Synthesis and Characterization of Bola-Amphiphilic Porphyrin-Perylenebisimide Architectures

We report on the synthesis and characterization of a family of three water-soluble bola-amphiphilic zinc-porphyrin-perylenebisimide triads containing oligo carboxylic-acid capped Newkome dendrons in the periphery. Variations of the perylenebisimide (PBI) core geometry and dendron size (G1 and G2 dendrons with 3- and 9-carboxylic acid groups respectively) allow for tuning the supramolecular aggregation behavior with respect to variation of the molecular architecture. The triads show good solubility in basic aqueous media and aggregation to supramolecular assemblies. Theoretical investigations at the DFT level of theory accompanied by electrochemical measurements unravel the geometric and electronic structure of the amphiphiles. UV/Vis and fluorescence titrations with varying amounts of THF demonstrate disaggregation.

Panchromatic Absorbers Tethered for Bioconjugation or Surface Attachment

The syntheses of two triads are reported. Each triad is composed of two perylene-monoimides linked to a porphyrin via an ethyne unit, which bridges the perylene 9-position and a porphyrin 5- or 15-position. Each triad also contains a single tether composed of an alkynoic acid or an isophthalate unit. Each triad provides panchromatic absorption (350–700 nm) with fluorescence emission in the near-infrared region (733 or 743 nm; fluorescence quantum yield ~0.2). The syntheses rely on the preparation of trans-AB-porphyrins bearing one site for tether attachment (A), an aryl group (B), and two open meso-positions. The AB-porphyrins were prepared by the condensation of a 1,9-diformyldipyrromethane and a dipyrromethane. The installation of the two perylene-monoimide groups was achieved upon the 5,15-dibromination of the porphyrin and the subsequent copper-free Sonogashira coupling, which was accomplished before or after the attachment of the tether. The syntheses provide relatively straightforward access to a panchromatic absorber for use in bioconjugation or surface-attachment processes.

Columnar Self-Assembly of Electron-Deficient Dendronized Bay-Annulated Perylene Bisimides

Three new heteroatom bay-annulated perylene bisimides (PBIs) have been synthesized by microwave-assisted synthesis in excellent yield. N-annulated and S-annulated perylene bisimides exhibited columnar hexagonal phase, whereas Se-annulated perylene bisimide exhibited low temperature columnar oblique phase in addition to the high temperature columnar hexagonal phase. The cup shaped bay-annulated PBIs pack into columns with enhanced intermolecular interactions. In comparison to PBI, these molecules exhibited lower melting and clearing temperature, with good solubility. A small red shift in the absorption was seen in the case of N-annulated PBI, whereas S- and Se-annulated PBIs exhibited blue-shifted absorption spectra. Bay-annulation increased the HOMO and LUMO levels of the N-annulated perylene bisimide, whereas a slight increase in the LUMO level and a decrease in the HOMO levels were observed in the case of S- and Se-annulated perylene bisimides, in comparison to the simple perylene bisimide. The band gaps of PBI and PBI-N were almost same, whereas an increase in the band gaps were observed in the case of S- and Se-annulated PBIs. The tendency to freeze in the ordered glassy columnar phase for PBI-N and PBI-S will help to overcome the charge traps due to crystallization, which are detrimental to one-dimensional charge carrier mobility. These solution processable electron deficient columnar semiconductors possessing good thermal stability may form an easily accessible promising class of n-type materials.

Chlorophyll-Inspired Red-Region Fluorophores: Building Block Synthesis and Studies in Aqueous Media

Fluorophores that absorb and emit in the red spectral region (600-700 nm) are of great interest in photochemistry and photomedicine. Eight new target chlorins (and 19 new chlorins altogether)-analogues of chlorophyll-of different polarities have been designed and synthesized for various applications; seven of the chlorins are equipped with a bioconjugatable tether. Hydrophobic or amphiphilic chlorins in a non-polar organic solvent (toluene), polar organic solvent (DMF), and aqueous or aqueous micellar media show a sharp emission band in the red region and modest fluorescence quantum yield (Φ_f = 0.2-0.3). A Poisson analysis implies most micelles are empty and few contain >1 chlorin. Water-soluble chlorins each bearing three PEG (oligoethyleneglycol) groups exhibit narrow emission bands (full-width-at-half maximum <25 nm). The lifetime of the lowest singlet excited state and the corresponding yields and rate constants for depopulation pathways (fluorescence, intersystem crossing, internal conversion) are generally little affected by the PEG groups or dissolution in aqueous or organic media. A set of chlorin-avidin conjugates revealed a 2-fold increase in Φ_f with increased average chlorin/avidin ratio (2.3-12). In summary, the chlorins of various polarities described herein are well suited as red-emitting fluorophores for applications in aqueous or organic media.

