Metal-Free Phthalocyanines Bearing Eight Alkylsulfonyl Substituents: Design, Synthesis, Electronic Structure, and Mesomorphism of New Electron-Deficient Mesogens

Abstract

This paper describes the synthesis and physicochemical characterization of novel metal-free phthalocyanines Pc(SO 2 R) 8 , bearing eight peripheral alkylsulfonyl substituents. The key synthetic step is the efficient eightfold oxidation of sulfanyl (SR) into sulfonyl (SO2R) functions in the precursor Pc(SR) 8 . Quantum-chemical calculations show a considerable stabilization of the HOMO and LUMO levels of Pc(SO 2 R) 8 as a result of the presence of the strongly electron-withdrawing groups, while the HOMO−LUMO gap remains nearly unaffected. The redox behavior and electronic spectra of Pc(SO 2 R) 8 were investigated by cyclic voltammetry and electronic absorption spectroscopy, respectively, to confirm the theoretical predictions. Particularly noteworthy is the first reduction potential of −0.14 V vs the saturated calomel electrode (SCE), which falls within the empirically established air-stability window for n-type semiconductors. Supramolecular structures of mesophases of Pc(SO 2 R) 8 and their synthetic precursors Pc(SR) 8 were studied in detail with the aid of powder X-ray diffraction in combination with differential scanning calorimetry and polarized light optical microscopy. As it was demonstrated earlier for many different discotic mesogens, installation of either linear or swallow-tail branched peripheral alkyl substituents plays an important role in the formation of mesophases. However, an unusual behavior was found for the Pc(SO 2 R) 8 series: swallow-tail alkyl chains resulted in higher order in columnar mesophases compared to the linear analogues.

Synthesis of substituted phthalocyanines

“…macrocyclization reaction of corresponding nitriles, 153 aminoiminoisoindolenines, 154 and oxidation of thioalkyl substituents on the phthalocyanine core. 155 The alkyl-and arylsulfonyl and sulfinyl substituted phthalonitriles can be prepared by oxidation of the corresponding alkyl-or arylthiophthalonitriles obtained by nucleophilic aromatic substitution reactions between nitro-or chloro-phthalonitriles and an appropriate thiol under basic conditions (Scheme 38). Higher reaction temperatures favor formation of the sulfonyl substituents, while low reaction temperatures result in isolation of the sulfinyl-containing phthalonitriles.…”

“…The preparation of the metal-free sulfonyl-containing phthalocyanines requires some caution because of possible aromatic nucleophilic substitution of the sulfonyl group by alkoxide ion. 155 This problem can be overcome by oxidation of 2,3,9,10,16,17,23,24-octakis(alkylsulfanyl)phthalocyanines to corresponding octakis-(alkylsulfonyl)phthalocyanines in 53-79% yield using m-chloroperoxybenzoic acid in CH 2 Cl 2 .…”

Combining Electron‐Accepting Phthalocyanines and Nanorod‐like CuO Electrodes for p‐Type Dye‐Sensitized Solar Cells

“…In light of the latter, tuning the physicochemical features of phthalocyanines towards new electron-accepting dyes [17,18] by means of placing electron-withdrawing substituents at their periphery, complements, in the current work, our research regarding nanorod-like CuO electrodes. [19] ; ii) IBX, DMSO/THF; iii) H3NSO3/H2O followed by NaClO2; iv) propargyl alcohol, Pd(PPh3)2Cl2, CuI, NEt3, THF Notably, the synergy of nanorod-like CuO DSSCs and electronaccepting Pcs enables the construction of p-DSSCs with efficiencies as high as 0.103% and 0.191% with iodine-and cobalt-based electrolytes, respectively. The latter represents the highest values ever reported for pure CuO-based DSSCs.…”

Self-assembled 1D Semiconductors: Liquid Crystalline Columnar Phase

“…Zang et al, designed DLC 23 with benzene core and three (trialkoxyaryl)oxadiazole arms and reported TOF electron mobility of 1.0 × 10 −3 cm 2 V −1 s −1 in the columnar phase [72]. Geert's group reported metal free phthalocyanine based DLCs bearing peripheral alkylsulfonyl substituents (for example, 13b) as potential air-stable n-type semiconductors [73].…”