Photophysical Properties of a Series of Free-Base Corroles

Development of Ion Chemosensors Based on Porphyrin Analogues

Sensing of metal ions and anions is of great importance because of their widespread distribution in environmental systems and biological processes. Colorimetric and fluorescent chemosensors based on organic molecular species have been demonstrated to be effective for the detection of various ions and possess the significant advantages of low cost, high sensitivity, and convenient implementation. Of the available classes of organic molecules, porphyrin analogues possess inherently many advantageous features, making them suitable for the design of ion chemosensors, with the targeted sensing behavior achieved and easily modulated based on their following characteristics: (1) NH moieties properly disposed for binding of anions through cooperative hydrogen-bonding interactions; (2) multiple pyrrolic N atoms or other heteroatoms for selectively chelating metal ions; (3) variability of macrocycle size and peripheral substitution for modulation of ion selectivity and sensitivity; and (4) tunable near-infrared emission and good biocompatibility. In this Review, design strategies, sensing mechanisms, and sensing performance of ion chemosensors based on porphyrin analogues are described by use of extensive examples. Ion chemosensors based on normal porphyrins and linear oligopyrroles are also briefly described. This Review provides valuable information for researchers of related areas and thus may inspire the development of more practical and effective approaches for designing high-performance ion chemosensors based on porphyrin analogues and other relevant compounds.

Photoinduced Electron Transfer between Anionic Corrole and DNA

The interaction between a water-soluble anionic Ga(III) corrole [Ga(tpfc)(SO3Na)2] and calf thymus DNA (ct-DNA) has been investigated by using femtosecond transient absorption spectroscopy. A significant broadening from 570 to 585 nm of positive absorption band of the blend of Ga(tpfc)(SO3Na)2 and ct-DNA (Ga(tpfc)(SO3Na)2-ctDNA) has been observed from 0.15 to 0.50 ps after photoexcitation of Ga(tpfc)(SO3Na)2 into the Soret band. The control experiment has been performed on the model DNA ([poly(dG-dC)]2) rich in guanine bases, which exhibits a similar spectral broadening, whereas it is absent for [poly(dA-dT)]2 without guanine bases. The molecular orbital calculation shows that HOMO of Ga(tpfc)(SO3Na)2 is lower than that of guanine bases. The results of the electrochemical experiment show the reversible electron transfer (ET) between Ga(tpfc)(SO3Na)2 and guanine bases of ct-DNA is thermodynamically favorable. The dynamical analysis of the transient absorption spectra reveals that an ultrafast forward ET from the guanine bases to Ga(tpfc)(SO3Na)2 occurs within the pulse duration (156 fs), leading to the formation of an intermediate state. The following back ET to the ground state of Ga(tpfc)(SO3Na)2 may be accomplished in 520 fs.

The impact of solvents on the singlet and triplet states of selected fluorine corroles – absorption, fluorescence, and optoacoustic studies

This paper examines the influence of aprotic solvents on the spectroscopic properties as well as the energy deactivation of two free-base corrole dyes substituted with C₆F₅ and/or 4-NO₂C₆H₄ groups.

Efficient energy transfer in ethynyl bridged corrole–BODIPY dyads

Corrole–BODIPY dyads bridged by ethynyl linkages have been synthesized in high yield. The efficiency and direction of energy transfer has been found to depend on the number of corrole rings and their connection position on the BODIPY core.

Excited-state torsional relaxation dynamics of meso–meso directly linked corrole dimers: importance of linking position

The effect of linking position on the excited-state dynamics of meso-meso directly linked corrole dimers is explored.

Phosphorescence of free base corroles

The phosphorescence features of free base corroles have been analysed, completing the picture on their excited state photophysical properties.