Synthesis and Functionalization of Porphyrins through Organometallic Methodologies

This review focuses on the postfunctionalization of porphyrins and related compounds through catalytic and stoichiometric organometallic methodologies. The employment of organometallic reactions has become common in porphyrin synthesis. Palladium-catalyzed cross-coupling reactions are now standard techniques for constructing carbon-carbon bonds in porphyrin synthesis. In addition, iridium- or palladium-catalyzed direct C-H functionalization of porphyrins is emerging as an efficient way to install various substituents onto porphyrins. Furthermore, the copper-mediated Huisgen cycloaddition reaction has become a frequent strategy to incorporate porphyrin units into functional molecules. The use of these organometallic techniques, along with the traditional porphyrin synthesis, now allows chemists to construct a wide range of highly elaborated and complex porphyrin architectures.

Self-Assembled PDINH Supramolecular System for Photocatalysis under Visible Light

A self-assembled perylene-3,4,9,10-tetracarboxylic diimide(PDINH) supramolecular system consisting of all-organic PDINH molecule building blocks through non-covalent interactions works as a visible light photocatalyst with high activity.

Bioconjugatable, PEGylated Hydroporphyrins for Photochemistry and Photomedicine. Narrow-Band, Red-Emitting Chlorins

Chromophores that absorb and emit in the red spectral region (600-700 nm), are water soluble, and bear a bioconjugatable tether are relatively rare yet would fulfill many applications in photochemistry and photomedicine. Here, three molecular designs have been developed wherein stable synthetic chlorins - analogues of chlorophylls - have been tailored with PEG groups for use in aqueous solution. The designs differ with regard to order of the installation (pre/post-formation of the chlorin macrocycle) and position of the PEG groups. Six PEGylated synthetic chlorins (three free bases, three zinc chelates) have been prepared, of which four are equipped with a bioconjugatable (carboxylic acid) tether. The most effective design for aqueous solubilization entails facial encumbrance where PEG groups project above and below the plane of the hydrophobic disk-like chlorin macrocycle. The chlorins possess strong absorption at ~400 nm (B band) and in the red region (Q_y band); regardless of wavelength of excitation, emission occurs in the red region. Excitation in the ~400 nm region thus provides an effective Stokes shift of >200 nm. The four bioconjugatable water-soluble chlorins exhibit Q_y absorption/emission in water at 613/614, 636/638, 698/700 and 706/710 nm. The spectral properties are essentially unchanged in DMF and water for the facially encumbered chlorins, which also exhibit narrow Q_y absorption and emission bands (full-width-at-half maximum of each <25 nm). The water-solubility was assessed by absorption spectroscopy over the concentration range ~0.4 μM - 0.4 mM. One chlorin was conjugated to a mouse polyclonal IgG antibody for use in flow cytometry with compensation beads for proof-of-principle. The conjugate displayed a sharp signal when excited by a violet laser (405 nm) with emission in the 620-660 nm range. Taken together, the designs described herein augur well for development of a set of spectrally distinct chlorins with relatively sharp bands in the red region.

Charge separation and charge recombination photophysical studies in a series of perylene–C60linear and cyclic dyads

A new donor–acceptor doubly bridged perylenediimide–fullerene dyad (PDI–C₆₀,DB-3), where the perylenediimide (PDI) acts as a donor, has been synthesized and studied by time-resolved absorption spectroscopy.

Synthetic bacteriochlorins bearing polar motifs (carboxylate, phosphonate, ammonium and a short PEG). Water-solubilization, bioconjugation, and photophysical properties

A bacteriochlorin scaffold has been derivatized for life sciences applications.

