Synthesis and Photophysical Properties of a Sc3N@C80-Corrole Electron Donor-Acceptor Conjugate

Controlling Electronic Events Through Rational Structural Design in Subphthalocyanine-Corrole Dyads: Synthesis, Characterization, and Photophysical Properties

Porphyrinoids are considered perfect candidates for their incorporation into electron donor-acceptor (D-A) arrays due to their remarkable optoelectronic properties and low reorganization energies. For the first time, a series of subphthalocyanine (SubPc) and corrole (Cor) were covalently connected through a short-range linkage. SubPc axial substitution strategies were employed, which allowed the synthesis of the target molecules in decent yields. In this context, a qualitative synthetic approach was performed to reverse the expected direction of the different electronic events. Consequently, in-depth absorption, fluorescence, and electrochemical assays enabled the study of electronic and photophysical properties. Charge separation was observed in cases of electron-donating Cors, whereas a quantitative energy transfer from the Cor to the SubPc was detected in the case of electron accepting Cors.

Metallofullerene photoswitches driven by photoinduced fullerene-to-metal electron transfer

We report on the discovery and detailed exploration of the unconventional photo-switching mechanism in metallofullerenes, in which the energy of the photon absorbed by the carbon cage π-system is transformed to mechanical motion of the endohedral cluster accompanied by accumulation of spin density on the metal atoms. Comprehensive photophysical and electron paramagnetic resonance (EPR) studies augmented by theoretical modelling are performed to address the phenomenon of the light-induced photo-switching and triplet state spin dynamics in a series of Y _x Sc_3-x N@C₈₀ (x = 0-3) nitride clusterfullerenes. Variable temperature and time-resolved photoluminescence studies revealed a strong dependence of their photophysical properties on the number of Sc atoms in the cluster. All molecules in the series exhibit temperature-dependent luminescence assigned to the near-infrared thermally-activated delayed fluorescence (TADF) and phosphorescence. The emission wavelengths and Stokes shift increase systematically with the number of Sc atoms in the endohedral cluster, whereas the triplet state lifetime and S₁-T₁ gap decrease in this row. For Sc₃N@C₈₀, we also applied photoelectron spectroscopy to obtain the triplet state energy as well as the electron affinity. Spin distribution and dynamics in the triplet states are then studied by light-induced pulsed EPR and ENDOR spectroscopies. The spin-lattice relaxation times and triplet state lifetimes are determined from the temporal evolution of the electron spin echo after the laser pulse. Well resolved ENDOR spectra of triplets with a rich structure caused by the hyperfine and quadrupolar interactions with ¹⁴N, ⁴⁵Sc, and ⁸⁹Y nuclear spins are obtained. The systematic increase of the metal contribution to the triplet spin density from Y₃N to Sc₃N found in the ENDOR study points to a substantial fullerene-to-metal charge transfer in the excited state. These experimental results are rationalized with the help of ground-state and time-dependent DFT calculations, which revealed a substantial variation of the endohedral cluster position in the photoexcited states driven by the predisposition of Sc atoms to maximize their spin population.

Metal-free insertion of sulfur dioxide with aryl iodides under ultraviolet irradiation: direct access to sulfonated cyclic compounds

Metal-free insertion of sulfur dioxide with aryl iodides and silyl enolates or allylic bromide under ultraviolet irradiation at room temperature is accomplished. This protocol provides a convenient route to sulfonated cyclic compounds under mild conditions.

A copper-catalyzed insertion of sulfur dioxide via radical coupling

A copper-catalyzed reaction of O-acyl oximes, DABCO·(SO₂)₂, and 2H-azirines is developed under mild conditions, leading to diverse tetrasubstituted β-sulfonyl N-unprotected enamines with excellent stereoselectivity and regioselectivity.

Recent advances in the direct β-C(sp2)–H functionalization of enamides

Recent advances in the direct β-C(sp²)–H functionalization of enamides, mainly including arylation, alkenylation, alkynylation, alkylation, acylation, sulfonylation, phosphorylation, and others, are reported.

