Hemiporphycene: A pH-tunable specific probe for Zn2+ and Cu2

Porphyrins and their isomers possess high affinity towards the formation of complexes with metal cations, but their use for the determination of metal cations is rather limited, due to low selectivity. In this study, we have investigated the unsubstituted hemiporphycene, which shows a highly irregular shape of the inner cavity, and very different reactivity with various metal cations in methanol:water solutions. It was found that hemiporphycene can act as a pH-tunable specific probe for the determination of Zn2+ at pH 8.6 and specific for Cu2+ detection at pH 5.5.

Understanding solvent polarity effects on the separation of uranyl porphyrin-derivative complexes

Solvation is a crucial task in developing efficient and selective extractants for actinide elements, but an understanding and perspective of solvent effects on the extraction of uranyl are still lacking. Herein, we present investigations into solvent effects on the geometry, stability and bonding properties of five uranyl porphyrin derivative complexes (UO2(L)) in four solvents via relativistic quantum chemical calculations, and reveal some trends in the influence of solvent polarity on uranyl compounds. All five [L]2- ligands equatorially coordinate [UO2]2+ in a hexa-dentate (κ6) fashion. Thus, the uranium center is bound to six N atoms by U-N bonds, and the properties of the U-N bond are affected by the ligands rather than by the solvent. The relative stability of these UO2(L) complexes is obviously affected by the solvent polarity; lower polar solvents stabilize more UO2(L) complexes from higher polar solvents, resulting in more extensive interaction of U-N. By computing the reaction energy, we track the conversion of pure [UO2]2+ to UO2(L) complexes in different solvents; the uranyl dipentafluorobenziamethyrin species exhibit the greatest selectivity to higher polarity solvents, with significant orbital interactions of U-N accounting for this stability and selectivity. This study provides a general procedure for theoretical screening of the binding ability and solvent selectivity of macrocyclic ligands towards uranyl, and searching for suitable ligands and solvents that will later be applied in nuclear science disciplines.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Lanthanide-dye hybrid luminophores for advanced NIR-II bioimaging

In vivo luminescence imaging in the second near-infrared window (NIR-II, 1000-2000 nm) is a potent technique for observing deep-tissue life activities, leveraging reduced light scattering, minimized autofluorescence, and moderate absorption attenuation to substantially enhance image contrast. Pushing the frontiers of NIR-II luminescence imaging forward, moving from static to dynamic event visualization, monochromatic to multicolor images, and fundamental research to clinical applications, necessitates the development of novel luminophores featuring bright emission, extendable wavelength, and optimal biocompatibility. Recently, lanthanide-dye hybrid luminophores (LDHLs) are gaining increasing attention for their wavelength extensibility, molecular size, narrowband emission, mega stokes shift, long lifetime, and high photostability. In this review, we will summarize the recent advances of NIR-II LDHLs and their applications in imaging and analysis of living mammals, and discuss future challenges in designing new LDHLs for deep-tissue imaging.

Pushing the Limit of Photo-Controlled Polymerization: Hyperchromic and Bathochromic Effects

The photocatalyst (PC) zinc tetraphenylporphyrin (ZnTPP) is highly efficient for photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. However, ZnTPP suffers from poor absorbance of orange light by the so-called Q-band of the absorption spectrum (maximum absorption wavelength λmax = 600 nm, at which molar extinction coefficient εmax = 1.0×104 L/(mol·cm)), hindering photo-curing applications that entail long light penetration paths. Over the past decade, there has not been any competing candidate in terms of efficiency, despite a myriad of efforts in PC design. By theoretical evaluation, here we rationally introduce a peripheral benzo moiety on each of the pyrrole rings of ZnTPP, giving zinc tetraphenyl tetrabenzoporphyrin (ZnTPTBP). This modification not only enlarges the conjugation length of the system, but also alters the a1u occupied π molecular orbital energy level and breaks the accidental degeneracy between the a1u and a2u orbitals, which is responsible for the low absorption intensity of the Q-band. As a consequence, not only is there a pronounced hyperchromic and bathochromic effect (λmax = 655 nm and εmax = 5.2×104 L/(mol·cm)) of the Q-band, but the hyperchromic effect is achieved without increasing the intensity of the less useful, low wavelength absorption peaks of the PC. Remarkably, this strong 655 nm absorption takes advantage of deep-red (650-700 nm) light, a major component of solar light exhibiting good atmosphere penetration, exploited by the natural PC chlorophyll a as well. Compared with ZnTPP, ZnTPTBP displayed a 49% increase in PET-RAFT polymerization rate with good control, marking a significant leap in the area of photo-controlled polymerization.

