Toward Volatile and Nonvolatile Molecular Memories: Fluorescence Switching Based on Fluoride-Triggered Interconversion of Simple Porphyrin Derivatives

Analyte Interactions with Oxoporphyrinogen Derivatives: Computational Aspects

Abstract:

The binding of anions by highly-coloured chromophore compounds is of interest from the point-of-view of the development of optical sensors for analyte species. In this review, we have summarised our work on the interactions between oxoporphyrinogen type host compounds and different analyte species using computational methods. The origin of our interest in sensing using oxoporphyrinogens stems from an initial finding involving anion-host interactions involving a conjugated oxoporphyrinogen molecule. This review starts from that point, introducing some additional exemplary anion binding data, which is then elaborated to include descriptions of our synthesis work towards multitopic and ion pair interactions. In all the projects, we have consulted computational data on host structure and host-guest complexes in order to obtain information about the interactions occurring during complexation. Density functional theory and molecular dynamics simulations have been extensively used for these purposes. Oxoporphyrinogens are highly colored synthetically flexible compounds whose interactions with anions, ion pairs, and other species have been modelled using computational methods.

Fused Nickel(II) Porphyrins-Sensing of Toxic Anions and Selected Metal Ions Through Supramolecular Interactions

Ni(II) porphyrins having fused -NH group were synthesized and characterized by various spectroscopic techniques. The fused porphyrins 1 and 2 were used to detect species of opposite polarity. 1 was used to sense toxic anions viz. cyanide and fluoride ions whereas 2 was used for detecting some selective metal ions including toxic mercury(II) ions. 1 is having acidic -NH proton, which detects anions via hydrogen bonding interactions followed by anion-induced deprotonation. On the other hand, 2 senses the metal species via weak charge transfer interactions from oxygen atom of the formyl group to the added metal ions. The limit of detection was calculated in case of 1 as 2.13 and 3.15 ppm for cyanide and fluoride ions, respectively. Similarly, the detection limit was found to be 0.930, 2.231, and 0.718 ppm for Cu(II), Fe(III), and Hg(II) ions, respectively, for probe 2. The probes were recovered and reused for several cycles.

Photoacoustic Detection of Superoxide Using Oxoporphyrinogen and Porphyrin

The superoxide (O₂^•-) ion is a highly reactive oxygen species involved in many diseases; hence, its noninvasive detection is desirable to identify the onset of pathological processes. Here, we employed photoacoustic (PA) spectroscopy, which enables imaging at ultrasound resolution with the sensitivity of optical modality, for the first time to detect O₂^•-, using stimuli-responsive contrast agents. meso-(3,5-Di-tert-butyl 4-hydroxyphenyl) porphyrins and oxoporphyrinogens were used as PA contrast agents, which trap the O₂^•- and enable its detection. The trapped O₂^•- increased the PA signal amplitude of chromophores up to 9.6-fold, and induced a red-shift in the PA signal maxima of up to 225 nm. Therefore, these trigger-responsive probes may be highly valuable as smart diagnostic PA probes to investigate pathological events stimulated by O₂^•- species.

Switching between porphyrin, porphodimethene and porphyrinogen using cyanide and fluoride ions mimicking volatile molecular memory and the ‘NOR’ logic gate

β-Substituted porphyrins were developed as a quantitatively operating “lab-on-a-molecule” for the detection of F⁻and CN⁻ions, by switching between porphyrin, porphodimethene and porphyrinogen along with distinct solution colour changes and reversibility.

Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

Naked-eye discrimination of methanol from ethanol using composite film of oxoporphyrinogen and layered double hydroxide

Methanol is a highly toxic substance, but it is unfortunately very difficult to differentiate from other alcohols (especially ethanol) without performing chemical analyses. Here we report that a composite film prepared from oxoporphyrinogen (OxP) and a layered double hydroxide (LDH) undergoes a visible color change (from magenta to purple) when exposed to methanol, a change that does not occur upon exposure to ethanol. Interestingly, methanol-induced color variation of the OxP-LDH composite film is retained even after removal of methanol under reduced pressure, a condition that does not occur in the case of conventional solvatochromic dyes. The original state of the OxP-LDH composite film could be recovered by rinsing it with tetrahydrofuran (THF), enabling repeated usage of the composite film. The mechanism of color variation, based on solid-state (13)C-CP/MAS NMR and solution-state (13)C NMR studies, is proposed to be anion transfer from LDH to OxP triggered by methanol exposure.

Design of a universal reversible bidirectional current switch based on the fullerene-phthalocyanine supramolecular system

A novel bidirectional current ON-OFF switch controlled by electron injection and deprivation was proposed on the basis of the density functional theory (DFT) calculation over a fullerene-phthalocyanine supramolecular system PcCoC(60) for the first time. The electron density for PcCoC(60) was revealed to move from fullerene to phthlocyanine only in the oxidized form and from phthlocyanine to fullerene only in the reduced form, reaching the control of electron movement direction by changing the oxidation state of this supramolecular system.

Reversible photoredox switching of porphyrin-bridged bis-2,6-di-tert-butylphenols

Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV-vis spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions. Conversely, photoreduction occurs in the presence of a sacrificial electron donor. Transient absorption spectroscopy and electron spin resonance spectroscopy were applied to investigate the processes in photochemical reaction, and radical intermediates were characterized. That is, photooxidation initially results in a phenol-substituent-centered radical, while the reduction process occurs via a delocalized radical state involving both the macrocycle and 5,15-substituents. Forward and reverse photochemical processes are governed by different chemical mechanisms, giving the important benefit that conversion reactions are completely isolated, leading to better separation of the end states. Furthermore, energy diagrams based on electrochemical analyses (cyclic voltammetry) were used to account for the processes occurring during the photochemical reactions. Our molecular design indicates a simple and versatile method for producing photoredox macrocyclic compounds, which should lead to a new class of advanced functional materials suitable for application in molecular devices and machines.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the year 2009

This critical review is focused on examples reported in the year 2009 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions (264 references).

Self-assembly of optical molecules with supramolecular concepts

Fabrication of nano-sized objects is one of the most important issues in nanoscience and nanotechnology. Soft nanomaterials with flexible properties have been given much attention and can be obtained through bottom-up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and techniques. Among the various functional molecules, dyes have become important materials in certain areas of nanotechnology and their self-assembling behaviors have been actively researched. In this short review, we briefly introduce recent progress in self-assembly of optical molecules and dyes, based mainly on supramolecular concepts. The introduced examples are classified into four categories: self-assembly of (i) low-molecular-weight dyes and (ii) polymeric dyes and dye self-assembly (iii) in nanoscale architectures and (iv) at surfaces.