Sc3N@Ih-C80 based donor–acceptor conjugate: role of thiophene spacer in promoting ultrafast excited state charge separation

Photoinduced charge separation and dark charge recombination occurring within picoseconds is observed in newly synthesized triphenylamine–thiophene-Sc₃N@I_h-C₈₀ and triphenylamine–thiophene-C₆₀ conjugates.

Photoinduced synthesis of 2-sulfonylacetonitriles with the insertion of sulfur dioxide under ultraviolet irradiation

Metal-free insertion of sulfur dioxide with aryl iodides and 3-azido-2-methylbut-3-en-2-ol under ultraviolet irradiation at room temperature is achieved, giving rise to 2-(arylsulfonyl)acetonitriles in moderate to good yields. Alkyl iodide is also workable under these conditions. This transformation proceeds smoothly under mild conditions with a broad substrate scope. Various functional groups are compatible including amino, ester, halo, and trifluoromethyl groups. No metal catalyst or additive is needed during the reaction process. Mechanistic studies show that under ultraviolet irradiation, an aryl radical is generated in situ from aryl iodide, which undergoes subsequent sulfonylation via the insertion of sulfur dioxide leading to arylsulfonyl radical intermediates. Then the arylsulfonyl radical reacts with 3-azido-2-methylbut-3-en-2-ol giving rise to the corresponding 2-(arylsulfonyl)acetonitrile.

Copper-catalyzed synthesis of sulfonamides from nitroarenes via the insertion of sulfur dioxide

A three-component reaction of arylboronic acids, nitroarenes, and potassium metabisulfite under copper catalysis proceeds smoothly, giving rise to a range of sulfonamides in good to excellent yields with broad substrate scope.

Photoredox-Catalyzed Sulfonylation of O-Acyl Oximes via Iminyl Radicals with the Insertion of Sulfur Dioxide

A multicomponent sulfonylation of O-acyl oximes via iminyl radicals with the insertion of sulfur dioxide under photoredox catalysis is achieved. This multicomponent reaction of O-acyl oximes, potassium metabisulfite, alkenes, and nucleophiles under visible-light irradiation is efficient, giving rise to a range of sulfones in moderate to good yields. A broad reaction scope is presented with good functional group compatibility.

Intramolecular electron transfer in porphyrin-anthraquinone donor–acceptor systems with varying molecular bridges

Photoinduced electron transfer has been investigated in porphyrin anthraquinone (ZnTTP-AQ) donor–acceptor dyads having either ester (ZnTTP-AQ1) or ether (ZnTTP-AQ2) linkages. Both dyads were characterized by spectroscopic and electrochemical methods. Absorption spectra show absence of any ground state interaction between the porphyrin and anthraquinone moieties. The quenched fluoresence and lifetime indicate electron transfer from the porphyrin to the anthraquinone moiety. The quenching is more pronounced in ZnTTP-AQ1 with ester linkage, suggesting efficient electronic coupling compared to the ether linkage in ZnTTP-AQ2. Computational analysis and frontier molecular orbitals confirmed the formation of charged separated state por[Formula: see text]AQ[Formula: see text]. The electron transfer rates ([Formula: see text] of these triads are found in the range 0.43 × 108 to 10.52 × 109 s[Formula: see text] and are found to be solvent polarity dependent.

Photoredox-catalyzed hydrosulfonylation reaction of electron-deficient alkenes with substituted Hantzsch esters and sulfur dioxide

A sulfonylation reaction of 4-substituted Hantzsch esters, DABCO·(SO₂)₂, and electron-deficient alkenes at room temperature in the presence of photoredox catalysis under visible light irradiation is described.

An unexpected reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea under photoinduced conditions

A photoinduced synthesis of S-aryl thiosulfonates through a three-component reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea is achieved. In this transformation, a radical coupling pathway is proposed.

“Off–on–off” type of selectively pH-sensing 8-hydroxyquinoline-substituted gallium(iii) corrole

We herein reported the synthesis and pH sensing property of a novel gallium corrole derivatives based on 8-hydroxyquinoline. Ga-corrole derivative showed good fluorescent response upon changing the pH values in the wide region of pH 1 to 12.