Vegetable-based dye-sensitized solar cells

In this review we provide an overview of vegetable pigments in dye-sensitized solar cells, starting from main limitations of cell performance to cost analysis and scaling-up prospects.

Pitfalls in bromination reactions of zinc porphyrins: two-sided ring opening of the porphyrin macrocycle

Reaction of [Zn(II)(TTP)] (1) (TTP = dianion of 5,10,15,20-meso-tetrakis(p-tolyl)porphyrin) with 16 equiv of N-bromosuccinamide (NBS) in methanol at reflux led to the unexpected two-sidedd open-ring brominated product [Zn(II)(C26H20N2O2Br5)2] (2). Similar observations have been made with other meso-substituted zinc porphyrins as well [Zn(II)(por)] {por = dianion of 5,10,15,20-meso-tetrakis(aryl)porphyrin; aryl = phenyl (TPP), p-(t)Bu-phenyl (TBPP), m-Cl-phenyl (TClPP)}. The respective products [Zn(II)(C24H16N2O2Br5)2] (3), [Zn(II)(C32H32N2O2Br5)2] (4), and [Zn(II)(C24H14N2O2Cl2Br5)2] (5) have been isolated in good to moderate yields and characterized by elemental analysis and UV-vis, (1)H NMR, and mass spectrometry. Additional bromination reaction of 1 with 8 equiv of NBS in a chloroform/methanol mixture led (after the two-sided ring opening) to nonmetalated brominated bi(pyrrole) product, C36H34N2O4Br4 (6). The detailed structures of complexes 1, 2, 3, and 6, available in a single crystal form, have been confirmed by X-ray diffraction analysis.

Synthesis of perylene-porphyrin dyads for light-harvesting studies

The spectral coverage of porphyrin-based light-harvesting arrays can be enhanced through the use of suitable accessory pigments. Perylene-monoimide dyes can serve as valuable accessory pigments with porphyrins. To investigate the choice of perylene-monoimide and the effects of molecular architecture on light-harvesting efficacy, five perylene-porphyrin dyads were prepared. Each dyad employs a diphenylethyne linker that bridges the perylene N-imide site and the porphyrin meso-position. Three dyads incorporate a mono-phenoxy perylene at the o-, m-, or p-position of the meso-aryl group on the porphyrin. The two remaining dyads incorporate a perylene-monoimide (bearing zero or three phenoxy substituents) at the p-position of the meso-aryl group on the porphyrin. The introduction of phenoxy groups on the perylenes increases the solubility, a key requirement for use in light-harvesting arrays. The long-wavelength absorption band of the perylene shifts from 506 nm to 532 or 533 nm upon substitution with one or three phenoxy groups, respectively. The synthesis of the dyads entails Pd -mediated coupling of a bromo-perylene and an ethynyl porphyrin, or the mixed-aldehyde condensation with a perylene-aldehyde, mesitaldehyde, and pyrrole. Five perylene-monoimide dyes bearing an ethyne or bromo substituent at the p-position of the N-aryl unit were developed for this modular chemistry. Each perylene-porphyrin dyad exhibits efficient energy transfer from the excited perylene to the ground-state porphyrin.

Preparation of novel highly conjugated bis-porphyrin bridged with a polyene linker

This paper describes the preparation of a bis free-base porphyrin and a bis-zinc porphyrin system in which the two 5,10,15-tris(3,5-ditertbutylphenyl)porphyrinyl units are connected in meso position by a tetraenic chain. The preparation of the dyad relies on the Wittig-Horner-Emmons reaction between diethyl 3-[5-[10,15,20-tris(3,5-ditert-butyl-phenyl)-porphyrinyl]] prop-2-enyl phosphonate and the aldehyde-1,3-diene[5-[10,15,20-tris(3,5-ditert-butyl-phenyl)-porphyrinyl]]. The two latter porphyrin derivatives were obtained via a Stille cross-coupling reaction between the corresponding tributyltin derivatives and the 5-iodo-10,15,20-tris(3,5-ditert-butyl-phenyl)-porphyrin. The UV-visible absorption and fluorescence spectra of the bis-porphyrin systems are measured and indicate that both the energy level and the lifetime of the porphyrin singlet excited state are reduced upon the attachment of the polyene chain to the porphyrin unit.

