Metalla-Carbaporphyrinoids Consisting of an Acyclic N-Confused Tetrapyrrole Analogue Served as Stable Near-Infrared-II Dyes.

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique dπ-pπ-conjugated electronic structures involving the metal dπ-ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF2 and 1Pt-BF2) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ-pπ-conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes.

Copper 1,19-Diaza-21,24-dicarbacorrole: A Corrole Analogue with an N-N Linkage Stabilizes a Ground-State Singlet Organocopper Species.

A copper complex of a heterocorrole analogue with an N-N linkage, 1,19-diaza-21,24-dicarbadibenzocorrole (Cu-5), was successfully synthesized via oxidative metalation-cyclization of a tetrapyrrolic precursor. The N-N linkage in the skeleton of Cu-5, which serves as a mediator of π-electron delocalization, features an 18π aromatic system. The electronic structure of Cu-5 is best described as a ground-state singlet species stabilized by the distinct NNCC coordination core. This finding shows how the ligand's design can be used to modulate the Cu 3 d x 2 - y 2 orbital energy, thereby making such compounds invaluable for copper-based catalytic applications.

A tris-(manganese(iii))corrole-porphyrin-corrole triad: synthesis, characterization and catalytic epoxidation.

A homotrimetallic manganese(iii) corrole-porphyrin-corrole triad has been synthesized and structurally characterized. Corrole and porphyrin rings in the free base corrole-porphyrin-corrole triad are found to be roughly perpendicular to each other having a dihedral angle of 83° in the solid state. A dihedral angle of nearly 67° was found between Mn(iii)-corroles and Mn(iii)-porphyrin rings in the manganese triad complex, 1-Mn. The absorption spectrum of the manganese triad was observed to be the sum of the absorptions from manganese corrole and manganese porphyrin. The catalytic activity of the manganese triad complex was investigated for the epoxidation of styrene using iodobenzene diacetate as an oxygen source. Preliminary results obtained showed the superior activity of the manganese triad as an oxidation catalyst as compared to the respective monomer catalysts. Moreover, product yield in the oxidation of styrene catalyzed by the manganese triad was found to be higher than that of the combined activity of both monomers taken in same equivalence. The reason behind this higher yield may be attributed to an increased local concentration of the catalytic centers at the reaction site.

Corrole-BODIPY Dyad as Small-Molecule Donor for Bulk Heterojunction Solar Cells.

Dyes based on charge-transfer (CT) characteristics are attractive candidates for organic photovoltaics due to their intense and broad absorption window. In these molecular frameworks, electron-rich donors and electron-deficient acceptors are covalently linked to achieve an effective CT process. Corrole, a tetrapyrrolic congener of porphyrin, is an excellent example of an electron-rich molecule with a large molar extinction coefficient. BODIPY, on the other hand, is a well-known electron-deficient bypyrrolic boron difluoride complex with intense absorption complementary to the corrole. A combination of these two structural motifs should result in a dyad having a wide absorption window, which will be suitable for organic photovoltaics. Herein, a corrole derivative has been envisaged as an efficient donor for solution-processed bulk heterojunction solar cells with PC71BM as an acceptor for the first time. The current molecule exhibits broad absorption in the visible range in solution as well as in thin films, with a high molar extinction coefficient and a low band gap of 1.79 eV. Frontier molecular orbital energy levels were found to be complementary to those of the well-known acceptor PC71BM. The optimized devices based on Cor-BODIPY:PC71BM showed a high power conversion efficiency (PCE) of 6.6% with Jsc = 11.46 mA/cm2, Voc = 0.90 V, and FF = 0.61. A remarkable value of incident photon-to-current conversion efficiency (IPCE) of 61% has also been observed.

The Curious Case of a Parasitic Twin of the Corroles.

An expanded porphyrinoid has been obtained by a simple ring expansion from a contracted porphyrinoid, namely corrole. Spectroscopic, structural, and computational investigations reveal peculiar π-conjugation and geometry. The effect of extended π-conjugation is evident from perturbed redox behavior and photophysical properties. Owing to the strong diatropic ring current of the corrole and cross-conjugation, the molecule exhibits a non-aromatic nature for the expanded π-circuit, as evident from NMR studies.

Evidence for a [17] π-Electronic Full-Fledged Non-innocent Gallium(III)-Corrole Radical.

One-electron oxidation of a GaIII -corrole with N(4-BrC6 H4 )3 SbCl6 resulted in an air-stable non-innocent GaIII -corrole radical. The single-crystal X-ray crystallography of the 2,17-bis-formyl-5,10,15-tris(pentafluorophenyl)corrolato gallium(III)(chloride) radical ([3-Cl]. ) revealed delocalization of the unpaired electron, which was further confirmed by electron spin resonance (ESR) spectroscopy and spin density distribution plot. In addition, the nucleus-independent chemical shift (NICS), anisotropy-induced current density (AICD) and harmonic oscillator model of aromaticity (HOMA) supported a [17] π-electron-conjugated (or antiaromatic) radical.

Gallium(III)corrole-BODIPY hybrid: novel photophysical properties and first observation of B-F∙∙∙F interactions.

Anchoring a BODIPY onto Ga(III)corrole via a meso-ß linkage facilitated PeT in polar solvents, which quenched the fluorescence, and is further confirmed by electrochemical studies. The triad exhibits unprecedented crystal emission, which is not known for a corrole derivative, due to unique packing. Compound 4 hosts the first example of a novel B-F∙∙∙F interaction as well.

Corrole-BODIPY Dyads: Synthesis, Structure, and Electrochemical and Photophysical Properties.

A free-base and its Cu(III) derivative of bichromophoric meso-ß linked corrole-BODIPY dyad were synthesized and structurally characterized by single crystal X-ray diffraction (XRD). Both corrole and BODIPY fragments maintained respective ground state electronic isolation despite their connection through a single bond due to a tilted orientation as observed by XRD. This was further supported by UV-vis and cyclic voltammetric studies. The Cu(III)-metalated dyad exhibits temperature-dependent paramagnetic behavior as observed in the variable temperature (1)H NMR due to the presence of a Cu(II)-corrole-π-cation radical. Importantly, the free-base exhibits complete fluorescence quenching probably due to photoinduced electron transfer to a low lying charge separated state. Interestingly, emission was regained upon addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) due to the deprotonation of corrole. The "turn on" fluorescence behavior and the presence of acidic NH protons were further exploited toward basic anion sensing utility.