (left) in dichloromethane and emission spectra (right)
of the chromophores at the same concentration in dichloromethane.
The chromophores ADA-1, ADA-2 and ADA-4 typically showed weak photoluminescence at
solution state, as shown in Figure 1, right. Only the chromophores ADA-3 and ADA-5 exhibited
considerable PL intensity. The PL spectra of the chromophores were notably broad, covering the
entire visible area (~500–850 nm). The same trend was noted for the PL spectra, as was observed
for their absorbance spectra, which demonstrated red-shifting maxima of from 584 to 683 nm
with increasing electron-withdrawing ability, except the chromophore ADA-5 was atypical in
exhibiting a lower PL maximum which could be attributed to particular solvent-solute relations.
Furthermore, this anomaly behavior for ADA-5 could be due to a lesser geometric change from
ground to ICT excited state because ADA-5 is already non-planar in the ground state which was
7

supported by higher dihedral angles obtained in the DFT calculations. The large red shift in the
emission maxima (λ ) for ADA-(1-4) changing from 584 to 683 nm might be attributed to the
Pl
formation of excited species through strong π–π interactions. The PL spectra overall showed
single-peak, with some shoulders at higher wavelength in DCM (presumably emission peaks due
to aggregation). Stokes shifts in DCM are given in Table 1. The large Stokes shifts are evidence
for large dipole moment shift at excited state due to the presence of both donor and acceptor
1
6
units connected by a π-conjugated spacer. The large Stokes shifts were observed ranging from
4
1 nm to 106 nm with ADA-3 having the highest shift while ADA-5 has the lowest. The larger
Stokes shift in ADA-3 versus ADA-5 implies a larger geometric variation between ground and
excited ICT states in ADA-3.
Table 1. Optical and DFT data for the chromophores.
Absmax PLmax Absonset
ϵ
M
cm
x 10 )
Stokes Egopt
Shift
(nm) (eV) (°) (°)
α
β
EHOMO ELUMO EgDFT
-
(
1
-1
3
(nm)
(nm)
(nm)
(eV)
(eV)
(eV)
ADA-1
ADA-2
ADA-3
ADA-4
ADA-5
490
525
556
580
584
584
614
662
683
625
564
606
651
683
698
51.8
94
89
2.2 -1 -1
-5.42
-2.81
-2.47
-3.19
-3.07
-2.89
2.61
2.38
2.36
2.35
2.31
45.8
98
2.05 -7 -17 -4.85
106
103
41
1.9 27 22
1.82 36 42
1.78 38 46
-5.55
-5.42
-5.2
47.3
101.5
Egopt: optical band gap, estimated from UV–vis absorption edge. EHOMO and ELUMO were obtained
by DFT calculations.
Molar extinction coefficients of the push−pull chromophores are presented in Table 1. All the
chromophores showed relatively high molar extinction coefficients ranging from 45,000 M−1
−
1
−1
−1
cm to 101,500 M cm at the maximum absorption wavelength (λmax) in dichloromethane.
8

−
1
−1
The chromophore ADA-2 exhibited the lowest extinction coefficient (45,000 M cm ), which
might be due to its inefficient π–π* electron transitions. Compared with ADA-2 and ADA-4,
−
1
−1
ADA-1 showed a higher molar extinction coefficient (~52,000 M cm ), which is probably due
1
7
to larger dipole moments as a result of the inductive effect of fluorine atoms. Due to increased
electron delocalization over the conjugation on the most co-planar geometry, the chromophores
−
1
−1
ADA-3 and ADA-5 showed the highest extinction coefficient (98,000 M cm and 101,500
−
1
−1
M cm , respectively).
Egopt is the optical energy gap estimated by the onset point of the absorption edge and calculated
in the range of 1.8-2.2 eV (Table 1). The reduced optical band gap for ADA-5 as compared to
ADA-1 can be due to the stronger electron-accepting ability of pyrazolinone compared to
trifluoroacteone. The lower band gap of the novel chromophores originates from a favorable ICT
between donor and acceptor units.
Theoretical Calculations
Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level were carried out on
the chromophores to gain insight into optimized geometries and molecular frontier orbitals. For
simplicity, the hexyl side-chains on the donor group were replaced by methyl groups. The
chromophores ADA-(1-5) all showed that the highest occupied molecular orbital (HOMO)
electron distributions were mainly localized on the vertical axes of on the donor moieties
including aryl-, neighboring with vinylene bridges and thiophenes. The lowest unoccupied
molecular orbital (LUMO) electron distributions in all chromophores were similar to one
another, were mainly delocalized along the horizontal axes of on the donor moieties and acceptor
groups on the edges. The phenyl moieties on the acceptors indanone (ADA-2) and pyrazolinone
9

