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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. [ABSTRACT FROM AUTHOR]

Sapphyrin is a pentapyrrolic expanded porphyrin with a 22π aromatic character. Herein, we report the synthesis of a 20π antiaromatic sapphyrin isomer 1 by oxidative cyclization of a pentapyrrane precursor P5 with a terminal β‐linked pyrrole. The resulting isomer 1, containing a mis‐linked bipyrrole unit in the skeleton, exhibits a reactivity for further oxidation due to the distinct antiaromatic electronic structure, affording a fused macrocycle 2, possessing a spiro‐carbon‐containing [5.6.5.6]‐tetracyclic structure. Subsequent treatment with an acid afforded a weakly aromatic pyrrolone‐appended N‐confused corrole 3, and thermal fusion gave a [5.6.5.7]‐tetracyclic‐ring‐embedded 14π aromatic triphyrin(2.1.1) analog 4. The cyclization at the mis‐linked pyrrole moiety of P5 played a crucial role in synthesizing the antiaromatic porphyrinoid susceptible to facile transformation to novel porphyrinoids with variable aromaticity. [ABSTRACT FROM AUTHOR]

The synthesis of organometallic complexes of modified 26π‐conjugated hexaphyrins with absorption and emission capabilities in the third near‐infrared region (NIR‐III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis‐PdII and bis‐PtII complexes of hexaphyrin via N‐confusion modification led to substantial metal dπ–pπ interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO–LUMO energy gap. A remarkable long‐wavelength shift of the lowest S0→S1 absorption beyond 1700 nm was achieved with the bis‐PtII complex, t‐Pt2‐3. The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t‐Pt2‐3 potentially useful as a NIR‐III PA contrast agent. The rigid bis‐PdII complexes, t‐Pd2‐3 and c‐Pd2‐3, are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR‐III‐emissive and photoacoustic‐response capabilities. [ABSTRACT FROM AUTHOR]

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 3dx2-y2 orbital energy, thereby making such compounds invaluable for copper‐based catalytic applications. [ABSTRACT FROM AUTHOR]

An N‐confused phlorin isomer bearing a dipyrrin moiety at the α‐position of the confused pyrrole ring (1) was synthesized. PdII and BIII coordination at the peripheral prodigiosin‐like moiety of 1 afforded the corresponding complexes 2 and 3. Reflux of 2 in triethylamine (TEA) converted the meso‐phenyl into the PdII‐coordinating phenoxy group to afford 4. Under the same reaction conditions, TEA was linked to the α‐position of the dipyrrin unit in 3 as an N,N‐diethylaminovinyl group to afford 5. Furthermore, peripheral coordination of BIII in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of AgIII at the inner cavity to afford 3‐Ag and 5‐Ag, respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination. [ABSTRACT FROM AUTHOR]

Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green‐to‐red region (500–700 nm) and the near‐ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S1) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S1 states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S1 states. [ABSTRACT FROM AUTHOR]

A hybrid thia‐norhexaphyrin comprising a directly linked N‐confused pyrrole and thiophene unit (1) revealed unique macrocycle transformations to afford multiply inner‐annulated aromatic macrocycles. Oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone triggered a cleavage of the C−S bond of the thiophene unit, accompanied with skeletal rearrangement to afford unique π‐conjugated products: a thiopyrrolo‐pentaphyrin embedded with a pyrrolo[1,2]isothiazole (2), a sulfur‐free pentaphyrin incorporating an indolizine moiety (3), and a thiopyranyltriphyrinoid containing a 2H‐thiopyran unit (4). Furthermore, 2 underwent desulfurization reactions to afford a fused pentaphyrin containing a pyrrolizine moiety (5) under mild conditions. Using expanded porphyrin scaffolds, oxidative thiophene cleavage and desulfurization of the hitherto unknown N‐confused core‐modified macrocycles would be a practical approach for developing unique polypyrrolic aromatic macrocycles. Oxidation of a nonaromatic thia‐modified norhexaphyrin with directly linked N‐confused pyrrole and thiophene rings triggered cleavage of a C−S bond to afford three multiply annulated polypyrrolic aromatic macrocycles with global or local aromaticity. This approach is a path to porphyrinoids with tunable structures and aromaticity based on thiophene cleavage and desulfurization. [ABSTRACT FROM AUTHOR]

A novel [36]octaphyrin analogue embedding two N-confused pyrrole units demonstrated unique prototropy-coupled isomerization between the Figure-of-eight and dumbbell conformers. Upon bis-metal coordination, fixation of fully π-conjugated Figure-of-eight structures was achieved as referred from the X-ray crystal structure. Chirogenesis of the helical enantiomers was proved by intense circular dichroism (CD) response in the near infrared (NIR) region. [ABSTRACT FROM AUTHOR]

Complexation of novel multiply N-confused expanded calix[ n]phyrins with boron difluoride afforded a new class of cyclic BODIPY (boron-dipyrromethene) arrays. The structures of circularly arranged BODIPY subunits linked in an N-confused fashion give rise to such photophysical properties unique to the macrocycles as redshifted emission wavelengths along with apparent large Stokes shifts, long emission lifetimes, and solid-state lasing. The DFT calculations support the size-dependent excited-state dynamics of the macrocycles. [ABSTRACT FROM AUTHOR]

Three kinds of fused porphyrinoids, L2- L4, possessing different types of corrole-based frameworks were synthesized from a pyrrole-substituted corrole isomer (norrole L1). Oxidation of L1 afforded a unique N-Cmeso-fused pyrrolyl isonorrole L2, involving the fusion of an auxiliary pyrrolic NH moiety with a meso-sp3-hybridized carbon atom. Subsequently, L2 underwent macrocycle transformations to give singly and doubly N-CAr-fused N-confused corroles, L3 and L4, respectively. L3 and L4 contain fused [5.7.6.5]-tetra- and [5.6.7.7.6.5]-hexacyclic structures, respectively, prepared through lateral annulation. These skeletal transformation reactions from norrole to its isomer isonorrole and finally to N-confused corrole indicate that multiply fused porphyrinoids could be readily synthesized from pyrrole-appended confused porphyrinoids. [ABSTRACT FROM AUTHOR]

A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para- and meta-quinodimethane-bridged BODIPY dimers BD-1 and BD-2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm ( ɛ=6.65×105 M−1 cm−1) and 1136 nm ( ɛ=6.44×105 M−1 cm−1), respectively, together with large two-photon-absorption cross-sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn-on response in the presence of the hydroxyl radical but not with other reactive oxygen species. [ABSTRACT FROM AUTHOR]

A contracted doubly N-confused dioxohexaphyrin derivative served as a dinucleating metal ligand for unsymmetrical coordination. The complexation of two palladium(II) cations led to the formation of π-radical species that were persistent in atmospheric air in the presence of moisture. Effective delocalization of an unpaired electron over the hexaphyrin backbone could contribute to the distinct chemical stability. [ABSTRACT FROM AUTHOR]

Biradicaloids based on quinoidal rylenes! Soluble and stable tetracyanoquaterrylenequinodimethane (QR‐CN) and tetracyanohexarylenequinodimethane (HR‐CN) were synthesized. QR‐CN has a closed‐shell quinoidal structure in the ground state, whereas HR‐CN has a singlet biradical ground state. Both compounds showed very strong one‐photon and two‐photon absorption in the NIR range. [ABSTRACT FROM AUTHOR]