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Apparently solvent-mediated and not through-bond photoinduced electron transfer (ET) takes place from the porphyrin (P) unit to the methylviologen (MV2+ ) unit in the rigid U-shaped molecules 1 (i.e., kTSET >kTBET ; TS=through-solvent, TB=through-bond). The ratio of the rates of charge separation to charge recombination is greater than 1400:1.

In suitably designed supramolecular systems, composed of a macrocycle and two different thread-like compounds, it is possible to choose, by means of chemical inputs, which thread enters the macrocycle's cavity, and it is also possible to cause reversible interchange between the two threads. Two such systems are described. In one of them, the macrocyclic component is 1,5-dinaphtho-38-crown-10, the potential threads are 1,1′-dibenzyl-4,4′-bipyridinium and 2,7-dibenzyldiazapyrenium dications, and the chemical input used is amine/acid. In the other system, the macrocyclic component is the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), the potential threads are tetrathiafulvalene and a 1,5-dioxynaphthalene derivative, and the input is reduction/oxidation. These systems are examples of chemically driven molecular-level mechanical machines.

[reaction: see text] The 3,3',4'4'-tetranitrodibenzocrown ethers TNDB24C8 and TNDB30C10 form organogels with chloroalkanes at 3% w/v. Atomic force microscopy and scanning electron microscopy have been used to characterize the superstructure of the gels. Gels prepared using TNDB30C10 and CHCl(3) are more fibrous and are ordered into elongated domains attributable to exposed parts of intermingled fibers. Differential scanning calorimetry shows that the gel aids in the formation of supercooled CHCl(3) (DeltaT = 21 K, DeltaH(av) = 19.0 +/- 1.5 kJ mol(-)(1)) and that the gel liquefies at 307 K.

A new core-substituted naphthalene diimide (cNDI) compound that is sensitive to both H(+) and solvent polarity has been synthesised and characterised. Optical absorption and emission change upon protonation while emission quantum yield and decay kinetics of the unprotonated form vary significantly with solvent polarity due to delayed fluorescence.

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV–vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications.

Providing a comprehensive overview of current developments in innovative materials science and related topics, this book covers the core areas of materials science, inorganic, organic and solid state chemistry.

More and more chemists are beginning to realise that the conventional synthetic methodology of making compounds group-by-group or molecule-by-molecule, employing reagents or catalysts to make or break covalent bonds and so manipulate functional groups and transform molecular structures, is insufficient by itself to construct the materials they would like to make in the future. Along its many synthetic trails, nature does not rely upon the inefficient use of protecting groups and the complexity of reagents according to the usual manner and practice of the synthetic organic chemist in a traditional sense. Indeed, one of the keys to the efficient operation of biological systems is their ability to self-assemble,1 self-organise2 and self-replicate.3

The excited-state dynamics of two triads consisting of a naphthalenediimide (cNDI) substituted at the core by two zinc (ZnP) or free-base tetraphenylporphyrins (FbP) was investigated by ultrafast fluorescence and transient absorption spectroscopy. The electronic absorption spectra of the triads are almost the composites of those of the constituents, pointing to a weak electronic coupling and to a localization of the excitation energy on one of the porphyrins. In cyclohexane, the excited-state dynamics of the triads are essentially the same as those of the individual porphyrins, with the exception of the Soret emission of the ZnP triad, whose lifetime exhibits a more than 10 fold shortening compared to ZnP. A similarly ultrafast fluorescence decay was measured in tetrahydrofuran and benzonitrile. In these two solvents, charge separation from the excited porphyrin to the cNDI was found to take place with ∼1 ps and ∼25 ps time constants in the ZnP and FbP triads, respectively. The build up of the charge-separated state population in the ZnP triad is independent of the excitation wavelength, indicating that charge separation takes place from the lowest singlet excited state. Charge recombination occurs with a time constant of around 8 ps in both triads, i.e. it is slower than charge separation in the ZnP triad but faster in the FbP triad. These differences are rationalized in terms of the driving forces for charge separation and recombination.