Photoinduced electron and energy transfer from coumarin 153 to perylenetetracarboxylic diimide in bmimPF6/TX-100/water microemulsions

A perylenetetracarboxylic diimide (PDI) compound with an attached hydrophilic polyoxyethylene group at the imide nitrogen position was designed and synthesized. Photoinduced electron and energy transfer between coumarin 153 (C-153) and PDI in a ternary microemulsion with an ionic liquid (bmimPF(6)/TX-100/H(2)O) were investigated by steady state electronic absorption and fluorescence spectroscopy. The results revealed that both PDI and C-153 resided at the interface between the surfactant TX-100 and the ionic liquid bmimPF(6) in the ternary microemulsions. The absorption spectra suggested no interactions between C-153 and PDI in the ground states, but the fluorescence spectra revealed the presence of an efficient electron transfer and a less efficient energy transfer from C-153 to PDI. Moreover, the electron transfer was much more efficient in microemulsions than that in homogeneous conventional organic solvents due to the unique micro-environment of the microemulsion.

N-(2-(N',N'-diethylamino)ethyl)perylene-3,4-dicarboximide and its quaternized derivatives as fluorescence probes of acid, temperature, and solvent polarity

In this manuscript, we report the fluorescence properties of N-(2-(N',N'-diethylamino)ethyl)perylene-3,4-dicarboximide (1) and its quaternized derivative N-(2-(N',N'- diethyl-N'-methylammonium)ethyl)perylene-3,4-dicarboximide tosylate (2) in organic solvents. The effects of carboxylic acids and amines on the fluorescence properties of these compounds were investigated. In addition, we studied the aggregation and fluorescence properties of (2) and its 9-bromo-substituted derivative (3) in aqueous solution. The fluorescent properties of these compounds change dramatically with the extent of aggregation, thus allowing these compounds to be used as fluorescent probes for changes in temperature and solvent polarity. For instance, the fluorescence emission intensity of 3 increases by about 28 times as the temperature of the solution increases from 10°C to 85°C. The fluorescent intensities of 2 and 3 in methanol are higher than that in water by about 8 and 25 times, respectively.

Synthetic routes to meso-patterned porphyrins

Synthetic meso-substituted porphyrins offer significant attractions compared with naturally occurring beta-substituted porphyrins. The attractions include the rectilinear arrangement of the four meso substituents and potential synthetic amenability from pyrrole and simple acyl reactants, thereby avoiding the cumbersome syntheses of beta-substituted pyrroles. In practice, however, the classical methods for the synthesis of meso-substituted porphyrins were characterized by high-temperature reactions, limited scope of substituents, and statistical mixtures accompanied by laborious chromatography if porphyrins bearing two different types of substituents were sought. Such methods left unrealized the tremendous utility of meso-substituted porphyrins across the enormously broad field of porphyrin science, which touches pure chemistry; energy, life and materials sciences; and medicine. This Account surveys a set of strategies, developed over a generation, that provide rational access to porphyrins bearing up to four distinct meso substituents. A "2 + 2" route employs a dipyrromethane-1,9-dicarbinol and a dipyrromethane (bearing ABC- and D-substituents, respectively) in a two-step, one-flask process of acid-catalyzed condensation followed by oxidation at room temperature to form the free base "ABCD-porphyrin." A "bilane" route relies on the acid-catalyzed reaction of a 1-acyldipyrromethane (CD substituents) and a 9-bromodipyrromethane-1-carbinol (AB substituents) to form the corresponding 19-acyl-1-bromobilane. Reaction of the latter compound in the presence of MgBr(2), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and toluene at reflux exposed to air affords the corresponding magnesium(II) porphyrin. The two routes are complementary, both in scope and in implementation. A suite of methods also affords trans-A(2)B(2)-porphyrins by reaction of a dipyrromethane and an aldehyde, self-condensation of a dipyrromethane-1-carbinol, or self-condensation of a 1-acyldipyrromethane. These new routes are also useful for preparing sparsely substituted porphyrins, which bear fewer than four meso substituents (e.g., trans-AB-porphyrins, A-porphyrins). Because of their compact size and the ability to incorporate hydrophilic or amphipathic groups, such molecules are ideal for biological applications. The success of these new synthetic strategies has relied on a number of advances including (1) the development of simple yet efficient routes to dipyrromethanes, acyldipyrromethanes, and dipyrromethane-carbinols, (2) the identification of acid catalysts and reaction conditions for condensations of pyrromethane species without accompanying acidolysis (which underlies scrambling and formation of a mixture of porphyrin products), (3) the development of analytical methods to rapidly screen for scrambling and to characterize the distribution of oligopyrromethanes and macrocycles, (4) selection and refinement of synthetic methods to increase yields and to limit or avoid use of chromatography, thereby achieving scalability to multigram levels, and (5) exploitation of discoveries concerning the fundamental chemistry of pyrrolic species. With these developments, the prior era of porphyrin synthesis has been supplanted with rational routes that proceed under very mild conditions and afford a single porphyrin bearing up to four distinct meso substituents. The meso substituents encompass a very wide range of molecular complexity. The resulting porphyrins can serve as building blocks in the construction of model systems, as components of molecular materials, and as surrogates for naturally occurring tetrapyrrole macrocycles.