(ADA-5) have no participation on both molecular frontier orbitals. Localization of the HOMO
over the electron-rich region of the molecule gives deep HOMO levels which are beneficial for
increased stability in air and are expected to generate larger open circuit voltages (V ) when
OC
utilized in organic photovoltaics.18
Scheme 2. Depiction of dihedral angles, optimized geometry (side view), and frontier molecular
orbitals of the chromophores.
The insertion of vinylene bonds along the conjugated backbone has demonstrated to be a
versatile method to increase the degree of coplanarity by decreasing steric hindrance since the
1
9
vinylene unit is less likely to be twisted. All the chromophores adopt (E, E) configurations and
show a conformation changing from highly planar to slight twist. The DFT results also indicated
that overall planarity of the chromophores generally decreases in the order of ADA-1 to ADA-5.
The dihedral angles between the electron-withdrawing and central electron-donating building
blocks were analyzed. In particular, dihedral angle α is defined between the electron-
1
0

withdrawing moieties and neighboring with thiophene whereas dihedral angle β is between the
electron-withdrawing moieties and central benzene in the main plane. Table 1 schematically
represents the calculated dihedral angles, HOMO, LUMO and electronic band gap for all the
chromophores. As shown in Scheme 2, both ADA-1 and ADA-2 displayed highly planar
conformations. Dihedral angles for ADA-1 and ADA-2 were found as α = 1°, β = 1.0° and α = -
7
°, β = -17°, respectively. Geometry optimization resulted in a slight deviation from planarity for
the chromophore ADA-3. Cyano electron-withdrawing groups are forced out of the central plane
with the dihedral angles of α = 27° and β = 22° due to steric interactions between a cyano
nitrogen and an adjacent oxygen group of EDOT ring (with a nitrogen−oxygen distance on the
order of 3 Å). The chromophore ADA-4 bearing isoxazolone units are not coplanar, but have
instead adopted a moderately twisted conformation to minimize steric hindrance between a
bulkier methyl group present on the acceptor ring and an adjacent oxygen group of EDOT ring
with a distance on the order of 2.3 Å. The calculated dihedral angles for the chromophore ADA-
4
5
were found as α = 36° and β = 42°. This dihedral angles are predicted slightly higher for ADA-
(α = 38° and β = 46°) compared to ADA-4. Steric hindrance between a bulkier methyl group
present on the acceptor ring and an adjacent oxygen group of EDOT ring forces to the
chromophore to adopt a twisted geometry. The rigidity of π-conjugated backbone is a significant
aspect determining electronic properties the materials. Even though some chromophores were
predicted to adopt a twisted conformation in the gas phase, they could be planar due to solid state
packing.
Using the optimized conformation of the chromophores, electronic band gaps were investigated
(Scheme 3). Narrowing of the theoretical energy band gap was observed across the series going
from the chromophore ADA-1 to ADA-5 in the order of 2.61, 2.38, 2.36, 2.35 and 2.31 eV. The
1
1

