Daniel T. Gryko

Recent Advances in the Synthesis of Corroles and Core-Modified Corroles

The aim of this review is to highlight recent progress in the synthetic methodologies leading to corroles and core-modified corroles. Emphasis is put on corroles with meso substituents. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Corrole−Fullerene Dyads: Formation of Long-Lived Charge-Separated States in Nonpolar Solvents

The first example of covalently linked free-base corrole-fullerene dyads is reported. In the newly synthesized dyads, the free-energy calculations performed by employing the redox and singlet excited-state energy in both polar and nonpolar solvents suggested the possibility of electron transfer from the excited singlet state of corrole to the fullerene entity. Accordingly, steady-state and time-resolved emission studies revealed efficient fluorescence quenching of the corrole entity in the dyads. Further studies involving femtosecond laser flash photolysis and nanosecond transient absorption studies confirmed electron transfer to be the quenching mechanism, in which the electron-transfer product, the fullerene anion radical, was able to be spectrally characterized. The rate of charge separation, kCS, was found to be on the order of 10(10)-10(11) s(-1), suggesting an efficient photoinduced electron-transfer process. Interestingly, the rate of charge recombination, kCR, was slower by 5 orders of magnitude in nonpolar solvents, cyclohexane and toluene, resulting in a radical ion-pair lasting for several microseconds. Careful analysis of the kinetic and thermodynamic data using the Marcus approach revealed that this novel feature is due to appropriately positioning the energy level of the charge-separated state below the triplet states of either of the donor and acceptor entities in both polar and nonpolar solvents, a feature that was not evident in donor-acceptor dyads constructed using symmetric tetrapyrroles as electron donors.

Photophysical characterization of free-base corroles, promising chromophores for light energy conversion and singlet oxygen generation

A detailed photophysical characterization of a series of six free-base corroles with different substitution patterns at meso-positions is presented. In air-free toluene at 295 K, the luminescence quantum yields range from 0.13 to 0.22 and lifetimes vary from 4.1 ns to 6.3 ns whereas in air-saturated toluene the lifetimes range from 3.8 ns to 5.6 ns. In glassy toluene at 77 K the lifetimes have values in the range 5.2 ns to 7.9 ns. Transient absorption spectra of the singlet excited states have positive bands art λ 680–700 nm. The transient absorption spectra of the lowest triplet display a band around 460–470 nm and bleaching features in the Q bands region, no absorption above 700 nm. The triplet lifetimes in air-free toluene are in the interval 50–150 μs. The lowest excited states react with oxygen and sensitized singlet oxygen (1Δg) yields of 0.51–0.77 are determined via its luminescence. Electron and energy transfer from the excited states to molecular oxygen is discussed. Effect of polar solvents on the luminescence parameters indicate that charge transfer (CT) excited states play a very minor role. Thermal and photo stability is excellent for most of the examined compounds in toluene and dichloromethane.

Recent advances in the chemistry of corroles and core-modified corroles

The aim of this review is to highlight recent progress in the chemistry of corroles and core-modified corroles. Emphasis is put on the synthetic and coordination aspects of corroles with meso substituents and corrolazines.

Adventures in the synthesis of meso-substituted corroles

This personal account describes how methodology for the synthesis of meso-substituted corroles reached the mature state within just a few years. Both latest developments and many dead-end attempts are described. The comprehensive comparison of conditions of the reaction of aldehydes with dipyrromethanes leading to trans-A2B-corroles is presented.

Photoinduced energy and electron transfer in 1,8-naphthalimide–corrole dyads

A series of corrole-1,8-naphthalimide dyads has been synthesized. The dyads were assembled in a convergent fashion from two fragments via a corrole forming reaction. Central to the success of the synthetic strategy was the preparation of suitably functionalized derivatives of naphthalene-1,8-carboxymide. Six different dyads possessing either a different linker (a meta-phenylene or a para-phenylmethylene) or a corrole with different substituents at the 5 and 15 positions were prepared. A photophysical and spectroscopic characterization of the dyads and the reference models show that whereas upon selective excitation of the corrole component no photo-induced process occurs, excitation of the naphthalimide unit results in very efficient energy or electron transfer processes. The electron transfer contributes to the quenching process with a ratio between 0% and 85% depending on the nature of the corrole accepting unit. The processes are discussed in the frame of current theories. This is the first report of stable corrole-based dyads with interesting photo-activity at ambient temperature.

