Subphthalocyanine-type dye with enhanced electron affinity: Effect of combined azasubstitution and peripheral chlorination
Graphical abstract
Introduction
Organic molecules combining extended π-chromophore system with enhanced electron donor or electron acceptor properties can be used as functional materials in various fields of organic electronics. Thus, the search for an optimal donor-acceptor pair is very important for achieving high conversion efficiency in organic photovoltaic cells (OPVC). While conjugated semiconducting polymers with donor and acceptor moieties are widely utilized in the solution-based OPVC processing, the vacuum processed OPVC require low molecular weight semiconductors. Today, a large number of small-molecule semiconductors possessing p-type conductivity are known. These are porphyrins, phthalocyanines, polyarenes or squaranine dyes, which are effective as electron donors, but among n-type semiconductors (acceptors) fullerenes still prevail [1,2]. Novel stable non-fullerene acceptors can widen the selection of an effective D/A pair for the molecular heterojunction in organic photovoltaics [2] and can find applications as n-type materials in other fields.
Subphthalocyanines (sPc) (Chart 1) are non-planar macroheterocyclic compounds consisting of three isoindole fragments assembled around tetrahedral boron (III) center, which bears halogen atom or group (usually aryloxy) in the axial position [3,4]. While phthalocyanines (Pc) containing four isoindole units are mostly planar and strongly absorb visible light in the red region, subphthalocyanines have a bowl-shaped structure of the macrocycle and are distinguished by intense absorbance in the green region. Unsubstituted sPc are easily available and basically used as electron donors in OPVC [5,6], though there are examples of their accepting (n-type) behavior [7,8]. Partial or full halogenation of benzene rings stabilizes the frontier π-molecular orbitals (both HOMO and LUMO) and enhances the electron affinity of the subphthalocyanine molecule, thus making halogenated sPc an attractive alternative to fullerenes as electron-acceptors for photovoltaic applications [[8], [9], [10]]. By varying the nature, number and position of the halogen atoms in the macrocycle, one can not only shift the HOMO and LUMO downwards, but also change the HOMO-LUMO gap of the acceptor. In the OPVC design, this is a convenient approach to tune the interface gap energy and thereby to achieve the high open-circuit voltage [11]. Although the use of the perhalogenated subphthalocyanines ([F12sPc] [12]) or [Cl12sPc] [13]) increases the D/A interface gap in the junction, the most impressive results are currently obtained for peripherally hexachlorinated derivative, [Cl6sPc] [[14], [15], [16], [17]], see also [18] for review].
Direct substitution of carbons in the fused benzene ring with electron-accepting heteroatoms is another way to strongly influence the frontier MO levels, as demonstrated in our recent works on heterocyclic subphthalocyanine analogues containing instead of benzene rings fused π-electron deficient heterocycles - pyrazine [[19](b), [19], [19](a)] or 1,2,5-thia (selena)diazole [[20], [20](a), [20](b), [20](c), [21], [22]]). Halogenation of the fused pyrazine rings might further increase the electron-deficient nature and acceptor properties of the macrocycle. Recently, this trend was revealed for perchlorinated tetrapyrazinoporphyrazine and its metal complexes with AlIII GaIII and InIII [23]. The FeII [24] and SnIV [25] complexes were also reported and structurally characterized. In the present study, we report on the synthesis and characterization of hexachlorinated tripyrazinoporphyrazinatoboron (III) chloride, [Cl6Pyz3sPA] (Scheme 1), and compare its optical and chemical properties with those of the well-known subphthalocyanine analogue [Cl6sPc] (Chart 2).
Section snippets
General
Mass-spectrometric measurements were carried out on a MALDI TOF Shimadzu Biotech Axima Confidence and high-resolution ESI maXis Bruker mass-spectrometers in negative and positive modes. 11B and 13C spectra were measured with Bruker Avance 500 spectrometer. Electronic absorption spectra were recorded using a Cary 60 spectrophotometer. The IR spectra were obtained on a Cary 630 FT-IR spectrometer. Commercially available solvents were dried and distilled prior to use.
Synthesis
Synthesis and characterization
Subphthalocyanines and subporphyrazines are usually prepared as boron (III) complexes by template cyclotrimerization of the corresponding dicarbonitrile in the presence of BCl3 in p-xylene [3,4,14,19,20]. We have applied a similar approach for the synthesis of hexachlorotripyrazinosubporphyrazinatoboron (III) chloride, [Cl6Pyz3sPA] (see Chart 2 and Scheme 1) from 5,6-dichloropyrazine-2,3-dicarbonitrile. The dinitrile and BCl3 were taken in 1:1 ratio. A 3-fold excess of BCl3 was necessary since
Conclusions
A novel subphthalocyanine-type dye - perchlorinated pyrazine fused subporphyrazine [Cl6Pyz3sPA] was synthesized and fully characterized. Combined effect of hexaazasubstitution and peripheral chlorination in benzene rings strongly enhances the electron affinity of the subphthalocyanine macrocycle due to stabilization of the LUMO. The first reduction occurs at −0.20 V vs Ag/AgCl, that is by 0.50 V more easily than for peripherally hexachlorinated subphthalocyanine [Cl6sPc]. Azasubstitution
Declaration of competing interest
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.