difference in band gaps confirms that the effective conjugation is more limited in twisted
chromophores due to steric interactions observed between acceptor units and neighboring donor
units. Overall, the observed trends in theoretical calculations were in good agreement with
experimental results.
Scheme 3. Energy diagram of the chromophores as estimated by DFT calculations.
CONCLUSION
In summary, the present study shows an effective synthetic method for elaborating novel A-π-D-
π-A type structures by varying end groups (e.g., trifluoroacetone, indanone, dicyano, isoxazolone
and pyrazolinone). The effects of end group tuning on optical and electronic properties were
investigated thoroughly. This approach provides a rational route for tuning EHOMO, ELUMO, band
gaps, and molar extinction strength. DFT calculations enabled the understanding of the
relationship between structures and the optical properties. The chromophore bearing
trifluoroacteone moiety has the weakest electron-withdrawing ability while pyrazolinone moiety
1
2

has the strongest electron-withdrawing ability. The use of ICT yielded compounds with strong
absorption throughout the visible region (an optical band gap of 1.8-2.2 eV) and high molar
−
1
−1
−1
−1
extinction coefficients ranging from 45,000 M cm to 101,500 M cm . Additional study
area includes testing them in organic electronic applications.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was supported as part of Polymer-Based Materials for Harvesting Solar Energy
(PHaSE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office
of Basic Energy Sciences under Award Number DE-SC0001087. Any thoughts, results, and
decisions or suggestions stated in this contribution are those of the authors and do not express the
opinions of the U.S. Department of Energy, Office of Basic Energy Sciences.
A. Supplementary data
Supplementary data associated with this article can be found in the online version.
1
3

References
Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐
The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
1
4

Tunable optical properties of push-pull chromophores: End group effect
Murat Tonga a,b
aDepartment of Chemistry, University of Massachusetts, Amherst MA, 01003, USA
bPresent Address: Polnox Corporation, 225 Stedman St Suite 23, Lowell MA, 01851, USA
e-mail: murattonga@gmail.com
Phone: 1-413-545-2291, Fax: 1-413-545-4490





A-π-D-π-A type chromophores with various acceptor groups were synthesized.
The effects of end group tuning on optical and electronic properties were studied.
The use of ICT yielded strong absorption throughout the visible region (1.8-2.2 eV).
−
1
−1
They gave excellent molar extinction coefficients (45,000-101,500 M cm ).
DFT calculations compare the correlation between structures and optical properties.
1
a) Yan C, Barlow S, Wang Z, Yan H, Jen AKY, Marder SR, Zhan X. Nat. Rev. Mater. 2018; 3:
1
8003. b) Meng L, Zhang Y, Wan X, Li C., Zhang X, Wang Y, Ke X, Xiao Z, Ding L, Xia R,
Yip HL, Cao Y, Chen Y. Science 2018; 361: 1094. c) Shao S, Wang S, Xu X, Yang Y, Lv J,
Ding J, Wang L, Jing X, Wang F. Chem. Sci. 2018; 9: 8656–8664.d) Wang Q, Yang F, Zhang Y,
Chen M, Zhang X, Lei S, Li R, Hu W. J. Am. Chem. Soc. 2018; 140: 5339–5342. e) Xu H, Liu F,
1
5

