Fused Porphyrin Dimer Research Articles

Strained Porphyrin Tape-Cycloparaphenylene Hybrid Nanorings.

V-Shaped porphyrin dimers, with masked p-phenylene bridges, undergo efficient oxidative coupling to form meso-meso linked cyclic porphyrin oligomers. Reductive aromatization unmasks the p-phenylenes, increasing the strain. Oxidation then fuses the porphyrin dimers, providing a nanoring with curved walls. The strain in this macrocycle bends the p-phenylene and fused porphyrin dimer units (radii of curvature of 11.4 and 19.0 Å, respectively), but it does not significantly alter the electronic structure of the fused porphyrins.

N-Heterocycle-fused Ni(ii) porphyrin dimers upon heating of meso-amino Ni(ii) porphyrins in nitrobenzene

Simple refluxing of amino Ni(ii) porphyrins 5 and 6 in nitrobenzene gave fused porphyrin dimers 9 and 11 with roughly coplanar structure. Q-like bands of the resulting 2,6-naphthyridine-fused porphyrin dimers are significantly red-shifted.

Helically Twisted Benzene-1,3,5-triamine-fused Porphyrin Dimers

NiII-2,18-dibromo-20-chloroporphyrin was fused with N1,N3,N5-triaryl-1,3,5-benzenetriamine via t-BuONa-promoted one-pot reaction to give a helically twisted nitrogen-doped fused porphyrin dimer wit...

Pentacene Fused Porphyrin Dimer Exhibiting High Stability and Solubility

Acenes have the potential to be used in the next gengeration of electronic devices due to their unique electronic properties. Pentacene is one of the most widely utilized organic compounds for organic-filed effect transistor (OFET) because of its high charge mobility. However, solubility and stability are two critical factors that limit their use in practical application. Ethynylation has shown to be one of the best strategies to stabilize pentacene. Our group is interested in linearly fusing another aromatic chromophore such as porphyrin with alkynyl-substituted pentacene to further increase its stability and solubility. In this work, a new pentacene fused porphyrin dimer with high stability and solubility was prepared and characterized. The new pentacene fused porphyrin dimer exhibits a narrow energy gap up to 1.4 eV. Photodegradation studies using UV-Vis and 1H NMR reveal that the new pentacene derivative exhibits an increased solubility and stability up to 16 times compared to 6,13-bis(phenyethynyl)pentacene. Figure 1

N-annulated perylene-substituted and fused porphyrin dimers with intense near-infrared one-photon and two-photon absorption.

Fusion of two N-annulated perylene (NP) units with a fused porphyrin dimer along the S0-S1 electronic transition moment axis has resulted in new near-infrared (NIR) dyes 1 a/1 b with very intense absorption (ε>1.3×10(5) M(-1) cm(-1)) beyond 1250 nm. Both compounds displayed moderate NIR fluorescence with fluorescence quantum yields of 4.4×10(-6) and 6.0×10(-6) for 1 a and 1 b, respectively. The NP-substituted porphyrin dimers 2 a/2 b have also been obtained by controlled oxidative coupling and cyclodehydrogenation, and they showed superimposed absorptions of the fused porphyrin dimer and the NP chromophore. The excited-state dynamics of all of these compounds have been studied by femtosecond transient absorption measurements, which revealed porphyrin dimer-like behaviour. These new chromophores also exhibited good nonlinear optical susceptibility with large two-photon absorption cross-sections in the NIR region due to extended π-conjugation. Time-dependent density functional theory calculations have been performed to aid our understanding of their electronic structures and absorption spectra.

Synthesis of directly fused porphyrin dimers through Fe(OTf)3-mediated oxidative coupling.

An efficient and general Fe(OTf)3-mediated oxidative coupling method was developed for the synthesis of doubly or triply linked porphyrin dimers. Besides the central metal and peripheral substituent, regioselectivity of the oxidative coupling was found to be closely relevant to the onset oxidation potential of the porphyrin substrate, and the reactant with higher E(onset(ox)) tends to generate meso-β doubly fused porphyrin dimer.