Photoinduced electron transfer and unusual environmental effects in fullerene–Zn-porphyrin–BODIPY triads

Molecular arrays containing donor–acceptor sites and antenna molecules are promising candidates for organic photovoltaic devices.

Synthesis of β-hydroxysulfones through a copper(ii)-catalyzed multicomponent reaction with the insertion of sulfur dioxide

A copper(ii)-catalyzed aerobic oxidative reaction of arylhydrazines, DABCO·(SO₂)₂ and alkenes is reported. Diverse β-hydroxysulfones are generated in moderate to good yields through the hydroxysulfonylation of alkenes with the insertion of sulfur dioxide under mild conditions. In some cases, β-ketosulfones are produced.

Combinatorial synthesis and biological evaluations of (E)-β-trifluoromethyl vinylsulfones as antitumor agents

Combinatorial synthesis of (E)-β-trifluoromethyl vinylsulfones is accomplished through a reaction of alkynes, Togni reagent, and sodium benzenesulfinates in DMSO under metal-free conditions at room temperature. These compounds are evaluated in several assays against different tumor cells. Some hits are identified against ES-2, HO-8910, and K562.

(E)-β-Trifluoromethyl vinylsulfones is accomplished through a reaction of alkynes, Togni reagent, and sodium benzenesulfinates under metal-free conditions. p-Acetylphenyl in R¹ has the best activities against several tumor cells.

Metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions

Recent advances in the metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions are summarized. Usually, a broad reaction scope is observed including tertiary, secondary, and primary alkyl halides, with good functional group compatibility.

ortho-Amide-directed 2,4-dibromohydration of conjugated enynes

A NBS-mediated and ortho-amide-directed 2,4-dibromohydration of enynes is described in this paper.

Photoredox-catalyzed sulfonylation of alkenylcyclobutanols with the insertion of sulfur dioxide through semipinacol rearrangement

A photoredox-catalyzed sulfonylation of alkenylcyclobutanols with the insertion of sulfur dioxide through semipinacol rearrangement under visible light irradiation is developed.

A novel empirical method for quickly estimating the charge-transfer state of fullerene-donor derivatives

A new convenient equivalent conjugated electron number technique is put forward to predict the charge-transfer state in fullerene-donor derivatives.

Hypsochromic solvent shift of the charge separation band in ionic donor–acceptor Li+@C60⊂[10]CPP

Photoinduced electron transfer in CPP-based donor–acceptor complexes C₆₀⊂[10]CPP and Li⁺@C₆₀⊂[10]CPP was studied using DFT/TDDFT. Unusual blue shift of charge separated states for Li⁺@C₆₀⊂[10]CPP complexes in the polar medium is predicted.

Intermolecular packing and charge transfer in metallofullerene/porphyrin cocrystals

Charge transfer in metallofullerene/porphyrin cocrystals is revealed for the first time.

A DFT analysis of the ground and charge-transfer excited states of Sc3N@Ih-C80 fullerene coupled with metal-free and zinc-phthalocyanine

Endohedral metallofullerenes and phthalocyanine derivatives are recognized as excellent active materials in organic photovoltaics (OPVs). The tri-metallic nitride endohedral C80 fullerenes have greater absorption coefficients in the visible region and electron-accepting abilities similar to C60, which can allow for higher efficiencies in OPV devices. In this work, we have investigated the ground and charge transfer excited states of two co-facial donor-acceptor (D-A) molecular conjugates formed by the non-covalent coupling of trimetallic nitride endohedral fullerene (Sc3N@Ih-C80) with metal-free (H2Pc) and zinc-phthalocyanine (ZnPc) chromophores using DFT calculations. The charge transfer (CT) excitation energies are calculated using the perturbative delta-SCF method that enforces orthogonality between the ground and excited states. The binding energies calculated using the PBE and DFT-D3 methods indicate that the dispersion effects play an important role in the stabilization of these complexes. The ground state dipole moment of the Sc3N@C80-H2Pc dyad is much larger than that of Sc3N@C80-ZnPc, but this is reversed in the excited state where the dipole moment of Sc3N@C80-ZnPc increases significantly. The lowest few excitation energies in the gas phase for the two complexes are very close, in the range of 1.51-2.66 eV for Sc3N@C80-ZnPc and 1.51-2.71 eV for the Sc3N@C80-H2Pc complex. However, the lower ionization potential and lower exciton binding energy make the Sc3N@C80-ZnPc dyad a better candidate for OPVs as compared to the Sc3N@C80-H2Pc dyad.