Synthetic access to a set of metallo- and free base bis-porphyrins has been provided by a stepwise approach involving sequential peptide and Suzuki couplings. Linking these porphyrins through a 3,3′-biphenyl bridge enables cooperative binding to ditopic ligands such as the bipyridyls. Association constants and binding stoichiometry has been determined by spectroscopic/spectrophotometric means and the differences in the binding affinities of a small series of diaza ligands is discussed in the context of structural fit and microscopic association constants.

International audience; A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric PTTFP triads 1?ac and asymmetric PTTF dyads 2?a,b in good yields. These planar and extended p-conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge-transfer excitations within the donoracceptor assemblies. Quantum-chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited-state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2?a,b but not in triads 1?ac. Clear evidence for a photoinduced and relatively long lived charge-separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnPTTF dyad and a pyridine-functionalized C60 acceptor unit. This specific excited state results in a (ZnPTTF).+...(C60py).- state. The binding constant of ZnII...py is evaluated by constructing a BenesiHildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20X104?M-1, which is remarkably high for bonding of pyridine to ZnP.

Inspired by nature and its ability to form well-defined architectures on the nanoscale, this chapter investigates not only examples of hybrid nanostructured materials that utilize the building blocks of nature, such as DNA, biopolymers, and bilayers, but also of biomimicry.

Hydrogel of carboxymethyl sago pulp (CMSP) of various degree of substitution (DS) was prepared by electron beam irradiation of various radiation doses. The CMSP hydrogels were subjected to swelling in different ionic strength solutions of KCl, NaCl, and CaCl2. The CMSP hydrogels, due to its polyelectrolyte nature, were found to be highly sensitive to ionic strength of the medium. All the CMSP hydrogels showed the absorption of K+ and Ca2+ increases with the increase in the concentrations of the respective cation solutions. The cation absorption also decreases with DS and % gel fraction (%GF) of the CMSP hydrogels. Subjecting the CMSP hydrogels in NaCl results in deswelling and releases Na+ to swelling medium where the Na+ release increases with the increase of DS and %GF. The sorption capacity depends on the extent of crosslinking and decreases with the increase in the extent of crosslinking.

Dibenzo-24-crown-8 crystallizes with ammonium hexa­fluoro­phosphate to produce a complex in which the ammonium ion is encapsulated by the crown ether, NH4+·C24H32O8·PF6−.

Molecular cavities constructed within rigid monolayers of yoctolitre (1 yL = 10(-24) L) volume, the so-called yoctowells, are novel surface-engineered systems capable of studying the separation, containment and manipulation of individual molecules. The properties of the yoctowell can be fine-tuned by the nature of the monolayer, or by post-functionalisation leading to amongst others, the exploitation of electrostatic effects. The derivatisation of the cavities implies they can be used as a means of discriminating between substrates with application in molecular sorting of two or more molecular entities in solid devices, or become useful as an appropriate model with which to study molecular interactions. Of prime importance to all the cases described herein is the use of porphyrins as an optical readout (absorption, emission) of the recognition event. In this tutorial review, we describe the development of yoctowell chemistry and comment on future advances in this technology in light of other literature approaches.

A small series of variable-depth yoctowell cavities with 'functional' walls on aminated silica particles and gold electrodes has been established. The dimensions of the gaps formed were 2.2 nm in diameter with varying 'functional' depths of 5, 10, and 15 A, depending on the length of bolaphiles applied and the position of the positive rim; these gaps were prepared through a Michael addition of the incorporated ene-amide groups. Using this construct and electrostatic interactions between the positive rim and anionic quinones as a means of immobilization, a porphyrin-quinone dyad system has been prepared. The distance between the donor and acceptor was changed systematically in aqueous solution, whilst maintaining a similar environment in each case. Upon photoexcitation of the porphyrin, efficient electron transfer occurs between the porphyrin and quinone units in a distance-dependent manner on the nanosecond timescale.

