Homo‐ and Heteronuclear meso,meso‐(E)‐Ethene‐1,2‐diyl‐Linked Diporphyrins: Preparation, X‐ray Crystal Structure, Electronic Absorption and Emission Spectra and Density Functional Theory Calculations

Abstract

Homo- and heteronuclear meso,meso-(E)-ethene-1,2-diyl-linked diporphyrins have been prepared by the Suzuki coupling of porphyrinylboronates and iodovinylporphyrins. Combinations comprising 5,10,15-triphenylporphyrin (TriPP) on both ends of the ethene-1,2-diyl bridge M(2)10 (M(2) =H(2)/Ni, Ni(2), Ni/Zn, H(4), H(2)Zn, Zn(2)) and 5,15-bis(3,5-di-tert-butylphenyl)porphyrinato-nickel(II) on one end and H(2), Ni, and ZnTriPP on the other (M(2)11), enable the first studies of this class of compounds possessing intrinsic polarity. The compounds were characterized by electronic absorption and steady state emission spectra, (1)H NMR spectra, and for the Ni(2) bis(TriPP) complex Ni(2)10, single crystal X-ray structure determination. The crystal structure shows ruffled distortions of the porphyrin rings, typical of Ni(II) porphyrins, and the (E)-C(2)H(2) bridge makes a dihedral angle of 50° with the mean planes of the macrocycles. The result is a stepped parallel arrangement of the porphyrin rings. The dihedral angles in the solid state reflect the interplay of steric and electronic effects of the bridge on interporphyrin communication. The emission spectra in particular, suggest energy transfer across the bridge is fast in conformations in which the bridge is nearly coplanar with the rings. Comparisons of the fluorescence behaviour of H(4)10 and H(2)Ni10 show strong quenching of the free base fluorescence when the complex is excited at the lower energy component of the Soret band, a feature associated in the literature with more planar conformations. TDDFT calculations on the gas-phase optimized geometry of Ni(2)10 reproduce the features of the experimental electronic absorption spectrum within 0.1 eV.

Oligoporphyrins with One-and Two-Atom Covalent Bridges: Synthesis and Reactivity, Solid-State, Solution and Electronic Structures, Spectroscopy and Applications

“…There are two reported structures with the (E)-C 2 H 2 bridge in β-unsubstituted porphyrin dimers, namely 42b ⋅ ⋅2py [PEDXOM], with 5-coordinate Zn(II) centers, 67 and 47c [844354], the dinickel TriPP complex. 68 The former complex has a RB of 46.7°, representing a semi-conjugated dimer, as evident also from its electronic absorption and emission spectra, discussed below in Section IV.A. The structure features almost flat ZnPor units, with slight doming as expected for 5-coordination, and is remarkable for its very small MPS of 1.48 Å.…”

“…This makes the conformational landscape somewhat simpler, and asymmetric structures as proposed above are presumably very minor contributors. The spectra presented by Frampton et al 66 and Locos et al 68 on several examples of this class show a typical Soret band profile, with a prominent splitting of the Soret manifold into two major maxima. The lower-energy component, around 470-490 nm depending on whether a coordinating solvent is present, varies in intensity relative to the broader higher-energy band.…”

“…In 2012, Locos coupling of MTriPP boronates 45a-44c with meso-2-iodovinylNiDAP or -MTriPP to prepare a suite of homo-and heterodinuclear dyads 46a-44c and 47a-44f in yields between 10% and 55%. 68 This was the first report of the preparation of heterodimetallic and heterodiporphyrin dyads of the (E)-C 2 H 2 type that did not rely on sequential unselective metalation of a pre-formed dimer. In 1998, an unsuccessful attempt to apply the McMurry route to β-unsubstituted meso-formylNiDAP, to prepare the C 2 H 2 dimer, was frustrated by numerous interfering side-reactions.…”

“…137 The difference in steric requirements between OAP and DAP/TriAP as the porphyrin component of dimers is illustrated by the diminution of the broad Q band tail in dimers 42 and 47, etc. 66,68 However, the top of the Q band is noticeably rounded, and NLO experiments show resonance effects as far into the NIR as 940 nm, meaning some molecules in the population are absorbing in this region. 66 In these cases, instead of flanking ethyl groups occluding the C 2 H 4 bridge, only β-Hs are present.…”

Watching energy transfer in metalloporphyrin heterodimers using stimulated X-ray Raman spectroscopy

“…Porphyrin-based molecules hold a pivotal position in the chemistry of engineered photoactive organic compounds, and extensive electronic structure calculations of monomeric (15) and oligomeric (16,17) porphyrin molecules, porphyrin structures in biomacromolecules (18,19), and quasi-1D and -2D porphyrin systems with infinite sizes have been carried out (13,14,(20)(21)(22)(23). Most applications involve multiporphyrin arrays, either in linear or in cyclic shape, or dendrimers (24).…”