Columnar liquid crystals based on antiaromatic expanded porphyrins

Three naphthorosarins, antiaromatic expanded porphyrins bearing different meso substituents (NRos 1-3), designed to self-assemble into columnar liquid crystalline (LC) structures, were synthesized and characterized using polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), as well as supporting computational calculations. The substituents were found to play a crucial role in modulating the LC behaviour.

π-Extended Porphyrin-Phthalocyanine Heterojunction Devices Exhibiting High Ammonia Sensitivity with a Remarkable Light Effect

π-Extended porphyrins represent an attractive class of organic compounds because of their unique photophysical, optoelectronic, and physicochemical properties. Herein, cross-conjugated (Ace-PQ-Ni) and linear-conjugated (AM6) porphyrins are used to build double-layer heterojunction devices by combining them with a lutetium bisphthalocyanine complex (LuPc2). The heterojunction effect at the porphyrin-phthalocyanine interface plays a key role in the charge transport properties. Both devices exhibit exceptionally high ammonia sensitivity at room temperature and under ambient relative humidity, with limit of detection values of 156 and 115 ppb for Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors, respectively. Interestingly, the Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors display opposite effects upon light illumination. While the former sensors show largely decreased ammonia sensitivity under light illumination, the current variation of the latter under ammonia is remarkably enhanced with a multiplication factor of 13 and a limit of detection (LOD) of 83 ppb. The striking difference in their sensing properties upon light illumination is attributed to their different π-conjugation pathways (cross-conjugation versus linear conjugation).

Parallel Chirality Inductions in Möbius Zn(II) Hexaphyrin Transformation Networks

Networked chemical transformations are key features of biological systems, in which complex multicomponent interactions enable the emergence of sophisticated functions. Being interested in chirality induction phenomena with dynamic Möbius π-systems, we have designed a pair of Möbius [28]hexaphyrin ligands in order to investigate mixtures rather than isolated molecules. Thus, a hexaphyrin bearing a chiral amino arm was first optimized and found to bind a ZnOAc moiety, triggering an impressive quasi-quantitative chirality induction over the Möbius π-system. Second, this amino-type hexaphyrin was mixed with a second hexaphyrin bearing a chiral carboxylate arm, affording at first ill-defined coordination assemblies in the presence of zinc. In contrast, a social self-sorting behavior occurred upon the addition of two exogenous achiral effectors (AcO- and BuNH2), leading to a well-defined 1:1 mixture of two Möbius complexes featuring a sole Möbius twist configuration (parallel chirality inductions). We next successfully achieved compartmentalized switching, i.e., a single-component transformation from such a complex mixture. The BuNH2 effector was selectively protected with Boc2O, owing to a lower reactivity of the arm's NH2 function intramolecularly bound to zinc, and subsequent addition of BuNH2 restored the initial mixture, retaining parallel chirality inductions (five cycles). By changing the nature and twist configuration of only one of the two complexes, at initial state or by switching, this approach enables a "two-channel" tuning of the chiroptical properties of the ensemble. Such multiple dynamic chirality inductions, controlled by selective metal-ligand recognition and chemical reactivity, set down the basis for Möbius-type stereoselective transformation networks with new functions.

Naphthodithiophene-Fused Porphyrins: Synthesis, Characterization, and Impact of Extended Conjugation on Aromaticity

The fusion of tetrapyrroles with aromatic heterocycles constitutes a useful tool for manipulating their opto-electronic properties. In this work, the synthesis of naphthodithiophene-fused porphyrins was achieved through a Heck reaction-based cascade of steps followed by the Scholl reaction. The naphthodithiophene-fused porphyrins display a unique set of optical and electronic properties. Fusion of the naphtho[2,1-b:3,4-b']dithiophene to porphyrin (F2VTP) leads to a ~20% increase in the fluorescence lifetime, which is accompanied, unexpectedly, by a more than two-fold drop in the emission quantum yield (ϕ=0.018). In contrast, fusion of the isomeric naphtho[1,2-b:4,3-b']dithiophene to porphyrin (F3VPT) results in a ~1.5-fold increase in the fluorescence quantum yield (ϕ=0.13) with a concomitant ~30 % increase in the fluorescence lifetime. This behavior suggests that fusion of the porphyrin with the naphthodithiopheno-system mainly affects the radiative rate constant in the Q-state deactivation pathway, where the effects of the isomeric naphtho[2,1-b:3,4-b']dithiophene- versus naphtho[1,2-b:4,3-b']dithiophene-fusion are essentially the opposite. Interestingly, nucleus-independent chemical shifts analysis revealed a considerable difference between the aromaticities of these two isomeric systems. Our results demonstrate that subtle structural differences in the fused components of the porphyrin can be reflected in rather significant differences between the photophysical properties of the resulting systems.