The self-assembly of core-substituted naphthalene diimides bearing triethylene glycol motifs leads to the formation of stable vesicles in DMSO and CHCl(3)/MeOH (6 : 4, v/v) solvents. The vesicles were evaluated by means of UV/vis and fluorescence spectroscopy, transmission electron microscopy, atomic force microscopy and dynamic light scattering.

The photophysics and excited-state dynamics of two dyads consisting of either a free-base or a zinc-tetraphenylporphyrin linked through a rigid bridge to a core-substituted naphthalenediimide (NDI) have been investigated by femtosecond-resolved spectroscopy. The absorption and fluorescence spectra differ substantially from those of the individual units, pointing to a substantial coupling and to a delocalisation of the excitation over the whole molecule, as confirmed by quantum chemistry calculations. A strong dependence of their excited-state dynamics on the solvent polarity has been observed. In toluene, the fluorescence quantum yield of the dyads is of the order of a few percent and the main decay channel of the emitting state is proposed as intersystem-crossing to the triplet state. However, in a medium polarity solvent like dichloromethane, the emitting state undergoes charge separation from the porphyrin to the NDI unit within 1-3 ps, and the ensuing charge-separated state recombines in about 10-20 ps. This solvent dependence can be explained by the weak driving force for charge separation in polar solvents and the large electronic coupling between the porphyrin and NDI moieties, making charge separation a solvent-controlled adiabatic process.

An olefination approach to the construction of covalently linked cyclic metalloporphyrin trimers is presented using fullerenes such as C(60) or C(70) as a template. Yields of the trimer approach 60%. In the absence of a template, the major product is the cyclic dimer (50% yield) with only a small amount of trimer (10%) formed, indicating this is a template-directed approach.

The fabrication of increasingly smaller machines to the nanometer scale can be achieved by either a “top-down” or “bottom-up” approach. While the former is reaching its limits of resolution, the latter is showing promise for the assembly of molecular components, in a comparable approach to natural systems, to produce functioning ensembles in a controlled and predetermined manner. In this review we focus on recent progress in molecular systems that act as molecular machine prototypes such as switches, motors, vehicles and logic operators.

Sequential condensation of a variety of porphyrin-2,3-diones with 1,2,4,5-benzenetetramine and 1,10-phenanthroline-5,6-dione generate conjugated phenanthroline-appended porphyrin systems; this chemistry provides a means by which porphyrin π-systems can be connected to external redox centres.

The structural, coordinative, photochemical and electrochemical properties of the porphyrin macrocycle that make them the functional element of choice in ubiquitous biological systems, e.g., chlorophyll, cytochrome P450 and hemoglobin, also contribute to making porphyrins and metalloporphyrins desirable in a “bottom-up” approach to the construction of nanosized devices. This paper highlights some recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that display optically readable functions as a result of photonic or chemical stimuli.

The requirements for the self-assembly of 2,3-annulated core-substituted NDIs into discrete worm-like nanostructures are explored in MeOH-CHCl(3) solutions. AFM was used to visualize and characterize the structures formed at precise proportions of solvent mixes.

The synthesis and characterization of a highly fluorescent core-substituted naphthalene diimide sensor (varphi = 0.34) bearing a bis-sulfonamide group is described. The compound shows a unique selectivity and reactivity for the fluoride ion over other anions in CHCl(3) by a two-stage deprotonation process leading to a colorimetric response. In DMSO solution, the sensor is shown to be highly selective for fluoride (K(a) approximately 10(6) M(-1)) over other anions with more pronounced changes in absorption characteristics.

The synthesis and physical properties of the ternary complex 3(2+), prepared by reaction of a naphthalene diimide dicarboxylate 2 with the binucleating dinickel(II) cavitand 1, are discussed. The complex 3(2+) is characterised by cyclic voltammetry which shows a wealth of metal-centred and diimide-based processes at -1.62, -1.04 and 0.15 V vs Fc/Fc+. Absorption and fluorescence spectroscopy of 3(2+) in CH2Cl2 compared to the components 4+ and 5, respectively, are used to characterise the complex further. In particular there is a substantial quenching (approximately 95%) of the diimide fluorescence upon complexation. X-Ray crystallography has been used to characterise complex 3(2+) in the solid state. Of particular interest is the supramolecular structure in which the naphthalene diimide is included between the two metallocavitand hemispheres.