Study of Intermolecular Interactions in the Corrole Matrix by Solid‐State NMR under 100 kHz MAS and Theoretical Calculations

Recent progress in solid-state (SS)NMR spectroscopic methods based on fast magic angle spinning (MAS) has enabled new opportunities for the structural study of small quantities (< 5 mg) of natural abundance samples. Utilizing throughspace and through-bond polarization transfer, indirect detection of low-g nuclei, and suitable homoand heteronuclear decoupling, oneand two-dimensional (1D and 2D) spectra of such samples can be measured with excellent sensitivity and resolution. However, determination of the short-range intermolecular order often remains elusive. Such analyses can be well-served by studying heteronuclear correlations that take advantage of the large chemical shift range of most low-g nuclei (for example, C or N). Indeed, heteronuclear correlation (HETCOR) NMR spectroscopy and measurements of internuclear distances, often in concert with theoretical calculations, have provided structural details of complex hydrogen-bonded systems in chemistry and biology, blended materials, and host–guest pairs. Still, intermolecular polarization transfers to low-g nuclei are often hampered by low sensitivity. A promising solution to this challenge is offered by homonuclear H–H 2D correlation methods, such as double-quantum (DQ)MAS or spin-diffusion (NOESYlike) experiments, provided that sufficient resolution is achieved in both dimensions. One of the possible approaches is the use of H CRAMPS decoupling in concert with fast MAS to boost resolution in these experiments. The recent development of ultrafast MAS (at 100 kHz and more) provides access to appropriate H resolution without RF decoupling. Herein, we report the first application of H 2D SSNMR measurements under MAS at 100 kHz, which are used in combination with indirectly detected H{C} and H{N} HETCOR experiments and theoretical calculations to scrutinize the interactions within a host–guest (HG) system consisting of 5,10,15-tris(pentafluorophenyl)corrole 1, and toluene (Scheme 1).

Bright, emission tunable fluorescent dyes based on imidazole and π-expanded imidazole

A diverse set of imidazole- and π-expanded imidazole derivatives displaying excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The effect of structural variation on photophysical properties was studied in detail for nine dyes. The relationship between the structure and photophysical properties was thoroughly elucidated also by comparing with analogues with blocked ESIPT functionality. All but one of the obtained compounds exhibit ESIPT, as demonstrated by large Stokes shifts (6500–15 600 cm−1). The type of π-expansion strongly influences the overall optical phenomena: while typical π-expansion preserves ESIPT activity, the direct fusion of imidazole with a naphthalene unit at positions 4 and 5 results in dyes which do not exhibit ESIPT. The compound possessing an acidic NH group as part of an intramolecular hydrogen bond system has a much higher fluorescence quantum yield and Stokes shift than its analogue bearing an OH group. The occurrence of ESIPT for tosylamide analogues is less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amines. Two-photon absorption cross-sections of the selected derivatives are in the range of 5–100 GM.

Preparation of a Family of 10-Hydroxybenzo[h]quinoline Analogues via a Modified Sanford Reaction and Their Excited State Intramolecular Proton Transfer Properties

We have developed a highly optimized methodology that allows for the oxidative acetoxylation of a sterically and electronically demanding library of analogues of benzo[h]quinoline. The optimal conditions for the insertion of an OAc group were identified after examining various reaction parameters (solvent, oxidant, catalyst, temperature, time). The conditions identified (Pd(OAc)(2), PhI(OAc)(2), MeCN, 150 °C, 16 h), combined with the hydrolysis of acetates, resulted in the formation of hydroxybenzoquinolines in 27-59% yield, whereas all previously published procedures were ineffective. This synthesis was compatible with diverse functionalities (ester, aldehyde, carbon-carbon triple bond) and, most importantly, worked for sterically hindered analogues as well as for compounds possessing electron-donating and electron-withdrawing substituents at various positions. All the obtained compounds demonstrated excited-state intramolecular proton transfer (ESIPT) manifesting as small fluorescence quantum yields and large Stokes shifts (8300-9660 cm(-1)). The effect of structural variations in eight 10-hydroxybenzo[h]quinoline analogues on absorption and emission properties was studied in detail.

Reversible O−O Bond Cleavage and Formation between Mn(IV)-Peroxo and Mn(V)-Oxo Corroles

Mn(IV)-peroxo and Mn(V)-oxo corroles were synthesized and characterized with various spectroscopic techniques. The intermediates were directly used in O-O bond cleavage and formation reactions. Upon addition of proton to the Mn(IV)-peroxo corrole, the formation of the Mn(V)-oxo corrole was observed. Interestingly, addition of base to the Mn(V)-oxo corrole afforded the formation of the Mn(IV)-peroxo corrole. Thus, we were able to report the first example of reversible O-O bond cleavage and formation reactions using in situ generated Mn(IV)-peroxo and Mn(V)-oxo corroles.