Molecular Engineering of Corrole Radicals by Polycyclic Aromatic Fusion: Towards Open-Shell Near-Infrared Materials for Efficient Photothermal Therapy

Open-shell radicals are promising near-infrared (NIR) photothermal agents (PTAs) owing to their easily accessible narrow band gaps, but their stabilization and functionalization remain challenging. Herein, highly stable π-extended nickel corrole radicals with [4n+1] π systems are synthesized and used to prepare NIR-absorbing PTAs for efficient phototheranostics. The light-harvesting ability of corrole radicals gradually improves as the number of fused benzene rings on β-pyrrolic locations increases radially, with naphthalene- and anthracene-fused radicals and their one-electron oxidized [4n] π cations exhibiting panchromatic visible-to-NIR absorption. The extremely low doublet excited states of corrole radicals promote heat generation via nonradiative decay. By encapsulating naphthocorrole radicals with amphiphilic polymer, water-soluble nanoparticles Na-NPs are produced, which exhibit outstanding photostability and high photothermal conversion efficiency of 71.8 %. In vivo anti-tumor therapy results indicate that Na-NPs enable photoacoustic imaging of tumors and act as biocompatible PTAs for tumor ablation when triggered by 808 nm laser light. The "aromatic-ring fusion" strategy for energy-gap tuning of corrole radicals opens a new platform for developing robust NIR-absorbing photothermal materials.

Pd(II), Ni(II), and Cu(II) complexes of α,α'-ditolylmethanone dipyrroethene

Dipyrromethenes containing two pyrrole rings connected by one meso-carbon are versatile monoanionic bidentate ligands and form coordination complexes with many metals/nonmetals/metalloids. Dipyrroethenes containing one additional meso-carbon compared to dipyrromethenes have more space between coordinating pyrrole nitrogens and provide a good coordination environment but have not been explored as ligands in coordination chemistry. Dipyrroethenes are dianionic bidentate ligands and by suitable modifications, the coordination environment of dipyrroethenes can be changed further. Herein, we successfully synthesized α,α'-ditolylmethanone dipyrroethene which is a bipyrrolic tetradentate ligand with an ONNO ligand core and used it for the synthesis of novel Pd(II), Ni(II), and Cu(II) metal complexes by treating it with respective metal salts in CH₂Cl₂/CH₃OH at room temperature. The X-ray crystallographic structure of the metal complexes showed that the M(II) ion was coordinated to the ONNO atoms of the ligand in a perfect square planar geometry. The NMR studies of Pd(II) and Ni(II) complexes also supported the highly symmetric nature of the metal complexes. The absorption spectra of the metal complexes showed strong bands in the region of 300-550 nm. The electrochemical studies of metal complexes revealed that only ligand-based oxidation and reduction were observed. The DFT and TD-DFT studies were in agreement with the experimental observations. Our preliminary studies indicated that the Pd(II) complex can be used as a catalyst for the Fujiwara-Moritani olefination reaction.

Aromatic heterobicycle-fused porphyrins: impact on aromaticity and excited state electron transfer leading to long-lived charge separation

A new synthetic method to fuse benzo[4,5]imidazo[2,1-a]isoindole to the porphyrin periphery at the β,β-positions has been developed, and its impact on the aromaticity and electronic structures is investigated. Reactivity investigation of the fused benzoimidazo-isoindole component reveals fluorescence quenching of a zinc porphyrin (AMIm-2) upon treatment with a Brønsted acid. The reaction of the zinc porphyrin (AMIm-2) with methyl iodide initiated a new organic transformation, resulting in the ring-opening of isoindole with the formation of an aldehyde and dimethylation of the benzoimidazo component. The fused benzoimidazo-isoindole component acted as a good ligand to bind platinum(ii), forming novel homobimetallic and heterobimetallic porphyrin complexes. The fusion of benzoimidazo-isoindole on the porphyrin ring resulted in bathochromically shifted absorptions and emissions, reflecting the extended conjugation of the porphyrin π-system. Time-resolved emission and transient absorption spectroscopy revealed stable excited state species of the benzoimidazo-isoindole fused porphyrins. Zinc porphyrin AMIm-2 promoted excited state electron transfer upon coordinating with an electron acceptor, C60, generating a long-lived charge-separated state, in the order of 37.4 μs. The formation of the exceptionally long-lived charge-separated state is attributed to the involvement of both singlet and triplet excited states of AMIm-2, which is rarely reported in porphyrins.

