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Photoinduced twisted intramolecular charge transfer (TICT) of meso-(4-dimethylamino)phenylamino subporphyrin 2 and meso- (4-nitro)phenylamino subporphyrin 3 has been revealed by steady- state and time-resolved absorption/fluorescence experiments and quantum calculations. Subporphyrins 2 and 3 undergo molecular twisting at the Cmeso-N bond and the N-Cipso bond, respectively, to trigger intramolecular charge separation, which is restricted at low temperature or in viscous paraffin oil with concurrent fluorescence recovery of local excited states. [ABSTRACT FROM AUTHOR]

A p-extended tetrathiafulvalene-boradiazaindacene chimera, ex-TTFBODIPY, has been prepared. The resulting system undergoes sequential one-electron oxidations, allowing access to both the mono-oxidized radical cationic and dicationic states. Additionally, ex-TTF-BODIPY displays electrochromic and electrofluorochromic behaviour in the near-IR portion of the electromagnetic spectrum and functions as a redox switched ''on-off-on'' emissive system. [ABSTRACT FROM AUTHOR]

An o-phenylenevinylene-bridged tetrapyrrolic macrocycle (2) was synthesized by means of a Horner-Wadsworth-Emmons reaction between benzylbisphosphonate and SEM-protected diformylpyrrole, followed by deprotection of the SEM groups. This conformationally flexible tetrapyrrole can be considered as an expanded calix[4]pyrrole analogue, which acts as a receptor for the chloride and bromide anions in THF-d8, but undergoes deprotonation upon exposure to the fluoride anion. [ABSTRACT FROM AUTHOR]

Recently, expanded porphyrins have come to the forefront in the research field of aromaticity, and been recognized as the most appropriate molecular system to study both Hückel and Möbius aromaticity because their molecular topologies can be easily changed and controlled by various methods. Along with this advantage, many efforts have been devoted to the exploration of the aromaticity–molecular topology relationship based on electronic structures in expanded porphyrins so that further insight into the aromaticity – a very attractive field for chemists – can be provided. In this tutorial review, we describe the recent developments of various topology-controlled expanded porphyrins and their photophysical properties, in conjunction with the topological transformation between Hückel and Möbius aromaticity by various conformational control methods, such as synthetic methods, temperature control, and protonation. [ABSTRACT FROM AUTHOR]

During the last decade, molecular photonics has been highlighted in the field of materials chemistry, providing the possibility of the construction of photonic devices at individual molecular level. In parallel, well-established single molecule fluorescence spectroscopy enables us to assess the functionality of individual devices in the solid state, as such, to propose a better design for actual utilization. In this Highlight, we discuss our single molecule investigations on the excitation energy transfer processes and the conformational dynamics occurring in various porphyrin arrays with a particular focus on the applicability as photonic materials. For the fabrication of molecular photonic devices in the solid state, the maintenance of structural rigidity is of utmost importance to achieve efficient signal transmission. [ABSTRACT FROM AUTHOR]

Porphyrins, which consist of four pyrrolic subunits, are a ubiquitous class of naturally occurring compound with versatile photophysical properties. As an extension of the basic structure of the porphyrin macrocycle, there have been a multitude of approaches to synthesize expanded porphyrins with more than four pyrrole rings, leading to the modification of the macrocyclic ring size, planarity, number of π-electrons and aromaticity. However, the relationship between the photophysical properties and the structures of expanded porphyrins has not been systematically investigated. The main purpose of this article is to describe the structure–property relationships of a variety of expanded porphyrins based on experimental and theoretical results, which include steady-state and time-resolved spectroscopic characterizations, non-linear absorption ability and nucleus-independent chemical shift calculations. [ABSTRACT FROM AUTHOR]

