Synthesis, Electronic and Photophysical Characterization of π-Conjugated meso-Ferrocenyl-porphyrin Fluorescent Redox Switches

Photophysical and Electrochemical Properties of Push-Pull Oligo(ferrocenyl-phenyleneethynylene)s: Supramolecular Orders in Molecular Films

We report on the optoelectronic properties of a series of unsymmetrical π-conjugated phenyleneethynylene macromolecules bearing ferrocene (Fc) as the electron-donor group (D), (benzyl) benzoate (Bz) or benzoic acid (Ac) as the electron attractor group (A) and connected through 2,5-di(alcoxy) phenyleneethynylene(s) (nPE) with n = 1, 2, 3 as π-conjugated bridges. In the series, by increasing the distance between the electron-attracting and electron-donor groups, the push-pull effect decreases. The intramolecular charge transfer (D → π → A) was evaluated by static and dynamic spectroscopy, electrochemistry, and density functional theory (DFT) theoretical calculations. The longest oligomer Fc3PEBz formed the best optical quality films. A study at the atomic level by scanning tunneling microscopy (STM) revealed that the molecules self-assemble on highly ordered pyrolytic graphite (HOPG) in domains with a short-range order. Films are mesoporous and the molecules arrange in a lamellar-like pattern, with an edge-on conformation with respect to HOPG, where the conjugated backbones lie parallel to the surface. Two different assemblies were identified in the monoatomic film, which depends on the ferrocene-ferrocene or benzyl-benzyl interactions.

Two state “ON–OFF” NLO switch based on coordination complexes of iron and cobalt containing isomeric ligand: a DFT study

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values. Moreover, switchable NLO response is also important in coordination complexes. Herein, we report two state ON–OFF switchable NLO contrast of coordination complexes of Fe and Co containing isomeric ligands. The optical, UV-visible, and electronic properties besides the “ON–OFF” switching effect are calculated using the CAM-B3LYP/6-31+G (d) method. The NLO responses of ligand–metal isomers are qualitatively evaluated through variation in charge transference (CT) style through TD-DFT. The higher β_o in each isomeric pair is strongly dependent on the HOMO–LUMO gap. The isomer 4b with lowest HOMO–LUMO gap shows the highest NLO response. The charge transfer pattern in these complexes results in variation of their β_o values. The notable β_o contrast of 21.15 in isomeric pairs 3a and 3b makes these complexes a favorable material for genuine NLO switches. Hence, the outcome of the current investigation reveals that these ligand–metal isomeric complexes exhibit a two-state switch “ON–OFF” effect.

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values.

Second-order NLO properties and two-state switching effects of transition metal redox complexes of iron and cobalt: A DFT study

Designing switchable materials with large contrasts of nonlinear optical properties has been the focus of research in recent decades because of their widespread applications. Redox-active metal complexes due to charge transfer excitation are suitable to produce switchable nonlinear optical (NLO) material. In this regard, we present here the redox switchable NLO response of active metal complexes of iron and cobalt. The geometric, electronic, molecular absorption, nonlinear optical properties, and switch "ON/OFF" style of these metal complexes are studied at the CAM-B3LYP/6-31 + G(d) level of theory. NLO responses of these redox metal complexes are described in terms of change in the charge transfer (CT) patterns by time dependent density functional theory (TD-DFT). The highest β_o value of 301534 × 10^-30 esu is noticed in [Fe-ethynyl-ZnP]¹⁺ complex, because of obvious charge transfer transition from metal to ligand i.e meatal-ligand charge transfer (MLCT) in redox metal complex. In each redox metal isomeric pair, the greater hyperpolarizability value of individual isomer is quite consistent with its smaller energy gap (H-Lgap) between highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), low crucial excitation energy, and bathochromic shift of λ_max. The remarkable β_o contrasts of these isomeric redox complexes illustrate that they can be appropriate for effective redox-triggered NLO switches. Thus, the results reveal that these redox pair complexes show two-state switching "ON/OFF" effect.

Similar, Yet Different: Long-Range Metal-Metal Coupling and Electron-Transfer Processes in Metal-Free 5,10,15,20-Tetra(ruthenocenyl)porphyrin

The electronic structure, redox properties, and long-range metal-metal coupling in metal-free 5,10,15,20-tetra(ruthenocenyl)porphyrin (H₂TRcP) were probed by spectroscopic (NMR, UV-vis, magnetic circular dichroism (MCD), and atmospheric pressure chemical ionization (APCI)), electrochemical (cyclic voltammetry, CV, and differential pulse voltammetry, DPV), spectroelectrochemical, and chemical oxidation methods, as well as theoretical (density functional theory, DFT, and time-dependent DFT, TDDFT) approaches. It was demonstrated that the spectroscopic properties of H₂TRcP are significantly different from those in H₂TFcP (metal-free 5,10,15,20-tetra(ferrocenyl)porphyrin). Ruthenocenyl fragments in H₂TRcP have higher oxidation potentials than the ferrocene groups in the H₂TFcP complex. Similar to H₂TFcP, we were able to access and spectroscopically characterize the one- and two-electron oxidized mixed-valence states in the H₂TRcP system. DFT predicts that the porphyrin π-system stabilizes the [H₂TRcP]⁺ mixed-valence cation and prevents its dimerization, which is characteristic for ruthenocenyl systems. However, formation of the mixed-valence [H₂TRcP]²⁺ is significantly less reproducible than the formation of [H₂TRcP]⁺. DFT and TDDFT calculations suggest the ruthenocenyl fragment dominance in the highest occupied molecular orbital (HOMO) energy region and the presence of the low-energy MLCT (Rc → porphyrin (π*)) transitions in the visible region with energies higher than the predominantly porphyrin-centered Q-bands.

A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-Pyridyl Zinc Porphyrins

Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct ¹ H NMR spectrum in CDCl₃ , which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the ¹ H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.

A mechanistic study of microstructure modulation in olefin polymerizations using a redox-active Ni(ii) α-diimine catalyst

Density functional theory and experimental evidence provide insight into the mechanism of polyolefin microstructure modulation using redox-active Ni(ii) α-diimine catalysts.

Diaqua-β-octaferrocenyltetraphenylporphyrin: a multiredox-active and air-stable 16π non-aromatic species

Herein the synthesis and properties of the first β-octaferrocenyltetraphenylporphyrin, {TPPFc₈(H₂O)₂}, in its extraordinary stable and non-aromatic 16π form are reported, showing seven separate reversible redox events.

Redox-driven porphyrin based systems for new luminescent molecular switches

This work explores the possibility of controlling the fluorescence of porphyrins via oxidation of a ruthenium acetylide unit. The modulation depends on the nature of the porphyrin unit(s).

Rigid triarylamine donor–π–acceptor porphyrin dyes and their application in dye-sensitized solar cells

Three donor–π–acceptor porphyrin dyes bearing the rigid 5-phenyl-carbazole, 5-phenyl-iminodibenzyl and 5-phenyl-iminostilbene donor groups were synthesized and their performance evaluated in TiO₂ based dye-sensitized solar cells.

Photoinduced electron transfer as a design concept for luminescent redox indicators

The exploitation of photoinduced electron transfer as a general design principle for the development of luminescent redox indicators and logic gates is described. Potential future applications in biology, environmental analysis, biomedical diagnostics, corrosion science and materials science are mentioned.