“Axial-Bonding”-Type Hybrid Porphyrin Arrays:  Synthesis, Spectroscopy, Electrochemistry, and Singlet State Properties

Abstract

A series of phosphorus(V), germanium(IV), and tin(IV) porphyrin-based, "axial-bonding"-type hybrid trimers have been readily constructed by employing a new "building-block" approach. The approach is modular in nature, and it involves simple "inorganic" reactions such as axial bond formation of main group element containing porphyrins and insertion of metal/"metalloid" ions into the porphyrin cavity. The architecture of these arrays is such that, while a phosphorus(V), germanium(IV), or tin(IV) complex of meso-5,10,15,20-(tetratolyl)porphyrin forms the basal scaffolding unit, the free-base, vanadyl, cobalt(II), nickel(II), copper(II), or zinc(II) porphyrins occupy the two axial sites via an aryloxy bridge. Synthesis of an "all-phosphorus" array containing three phosphorus(V) subunits has also been accomplished. Each new porphyrin array investigated in this study has been fully characterized by various physical methods that include mass (FAB), UV-visible, infrared, fluorescence, electron spin resonance (ESR), and (1)H and (31)P nuclear magnetic resonance (NMR; 1D and 2D) spectroscopies and cyclic voltammetry. The UV-visible and ESR spectral parameters and also the redox potential data suggest that there exists no interaction between the pi-planes of the constituent monomeric porphyrins in these arrays. Detailed (1)H NMR investigations carried out with the trimers containing diamagnetic porphyrins reveal characteristic shielding/deshielding effects for the various protons on the axial porphyrin subunits. The ground state data, as probed by the spectroscopic and electrochemical techniques, collectively indicate that there exists a symmetric but nonparallel disposition of the two axial porphyrins with respect to plane of the central porphyrin. Singlet state activity of the photoactive trimers has been probed by the steady state fluorescence method with selective excitation into the bands corresponding to the two constituent monomeric species. Analysis of the fluorescence emission and excitation spectral data suggests the occurrence of electronic energy transfer as well as photoinduced electron transfer reactions in trimers endowed with free-base or zinc(II) porphyrin axial subunits. Efficiencies of the excited state processes of these trimeric arrays are shown to be dependent on the type of metal/metalloid ions present in the porphyrin crevice.

Porphyrin‐Based Molecular Rotors as Fluorescent Probes of Nanoscale Environments

“…[24][25][26] The high charge on the tin centre renders the porphyrin a relatively hard Lewis acid with selectivity for oxo ligands (phenols, carboxylic acids) over softer nitrogenous ligands in solution. [24][25][26][27][28][29][30][31] Importantly for this study, the inductive effect of the high charge on the metal makes tin(IV) porphyrins very stable to ring reduction. [32] In this respect, studies by Reddy and Maiya indicated that ET can occur from a phenolate ligand to the photoexcited porphyrin, the efficiency of which increases with the basicity of the phenolate.…”

Synthesis of Ru(II) and Sn(IV) Tetraphenylporphyrin Complexes with One - and Two -center Organic Substrates

“…[23] В 1 Н ЯМР спектре комплекса 8 сигналы протонов имидазольного фрагмента субстрата сдвинуты в сильное поле, по сравнению с сигналами соответствующих протонов в спектре 4-(имидазол-1-ил)-фенола (Рису-нок 2а). Согласно литературным данным [11][12][13]24] и ре-зультатам собственных исследований [15,17] это является следствием экранирующего эффекта кольцевого тока тетрапиррольного макроцикла. Расположенные на значительном удалении от макроцикла протоны фенольного фрагмента субстрата не подвергаются влиянию этого фактора и проявляются в той же области, что и соответствующие протоны в спектре 4-(имидазол-1-ил)-фенола.…”

“…Они предпочтительно связывают кислород содержащие лиганды (карбокси-латы и феноляты) и являются комплексами с транс-диаксиальной координацией ионных или нейтральных субстратов. [10][11][12][13][14] Относительно лабильные карбокси-латные комплексы порфиринатов Sn(IV) легко образу-ются при взаимодействии карбоновой кислоты с дигидроксипорфиринатом Sn(IV) [(OH) 2 SnP] в органи-ческих растворителях при комнатной температуре. Скорость процесса определяется кислотными свойст-вами органической кислоты.…”

“…Более устойчивые фено-лятные комплексы порфиринатов Sn(IV) образуются при кипячении фенола с (OH) 2 SnР в бензоле или пиридине в течение нескольких часов. [12] В продолжение наших исследований в области синтеза и координационной химии порфиринатов металлов различной природы [15][16][17][18][19] в настоящей работе осуществлен синтез и методами электронной, …”

A Tin(IV) Porphyrin with Two Axial Organometallic NCN‐Pincer Platinum Units

“…Maiya and co-workers used tin(IV) porphyrins to axially connect other metalloporphyrins by Lewis base/ Lewis acid interactions [14,15]. Very recently, a tin(IV) porphyrin was used to interconnect two carboxy-functionalized fullerene moieties and the resulting porphyrin-fullerene complex showed strong interactions between its components [16].…”