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The photophysical consequences of replacing the nitrogen heteroatom in phenothiazine with methylene are investigated for both solutions and crystalline solids. We analysed the excited state dynamics of four xanthene derivatives and observed an anomalous fluorescence from an energy level higher than the S1 state with lifetimes between 2.8 ns and 5.8 ns in solution and as solids. Additionally, the solid-state xanthene derivatives exhibited long-lived emission consistent with a triplet excited state, displaying millisecond lifetimes that ranged from 0.1 ms to 3.4 ms at ambient temperature in air. Our findings were supported by optical studies, crystallographic structural analyses, and DFT computations, which corroborated the photophysical measurements. It was concluded that the presence of the nitrogen atom in phenothiazine is crucial for achieving ultra-long emission lifetimes and that these results contribute to a deeper understanding of excited state dynamics which have potential implications for applications, such as display technologies, anticounterfeiting technologies, and sensors. [ABSTRACT FROM AUTHOR]

A free-base tetraarylporphyrin was synthesized by the [2 + 2] macrocyclization of a dipyrromethane derivative with 3,4,5-tris(dodecyloxy)benzaldehyde in 61% yield. The free-base porphyrin was metallated with zinc acetate in 94% conversion. The free-base and metallated porphyrins show typical intense Soret bands at 426 and 425 nm, respectively, along with the expected number and intensity of Q-bands. Both porphyrins are also fluorescent and display small Stokes shifts between 13 and 18 nm. Cyclic voltammetry established that each porphyrin underwent two reversible one-electron oxidations at 492 and 725 mV (vs Fc/[Fc.sup.+] (ferrocene reference)) for the free-base porphyrin and at 329 and 589 mV (vs Fc/[Fc.sup.+]) for the Zn-metalloporphyrin. Electron-transfer rates were also determined to fall between 1.2 x [10.sup.-3] and 2.4 x [10.sup.-3] cm [s.sup.-1]. In addition, spectroelectrochemistry and density functional theory calculations of the oxidized products were carried out to confirm the macrocyclic ring oxidations. Key words: porphyrinoids, electrochemistry, redox chemistry, photochemistry, density functional calculations. On a realise la synthase d'une tetraaraylporphyrine sous la forme de base libre avec un rendement de 61 % par macrocyclisation [2 + 2] d'un derive; de dipyrromethane avec du 3,4,5-tris(docecyloxo)benzaldehyde. On a effectue la metallation de la porphyrine a l'etat de base libre, avec un rendement de 94 %, par traitement avec de l'acetate de zinc. La base libre et la porphyrine metallee presentent respectivement les bandes typiques intenses de Soret a 426 et a 425 nm ainsi que le nombre et l'intensite attendu des bandes Q. Les deux porphyrines sont aussi fluorescentes et elles presentent de faibles deplacements de Stokes, entre 13 et 18 nm. La voltamperometrie cyclique a permis d'etablir que chaque porphyrine subit deux oxydations reversibles a un electron, a 492 et 725 mV (vs Fc/[Fc.sup.+]) pour la base libre et a 329 et 589 mV (vs Fc/[Fc.sup.+]) pour la Zn-metalloporphyrine. On a aussi determine que les vitesses de transfert d'electron se situent entre 1,2 x [10.sup.-3] et 2,4 x [10.sup.-3] cm [s.sup.-1]. De plus, de la spectroelectrochimie et des calculs d'apres la theorie de la fonctionnelle de la densite effectues sur les produits oxydes pour confirmer les oxydations des noyaux macrocycliques. Mots-cles: porphyrinoldes, electrochimie, chimie d'oxydoreduction, photochimie, calculs de la fonctionnelle de la densite. [Traduit par la Redaction], Introduction Porphyrinoids are commonly found compounds in both the animal and plant kingdoms, as they play important roles in the key steps of photosynthesis that ultimately convert sunlight into chemical [...]