Synthesis and Coordination Chemistry of a Benzannulated Bipyridine: 6,6'-Biphenanthridine

The synthesis, characterization, and coordination chemistry of a doubly π-extended bipyridine analogue, 6,6'-biphenanthridine (biphe), is presented. The structure of the molecule has been determined in the solid state by X-ray diffraction, showing an angle of 72.6° between the phenanthridine planes. The free, uncoordinated organic molecule displays blue fluorescence in solution. It can be singly protonated with strong acids, and the protonated form displays more intense yellow emission. The effect of acid on the excited states is interpreted with the aid of TDDFT calculations. Two Ru(II) coordination complexes, tris(6,6'-biphenanthridine)ruthenium(II) dichloride, [Ru(biphe)₃]Cl₂, and bis(2,2'-bipyridine)(6,6'-biphenanthridine)ruthenium(II) tetraphenylborate, [Ru(bpy)₂(biphe)](BPh₄)₂, are also reported and their structures determined in the solid state by X-ray diffraction. Both complexes display emission at 77 K that is strongly bathochromically shifted by almost 200 nm compared to that of the archetypal ³MLCT emitter [Ru(bpy)₃]²⁺. Such a red shift is consistent with the more extended conjugation and lower-energy π* orbitals associated with the biphe ligand, lowering the energy of the ³MLCT excited state, as revealed by TDDFT calculations. The efficient non-radiative decay that is typical of such low-energy emitters renders the phosphorescence extremely weak and short-lived at ambient temperature, and rapid ligand photodissociation also competes with radiative decay, especially in the heteroleptic complex. Electrochemical analysis illustrates the effect of biphe's stabilized vacant π* manifold, with multiple reversible reductions evident at much less negative potentials than those observed for [Ru(bpy)₃]²⁺.

Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation

Unsymmetric pentacenequinone-fused (cross-conjugated) and pentacene-fused (linear-conjugated) porphyrins were designed and synthesized. The cross-conjugated (AM ₁ -AM ₃ ) and linear-conjugated (AM ₅ -AM ₇ ) porphyrins displayed strikingly different sets of optical and electronic properties, both of which are unusual and nontypical of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple charge transfer states exist in both π-conjugated systems, which contributes to the complex absorption and MCD spectra of these molecular systems. The general Gouterman's four-orbital model used to explain porphyrin spectroscopy led to contradicting theoretical and experimental data, and is thus not applicable for these molecular systems. The "2 + 4" and "3 + 3" active spaces have been deduced and have proven effective to interpret the absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated) and pentacene-fused (linear-conjugated) porphyrins, respectively. Spectroelectrochemistry of AM ₅ -AM ₇ revealed broad and intense IR absorptions in the range of 1500-2500 nm, illustrating the exceptional ability of these pentacene-fused systems to accommodate positive charges. A pronounced metal effect was observed for pentacene-fused porphyrins. While pentacene-fused Ni(II) porphyrin (AM₆ ) demonstrated an abnormal ability to stabilize pentacene with a half-life of >28.3 days, the half-life of the free base and Zn(II) counterparts were normal, similar to those of pentacene analogues. This work provides important and useful information on guiding new material designs.

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.

Chain Length Modulated Dimerization and Cyclization of Terminal Thienyl-Blocked Oligopyrranes

Oxidation of thienyl-blocked bilane and pentapyrrane afforded chain length dependent products of the symmetric dimer D1 and the thienyloligopyrrin-appended pentaphyrin analogue P2, respectively, with the latter formed by simultaneous dimerization and cyclization. Coordination of D1 and P2 with Cu(II) afforded di- and monometallic complexes D1-Cu2 and P2-Cu, respectively. These compounds exhibit distinct NIR absorption, with the absorption tail of D1-Cu2 extended to ca. 1900 nm despite its smaller conjugation framework than that of P2-Cu.

Chemical bonding in actinyl(V/VI) dipyriamethyrin complexes for the actinide series from americium to californium: a computational investigation

