Inverted and fused expanded heteroporphyrins

C-H-activated Csp2-Csp3 diastereoselective gridization enables ultraviolet-emitting stereo-molecular nanohydrocarbons with mulitple H···H interactions

Gridization is an emerging molecular integration technology that enables the creation of multifunctional organic semiconductors through precise linkages. While Friedel-Crafts gridization of fluorenols is potent, direct linkage among fluorene molecules poses a challenge. Herein, we report an achiral Pd-PPh3-cataylized diastereoselective (>99:1 d.r.) gridization based on the C-H-activation of fluorene to give dimeric and trimeric windmill-type nanogrids (DWGs and TWGs). These non-conjugated stereo-nanogrids showcase intramolecular multiple H…H interactions with a low field shift to 8.51 ppm and circularly polarized luminescence with high luminescent dissymmetry factors (|gPL | = 0.012). Significantly, the nondoped organic light-emitting diodes (OLEDs) utilizing cis-trans-TWG1 emitter present an ultraviolet electroluminescent peak at ~386 nm (CIE: 0.17, 0.04) with a maximum external quantum efficiency of 4.17%, marking the highest record among nondoped ultraviolet OLEDs based on hydrocarbon compounds and the pioneering ultraviolet OLEDs based on macrocycles. These nanohydrocarbon offer potential nanoscafflolds for ultraviolet light-emitting optoelectronic applications.

One Pot Synthesis of Two Distinct Macrocycles: Aromatic p-Benzihexaphyrin and Nonaromatic Doubly Fused p-Benzihexaphyrin

Aromatic trithia p-benzihexaphyrins and nonaromatic doubly fused trithia p-benzihexaphyrins were synthesized in a one pot reaction by condensing a p-benzithiophene based tetrapyrrane with three different bithiophene diols under acid catalyzed conditions. The aromatic and nonaromatic macrocycles showed clear differences in colour, NMR, absorption, and electrochemical properties. Theoretical studies supported the observed aromatic and nonaromatic characteristics, respectively, of the p-benzihexaphyrins and their N-fused derivatives.

Synthesis, Spectral, Redox and Theoretical Studies of Stable Nonaromatic Dicarba Dithia Hexaphyrin(2.0.1.1.1.0)s with Two Inverted Thiophenes

A series of dicarba dithia hexaphyrin(2.0.1.1.1.0)s containing two p-phenylene rings, two thiophene rings, and two pyrrole rings connected via five meso carbons were synthesized by condensing the key precursor, hexapyrrane, which was prepared over a sequence of steps, with the appropriate aromatic aldehyde under acid catalytic conditions followed by alumina chromatographic purification. Detailed one-dimensional (1D) and two-dimensional (2D) NMR studies revealed that the two thiophene rings were inverted and facing outward from the macrocyclic core. Interestingly, one of the inverted thiophene rings adopts a normal orientation in the protonated derivatives of macrocycles generated by addition of trifluoroacetic acid to the appropriate macrocyclic solution. The spectroscopic studies support the non-aromatic nature of macrocycles, and the macrocycles exhibit a distinct sharp band at ∼425 nm along with a broad band in the range of 550-1000 nm, which experienced a red shift with a clear color change in the protonated derivatives. The redox studies showed lower oxidation potentials, indicating their electron-rich nature. The density functional theoretical (DFT) studies showed that the hexaphyrins adopt oval-shaped structures, and time-dependent-DFT (TD-DFT) studies parallelly matched the experimental observations of macrocycles.

Synthesis and Properties of Stable 20π Porphyrinoids

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins and differ from porphyrins in aromaticity which in turn affects the structure, properties and chemical reactivities. Research over the years indicated that the 20π porphyrinoids can be stabilized as non-aromatic/anti-aromatic or Mobius aromatic macrocycles using different strategies such as core-modification of porphyrins, non-metal/metal complexation of porphyrins, peripheral modification of porphyrins and expanded porphyrinoids. The structural properties such as aromaticity of the macrocycle can be controlled by choosing the right synthetic strategy. This review will provide an overview of the development in the chemistry of 20π porphyrinoids giving emphasize on the synthesis, structure and electronic properties of these macrocycles which have huge potential for various applications.

Conformationally rigid, π-extended annulated porphyrinoids derived from the naphthobipyrrole motif

π-Extension in porphyrinoids can be achieved by fusing additional aromatic rings onto the macrocycle's periphery and such porphyrinoids are referred to as annulated porphyrinoids. Annulated porphyrinoids display contrasting properties in comparison with their non-annulated congeners. While an annulation strategy can create π-extended systems, the simultaneous incorporation of conformational rigidity in such porphyrinoids can ensure that they adopt a planar structure, and the advantages associated with the extended π-network can be leveraged. Hence, while synthesizing such porphyrinoids, judicial selection of the precursor becomes important. The ease of synthesis and the presence of a β-β'-linked o-phenylene bridge qualify 3,8-1,10-dihydrobenzo[e]pyrrolo[3,2-g]indole, commonly known as naphthobipyrrole, to be one such precursor suitable for the synthesis of conformationally rigid annulated porphyrinoids. This field of study has started to bloom only in the last decade and the examples reported so far are confined to the naphtho-versions of porphycenes (isomeric porphyrin), a few members of the aromatic/antiaromatic expanded porphyrinoids, and calix[n]bipyrroles. In view of this, the current review article aims to summarize the up-to-date developments in this area and discusses the synthesis, structure, and properties of the reported naphthobipyrrole-derived annulated porphyrinoids.

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.