We have constructed supramolecular solar cells composed of a series of porphyrin–peptide oligomers [porphyrin functionalized α-polypeptides, P(H2P)n or P(ZnP)n (n = 1, 2, 4, 8, 16)], and fullerenes assembled on a nanostructured SnO2 electrode using an electrophoretic deposition method. Remarkable enhancement in the photoelectrochemical performance as well as the broader photoresponse in the visible and near-infrared regions is seen with increasing the number of porphyrin units in α-polypeptide structures. Formation of supramolecular clusters of porphyrins and fullerenes prepared in acetonitrile–toluene = 3 : 1 has been confirmed by transmission electron micrographs (TEM) and the absorption spectra. The highly colored composite clusters of porphyrin–peptide oligomers and fullerenes have been assembled as three-dimensional arrays onto nanostructured SnO2 films using an electrophoretic deposition method. A high power conversion efficiency (η) of ∼1.6% and the maximum incident photon-to-photocurrent efficiency (IPCE = 56%) were attained using composite clusters of free base and zinc porphyrin–peptide hexadecamers [P(H2P)16 and P(ZnP)16] with fullerenes, respectively. Femtosecond transient absorption and fluorescence measurements of porphyrin–fullerene composite films confirm improved electron-transfer properties with increasing number of porphyrins in a polypeptide unit. The formation of molecular assemblies between porphyrins and fullerenes with a polypeptide structure controls the electron-transfer efficiency in the supramolecular complexes, meeting the criteria required for efficient light energy conversion. [ABSTRACT FROM AUTHOR]

A series of phenylene-bridged subporphyrin--Zn(II) porphyrin (SubP-ZnP) hybrid systems undergo extraordinarily fast excitation energy transfer (EET) processes from the SubP to the ZnP, aided by conjugative electronic elongation of the SubP to the phenylene-bridge. [ABSTRACT FROM AUTHOR]

In a series of thiaaceneporphyrinoids, their conformers exhibit macro-cyclic π-conjugation pathways controlled by a dihedral angle between the porphyrin framework and acene planes. Conformational equilibria significantly affect the photophysical properties of these macrocycles. [ABSTRACT FROM AUTHOR]

The role of thiophene bridges in determining the photophysical properties of bridged core-modified hexaphyrins is investigated. Depending on the substituted chalcogen atoms and conjugational perturbation across the thiophene bridges, the bridged coremodified hexaphyrins reveal unique photophysical properties. [ABSTRACT FROM AUTHOR]

A macrocyclic host, a pair of zinc porphyrins bridged by two anion-acceptable indolocarbazole moieties, has shown strong positive homotropic allosterism upon anionic guest bindings with an inhibitory control mechanism by DABCO addition. [ABSTRACT FROM AUTHOR]

Doubly and triply N-confused hexaphyrins revealed quite unique photophysical properties arising from confusion of pyrrole rings in the macrocycle, and the molecular shape when compared with their parent regular hexaphyrin molecules. [ABSTRACT FROM AUTHOR]

Metalation of [28]hexaphyrin(1.1.1.1.1.1) with [RhCl(CO)2]2 resulted in the formation of an antiaromatic bis-Rh(I) complex, which can be oxidized to an aromatic bis-Rh(I) complex with retention of its rectangular structure. [ABSTRACT FROM AUTHOR]

An investigation of the photophysics of Ir(iii) complexes with controlled ligand structures and our quantum chemical calculations attest that the most probable explanation for the reported ‘aggregation-induced phosphorescent emission’, which was originally claimed to be related to an intermolecular excimer, is restricted intramolecular motion. [ABSTRACT FROM AUTHOR]

Intramolecular charge transfer in 5,15-bis(azulenylethynyl) substituted zinc(ii) porphyrin leads to a significant enhancement of two-photon absorption at near-IR region, which has been investigated by femtosecond Z-scan method. [ABSTRACT FROM AUTHOR]

Using the bidirectional NICS scan method in conjunction with two-photon absorption (TPA) measurements, it has proved possible to determine the relationship between π-conjugation and aromaticity in two structurally related expanded porphyrin systems, sapphyrin and inverted sapphyrin, and establish that differences in these defining factors depend on the presence or absence of a key sp3 hybrid molecular orbital within the macrocyclic periphery. [ABSTRACT FROM AUTHOR]