Functionalization of Carbon Spheres with a Porphyrin-Ferrocene Dyad

Nonlinear Optical Properties of Zn(II) Porphyrin, Graphene Nanoplates, and Ferrocene Hybrid Materials

Following some previous work by some of us on the second order nonlinear optical (NLO) properties of Zn(II) meso-tetraphenylporphyrin (ZnP), fullerene, and ferrocene (Fc) diads and triads, in the present research, we explore the NLO response of some new hybrids with two-dimensional graphene nanoplates (GNP) instead of a zero-dimensional fullerene moiety as the acceptor unit. The experimental data, collected by Electric Field Induced Second Harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, combined with Coupled-Perturbed (CP) and Finite Field (FF) Density Functional Theory (DFT) calculations, show a strongly enhanced contribution of the cubic electronic term γ(-2ω; ω, ω, 0), due to the extended π-conjugation of the carbonaceous acceptor moiety.

Effects of linkage between donors on photoinduced charge transfer in one-photon and two-photon absorption of Donor-π-Donor-π-Acceptor conjugates

Photoinduced charge transfer (CT) mechanisms of two Donor-π-Donor-π-Acceptor conjugates composed of ferrocene (Fc), zinc-porphyrin (ZnP), and fullerene (C₆₀) linked by phenylene-acetylene/acetylene during the one- (OPA) and the two-photon absorption (TPA) processes are analyzed theoretically based on the density functional theory calculations and visualization methods to study the effects of linkage between the two donors on the excitation characteristics. The change of bridge affects the efficiency of superexchange CT from Fc to ZnP in the OPA process. The one-photon excitations are dominated by local transitions of ZnP and Fc, and there is almost no efficient CT from the donors to the acceptor for both the two researched structures. In contrast, the advantage of superexchange CT from ZnP to C₆₀ becomes much larger than the other transition forms during the TPA process when the linkage between ZnP and Fc is changed from acetylene to phenylene-acetylene. This linkage effect in TPA would have great significance in designing novel optoelectronic devices.

Functionalization of Gold Nanoparticles with Ru-Porphyrin and Their Selectivity in the Oligomerization of Alkynes

Gold nanoparticles (AuNPs) were functionalized by ruthenium porphyrins through a sulfur/gold covalent bond using a three-steps reaction. The catalyst was characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) in order to control the binding of ruthenium porphyrin on AuNPs’ surface. The catalyst was tested and compared with an analog system not bound to AuNPs in the oligomerization reaction using 1-phenylacetylene as the substrate.

Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(-2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(-2ω; ω, ω)/5kT, as confirmed by computational evidence.

Designing Cascades of Electron Transfer Processes in Multicomponent Graphene Conjugates

A novel family of nanocarbon-based materials was designed, synthesized, and probed within the context of charge-transfer cascades. We integrated electron-donating ferrocenes with light-harvesting/electron-donating (metallo)porphyrins and electron-accepting graphene nanoplates (GNP) into multicomponent conjugates. To control the rate of charge flow between the individual building blocks, we bridged them via oligo-p-phenyleneethynylenes of variable lengths by β-linkages and the Prato-Maggini reaction. With steady-state absorption, fluorescence, Raman, and XPS measurements we realized the basic physico-chemical characterization of the photo- and redox-active components and the multicomponent conjugates. Going beyond this, we performed transient absorption measurements and corroborated by single wavelength and target analyses that the selective (metallo)porphyrin photoexcitation triggers a cascade of charge transfer events, that is, charge separation, charge shift, and charge recombination, to enable the directed charge flow. The net result is a few nanosecond-lived charge-separated state featuring a GNP-delocalized electron and a one-electron oxidized ferrocenium.

Panchromatic Light Harvesting and Stabilizing Charge-Separated States in Corrole-Phthalocyanine Conjugates through Coordinating a Subphthalocyanine

Owing to the electron-donating and -accepting nature of corroles (Corr) and phthalocyanines (Pc), respectively, we designed and developed two novel covalently linked Corr-Pc conjugates. The synthetic route allows the preparation of the target conjugates in satisfying yields. Comprehensive steady-state absorption, fluorescence, and electrochemical assays enabled insights into energy and electron-transfer processes upon photoexcitation. Coordinating a pyridine-appended subphthalocyanine (SubPc) to the Pc of the conjugate sets up the ways and means to realize the first example of an array composed by three different porphyrinoids, which drives a cascade of energy and charge-transfer processes. Importantly, the SubPc assists in stabilizing the charge-separated state, that is, one-electron oxidized Corr and the one electron-reduced Pc, upon photoexcitation by means of a reductive charge transfer to the SubPc. To the best of our knowledge, this is the first case of an intramolecular oxidation of a Corr within electron-donor-acceptor conjugates by means of just photoexcitation. Moreover, the combination of Corr, Pc, and SubPc guarantees panchromatic absorption across the visible range of the solar spectrum, with the SubPc covering the "green gap" that usually affects porphyrinoids.

Efficient Sunlight Harvesting by A4 β-Pyrrolic Substituted ZnII Porphyrins: A Mini-Review

Dye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived π^* singlet excited states. Moreover, the presence of four meso and eight β-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans-A₂BC push-pull Zn^II porphyrins, characterized by a strong and directional electron excitation process along the push-pull system, have been extensively investigated. On the other hand, A₄ β-pyrrolic substituted tetraaryl Zn^II porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A₄ β-substituted Zn^II porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso-substituted analogs.