A broad range of fundamental free radical reactions such as hydrogen atom transfer, radical deoxygenations, and radical cyclizations utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors at room temperature are investigated. The reactions proceed in good to excellent yields with some degree of enantioselectivity.

An approach to the formation of molecular timepieces is outlined based on differentiating between rotamers in diaxial Sn(IV) porphyrin phenolates. Two models are explored in detail. The first explores how the rates of rotation of the diaxial ligands is discriminated based on steric hindrance of the two porphyrin macrocycle faces at low temperature. The second model explores a ‘stopwatch’ function based on the ligation of Ag(I) ions to a 5,15-dipyridylporphyrinato tin(IV) complex bearing 3-hydroxypyridine ligands. The complexation inhibits rotation of the axial ligand, a result, which can be reversed by precipitation of Ag(I) using tetraethylammonium bromide. X-ray crystallography has also been used to characterize two Ag(I) 5,15-dipyridylporphyrinato tin(IV)complexes. The two isoforms differ in their supramolecular organization. One structure is formed through a cofacial stack linking each porphyrin by Ag(I) coordination. The other displays a sheet-like coordination polymer structure.

The conversion of allyl esters into carboxylic acids using radical initiators has been achieved in high yields in aqueous media.

A crystallography-instructed strategy to highly ordered layering of porphyrins with different topologies on HOPG is developed based on meso-tetraarylporphyrins bearing 2-ethoxyethanol side chains as “sticky ends”. These sticky ends are capable of displaying directive hydrogen bonding motifs with the inherent D4h symmetry of the porphyrins. Solvent effects are shown to have an important role in fabricating the adsorption. Metalation and subsequent axial ligation was a key controlling factor in the topology of the layer, leading to pseudo-2D structures on HOPG.

This tutorial review surveys recent developments in the chemistry of naphthalene diimides (NDIs) and explores their application in the fields of material and supramolecular science. It begins with a discussion of their general uses, methods of syntheses and their electronic and spectroscopic properties. Of interest to their application in the fields of conducting thin films and molecular sensors is the structure–function relationships that exist either as co-components of supramolecular ensembles as in the case of “nanotubes”, or as the sole components in molecular wires. Also discussed are advances in NDI research within the areas of energy and electron transfer (covalent and non-covalent systems) and in host–guest chemistry including foldamer, mechanically-interlocked and ligand-gated ion channel examples. Finally, we explore the developments in the recent field of core-substituted NDIs, their photophysical properties and applications in artificial photosynthesis. We conclude with our views on the prospects of NDIs for future research endeavours.

Yoctolitre-sized vessels (1 yL = 10–24 L) defined by encompassing porphyrin islands by rigid molecular monolayers of diamido bolaamphiphiles (with different characteristics) on smooth surfaces—the so-called yoctowells—have the ability to store (house) molecules in ways reminiscent of a molecular container. Such containers fill by kinetic or thermodynamic trapping processes allowing in some instances for the sorting and spatial positioning of molecular entities within the container. In this Emerging Area we describe the usefulness and versatility of yoctowells as the basis for modeling biological systems with a view to addressing some of the challenges in chemistry, molecular biology and biochemistry.

This tutorial review surveys recent developments in the chemistry of naphthalene diimides (NDIs) and explores their application in the fields of material and supramolecular science. It begins with a discussion of their general uses, methods of syntheses and their electronic and spectroscopic properties. Of interest to their application in the fields of conducting thin films and molecular sensors is the structure–function relationships that exist either as co-components of supramolecular ensembles as in the case of “nanotubes”, or as the sole components in molecular wires. Also discussed are advances in NDI research within the areas of energy and electron transfer (covalent and non-covalent systems) and in host–guest chemistry including foldamer, mechanically-interlocked and ligand-gated ion channel examples. Finally, we explore the developments in the recent field of core-substituted NDIs, their photophysical properties and applications in artificial photosynthesis. We conclude with our views on the prospects of NDIs for future research endeavours.