Synthesis and Functionalization of Triply Fused Porphyrin Dimers

AbstractCurrent applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorption, increasingly require the use of far‐red absorbing dyes. Modification of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers which limit the practical use of such chromophores. To further extend the absorption profile, a series of symmetric and unsymmetric dimeric and oligomeric porphyrin β–β, meso–meso, β′–β′ triply fused systems were synthesized by oxidative coupling methods. This required an analysis and optimization of the various synthetic strategies. These arrays exhibit a dramatic bathochromic shift into the near‐infrared region and many display absorption at wavelengths greater than 1050 nm. Additionally, post‐fusing chemical transformations, namely, organolithium, cycloaddition, and transition‐metal‐catalyzed reactions, at the meso and β positions enable the fine‐tuning of such arrays to enhance the bathochromic shift and their potential optical applications.

Selective oxidative synthesis of meso-beta fused porphyrin dimers

An efficient route to meso-β doubly connected fused porphyrin dimers was developed. Synthesis of the dimers incorporated two successive C–C bond-forming steps selectively coupling unsubstituted meso- and β-positions. Using Cu(BF4)2 as an oxidant in nitromethane solvent, the radical coupling of Cu(II) -porphyrins occurred in high yield and without side-products, allowing chromatography-free purification. Efficient demetalation of the product yielded free-base derivatives and the possibility to incorporate other metals into the macrocycles. The absorption and electrochemical properties vary with the inserted metal, showing broad UV-visible-NIR absorption and multiple one-electron oxidations/reductions in a relatively narrow electrochemical window.

Supramolecular Functionalization of Single-Walled Carbon Nanotubes with Triply Fused Porphyrin Dimers: A Study of Structure–Property Relationships

A triply fused porphyrin dimer bearing long alkyl chains for enhanced solubility was prepared and investigated for its ability to supramolecularly functionalize single-walled carbon nanotubes. It was found that this porphyrin dimer indeed binds strongly to the nanotube surface, allowing the removal of excess unbound porphyrin from solution without diminishing nanotube solubility. UV–vis spectroscopy indicated a bathochromic shift of the porphyrin Soret band upon binding to the nanotube surface, while Raman spectroscopy indicated that functionalization with the porphyrin dimer does not lead to any defects being formed on the nanotube wall. Transmission electron microscopy revealed the presence of individual nanotubes and small nanotube bundles that were heavily coated with porphyrin dimers. Comparison to analogous fused dimers bearing tert-butyl groups for solubility clearly demonstrated that long alkyl chains are necessary for prolonged solution stability of the nanotube complexes. While a previously investigated tert-butyl derivative was found to bind to the nanotube surface, the resulting complex precipitated out of solution within minutes. It was also found that the position of bulky substituents on the porphyrin dimer had a dramatic effect on whether it was able to interact with the nanotube surface.

Electron- or Hole-Transporting Nature Selected by Side-Chain-Directed π-Stacking Geometry: Liquid Crystalline Fused Metalloporphyrin Dimers

Novel liquid crystalline (LC) semiconductors were prepared from the copper complex of a fused porphyrin dimer as the electroactive core by attaching to its periphery dodecyl and semifluoroalkyl side chains site-specifically (P≡P(hetero)) and semifluoroalkyl side chains alone (P≡P(homo)). The former and latter formed rectangular columnar and orthorhombic LC mesophases, respectively, where the stacking geometries of the π-conjugated core are quite different from one another. Although the π-electronic properties of the core units in P≡P(hetero) and P≡P(homo) in solution are substantially identical to one another, transient photocurrent profiles of their LC states under time-of-flight conditions clearly showed that P≡P(hetero) behaves as an n-type semiconductor, whereas P≡P(homo), in contrast, behaves as a p-type semiconductor.