The separation of minor actinides in their dioxocation (i.e., actinyl) form in high-valence oxidation states requires efficient ligands for their complexation. In this work, we evaluate the complexation properties of actinyls including americyl, curyl, berkelyl, and californyl in their pentavalent and hexavalent oxidation states with the dipyriamethyrin ligand (L) using density functional theory calculations. The calculated bond parameters show shorter AnO_yl bonds with covalent character and longer An-N bonds with ionic character. The bonding between the actinyl cation and the ligand anion shows a flow of charges from the ligand to actinyl in all [An^V/VIO₂-L]^1-/0 complexes. However, across the series, backdonation of charges from the metal to the ligand becomes prominent and stabilizes the complexes. The thermodynamic parameters in the gas phase and solution suggest that the complex formation reaction is spontaneous for [Cf^V/VIO₂-L]^1-/0 complexes and spontaneous at elevated temperatures (>298.15 K) for all other complexes. Spin-orbit corrections have a quantitative impact while the overall trend remains the same. Energy decomposition analysis (EDA) reveals that the interaction between actinyl and the ligand is mainly due to electrostatic contributions that decrease from Am to Cf along with an increase in orbital contributions due to the backdonation of charges from the actinyl metal center to the ligand that greatly stabilizes the Cf complex. The repulsive Pauli energy contribution is observed to increase in the case of [An^VO₂-L]^1- complexes from Am to Cf while a decrease is observed among [An^VIO₂-L]⁰ complexes, showing minimum repulsion in [Cf^VIO₂-L]⁰ complex formation. Overall, the hexavalent actinyl complexes show greater stability (increasing from Am to Cf) than their pentavalent counterparts.

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.

Rational Design of Photocatalysts for Controlled Polymerization: Effect of Structures on Photocatalytic Activities

Over the past decade, the use of photocatalysts (PCs) in controlled polymerization has brought new opportunities in sophisticated macromolecular synthesis. However, the selection of PCs in these systems has been typically based on laborious trial-and-error strategies. To tackle this limitation, computer-guided rational design of PCs based on knowledge of structure-property-performance relationships has emerged. These rational strategies provide rapid and economic methodologies for tuning the performance and functionality of a polymerization system, thus providing further opportunities for polymer science. This review provides an overview of PCs employed in photocontrolled polymerization systems and summarizes their progression from early systems to the current state-of-the-art. Background theories on electronic transitions are also introduced to establish the structure-property-performance relationships from a perspective of quantum chemistry. Typical examples for each type of structure-property relationships are then presented to enlighten future design of PCs for photocontrolled polymerization.

Tailor-made aromatic porphyrinoids with NIR absorption

The highlight of this article is the recent progress in the state-of-the-art synthetic design and isolation of artificial porphyrinoids by swapping pyrrole component(s) with diverse functionalized pyrrolic(heterocyclic)/carbacycle building block(s) to compare the impact on the electronic absorption spectra and aromaticity of the incorporated isomeric/expanded porphyrinoids. Attention has been directed towards five distinct criteria of utilizing functionalized pyrrolic(heterocyclic)/aromatic hydrocarbons as synthons for NIR absorbing aromatic isomeric (N-confusion)/expanded porphyrinoids (with five/six heterocycles): (i) fused or annelated pyrrole (heterocycle), (ii) functionalized bi-pyrrole/bi-thiophene/bi-furan building blocks, (iii) azulene based carbacycle building block, (iv) vinylogous aromatic carbacycle/heterocycle(s) building block and (v) N-confused pyrrole ring(s), and N-confused fused pyrrole ring(s) leading to π-extension. These hybrid porphyrinoids are ideal candidates for basic research into macrocyclic aromaticity and for many potential applications owing to NIR absorption.

Second-Order Nonlinear Optics Response of the Boron-Dipyrromethenes-Based Mislinked Expanded Porphyrins: Revealing the Role of the -BF2 Group

Here, the mislinked expanded porphyrins singly (labeled A) and doubly (labeled B) neo-confused [22]smaragdyrin, the boron-dipyrromethenes-based mislinked expanded porphyrins singly (labeled C) and doubly (labeled D) neo-confused [22]smaragdyrin, where both C and D include a -BF₂ group, are chosen to serve as the study objects, and theoretical calculations are carried out to study the role of the -BF₂ group in the second-order nonlinear optics (NLO) behaviors. Results highlighted that the -BF₂ group plays an important role for the second-order behaviors in mislinked expanded porphyrins; namely, embedding the -BF₂ group well enhanced the hyper-Rayleigh scattering (HRS) value {β_HRS(0;0,0)}, C{βHRS(0;0,0)}A{βHRS(0;0,0)} = 2.0 and D{βHRS(0;0,0)}B{βHRS(0;0,0)} = 2.9, main owning to the fact that installing -BF₂ increases the electron delocalization degree and decreases the excited energy of the crucial excited state.

Porphyrin(2.1.2.1) as a novel binucleating ligand: synthesis and molecular structures of mono- and di-rhodium(I) complexes

The first example of monovalent and bimetallic porphyrins(2.1.2.1), the rhodium(I) complex of porphyrin(2.1.2.1), was readily obtained under controlled conditions. The coordinated rhodium(I) drastically influenced the molecular structure and optical and electronic properties. Our results clearly demonstrate that porphyrin(2.1.2.1) could be developed as a new binucleating ligand for the fabrication of bimetallic complexes.

