Dibenzofuran/Dibenzothiophene-Embedded Dithia-bis(calix)-sapphyrins

Synthesis of Phenothiazine Embedded Heteroporphyrins

A series of phenothiazine embedded heteroporphyrins containing one phenothiazine unit, two pyrrole rings and one heterocycle such as furan, thiophene, selenophene and tellurophene connected via four meso carbons were synthesized. The macrocycles were synthesized by condensing the phenothiazine based tripyrrane with corresponding 2,5-bis(hydroxymethyl)heterocycle under BF3  ⋅ OEt2 catalyzed conditions and compared the structural, spectral, and electrochemical properties with the reported phenothiazinophyrins. The studies showed that the phenothiazine embedded heteroporphyrins were nonaromatic and electronic properties were significantly altered by replacing the pyrrole ring from phenothiazinophyrin with different heterocycles. The X-ray structure of phenothiazine embedded thiaporphyrin revealed that the macrocycle was distorted with an inverted thiophene ring. Both mono-protonated and diprotonated derivatives of macrocycles were generated by the controlled addition of trifluoroacetic acid to the macrocycles. The macrocyclic protons experienced upfield/downfield shifts in protonated derivatives compared to their corresponding neutral phenothiazine embedded heteroporphyrins. However, the heterocyclic ring in both mono- and diprotonated derivatives retained its inverted conformation. The macrocycles in their neutral and protonated form exhibit nonaromatic absorption features. The studies indicated the electron rich nature of macrocycles and DFT/TD-DFT studies were carried out to justify the experimental observations.

Dibenzothiophene-Containing Thiacarbaporphyrinoids

A new type of expanded dibenzothiophene-containing thiacarbaporphyrinoid containing one dibenzothiophene, two p-phenylene, one thiophene, and two pyrrole rings connected via four meso carbons and two direct bonds was synthesized over a sequence of six steps starting with commercially available dibenzothiophene. The X-ray structure obtained for one of the macrocycles revealed that the macrocycle was very nonplanar and the two p-phenylene rings and dibenzothiophene unit were deviated from the mean plane, whereas the thiophene ring attained inverted conformation and was facing toward outside the macrocyclic core. The X-ray structure also revealed that the dibenzothiophene unit of the macrocycle maintained its π-electron delocalization and did not extend the π-electron delocalization with the rest of the macrocycle, and the effective π-conjugation was present only in the lower part of the macrocyclic core, i.e., the thiatripyrrin moiety. The spectral and theoretical studies support the nonaromatic nature of the macrocycles. The macrocycles exhibit one strong absorption band at ∼430 nm and one broad absorption band in the 500-800 nm region, which were bathochromically shifted in diprotonated derivatives which absorb strongly in the visible-NIR region. The electrochemical studies indicated the electron-rich nature of the macrocycles and the theoretical studies corroborated the experimental observations.

Synthesis of stable nonaromatic phenothiazinophyrins

Stable and nonaromatic phenothiazinophyrins which resulted from the replacement of one of the pyrrole rings of porphyrin with a phenothiazine unit were synthesized by condensing phenothiazine based tripyrrane with aryl aldehyde and pyrrole under acid catalysed conditions. NMR studies revealed that the pyrrole ring that is across the phenothiazine unit is inverted and DFT studies also supported that the pyrrole ring inverted phenothiazinophyrins were more stable. Phenothiazinophyrins and their protonated derivatives showed panchromatic absorption features and absorbed in the visible to NIR region.

Doubly Fused Unsymmetrical Calixdicarbahexaphyrins

Three novel doubly fused unsymmetrical calixdicarbahexaphyrins were synthesized by mild acid-catalyzed (4+2) condensation of dicarbatetrapyrrane with dipyrroethene diol followed by oxidation. The condensation formed doubly fused calixdicarbahexaphyrins instead of π-conjugated dicarbahexaphyrins, due to the unusual fusion of the pyrrole N with the α-carbon of the adjacent pyrrole ring to form a tripentacyclic ring and one usual fusion of the pyrrole N with the adjacent phenylene C to form a fused moiety containing two pentacycles and one hexacycle ring. Both fusions occurred on one side of the macrocycle, making the macrocycles unsymmetric. The crystal structure obtained for one of the macrocycles exhibited a saddle-shaped structure with two benzene rings and four pyrrole rings connected via two ethylene and four methene meso-carbon atoms. The crystal structure also revealed unusual fusions in the macrocyclic framework and the presence of one sp³ carbon that disrupts the π-electron delocalization. ¹H, ¹H-¹H COSY, NOESY, ¹³C, and HMBC NMR techniques were used to characterize the macrocycles. The absorption spectra of the macrocycles showed one intense sharp band at ∼485 nm along with a shoulder in the lower-energy region, suggesting its non-aromatic nature. Electrochemical studies indicated their electron rich nature, and DFT/TD-DFT studies corroborated the experimental observations.

Bis-(Fluorene)-Embedded Hexaphyrins

The polyaromatic hydrocarbon containing expanded porphyrins, bis-(fluorene)-embedded hexaphyrins, were synthesized by condensing fluorene-based tripyrrane with pentafluorobenzaldehyde in CH₂Cl₂ in the presence of 1 equiv of BF₃·OEt₂ under an inert atmosphere followed by oxidation with DDQ in open air at room temperature. The reaction worked only when 1 equiv of BF₃·OEt₂ was added to the reaction mixture under concentrated reaction conditions. The bis-(fluorene)-embedded macrocycles were characterized and studied by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), absorption, electrochemical, and density functional theory (DFT)/time-dependent (TD)-DFT techniques. In ¹H NMR, the hexaphyrins showed a few broad unresolved resonances at room temperature, but the NMR spectra were well-resolved at lower temperatures, indicating that the hexaphyrins were very flexible. The DFT-optimized structures indicated that the two fluorene units at the crossing point of the figure-eight loop makes an angle of ∼79.73° with each other, the fluorene moieties maintained their own planarity, and one of the fluorene moieties was not involved in conjugation with the rest of the macrocycle. The absorption spectra of hexaphyrins showed one intense sharp band in the higher energy region and a broad band in the lower energy region. The electrochemical studies indicated that expanded hexaphyrins are relatively electron-rich and showed three easier oxidations and one reduction. The DFT/TD-DFT studies are in agreement with the experimental observations.