Design and synthesis of water-soluble bioconjugatable trans-AB-porphyrins

Three free base porphyrins have been prepared that bear a polar and facially encumbering 2,4,6-tris(carboxymethoxy)phenyl motif at one meso (5-) position. The only other substituent (15-position) comprises phenyl, formyl, or p-aminophenyl. The porphyrins exhibit solubility in water (or aqueous buffer solutions) at pH >/=7 and concentrations >1 mM at room temperature. The concise syntheses, water-solubility, and bioconjugatable handle make these porphyrin constructs suitable for biological applications.

Formation of a perylenetetracarboxylic diimide network film by post electrochemical treatment

Perylenetetracarboxylic diimide (PDI) derivatives bearing two or four peripheral pyrrole pendants (PDI-nPy, n=2 or 4) are cross-linkable materials by electro/phototreatment. In this paper, we introduce a new posttreatment technique to produce an insoluble film. Unlike the common solution-phase electrochemical deposition, we first spin-coated PDI-nPy on an electrode and then electrotreated the coated surface in a monomer-free electrolyte solution. This method gives the film a smooth surface with no granules, while the common method induces a rough film with a lot of granules. The post electrochemical treatment also provides a merit of higher resolution in a patterning process on a specific metal electrode. As one of the applications, we carried out an electrochromic study on the posttreated PDI-4Py film. It turned purple (lambdamax=590 nm) and sky blue (lambdamax=797 nm) at 0 and -1.9 V vs Ag/Ag+, respectively. We believe this method will broaden the patterning concept with the desired film morphology and resolution using PDI on a specific electrode.

Formation of insoluble perylenetetracarboxylic diimide films by electro- or photo-crosslinking of pyrrole units

Perylenetetracarboxylic diimide derivatives bearing 2- or 4-peripheral pyrrole pendants could be efficiently crosslinked to form an insoluble film either by electropolymerization or visible light induced oxidative photopolymerization of the pyrrole units.

Synthesis of Supramolecular Polymers by Ionic Self-Assembly of Oppositely Charged Dyes

A new type of supramolecular polymer was prepared by ionic self-assembly (ISA) from two oppositely charged dyes; a perylenediimide and a copper-phthalocyanine derivative. Coulomb coupling stabilizes the whole structure, and a combination of charge-transfer interactions and discotic stacking facilitates the exclusive formation of one-dimensional polymeric chains. The supramolecular dye-polymers have a large association constant (2.4 x 10(7) L mol(-1)), high molecular weight, and high mechanical stability. The use of cryo-transmission electron microscopy (cryo-TEM) confirmed the existence of extended fibers of width 2.4 nm. Further image analysis revealed slight undulation and faint segmentation of the fibers, and density maxima were observed at a regular interval of 3.6 nm along the fiber axis. The fiber-like structure (and aggregate of fibers) is also found in the solid state, as shown by the results of mineralization contrasting experiments, atomic force microscopy (AFM), and X-ray analyses. A structural model is proposed, in which the structural subunits, arranged in a side-by-side conformation, form a stacked structure.