Search

Singlet oxygen sensitization involving a class of hemiquinonoid-substituted resorcinarenes prepared from the corresponding 3,5-di-t-butyl-4-hydroxyphenyl-substituted resorcinarenes is reported. Based on variation in the molecular structures, quantum yields comparable with that of the well-known photosensitizing compound meso-tetraphenylporphyrin were obtained for the octabenzyloxy-substituted double hemiquinonoid resorcinarene reported herein. The following classes of compounds were studied: benzyloxy-substituted resorcinarenes, acetyloxy-substituted resorcinarenes and acetyloxy-substituted pyrogallarenes. Single crystal X-ray crystallographic analyses revealed structural variations in the compounds with conformation (i.e., rctt, rccc, rcct) having some influence on the identity of hemiquinonoid product available. Multiplicity of hemiquinonoid group affects singlet oxygen quantum yield with those doubly substituted being more active than those containing a single hemiquinone. Compounds reported here lacking hemiquinonoid groups are inactive as photosensitizers. The term ‘fuchsonarene’ (fuchson + arene of resorcinarene) is proposed for use to classify the compounds.

Dye-sensitized solar cells (DSSCs) were built to probe the effect of the number of cyanocinnamic acid anchoring groups on the ring periphery of phenothiazine dyes. Two kinds of dyes, one with substitution on the N-terminal (1) and the other at the C-3 aromatic ring (2-5), have been synthesized for this purpose. Additionally, the number of cyanocinnamic acid groups have been increased to two in the case of compound 6. In the case of compounds 2-6, the N terminus was functionalized to carry methyl, 2-hydroxyethane, tris(ethylene oxide), or hexyl groups. Evidence for charge injection from the excited singlet state of phenothiazine to TiO2 was secured from femtosecond transient absorption spectral studies, wherein an ultrafast charge injection process (kCI ≈1010 -1011 s-1 ) was witnessed. The DSSCs were built on nanocrystalline TiO2 by using the traditional two-electrode method. Cell performance was better for carbon-functionalized phenothiazine dyes compared with that of nitrogen-functionalized dyes. The second cyanocinnamic group also increased the efficiency to 5.8 %.

International audience; Peripherally substituted tetradecaazaheptacene (NHp) compounds, exhibiting amphiprotism-coupled emission, have been synthesized. X-ray crystallography reveals a planar acene-like chromophore, and electronic absorption and emission occur in the near-infrared biological transparency window (650-900 nm). The compounds exhibit long-wavelength emission with photoluminescence quantum yields Φ up to ∼0.61 at 686 nm, with the monodeprotonated state Φ ≈ 0.58 at 712 nm. This unprecedented highly nitrogenous chromophore illustrates the stability and utility of the pyrazinacenes for different applications based on their photophysical properties and chemical structures.

Molecules that can exist in multiple states with the possibility of toggling between those states based on different stimuli have potential for use in molecular switching or sensing applications. Multimodal chemical or photochemical oxidative switching of an antioxidant-substituted resorcinarene macrocycle is reported. Intramolecular charge-transfer states, involving hemiquinhydrones are probed and these interactions are used to construct an oxidation-state-coupled molecular switching manifold that reports its switch-state conformation via striking variation in its electronic absorption spectra. The coupling of two different oxidation states with two different charge-transfer states within one macrocyclic scaffold delivers up to five different optical outputs. This molecular switching manifold exploits intramolecular coupling of multiple redox active substituents within a single molecule., Molecules that can switch between multiple stable states in response to stimuli are promising for many applications, but are challenging to construct. Here, the authors design a resorcinarene switching manifold with multiple oxidation states and coupled charge-transfer states, which can access up to five distinct switch-states with unique optical outputs.

TiO2 based nanostructures have been widely explored as photoanodes for dye-sensitized solar cells (DSSCs) because of their favourable band gap and corresponding compatibility with various sensitizers (dye molecules). Various morphologies and textures of titanium oxide have been thoroughly investigated to find the best efficiency in DSSCs. In this work, a detailed study of a nanocomposite of titanium dioxide partly derived from hydrogen titanate precursor has been reported. The current structure is realized in order to achieve optimal photogenerated charge carrier transport and reduced charge recombination. Among many combinations of the composites, the best photoanode showed power conversion efficiency (η) of 8.61% and corresponding open circuit voltage was 0.69 V and short circuit current 17.22 mA cm−2. The efficiency enhancement for the nanorod-nanoparticle composite photoanode is explained by structural, optical, and morphological properties and corroborated with electrochemical impedance spectroscopy.

Building on recent progress in the synthesis of functional porphyrins for a range of applications using the Cu-mediated azide–alkyne cycloaddition (CuAAC) reaction, we describe the active template CuAAC synthesis of interlocked triazole functionalised porphyrinoids in excellent yield. By synthesising interlocked analogues of previously studied porphyrin–corrole conjugates, we demonstrate that this approach gives access to rotaxanes in which the detailed electronic properties of the axle component are unchanged but whose steric properties are transformed by the mechanical “picket fence” provided by the threaded rings. Our results suggest that interlocked functionalised porphyrins, readily available using the AT-CuAAC approach, are sterically hindered scaffolds for the development of new catalysts and materials.

An electron-deficient copper(III) corrole was utilized for the construction of donor-acceptor conjugates with zinc(II) porphyrin (ZnP) as a singlet excited state electron donor, and the occurrence of photoinduced charge separation was demonstrated by using transient pump-probe spectroscopic techniques. In these conjugates, the number of copper corrole units was varied from 1 to 2 or 4 units while maintaining a single ZnP entity to observe the effect of corrole multiplicity in facilitating the charge-separation process. The conjugates and control compounds were electrochemically and spectroelectrochemically characterized. Computational studies revealed ground state geometries of the compounds and the electron-deficient nature of the copper(III) corrole. An energy level diagram was established to predict the photochemical events by using optical, emission, electrochemical, and computational data. The occurrence of charge separation from singlet excited zinc porphyrin and charge recombination to yield directly the ground state species were evident from the diagram. Femtosecond transient absorption spectroscopy studies provided spectral evidence of charge separation in the form of the zinc porphyrin radical cation and copper(II) corrole species as products. Rates of charge separation in the conjugates were found to be of the order of 10(10) s(-1) and increased with increasing multiplicity of copper(III) corrole entities. The present study demonstrates the importance of copper(III) corrole as an electron acceptor in building model photosynthetic systems.