Efficient energy transfer in a tri-chromophoric dyad containing BODIPYs and corrole based on a truxene platform

A star-shaped molecule was designed and synthesized based on a known central truxene platform. Two BODIPY derivatives and one corrole macrocycle were introduced and connected to the 2, 7 and 12-positions of the truxene unit by Suzuki coupling. The dyad was fully characterized by UV-vis absorption, proton nuclear magnetic resonance, mass spectrometry. The direction of energy transfer upon electronic excitation was explored, and the star-shaped molecule system exhibits a highly efficient photoinduced energy transfer process from the excited BODIPY part to the corrole unit.

Selectfluor-Mediated Benzo[d][1,2,3]Triazole Functionalisation of 4,4-Difluoro-4-Bora-3a,4a-Diaza-s-Indacene

8-Aryl-1-(1 H-benzo[ d][1,2,3]triazole-yl)-4,4-difluoro-4-bora-3a,4a-diaza- s-indacene and 8-aryl-3,5-di-(1 H-benzo[ d][1,2,3]triazole-yl)-4,4-difluoro-4-bora-3a,4a-diaza- s-indacene derivatives were synthesised by the reaction of 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene with benzo[ d][1,2,3]triazole in the presence of Selectfluor in moderate to good yields. The reaction took placed regioselectively on the 3(5)-position carbon of 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene, which was confirmed by X-ray analysis.

When metal clusters meet carbon cages: endohedral clusterfullerenes

Fullerenes have the characteristic of a hollow interior, and this unique feature triggers intuitive inspiration to entrap atoms, ions or clusters inside the carbon cage in the form of endohedral fullerenes. In particular, upon entrapping an otherwise unstable metal cluster into a carbon cage, the so-called endohedral clusterfullerenes fulfil the mutual stabilization of the inner metal cluster and the outer fullerene cage with a specific isomeric structure which is often unstable as an empty fullerene. A variety of metal clusters have been reported to form endohedral clusterfullerenes, including metal nitrides, carbides, oxides, sulfides, cyanides and so on, making endohedral clusterfullerenes the most variable and intriguing branch of endohedral fullerenes. In this review article, we present an exhaustive review on all types of endohedral clusterfullerenes reported to date, including their discoveries, syntheses, separations, molecular structures and properties as well as their potential applications in versatile fields such as biomedicine, energy conversion, and so on. At the end, we present an outlook on the prospect of endohedral clusterfullerenes.

Synthesis, characterization and photophysical properties of ferrocenyl and mixed sandwich cobaltocenyl ester linked meso-triaryl corrole dyads

We report here the design and synthesis of corrole-metallocene dyads consisting of a metallocene (either ferrocene (Dyad 1) or mixed sandwich [Formula: see text]-[C[Formula: see text]H[Formula: see text](COOH)]Co([Formula: see text]-C[Formula: see text]Ph[Formula: see text] (Dyad 2)) connected via an ester linkage at meso phenyl position. Both the dyads were characterized by [Formula: see text]H NMR, MALDI-TOF, UV-visible, fluorescence spectroscopies (steady-state, picosecond time-resolved), femtosecond transient absorption spectroscopy (fs-TA) and electrochemical methods. The absorption spectra of these dyads showed slight broadening and splitting of the Soret band that indicates a weak ground state interaction between the corrole macrocycle and metallocene part of the present donor–acceptor (D–A) system. However, in both the dyad systems, fluorescence emission of the corrole was quenched in polar solvents as compared to its parent compound 10-(4-hydroxyphenyl)-5,15-bis-(pentafluorophenyl ) corrole (Ph-Corr). The quenching was more pronounced in ferrocene derivatives than in cobaltocenyl derivatives. Transient absorption studies confirm the absence of photoinduced electron transfer from metallocene to correl for these dyad systems and the quenching of singlet state of corrole is found to enhance intersystem crossing due to heavy atom effect.