Acknowledgements
This work was supported by Russian Science Foundation (grant 17-13-01522). The authors are very thankful to Dr. Valentina Ilyushenkova (Institute of Organic Chemistry RAS) for her assistance in the measurements of high-resolution mass-spectra.
References (58)
- et al.
Subphthalocyanine azaanalogues – boron(III) subporphyrazines with fused pyrazine fragments
Dyes Pigments
(2019)et al.pH-sensitive subphthalocyanines and subazaphthalocyanines
Dalton Transactions
(2020) - et al.
Influence of heteroatom substitution in benzene rings on structural features and spectral properties of subphthalocyanine dyes
Dyes Pigments
(2019) - et al.
Fluorescence quantum yields of some rhodamine dyes
J Lumin
(1982) WinGX suite for small-molecule single-crystal crystallography
J Appl Crystallogr
(1999)- et al.
A density functional theory study of the structure and properties of the substituted subphthalocyanines
J Mol Struct THEOCHEM
(2002) - et al.
Photophysical and photochemical investigation of a dodecafluorosubphthalocyanine derivative
J Phys Chem
(1998) - et al.
Absolute potential of the standard hydrogen electrode and the problem of interconversion of potentials in different solvents
J Phys Chem B
(2010) - et al.
Dft study of molecular and electronic structure of Ca(II) and Zn(II) complexes with porphyrazine and tetrakis(1,2,5-thiadiazole)porphyrazine
Int J Mol Sci
(2020) - et al.
The strength of heterocyclic bases
J Chem Soc
(1948) - et al.
Small molecule semiconductors for high-efficiency organic photovoltaics
Chem Soc Rev
(2012)
New advances in non-fullerene acceptor based organic solar cells
RSC Adv
Phthalocyaninartige bor-komplexe
Monatshefte Fur Chemie
Subphthalocyanines: singular nonplanar aromatic CompoundsSynthesis
Reactivity, and Physical Properties
High voltage hybrid organic photovoltaics using a zinc oxide acceptor and a subphthalocyanine donor
Phys Chem Chem Phys
Boron subphthalocyanines as organic electronic materials
ACS Appl Mater Interfaces
Boron subphthalocyanine chloride as an electron acceptor for high-voltage fullerene-free organic photovoltaics
Adv Funct Mater
Acceptor properties of boron subphthalocyanines in fullerene free photovoltaics
J Phys Chem C
Perfluorinated subphthalocyanine as a new acceptor material in a small-molecule bilayer organic solar cell
Adv Funct Mater
Axial/peripheral chloride/fluoride-substituted boron subphthalocyanines as electron acceptors
Inorg Chem
Energy level tuning of non-fullerene acceptors in organic solar cells
J Am Chem Soc
Fluorinated phenoxy boron subphthalocyanines in organic light-emitting diodes
ACS Appl Mater Interfaces
Boron subphthalocyanines as triplet harvesting materials within organic photovoltaics
J Phys Chem Lett
Halogenated boron subphthalocyanines as light harvesting electron acceptors in organic photovoltaics
Adv Energy Mater
Interfacial electronic structure of Cl6SubPc non-fullerene acceptors in organic photovoltaics using soft X-ray spectroscopies
Phys Chem Chem Phys
Decreased recombination through the use of a non-fullerene acceptor in a 6.4% efficient organic planar heterojunction solar cell
Adv Energy Mater
The role of the axial substituent in subphthalocyanine acceptors for bulk-heterojunction solar cells
Angew Chem
Hexachlorinated boron(III) subphthalocyanine as acceptor for organic photovoltaics: a brief overview
Recent Adv. Boron-Containing Materials. IntechOpen
Heterocyclic subphthalocyanine analogue – boron(III) subporphyrazine with fused 1,2,5-thiadiazole rings
Macroheterocycles
Perfluorinated subphthalocynine analogues containing fused 1,2,5-thiadiazole fragments
J Fluor Chem
Molecular sructure of 1,2,5-selenadiazolo- dibenzosubporphyrazinatoboron(III) chloride and influence of perfluorination and perchlorination on its spectral properties
Macroheterocycles
Thiadiazole fused subporphyrazines as acceptors in organic photovoltaic cells
Macroheterocycles
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