Inverted and fused expanded heteroporphyrins

Expanded heteroporphyrins are a class of porphyrin macrocycles containing pyrrole, thiophene, furan, selenophene and other heterocyclic rings that are connected to form an internal ring pathway containing a minimum of 17 atoms and more than 18 delocalized π electrons in their conjugated macrocyclic framework. Considering that expanded heteroporphyrins are large in size, these macrocycles are structurally flexible and prefer to adopt various conformations in which one or more pyrrole(s)/heterocycle(s) tend to be in an inverted conformation and pointed outward from the centre of the macrocyclic core. The inverted expanded heteroporphyrins are divided into two classes as follows: (1) N-inverted expanded heteroporphyrins and (2) hetero-atom inverted expanded heteroporphyrins. Both inverted expanded heteroporphyrins show quite unique features in terms of their structure, aromaticity, and electronic and coordination properties. Sometimes, inverted expanded heteroporphyrins lead to the formation of fused expanded heteroporphyrins because of the intramolecular fusion of the pyrrole "N" with the "C" of the inverted heterocycle ring, which also exhibit unique features compared to inverted expanded heteroporphyrins. In this review, we attempt to describe the synthesis, structure, and aromatic, electronic and coordination properties of inverted and fused expanded heteroporphyrins. This review covers the synthesis, structure and properties of inverted and fused expanded heteroporphyrins containing a combination of pyrrole/heterocycle rings starting with five pyrrole/heterocycle-containing pentaphyrins, and then expanded heteroporphyrins containing six, seven, eight and more pyrrole/heterocyclic rings in their porphyrin macrocyclic framework.

Synthesis and Structural Properties of NIR-Absorbing Pyridine-Containing Heptaphyrins

Four examples of stable nonaromatic pyridine containing heteroheptaphyrins (pyrithiaheptaphyrins) 2-5 were synthesized in 8-13% yields by [5+2] condensation of newly synthesized pyridine-based pentapyrrane 8 and bithiophene diol 9 a-d. The X-ray crystallographic analysis of macrocycle 2 proved that the macrocycle assumes a highly planar structure with two inverted thiophene rings. The heteroheptaphyrins 2-5 are asymmetric and showed a greater number of resonances in ¹ H NMR spectra compared to our previously reported symmetric heterohexaphyrin (pyrithiahexaphyrin) 1 c. Most of the macrocyclic core protons in pyrithiahepaphyrins 2-5 experienced upfield/downfield shifts compared to pyrithiahexaphyrin 1 c indicating the alteration of π-conjugation in the macrocycles. The absorption bands were significantly red-shifted and located in the NIR region in macrocycles 2-5 compared to 1 c supporting the increase of π-delocalization. The theoretical studies support the experimental findings and NICS(0) value supports the non-aromaticity of the macrocycles.

Structural isolation of NIR absorbing ferrocenyl bridged N-confused fused expanded phlorin, N-confused porphodimethene and the π-extended corrorin isomer: synthesis and characterization

Concise syntheses and spectroscopic, solid state X-ray crystal structure and theoretical studies of three electronically appealing new generation hitherto unknown ferrocenyl bridged N-confused heterocyclic macrocycles with (without) fusion are reported. Intriguingly, the expanded N-confused fused phlorin (1.1.1.1.1) with the built-in tripentacyclic [5.5.5] moiety exhibits tailing of the NIR absorption band beyond 1000 nm while the nonconjugated porphodimethene and a new generation π-extended isomeric corrorin analogue exhibit UV-vis absorption.

Bringing Color to Sugars: The Chemical Assembly of Carbohydrates to BODIPY Dyes

The combination of carbohydrates with BODIPY fluorophores gives rise to a family of BODIPY-carbohydrate hybrids or glyco-BODIPYs, which mutually benefit from the encounter. Thus, from the carbohydrates standpoint, glyco-BODIPYs can be regarded as fluorescent glycoconjugate derivatives with application in imaging techniques, whereas from the fluorophore view the BODIPY-carbohydrate hybrids benefit from the biocompatibility, water-solubility, and reduced toxicity, among others, brought about by the sugar moiety. In this Account we have intended to present the collection of available methods for the synthesis of BODIPY-carbohydrate hybrids, with a focus on the chemical transformations on the BODIPY core.

Consequences of Amide Connectivity in the Supramolecular Polymerization of Porphyrins: Spectroscopic Observations Rationalized by Theoretical Modelling

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π-stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J- versus H-aggregates) of different lengths. In this study, the influence of amide connectivity on the self-assembly behavior of porphyrin-based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non-helical J-type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented.