Elder DL, Johnson LE, Coene YD, Clays K, Robinson BH, Dalton LR. Chem. Mater. 2020; 32:
408–1421. f) Tang R, Zhou S, Xiang W, Xie Y, Chen H, Peng Q, Yu G, Liu B, Zeng H, Li Q,
1
Li Z. J. Mater. Chem. C 2015; 3: 4545–4552. g) Szukalski A, Sahraoui B, Kulyk B, Lazar CA,
Manea AM, Mysliwiec J. RSC Advances 2017; 2017: 9941–9947.
2
a) He GS, Tan LS, Zheng Q, Prasad PN. Chem. Rev. 2008; 108: 1245–1330. b) Cheng YJ,
Yang SH, Hsu CS. Chem. Rev. 2009; 109: 5868–5923.
3
a) Li Z, He G, Wan X, Liu Y, Zhou J, Long G, Zuo Y, Zhang M, Chen Y. Adv Energy Mater.
2
012; 2: 74–77. b) Fitzner R, Mena-Osteritz E, Mishra A, Schulz G, Reinold E, Weil M, Körner
C, Ziehlke H, Elschner C, Leo K, Riede M, Pfeiffer M, Uhrich C, Bäuerle P. J. Am. Chem. Soc.
2
012; 134: 11064–11067.
4
Dou L, Liu Y, Hong Z, Li G, Yang Y. Chem. Rev. 2015; 115: 12633–12635.
a) Müllen K.; Scherf, U. Organic-Light Emitting Devices: Synthesis, Properties and
5
Applications; Wiley-VCH: Weinheim, Germany, 2006. b) Ravishankar S, Dudhea B, Jasmine S,
Kumar A, Rao VR. Sens. Actuators B 2010; 148: 158–165. c) Samuel DW, Turnbull GA. Chem.
Rev. 2007; 107: 1272–1295.
6
Lincker F, Bourgun P, Masson P, Didier P, Guidoni L, Bigot JY, Nicoud JF, Donnio B, Guillon
D. Org. Lett. 2005; 7: 1505–1508.
7
a) Langa F, Gomez- Escalonilla MJ, Rueff JM, Figueira Duarte TM, Nierengarten JF, Palermo
V, Samori P, Rio Y, Accorsi G, Armaroli N. Chem. Eur. J. 2005; 11: 4405–4415. b) Tao Y,
Donat-Bouillud A, d’Iorio M, Lam J, Gorjanc TC, Py C, Wong MS. Synth. Met. 2000; 417: 111-
1
12. c) Wu CW, Lin HC. Macromolecules 2006; 39: 7985–7997.
1
6

8
Shivananda KN, Cohen I, Borzin E, Gerchikov Y, Firstenberg M, Solomeshch O, Tessler N,
Eichen Y. Adv. Funct. Mater. 2012; 22: 1489–1501.
9
Guerlin A, Dumur F, Dumas E, Miomandre F, Wantz G, Mayer CR. Org. Lett. 2010; 12: 2382–
2
385.
1
0
Jorgensen M, Krebs FC. J. Org. Chem. 2004; 69: 6688–6696.
1
1
Abdellatif MM, Yorsaeng S, Inagaki A, Nomura K. Macromol. Chem. Phys. 2014; 215:
1
973−1983.
1
1
2
Tonga M, Lahti PM. Synthetic Met. 2019; 254: 75−84.
3
a) Dar AH, Gowri V, Gopal A, Muthukrishnan M, Bajaj A, Sartaliya S, Selim A, Ali Md. E,
Jayamurugan G. J. Org. Chem. 2019; 84: 8941−8947. b) Podlesný J, Pytela O, Klikar M,
Jelínková V, Kityk IV, Ozga K, Jedryka J, Rudyshde M, Bureš F. Org. Biomol. Chem. 2019; 17:
3
623−3634. c) Fenggang L, Hongyan X, Huajun X, Shuhui B, Chaolei H, Yanling H, Jialei L,
Zhen Z, Xinhou L, Ling Q. Dyes Pigments 2017; 136: 182−190.
1
1
4
5
Vijay K, Nandib C, Samant SD. RSC Adv. 2014; 4: 30712−30717.
Heravi MM, Derikvand F, Haeri A, Oskooie HA, Bamoharram F F. Synthetic Commun. 2008;
3
8: 135−140.
1
6
Fernandes SSM, Castro MCR, Pereira AI, Mendes A, Serpa C, Pina J, Justino LLG, Burrows
HD, Raposo MMM. ACS Omega 2017; 2: 9268–9279.
1
7
Saethre LJ, Berrah N, Bozek JD, Boerve KJ, Carroll TX, Kukk E, Gard GZ, Winter R,
Thomas TD. J. Am. Chem. Soc. 2001; 123: 10729–10737.
1
7

1
1
8
9
Potscavage Jr WJ, Sharma A, Kippelen B. Acc. Chem. Res. 2009; 42: 1758–1767.
Jebnounia A, Chemlia M, Lévêqueb P, Fallb S, Majdouba M, Leclerc N. Org. Electron. 2018;
5
6: 96–110.
1
8