Femtosecond to Microsecond Dynamics of Soret-Band Excited Corroles

We present a comprehensive photophysical investigation on a series of three corroles (TTC, P-TTC, Ge-TTC dissolved in toluene), employing femtosecond and nanosecond transient absorption spectroscopy (TAS) measurements. Systematic analyses of the TAS data determined the rates and corresponding time constants of photophysical processes: internal conversion (τ_IC) in the 898-525 fs range, vibrational relaxation (τ_{_VR}) in the 7.44-13.6 ps range, intersystem crossing (τ_ISC ) in the 033-1.09 ns range and triplet lifetime (τ__triplet) in the 0.8-3.5μs range. The estimated triplet quantum yields (Φ_Triplet) were in the 0.42 - 0.61 range. Comparatively, GeTTC displayed faster τ_IC and higher(Φ_Triplet). Additionally, the time-dependent density functional theory (DFT) calculations were performed for the three molecules. The HOMO/LUMO energy levels and the oscillator strengths of various transitions were determined and presented.

Semi-insulating behaviour of self-assembled tin(IV)corrole nanospheres

Three novel tin(iv)corrole complexes have been prepared and characterized by various spectroscopic techniques including single crystal X-ray structural analysis. Packing diagrams of the tin(iv)corroles revealed that corrolato-tin(iv)-chloride molecules are interconnected by intermolecular C-HCl hydrogen bonding interactions. HCl distances are 2.848 Å, 3.051 Å, and 2.915 Å, respectively, for the complexes. In addition, the C-HCl angles are 119.72°, 144.70°, and 147.08°, respectively, for the complexes. It was also observed that in one of the three synthesized complexes dimers were formed, while in the other two cases 1D infinite polymer chains were formed. Well-defined and nicely organized three-dimensional hollow nanospheres (SEM images on silicon wafers) with diameters of ca. 676 nm and 661 nm are obtained in the complexes, forming 1D polymer chains. By applying a thin layer of tin(iv)corrole nanospheres to an ITO surface (AFM height images of ITO films; ∼200 nm in height), a device was fabricated with the following composition: Ag/ITO-coated glass/tin(iv)corrole nanospheres/ITO-coated glass/Ag. The resistivity (ρ) of the nanostructured film was calculated to be ∼2.4 × 10(8) Ω cm, which falls in the range of semi-insulating semiconductors. CAFM current maps at 10 V bias show bright spots with a 10-20 pA intensity and indicate that the nanospheres (∼250 nm in diameter) are the electron-conducting pathway in the device. The semi-insulating behavior arises from the non-facile electron transfer in the HOMOs of the tin(iv)corrole nanospheres.

Combined MCD/DFT/TDDFT Study of the Electronic Structure of Axially Pyridine Coordinated Metallocorroles

A series of metallocorroles were investigated by UV-vis and magnetic circular dichroism spectroscopies. The diamagnetic distorted square-pyramidal main-group corrole Ga(tpfc)py (2), the diamagnetic distorted octahedral transition-metal adduct Co(tpfc)(py)2 (3), and paramagnetic distorted octahedral transition-metal complex Fe(tpfc)(py)2 (4) [H3tpfc = tris(perfluorophenyl)corrole] were studied to investigate similarities and differences in the electronic structure and spectroscopy of the closed- and open-shell metallocorroles. Similar to the free-base H3tpfc (1), inspection of the MCD Faraday B-terms for all of the macrocycles presented in this report revealed that a ΔHOMO < ΔLUMO [ΔHOMO is the energy difference between two highest energy corrole-centered π-orbitals and ΔLUMO is the energy difference between two lowest energy corrole-centered π*-orbitals originating from ML ± 4 and ML ± 5 pairs of perimeter] condition is present for each complex, which results in an unusual sign-reversed sequence for π-π* transitions in their MCD spectra. In addition, the MCD spectra of the cobalt and the iron complexes were also complicated by a number of charge-transfer states in the visible region. Iron complex 4 also exhibits a low-energy absorption in the NIR region (1023 nm). DFT and TDDFT calculations were used to elaborate the electronic structures and provide band assignments in UV-vis and MCD spectra of the metallocorroles. DFT and TDDFT calculations predict that the orientation of the axial pyridine ligand(s) has a very minor influence on the calculated electronic structures and absorption spectra in the target systems.