Synthesis and near-infrared luminescence of a deuterated conjugated porphyrin dimer for probing the mechanism of non-radiative deactivation

beta,meso,beta-Fused porphyrin oligomers have many attractive photophysical features such as strong absorption in the near-IR at wavelengths greater than 1000 nm, and high two-photon cross sections. However their ultrafast S(1)-S(0) deactivation (k(d) > 10(11) s(-1)) limits potential applications. We have synthesised a deuterated fused porphyrin dimer to test whether deuteration influences the rate of non-radiative deactivation. An efficient synthetic strategy was developed, starting with deuteration of dipyrromethane. Deuteration of the zinc porphyrin dimer does not affect its fluorescence quantum yield in CD(2)Cl(2)(Phi(fD)/Phi(fH)= 1.00 +/- 0.05). This implies that the ultrafast non-radiative deactivation is not simply a consequence of the small S(1)-S(0) energy gap. Comparison with other conjugated porphyrin oligomers confirms that the deactivation rate in the edge-fused oligomers is faster than would be expected from the energy gap law. This result indicates that it should be possible to create near-IR dyes with similar S(1)-S(0) energy gaps to the beta,meso,beta-fused porphyrin oligomers but with slower rates of S(1)-S(0) decay.

Triply Fused ZnII–Porphyrin Oligomers: Synthesis, Properties, and Supramolecular Interactions with Single‐Walled Carbon Nanotubes (SWNTs)

The photophysical, electrochemical, and self-assembly properties of a novel triply fused Zn(II)-porphyrin trimer were investigated and compared to the properties of a triply fused porphyrin dimer and the analogous monomer. The trimer exhibited significantly red-shifted absorption bands relative to the corresponding monomer and dimer. Electrochemical investigations indicated a clear trend in redox properties amongst the three porphyrin structures, with the lowest oxidation potential and the lowest HOMO-LUMO gap exhibited by the triply fused trimer. This electrochemical behavior is attributed to the extensive pi-electron delocalization in the trimeric structure relative to the monomer and dimer. Additionally, it was found that the trimer forms extremely strong and nearly irreversible supramolecular interactions with single-walled carbon nanotubes (SWNTs), resulting in stable solutions of porphyrin-nanotube complexes in THF. Formation of these complexes required the addition of trifluoroacetic acid (TFA) to the solvent. This allowed the oligomers to make close contact with the nanotubes, enabling the formation of stable supramolecular assemblies. Atomic force microscopy (AFM) was used to observe the supramolecular porphyrin-nanotube complexes and revealed that the porphyrin trimer formed a uniform coating on the SWNTs. Height profiles indicated that nanotube bundles could be exfoliated into either individual tubes or very small bundles by exposure to the porphyrin trimer during sonication.

Large Two-Photon Absorption (TPA) Cross-Section of Directly Linked Fused Diporphyrins

The excited state dynamics and two-photon absorption properties of four novel triply linked porphyrin dimers in toluene have been investigated. The fused porphyrin dimers exhibit extremely increased two-photon absorption cross-section values (12,000-15,000 GM) compared with porphyrin monomers owing to much enhanced pi-electron delocalization throughout the porphyrin dimer ring.

Reverse Saturable Absorption in the Near‐Infrared by Fused Porphyrin Dimers

Reverse Saturable Absorption in the Near‐Infrared by Fused Porphyrin Dimers

Resonance Raman spectroscopic study of fused multiporphyrin linear arrays

For prospective applications as molecular electric wires, triply linked fused porphyrin arrays have been prepared. As expected from their completely flat molecular structures, π-electron delocalization can be extended to the whole array manifested by a continuous redshift of the HOMO-LUMO transition band to infrared region up to a few μm as the number of porphyrin units in the array increases. To gain an insight into the relationship between the molecular structures and electronic properties, we have investigated resonance Raman spectra of fused porphyrin arrays depending on the number of porphyrin pigments in the array. We have carried out the normal mode analysis of fused porphyrin dimer based on the experimental results including Raman frequency shifts of two types of C13-isotope substituted dimers, Raman enhancement pattern by changing excitation wavelength, and depolarization ratio measurements as well as normal-mode calculations at the B3LYP/6-31G level. In order to find the origins for the resonance Raman mode enhancement mechanism, we have predicted both the excited state geometry changes (A-term) and the vibronic coupling efficiencies (B-term) for the relevant electronic transitions based on the INDO/S-SCI method. A detailed normal mode analysis of the fused dimer allows us to extend successfully our exploration to longer fused porphyrin arrays. Overall, our investigations have provided a firm basis in understanding the molecular vibrations of fused porphyrin arrays in relation to their unique flat molecular structures and rich electronic transitions.