Neo-Porphyrinoids: New Members of the Porphyrinoid Family

The four pyrrole rings and four meso carbons of tetrapyrrolic porphyrins can be arranged in different ways and the resulting porphyrin isomers exhibit very distinct electronic properties. The extensive research carried out on the porphyrins over the years has revealed that porphyrin can have several possible isomers and some of these have been identified and synthesized. Among the porphyrin isomers synthesized so far, porphycene and N-confused porphyrins have been investigated extensively whereas the other porphyrin isomers such as hemiporphycene, corrphycene and isoporphycene remain underdeveloped because of synthetic difficulties and their inherently unstable nature. Neoporphyrinoids are new members of the porphyrinoid family that were discovered serendipitously in 2011. Neoporphyrinoids are structural analogues of porphyrinoids with a confused pyrrole nitrogen linked to a meso carbon or the adjacent pyrrole carbon. Thus, neoporphyrinoids have an unusual structure in which pyrrole N is a part of a porphyrinoid framework and the lone pair of electrons on nitrogen participate in macrocyclic conjugation. It's been a decade since the discovery and different types of neoporphyrinoids, including regular, contracted and expanded neoporphyrinoids, have been synthesized by rational synthetic methodologies and their spectral, structural, aromatic and coordination properties have been studied. There is huge scope to develop different synthetic routes to produce new types of stable neoporphyrinoids to study their properties and potential applications. This article presents a brief overview of the synthesis, structure and properties of the neoporphyrinoids reported in this decade.

Assessment of New Expanded Porpholactones as UV/Vis/NIR Chromophores for Dye-Sensitized Solar Cell Applications

Expanded porphyrins arise as an alternative for potential application as chromophores in dye-sensitized solar cells. (DSSCs). The modification of the core of these compounds provides remarkable changes in the photoelectronic behavior. In the present article, the improvement of its properties for a potential application as UV/vis/NIR chromophores in DSSCs has been studied, when an oxazolone moiety has replaced an imine ring in analogy to the porpholactones first synthesized by Crossley et al. ( J. Chem. Soc., Chem. Commun. 1984, 920-922). These expanded porpholactones present a noticeable red shift as well as an increase in the intensity of the Q-bands regarding the parent compounds. The photophysical properties of Sapphyrin have been explored through DFT calculations and vibrationally resolved absorption spectra simulations. Energetic parameters showed favorable electron injection from the chromophore to the TiO₂ semiconductor. In addition, aromaticity was analyzed and rationalized using magnetic and delocalization criteria. Results showed qualitatively similar trends between aromaticity descriptors and Q bands giving a great opportunity to the use this property in the rational design of chromophores. Finally, the nonequilibrium Green's function formalism shows the ability of expanded porpholactones in electron transport.

Tuning the first hyperpolarizability of hexaphyrins with different connections of mislinked pyrrole units: a theoretical study

In the satisfactory design and synthesis of high-performance nonlinear optical (NLO) materials, for meeting the rapidly expanding demands of optoelectronic devices, a deeper understanding of the relationship between the structures and NLO properties has become a key issue. Herein, five novel mislinked expanded hexaphyrins with different connections of pyrrole units are selected to study the relationship between the structures and NLO properties. These five mislinked expanded hexaphyrins are neo-fused, neo-confused hexaphyrins, singly, doubly, and triply N-confused hexaphyrins. From theoretical results, the order of the static first hyperpolarizability (β₀) values is found to be: neo-fused hexaphyrin (β₀ = 4163 a.u.) < neo-confused hexaphyrin (β₀ = 5494 a.u.) < singly N-confused hexaphyrin (β₀ = 6510 a.u.) < doubly N-confused hexaphyrin (β₀ = 15 130 a.u.) < triply N-confused hexaphyrin (β₀ = 26 095 a.u.). Furthermore, β₀ values of the doubly and triply N-confused hexaphyrins are improved 2.1 and 3.7 times over that of their usual parent hexaphyrin (β₀ = 7120 a.u.), respectively. It is worth noting that increasing mislinked connection numbers and changing mislinked connection ways of the pyrrole units in these mislinked expanded hexaphyrins plays a crucial role in the tune of their second-order NLO responses.