Nondestructive readout fluorescence memory based on a gallium(III) corrole complex and photochromic cis-1,2-dithienylethene

Photochromic switching of fluorescence emission provides a viable principle to creation of all optical molecular memory. Successful operation of the fluorescence memory requires deliberate control of the energetics between a fluorophore and a photochrome. One essential requirement is that photoexcitation for fluorescence emission does not interfere with the photochromic processes. Gallium(III) corrole complexes outfit the condition because their fluorescence emissions display large Stokes shifts, permitting photoexcitation at the optical window where the photochromism of cis-1,2-dithienylethene is not executed. To demonstrate the capability for fluorescence memory, we prepared molecularly dispersed poly(methyl methacrylate) (PMMA) films of a gallium corrole complex and cis-1,2-dithienylethene. The memory cycle comprising fluorescence readout and reversible photochromic switching of the fluorescence emission is fully reversible without suffering from fatigue during repeated operation. The corresponding fluorescence on/off ratio is greater than those of previous memory based on porphyrins. Fluorescence lifetime measurements employing time-correlated single photon counting techniques reveal occurrence of fast energy transfer (~ 109 s-1) which is effectively gated by the photochromism.

Photophysical properties of electron-deficient free-base corroles bearing meso-fluorophenyl substituents

The ultrafast photophysical behaviors of a series of meso-flurophenyl substituted electron-deficient free base corroles F₀C, F₅C, F₁₀C and F₁₅C in toluene have been investigated using femtosecond time resolved absorption spectroscopy and steady spectroscopies.

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-β linkage facilitated PeT in polar solvents, which quenched the fluorescence, and is further confirmed by electrochemical studies.

Carbazole–corrole and carbazole–prophyrin dyads: synthesis, fluorescence and electrochemical studies

Carbazole–corrole and carbazole–porphyrin dyads were synthesized, and fluorescence studies indicated efficient energy transfer from carbazole-donor to corrole/porphyrin acceptor in the dyads.

A comparative study of optical nonlinearities of trans-A2B-corroles in solution and in aggregated state

The NLO properties of a series of FB corroles are studied in the solution as well as in the aggregated state (in the form of thin films).

Adventures in corrole features by electrospray ionization mass spectrometry studies

In this short review the importance of electrospray mass spectrometry in corrole chemistry is highlighted.

Synthesis of corrole–fullerene dyads via [4 + 2] cycloaddition reaction

Corrole–fullerene dyads were prepared by treating anthracene-functionalized corroles with fullerene. Photo physical study indicated that the excited corrole unit was quenched due to the introduction of fullerene.

Selective iodide chemosensing through a redox-active Cu-corrole

A one-electron redox couple between iodide and Cu(iii)-corrole serves as the basis for selective sensing of iodide.

A spectroscopic and theoretical investigation of a free-base meso-trithienylcorrole

The unique optical properties of free-base meso-tris(5-methylthien-2-yl)corrole were compared to those of the widely investigated meso-triphenyl-substituted analogue. A combination of spectroscopic and computational experiments was undertaken to elucidate the relationship between structural features of the neutral, mono-anionic and mono-cationic forms of the corroles and their corresponding optical properties. A general bathochromic shift was measured for the thienyl-substituted corrole. The experimental spectra are supported by excited state calculations. A systematic series of ground state minimizations were performed to determine energy minima for the flexible and solvent-sensitive molecules. Trithienylcorrole was found to have a more nonplanar macrocycle in conjunction with a high degree of π-overlap with the meso-substituents. Both structural features contribute to their bathochromically shifted optical spectra. The configurational character of the thienyl-substituted corrole is shown to have a larger degree of molecular orbital mixing and doubly excited character, which suggest a more complex electronic structure that does not fully adhere to the Gouterman four-orbital model. The reactivity of the thienyl groups, particularly with respect to their ability to be (electro)-polymerized, combined with the tight coupling of the meso-thienyl groups with the corrole chromophore elucidated in this work, recommends the meso-thienylcorroles as building blocks in, for instance, organic semiconductor devices.