The photophysics of two new substituted aminopropenyl naphthalene diimide (SANDI) dyes are reported. The molecules exhibit many of the photophysical properties required for fluorescence labeling applications including high photostability and high fluorescence quantum yields (> 0.5) in the visible region of the spectrum. Furthermore, the emission is sensitive to the number of substituents attached to the aromatic core, and to the surrounding environment. For example, in toluene as solvent, the mono-allyl SANDI has an emission maximum at 550 nm, whereas the di-allyl SANDI emits at 630 nm. The fluorescence decay times are in the range of ~8 - 12 ns and the Forster critical distance for fluorescence resonance energy transfer (FRET) between the mono- and di-allyl SANDI derivatives is 4.1 nm for a random donor-acceptor orientation. Single molecules of the di-allyl SANDI embedded in poly(methyl methacrylate) films show very low yields of photobleaching and very few fluorescence intermittencies or "blinks". These compounds are ideal candidates for applications at the single molecule level, for example, as FRET labels.

An overview of the evolution of artificial photosynthetic charge transfer systems containing porphyrin donors and pyromellitic or naphthalene diimide acceptor units is presented. Progression in this area of research is highlighted by the complexity of the systems, the nature of the medium separating donor and acceptor as well as the progression in the lifetime of the charge-separated state upon photoexcitation. A number of supramolecular systems that utilize hydrogen bonding or axial ligation of zinc porphyrins as a means for spatial orientation are highlighted.

Selective cross-metathesis of type I and type II meso-functionalized porphyrin olefins afforded alkenyl-coupled dimeric and trimeric porphyrin systems in good yield with excellent E/Z selectivity. The synthetic utility of the method is demonstrated through the preparation of mixed metalated (M = 2H, Zn) porphyrin dimer and trimer. [reaction: see text]

A pseudorotaxane formed in solution by self-assembly of a wire-type electron acceptor (2,7-dibenzyldiazapyrenium dication) and a macrocyclic electron donor (2,3-dinaphtho-30-crown-10) can be unthreaded and rethreaded by chemical inputs. Unthreading can be obtained by addition of stoichiometric amounts of acids or amines. After the unthreading process caused by addition of acid, rethreading can be obtained by addition of amine, and vice versa. The threading/unthreading processes are accompanied (and therefore can be monitored) by strong changes in the fluorescence properties of the system. The input (chemical)/output (fluorescence) characteristics of this molecular-level system correspond to those of an XOR logic gate.

Spectroscopic changes from a solution of the amphophile 5,10,15,20-tetraphenylporphyrin in N,N-dimethylformamide using inputs of acid (HClaq) and base (KOBut) are interpreted as XOR and INHIBIT logic operations. The combination of these two operations gives rise to a device that acts as a molecular half-subtractor.

Hydroxyl radical (·OH) is a reactive oxygen species produced during severe hypoxia, asphyxia, or ischemia that can cause cell death resulting in brain damage. Generation of ·OH may occur in the fetal brain during asphyxia in utero. The very short half-life of ·OH requires use of trapping agents such as salicylic acid or phenylalanine for detection, but their hydroxylated derivatives are either unstable, produced endogenously, or difficult to measure in the small volume of microdialysis samples. In the present study, we used terephthalic acid (TA), hydroxylation of which yields a stable and highly fluorometric isomer (excitation, 326 nm; emission, 432 nm). In vitro studies using ·OH generated by the Fenton reaction showed that hydroxylated TA formed quickly (