Computational Study of Actinyl Ion Complexation with Dipyriamethyrin Macrocyclic Ligands

Relativistic density functional theory has been employed to characterize [AnO₂(L)]^0/-1 complexes, where An = U, Np, Pu, and Am, and L is the recently reported hexa-aza porphyrin analogue, termed dipyriamethyrin, which contains six nitrogen donor atoms (four pyrrolic and two pyridine rings). Shorter axial (An═O) and longer equatorial (An-N) bond lengths are observed when going from An^VI to An^V. The actinide to pyrrole nitrogen bonds are shorter as compared to the bonds to the pyridine nitrogens; the former also play a dominant role in the formation of the actinyl (VI and V) complexes. Natural population analysis shows that the pyrrole nitrogen atoms in all the complexes carry higher negative charges than the pyridine nitrogens. Upon binding actinyl ions with the ligand a significant ligand-to-metal charge transfer takes place in all the actinyl (VI and V) complexes. The formation energy of the actinyl(VI,V) complexes in the gas-phase is found to decrease in the order of UO₂L > PuO₂L > NpO₂L > AmO₂L. This trend is consistent with results for the formation of complexes in dichloromethane solution. The calculated ΔG and ΔH values are negative for all the complexes. Energy decomposition analysis (EDA) indicates that the interactions between actinyl(V/VI) and ligand are mainly controlled by electrostatic components over covalent orbital interactions, and the covalent character gradually decreases from U to Am for both pentavalent and hexavalent actinyl complexes.

Rhodium-catalyzed annulation of pyrrole substituted BODIPYs with alkynes to access π-extended polycyclic heteroaromatic molecules and NIR absorption

A series of π-extended BODIPY derivatives fused with an indolizine scaffold were prepared smoothly via rhodium-catalyzed C–H functionalization/annulation. These fluorophores show significantly red-shifted absorption, reaching to the near infrared (NIR) region.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

NIR absorbing aromatic (antiaromatic) vinylogous carbasapphyrins (3.3.1.0.1) with built-in fused dipolar aromatic hydrocarbon: synthesis and characterization

Variants of vinylogous core modified carbasapphyrins with a built-in fused dipolar aromatic hydrocarbon moiety paving the way to a strong diatropicity/paratropicity with vis-NIR absorption.

Two- and three-dimensional β,β′-N-heterocycle fused porphyrins: concise construction, singlet oxygen production and electro-catalytic hydrogen evolution reaction

A series of 2D and 3D porphyrins fused with N-heterocycles were prepared by palladium-catalyzed. Photophysical and electrochemical properties, 1O2 production and electrocatalytic HER behaviours of the representative porphyrins were investigated.

Synthesis and electronic properties of carbazole-based core-modified diporphyrins showing near infrared absorption

Directly linked carbazole-based core-modified diporphyrin D2 and fused diporphyrin F2 were synthesized. These diporphyrins showed significant electronic interactions and conjugation allowing for redshifted near infrared (NIR) absorption and small HOMO-LUMO gaps as confirmed by NIR absorption spectroscopy, cyclic voltammetry (CV) measurements, and DFT calculations.

Noncovalent Intermolecular Interaction in Cofacially Stacked 24π Antiaromatic Hexaphyrin Dimer

π-π Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of π-π stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar β,β'-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24π-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed π-π interactions between the two subunits.

Development of synthetic protocols for porphyrins and their analogs based on distorted structures — a SPP/JPP Young Investigator Award paper

Creation of novel [Formula: see text]-conjugated molecules is an important research topic. I describe in this account an approach to this aim that is based on the use of the distorted conformation of porphyrins. Planarization of distorted molecules enables the synthesis of heteroatom-containing porphyrin derivatives. Furthermore, dearomatization reaction proves effective to construct distorted conformations from planar [Formula: see text]-conjugated molecules under mild reaction conditions. According to this protocol, we have succeeded in the synthesis of heteroatom-containing curved-[Formula: see text] conjugated molecules that had never been achieved by conventional protocols. In particular, a nitrogen-embedded buckybowl is the first example of a buckybowl having a heteroatom in its central position, which exhibits unique properties due to the incorporation of the heteroatom in its curved [Formula: see text]-surface.

Twisted-Planar-Twisted expanded porphyrinoid dimer as a rudimentary reaction-based methanol indicator

Directly linked porphyrin dimers have attracted considerable attention because of their intriguing electronic features. Most emphasis has been placed on either dimers with large dihedral angles between the constituent planar monomeric subunits or those with overall planarity, referred to as "Planar-Twisted-Planar" and "Planar-Planar-Planar", respectively. Herein, we report a "Twisted-Planar-Twisted" framework, the hexaphyrin dimer D that exists in a trans configuration. Treatment of D with MeOH affords two isomeric dimers, MD1 and MD2, both of which incorporate a methoxy moiety and exist in cis orientations with respect to the tethering linkage. The methanol-promoted conversion is accompanied by a readily discernible color change from green to brown and is not induced to an appreciable level by other alcohols. Dimer D thus acts as a rudimentary, albeit highly selective, reaction-based methanol indicator. This work provides a promising approach for constructing reaction-based chemosensors using porphyrinoid dimers of nonplanar subunits with biased reactivity.