Photophysical properties and singlet oxygen generation of three sets of halogenated corroles

The luminescence, excited-state absorption, and singlet oxygen generation measurements were performed on three kinds of halogenated corroles: monohydroxyl halogenated corroles (Corrole-F, Corrole-Cl, Corrole-I), peripherally fluorine-substituted corroles (F0, F5, F10, F15), and gallium complexes (F10-Ga, F15-Ga). The fluorescence intensities progressively decrease whereas the triplet quantum yields, oxygen quenching rates, and singlet oxygen quantum yields increase with the increasing of the monohydroxyl halogen atomic weight. Replacing hydrogen atoms of meso-phenyl groups with fluorine atoms induces the blue-shifts of the emission spectra, higher triplet quantum yield, and smaller oxygen quenching rates. Of all peripherally fluorine-substituted corroles, F10 exhibited the highest singlet oxygen quantum yield. In comparison with the free base corroles, both gallium corrole complexes display much stronger fluorescence with the large blue-shifts of emission peaks and slightly higher triplet quantum yields but smaller oxygen quenching rates and singlet oxygen quantum yields. The reasons for the different photophysical behaviors of these corroles are discussed.

Corrole NH tautomers: spectral features and individual protonation

Protonation of a free-base meso-pyrimidinyl-substituted AB(2)-corrole (H(3)AB(2)) in ethanol solution by stepwise addition of sulfuric acid has been studied in the temperature range from 293 to 333 K. The formation rate of protonated species was found to depend profoundly on the temperature at which the titration was undertaken. Two steps in the titration curve were identified at temperatures around 293-298 K, whereas one-step formation of protonated species was found to occur at temperatures above 308 K. The protonation product was the same in both cases, i.e., H(4)AB(2)(+) corrole, protonated at the macrocycle core nitrogen atoms. The two steps in the protonation kinetics at lower temperatures were attributed to protonation of individual tautomers of the free-base H(3)AB(2) corrole. To the best of our knowledge, this is the first well-illustrated (spectrophotometric) observation of individual properties of corrole NH tautomers in fluid solution. Concomitant increase in the NH tautomerization rate with increasing temperature is proposed to account for the one-step protonation. Evidences for the role of individual corrole NH tautomers in the protonation process as well as their optical features are discussed based on spectroscopic results and simulation data.

Alkynyl corroles: synthesis by Sonogashira coupling reaction and the physicochemical properties

Alkynyl corroles were synthesized from iodidphenyl corrole precursor by using Sonogashira coupling reaction with or without the presence of copper(I) iodide co-catalyst. The alkynyl group on corrole macrocycle has a significant effect on the photophysical and electrochemical properties of free-base and metal corrole derivatives.

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in oxidation state and axial ligands, namely, (pyridine) Sb (III)-, (oxo) Sb (V)- and (difluoro) Sb (V) complexes, were studied by time-resolved electron paramagnetic resonance spectroscopy and laser flash photolysis. The magnetic and orientational parameters of the corroles oriented in a nematic liquid crystal as well as their triplet lifetimes in liquid toluene were determined and interpreted in terms of their structure and geometry. The negative zero-field splitting parameter D assigned to all studied corroles is explained by the asymmetric π-electron withdrawal effect caused by perfluorinated peripheral aryl groups, which force the triplet electron spins to align in head-to-tail configuration. The effect of the axial ligands on the photoexcited triplet state properties of the corroles is correlated with their different efficiency to perform photoassisted aerobic oxygenation of some organic molecules. This is explained by the dependence of the main parameters of the photoexcited complexes on the interaction between the central ion and corrole π-system. This interaction is strongly influenced by axial ligands coordination, affecting the macrocycle symmetry, planarity, and rigidity.

Synthesis and photophysical and electrochemical properties of a binuclear Ru(bpy)3-Cu(III) corrole complex

A novel binuclear Ru - Cu complex, composed of a copper(III)-corrole and a ruthenium(II) tris(bipyridine) moiety linked by an amide bond, has been synthesized and characterized by 1 H NMR, UV-vis and mass spectrometry. The steady-state emission and the electrochemical properties were investigated. Compared to the parent [ Ru ( bpy )3]2+, the emission of the desired complex was substantially quenched when the MLCT of [ Ru ( bpy )3]2+ was selectively photoexcited.