With the advent of Raman spectrometers based on CCD array detectors, instruments have been coupled to optical microscopes leading to all the advantages of bright field microscopy with the added advantage of a direct chemical probe. The primary biological solvent, water, is a weak Raman scatterer and so these instruments can now be used to investigate the chemistry of living systems at spatial resolutions of 1 µm and below. We have developed techniques that allow us to study functional red blood cells and monitor the exchange of ligands and the development and chemistry of disease processes. These techniques take advantage of Aggregated Enhanced Raman Spectroscopy, which enables us to use the haem group of the haemoglobins and related haem pigments, such as the malarial pigment haemozoin, as a sensitive probe for changes in oxidation state, spin state and electronic structure. We have used the Raman microprobe to investigate the effect of drugs such as quinoline on the food vacuole of the malarial parasite in vivo. Sickle cell disease affects 1 out of 600 African American births and is caused by a mutant form ( β6 glu→ val) of haemoglobin (HbS). HbS polymerizes and forms higher order aggregates under hypoxic conditions, leading to distortion and rigidity of the erythrocyte. These rigid cells can block the microvasculature resulting in tissue ischaemia, organ damage, and ultimately death. The sensitivity of the Raman technique to haem aggregation provides a tool with which we can analyse the changes that occur between normal and sickle cells.

Resonance Raman spectra of beta-hematin and hemin are reported for a range of excitation wavelengths including 406, 488, 514, 568, 633, 780, 830, and 1064 nm. Dramatic enhancement of A(1g) modes (1570, 1371, 795, 677, and 344 cm(-1)), ring breathing modes (850-650 cm(-1)), and out-of-plane modes including iron-ligand modes (400-200 cm(-1)) were observed when irradiating with 780- and 830-nm laser excitation wavelengths for beta-hematin and to a lesser extent hemin. Absorbance spectra recorded during the transformation of hemin to beta-hematin showed a red-shift of the Soret and Q (0-1) bands, which has been interpreted as excitonic coupling resulting from porphyrin aggregation. A small broad electronic transition observed at 867 nm was assigned to a z-polarized charge-transfer transition d(xy) --> e(g)(pi). The extraordinary band enhancement observed when exciting with near-infrared excitation wavelengths in beta-hematin when compared to hemin is explained in terms of an aggregated enhanced Raman scattering hypothesis based on the intermolecular excitonic interactions between porphyrinic units. This study provides new insight into the electronic structure of beta-hematin and therefore hemozoin (malaria pigment). The results have important implications in the design and testing of new anti-malaria drugs that specifically interfere with hemozoin formation.

Sequential condensation of a variety of porphyrin-2,3-diones with 1,2,4,5-benzenetetramine and 1,10-phenanthroline-5,6-dione generate conjugated phenanthroline-appended porphyrin systems; this chemistry provides a means by which porphyrin π-systems can be connected to external redox centres.

This article reviews our recent work in constructing discrete multiporphyrin assemblies and supramolecular arrays through the application of two organising principles - crown ethers and tin(IV)porphyrin phenolates. The role of the crown ethers is illustrated by two examples: (a) the cation-induced control of the reduction potentials within a model 18 C 6 bearing naphthalene and naphthoquinone chromophores antipodally displaced on the crown ether in the presence of alkali metal cations and (b) in the complexation of dialkylammonium salt within the cavity of a 24 C 8 bischlorin system. Tin(IV)porphyrin phenolates provide a means of efficiently constructing multiporphyrin assemblies without the use of covalent bond formation. Their potential is illustrated through the formation of discrete trimers, using a “one pot” self-assembly strategy, as well as the generation of supramolecular arrays with sieve like networks.

[reaction: see text] The crystal and molecular structures of two six-coordinate tin(IV)porphyrin phenolate complexes show that infinite cylindrical channels of uniform pore dimension are formed along the crystallographic c-direction. The underlying recognition event responsible for the porosity is an extremely tight intermeshing of the meso-tolyl units between layers which is a result of Sn-O...H interactions. Thermogravimetric analysis and differential scanning calorimetry have been used to characterize the sieve-like materials.