Persubstituted Triphenylamine Bearing Zinc Porphyrin to Host Endohedral Fullerene, Sc3N@C80: Formation and Excited State Electron Transfer

Intramolecular Photoinduced Energy and Electron Transfer Reactions in Phenanthroimidazole-Boron Dipyromethane Donor-Acceptor Dyads

Donor-acceptor systems in which a donor phenanthroimidazole (PhI) is directly connected to a BODIPY acceptor (Dyad1) and separated by an ethynyl bridge between PhI and BODIPY (Dyad2) have been designed, synthesized, and characterized by various spectroscopic and electrochemical techniques. Optical absorption and 1H NMR characteristics of both dyads with those of constituent individuals suggest that there exists a minimum π-π interaction between phenanthroimidazole and BODIPY. Quenched emission of both the dyads was observed when excited either at phenthaoimidazole absorption maxima or at BODIPY absorption maxima in all three investigated solvents. The detailed spectral analysis provided evidence for an intramolecular photoinduced excitation energy transfer (PEnT) from the singlet excited state of phenanthroimidazole to BODIPY and photoinduced electron transfer (PET) from the ground state of phenanthroimidazole to BODIPY. Transient absorption studies suggest that charge-separated species (PhI•+ - BODIPY•-) are generated at a rate constant of (1.16 ± 0.01) × 108 s-1 for the dyads Dyad1 and (5.15 ± 0.03) × 108 s-1 and for Dyad2 whereas energy transfer rate constants were much higher and were on the order of (1.1 ± 0.02) × 1010 s-1 and (1.6 ± 0.02) × 1010 s-1 for Dyad1 and Dyad2, respectively, signifying their usefulness in light energy harvesting applications.

Nonplanar porphyrins: synthesis, properties, and unique functionalities

Porphyrins are variously substituted tetrapyrrolic macrocycles, with wide-ranging biological and chemical applications derived from metal chelation in the core and the 18π aromatic surface. Under suitable conditions, the porphyrin framework can deform significantly from regular planar shape, owing to steric overload on the porphyrin periphery or steric repulsion in the core, among other structure modulation strategies. Adopting this nonplanar porphyrin architecture allows guest molecules to interact directly with an exposed core, with guest-responsive and photoactive electronic states of the porphyrin allowing energy, information, atom and electron transfer within and between these species. This functionality can be incorporated and tuned by decoration of functional groups and electronic modifications, with individual deformation profiles adapted to specific key sensing and catalysis applications. Nonplanar porphyrins are assisting breakthroughs in molecular recognition, organo- and photoredox catalysis; simultaneously bio-inspired and distinctly synthetic, these molecules offer a new dimension in shape-responsive host-guest chemistry. In this review, we have summarized the synthetic methods and design aspects of nonplanar porphyrin formation, key properties, structure and functionality of the nonplanar aromatic framework, and the scope and utility of this emerging class towards outstanding scientific, industrial and environmental issues.

Synthesis, Optical Properties, and Electrochemical Behavior of 5,10,15,20-Tetraaryl-5,15-diazaporphyrin-Amine Hybrids

This work reports a series of covalently linked hybrids comprising 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAP; M = Ni, Zn, Cu) and amines. M-TADAP-amine hybrids were prepared via the metal-templated cyclization of the corresponding metal(II)-dipyrrin complexes and redox reactions on the DAP unit. In the UV/vis/near-IR absorption spectra of the hybrids containing an 18π-electron DAP ring, broad charge-transfer bands were observed, reflecting the electron-donating property of the para-aminophenyl groups and the electron-accepting property of the 18π TADAP dication. The electrochemical behavior of the M-TADAP-amine hybrids was strongly dependent on the structure of the peripheral amine units. Further electrochemical oxidation of the hybrids bearing N-Ph groups conceivably generated amine-centered radicals, which sequentially underwent irreversible coupling to form benzidine-linked M-TADAP polymer films. The Ni-TADAP-benzidine polymer exhibited the electric conductivity of 1×10^-3  S m^-1 .