Synthesis and Studies of Core-Modified Tellura Dithiasapphyrins

Four different aromatic meso-substituted tellurophene-containing dithiasapphyrins were synthesized by acid-catalyzed [3+2] condensation of 16-telluratripyrrane with bithiophene diol in 22-23% yields. The structural, spectral, and electrochemical properties of tellura dithiasapphyrins were studied and compared with those of previously reported aza (pyrrole)- and other heterocycle (furan, thiophene, and selenophene)-containing dithiasapphyrins. Nuclear magnetic resonance studies indicated that the tellurophene ring in tellura dithiasapphyrins is in the normal conformation, facing toward the inner core, but flips in diprotonated derivatives to an inverted conformation, facing away from the macrocyclic core, unlike aza- and other heterocycle-containing dithiasapphyrins in which pyrrole and the corresponding heterocycle ring always prefer to be in inverted conformation in their neutral and protonated forms. The crystal structure obtained for one of the tellura dithiasapphyrins showed that the macrocycle is highly planar and the tellurophene ring is in the normal conformation. The absorption spectra of tellura dithiasapphyrins exhibited slight hypsochromic shifts compared to those of pyrrole- and other heterocycle-containing dithiasapphyrins. The redox studies indicated that the tellura dithiasapphyrins are electron deficient and readily undergoes reductions. Density functional theory and nuclear independent chemical shift studies indicated that the macrocycles are aromatic, and the computational results closely matched the experimental observations.

Phenothiazine-Embedded Hexaphyrins

Unprecedented nonaromatic stable phenothiazine-embedded porphyrinoids were synthesized by incorporating phenothiazine subunits into the hexaphyrin framework. The crystal structure revealed that the macrocycle adopted a twisted conformation wherein the phenothiazine units maintained their planarity, which was an impediment in π-delocalization throughout the macrocyclic core. The macrocycles exhibited distinct absorption bands in the visible-near-infrared region, and electrochemical studies indicated their electron-rich nature. Theoretical studies were consistent with the experimental observations.

Syntheses of thiophene appended N-confused phlorin isomers

A doubly confused thiapentapyrrane NSP-5 was synthesized by acid-catalysed condensation. Subsequent oxidation with DDQ did not afford the expected thiasapphyrin-like product. Instead, two tetrapyrrolic macrocycles, i.e. neo-N-confused phlorin (1) and N-confused phlorin-II (2) were obtained in the yields of 14% and 18%, respectively. The compounds were characterized by NMR, HRMS, and X-ray diffraction analyses. Single crystal structures clearly reveal that the thienyl units are not embedded into the macrocycles, but appended as meso-substituents, and the C[Formula: see text]-N and C[Formula: see text]-C[Formula: see text] cyclization modes can be clearly revealed by the crystal structures of 1 and 2, respectively. The observation that the thienyl unit is not involved in oxidative cyclization may be related to the relatively low reactivity of the thiophene moiety compared with the more electron-rich pyrrole unit. These results indicate that oxidative cyclization of linear thiaoligopyrranes containing terminal thiophene units may be developed as an effective approach for synthesizing nonconjugated macrocycles like phlorin analogues.

Synthesis and Properties of Dibenzothiophene Embedded Heteroporphyrins

A series of new stable dibenzothiophene embedded heteroporphyrins were synthesized in 6-7% yields by condensing 1 equiv of dibenzothiophene-based tripyrrane with 1 equiv of four different diols, 2,5-bis(hydroxymethyl)heterocycles (furan, thiophene, selenophene, and tellurophene), under mild acid-catalyzed conditions in CH₂Cl₂. The formation of dibenzothiophene embedded heteroporphyrins was confirmed by high-resolution mass spectrometry and thoroughly characterized by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, absorption, electrochemical, and density functional theory/time-dependent density functional theory (DFT/TD-DFT) studies. The NMR studies indicated that the macrocycles were nonaromatic in nature. The electronic properties of the macrocycles were significantly altered as the heterocycle of the macrocycles was varied from furan to thiophene, selenophene, and tellurophene, as reflected clearly in the spectral and electrochemical properties. The macrocycles exhibited a sharp band in the region of 420-440 nm and a relatively broad absorption band(s) in the higher wavelength region of 550-800 nm. The oxa analogue was considerably blue-shifted as compared to the other macrocycles, whereas the tellura analogue exhibited relatively broadened and red-shifted absorption bands. Upon protonation of these macrocycles, the resulting diprotonated species displayed bathochromically shifted absorption bands, which were extended to the NIR region. DFT studies revealed that the macrocycles were highly distorted and strained and exhibited half chair conformation with restricted π-conjugation and confirmed their nonaromatic nature due to the lack of planarity of the macrocycle. TD-DFT studies were in agreement with the experimental spectral and electrochemical results.

Doubly fused fluorene embedded heterosapphyrins

Synthesis and studies of first examples of nonaromatic doubly fused fluorene embedded heterosapphyrins and their intermediate macrocycles, monofused fluorene embedded hetero calixsapphyrins are reported.