Victor V. Borovkov

Synthesis and properties of cis - 1,2 - bis (octaethylporphyrinyl)ethylene

Abstract A new cis-form of ethylene-bridged octaethylporphyrin dimer 3a has been obtained by isomerization of the corresponding trans-isomer 2a . On the basis of spectral data the structure of 3a was assigned to be close to a “face-to-face” orientation. Reflecting the peculiar structure of 3a UV-vis and 1 H NMR spectra are remarkably distinguished from those of ordinary porphyrins.

Supramolecular chirogenesis in zinc porphyrins: interaction with bidentate ligands, formation of tweezer structures, and the origin of enhanced optical activity.

The complexation behavior, binding properties, and spectral parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral bidentate guests (diamines and amino alcohols) have been studied by means of UV-vis, CD, fluorescence, (1)H NMR, and ESI MS techniques. It was found that the guest structure plays a decisive role in the chirogenesis pathway. The majority of bidentate ligands (except those geometrically unsuitable) exhibit two major equilibria steps: the first guest ligation leading to formation of the 1:1 host-guest tweezer structure (K(1)) and the second guest molecule ligation (K(2)) forming the anti bis-ligated species (1:2). The second ligation is much weaker (K(1) >> K(2)) due to the optimal geometry and stability of the 1:1 tweezer complex. The enhanced conformational stability of the tweezer complex ensures an efficient chirality transfer from the chiral guest to the achiral host, consequently inducing a remarkably high optical activity in the bis-porphyrin.

Phase-Sensitive Supramolecular Chirogenesis in Bisporphyrin Systems**

To date, the field of supramolecular chirality has attracted much attention in the scientific community, in the context of its direct connection with various natural systems and many practical applications in the areas of catalysis,[1] nonlinear optics,[2] polymer and materials science,[3] molecular recognition,[4] molecular devices,[5] and absolute configuration determination.[6] As noncovalent interactions are the key elements of supramolecular chemistry, there are various external and internal factors controlling chirality induction in these systems. Among these influences, the phase transition, or aggregation state, takes on particular significance in the light of the wide prospective applications of optically active systems in the solid state.[7] However, this important factor has not yet been well investigated and rationalized. Here, by applying supramolecular chemistry, solid-state optical spectroscopy, and exciton chirality principles, we describe a novel and intriguing phenomenon of phasetransition controlled chirality induction in a supramolecular system, which consists of an achiral host and a chiral guest.[8] Ethane-bridged bis(zinc octaethylporphyrin),[9] which is in a syn conformation in nonpolar solvents (see syn ZnD in Figure 1), was chosen as an achiral host molecule. This

Synthesis of Zn-, Mn-, and Fe-Containing Mono- and Heterometallated Ethanediyl-Bridged Porphyrin Dimers

New ethanediyl-bridged unsymmetrical mono- and heterometallated dimers of 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (H2oep) containing transition-metal ions (Mn and Fe) were synthesized by a facile stepwise metallation/demetallation process under mild conditions. The novel metallation strategy initially involved the predominant insertion of Zn into one of the two porphyrin rings of the free-base dimer, followed by the incorporation of Mn or Fe into the other porphyrin ring under exceptionally mild conditions, giving corresponding heterometallic dimers; the subsequent removal of Zn yielded mono-transition-metal dimers. The emission spectrum of the monozinc dimer predominantly exhibited fluorescence bands of the free-base porphyrin component, indicating a very efficient energy-transfer process. Conversely, emission of the free-base or Zn porphyrin component of transition metal containing dimers was strongly quenched due to photoinduced electron transfer.

Supramolecular Chirality in Porphyrin Chemistry

Supramolecular chirality, being an intelligent combination of supramolecular chemistry and chiral science, plays a decisive role in the functioning of various natural assemblies and has attracted much attention from the scientific community, due to different applications in modern technologies, medicine, pharmacology, catalysis and biomimetic research. Porphyrin molecules are of particular interest to study this phenomenon owing to their unique spectral, physico-chemical and synthetic properties. This review highlights the most important types of chiral porphyrin structures by using the best-suited representative examples, which are frequently used in the area of supramolecular chirality.

Temperature Controlled Syn-Anti Conformational Switching in Zinc Containing Porphyrin Dimers via Ligand Assistance

Unique temperature dependent syn-anti conformational changes in bis- and monozinc ethane-bridged porphyrin dimers take place in alcohol containing solvents; these dimers adopt a syn conformation at room temperature, while a decrease in temperature results in the gradual shift of the conformational equilibrium towards the ant/conformer.

Syn–anti conformation switching of a bis-porphyrin derivative at the air–water interface and in the solid state as an effective tool for chemical sensing

A Langmuir film of bis(zinc octaethylporphyrin) (ZnPP) was characterised at the air–water interface and its syn–anti conformation switching induced upon addition of aromatic amines was studied by infrared and UV–vis reflection spectroscopic methods. The highly specific interaction of ZnPP with aromatic amines was maintained even after the floating film was transferred onto solid supports by the Langmuir–Schaefer (LS) technique, enabling us to selectively sense aromatic amines at concentrations as low as 20 ppb. Furthermore, LS ZnPP active layer selectivity was evaluated in the presence of aliphatic amines.

Supramolecular chirogenesis in weakly interacting hosts: role of the temperature, structural, and electronic factors in enhancement of chiroptical sensitivity.

A new supramolecular chirogenic system on the basis of tetrakis(nickel porphyrin) and various enantiopure solvents, which was specifically designed for investigation of the chirogenic phenomenon upon extremely weak interaction modes and marginal chiroptical responses, is reported. The temperature was found to be a key factor controlling the chirality transfer process in these assemblies.

Conformational switching in bis(zinc porphyrin) Langmuir–Schaefer film as an effective tool for selectively sensing aromatic amines

A conformational switching of bis(zinc octaethylporphyrin) was observed, for the first time, in a Langmuir-Schaefer film as a consequence of appropriate host-guest interactions. The spectral changes are completely reversible and the high sensitivity (~20 ppb) and specificity for aromatic amines open up interesting prospects of this functional material as a performing sensor for amines.

Structurally Controlled Porphyrin-Aggregation Process in Phospholipid Membranes

Abstract— Structurally controlled aggregation course for five porphyrins (etioporphyrin [EP], 5‐mono‐ and 5,15‐di‐[p‐tol‐yl]etioporphyrin [TP and DTP], 5,10,15,20‐tetrakis[p‐tol‐y1]porphin [TTP], and 5,10,15,20‐tetrakis[3,5‐di‐tert‐bu‐tylphenyl]porphin [TBP]) in dipalmitoyl‐phosphatidyl‐choline liposomes has been monitored by fluorescence and absorption spectroscopy. While TBP shows no tendency to aggregate in liposomes, EP, TP, DTP and TTP form a porphyrin‐enriched domain in membrane interior with time. The further aggregation steps within porphyrin clusters resulting in formation of stacked porphyrin aggregates have been observed for EP, TP and DTP.