Synthesis of 2-Cyano-3-Nitroporphyrin Derivatives with Silyl Cyanide

2-Cyano-3-nitroporphyrin derivatives were synthesised by the reaction of 2-nitroporphyrin with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride with moderate yields. The reaction took place regioselectively on the 3-position carbon of the porphyrins, which was confirmed by X-ray analysis.

Catching metallic nitride endohedral fullerenes in organic and aqueous media

Two bis-tetraphenylporphyrin tweezers-like conjugates bearing different linkers have been characterized by means of electrochemical and photophysical methods. The thrust of this work was the complexation of these bis-porphyrins with C[Formula: see text] and metallic nitride endohedral fullerenes (MNEF) like Sc3N@C[Formula: see text] in organic and in aqueus media — studied by a combination of steady-state and time-resolved spectroscopies. In the context of charge separation evidence for the formation of the 1a[Formula: see text]-Sc3N@C[Formula: see text] and 1c[Formula: see text]-Sc3N@C[Formula: see text] charge separated states in organic and aqueous media, respectively, came from transient absorption spectroscopy. Multi-wavelength analyses afforded charge separated state lifetimes of around 400 ps.

Strategies for Corrole Functionalization

This review covers the functionalization reactions of meso-arylcorroles, both at the inner core, as well as the peripheral positions of the macrocycle. Experimental details for the synthesis of all known metallocorrole types and for the N-alkylation reactions are presented. Key peripheral functionalization reactions such as halogenation, formylation, carboxylation, nitration, sulfonation, and others are discussed in detail, particularly the nucleophilic aromatic substitution and the participation of corroles in cycloaddition reactions as 2π or 4π components (covering Diels-Alder and 1,3-dipolar cycloadditions). Other functionalizations of corroles include a large diversity of reactions, namely Wittig reactions, reactions with methylene active compounds, formation of amines, amides, and imines, and metal catalyzed reactions. At the final section, the reactions involving oxidation and ring expansion of the corrole macrocycle are described comprehensively.

NMR spectroscopy of the phenyl derivative of germanium(IV) 5,10,15-tritolylcorrole

A thoroughly structural characterization of (TTC)GePh (TTC [Formula: see text] 5,10,15-tritolylcorrole; Ph [Formula: see text] phenyl) in solution has been carried out through a combination of 2D NMR (1H-1H COSY, 1H-1H ROESY, 1H-[Formula: see text]C HSQC and 1H-[Formula: see text]C HMBC) experiments and density functional theory (DFT) calculations of the molecular and electronic structure and the shielding constants. The 1H and [Formula: see text]C chemical shifts computed at DFT-S12g and DFT-SAOP levels of theory nicely reproduce the experimental values, the agreement between theory and experiment being especially good for the DFT-S12g results. The calculations prove to be able to capture the fine details of the NMR spectra and to resolve some assignment ambiguities related to the inherent conformational flexibility of the macrocycle. The calculations also provide an explanation of the observed chemical shift trends in terms of diamagnetic and paramagnetic components of the shielding tensor.

A multicomponent molecular approach to artificial photosynthesis – the role of fullerenes and endohedral metallofullerenes

In this review article, we highlight recent advances in the field of solar energy conversion at a molecular level.

The electronic structure and charge transfer excited states of the endohedral trimetallic nitride C80 (Ih) fullerenes–Zn-tetraphenyl porphyrin dyads

Replacing C₆₀ or C₇₀ by an M₃N@C₈₀ (M = Sc, Y) in co-facial dyads with ZnTPP increases charge transfer excited state energies.