Microelectrode arrays having eight 10-[micro]m-diameter gold microelectrodes arranged on a gold-covered Si chip were designed and characterized. The chips prove useful for the detection of single-nucleotide mismatches in unlabeled and prehybridized DNA by electrochemical impedance spectroscopy.

The synthesis and characterization of a series of ferrocene (Fc-) and cystamine (CSA) peptides of the sequence [Fc-(Pro-Pro-Gly)n-CSA]2, where n=1-3 is conducted. Circular dichroism studies suggest significant parallels in the structure of the Fc-labeled peptide assemblies.

The detection of a single-nucleotide mismatch in unlabeled duplex DNA by electrochemical methods is presented. Impedance spectroscopy is used to characterize a perfect duplex monolayer and three DNA monolayers differing in the position of the mismatch. The monolayers were studied as B-DNA (normal duplex DNA) and after conversion to M-DNA (a metalated duplex). Modeling of the impedance data to an equivalent circuit provides parameters that are useful in discriminating the four monolayer configurations. The resistance to charge transfer, [R.sub.CT], was lower for all duplexes after conversion to M-DNA. Contrary to expectations, [R.sub.CT] was also found to decrease for duplexes containing a mismatch. However, [R.sub.CT] was found to be diagnostic for mismatch detection. In particular, the difference in [R.sub.CT] between B- and M-DNA ([DELTA][R.sub.CT]) decreased from 190(22) [OMEGA]x[cm.sup.2] for a perfectly matched duplex to 95(20), 30(20), and 85(20) [OMEGA]x[cm.sup.2] for a mismatch at the top (distal), middle, and bottom (proximal) positions of the monolayer with respect to the gold surface. Further, a method to form loosely packed single-stranded (ss)-DNA monolayers by duplex dehybridization that is able to rehybridize to target strands is presented. Rehybridization efficiencies were in the range of 40-70%. Under incomplete hybridization conditions, the [R.sub.CT] was the same for matched and mismatched duplexes under B-DNA conditions. However, [DELTA][R.sub.CT] between B- and M-DNA, under incomplete hybridization, still provided a distinction. The [DELTA][R.sub.CT] for a perfect duplex was 76(12) [OMEGA]x[cm.sup.2], whereas a mismatch in the middle of the sequence yielded a [DELTA][R.sub.CT] value of 30(15) [OMEGA]x[cm.sup.2]. The detection limit was measured and the impedance methodology reliably detected single DNA base pair mismatches at concentrations as low as 100 pM.

A new theory for relating the dielectric constant to the internal structure of association fluids containing any number of associating components, the molecules of which may posses any number of electronrich and electron-deficient sites is proposed.

The syntheses and full characterization of several symmetric ferrocenoyl (Fe)-peptide cystamines together with an unsymmetric Fc-Ala-Ala-CSA-Ala-Fc is reported. The results differ significantly from Hirao's work in disubstituted 1,1' -Fc-peptide systems which exhibit exclusively intramolecular H-bonding interactions, leading to chiral patterning in the solid state.

Exploration of the sterically‐congested ethane diethyl dixanthenyl‐9,9′‐dicarboxylate has revealed the dynamic behavior arising from its congested C−C bond. Interlocking 'geared' substituents and favorable dispersion interactions around this bond result in a conformational preference for partially cofacial xanthene moieties both in solid state and as dilute solutions. The weak, centrally located C−C bond is 1.628 Å long and permits selective thermolysis to yield two carbon‐centered ethyl xanthenyl‐9‐carboxylate radicals, which dimerize with high fidelity into the original sterically‐congested ethane. Recombination of the radicals into this symmetrical head‐to‐head dimer is highly reproducible – by observing the equilibrium, the bond dissociation enthalpy was calculated to be 20.4 kcal ⋅ mol−1. The substituents around the central carbon provide insufficient stabilization against oxygen, which consumes the radicals and unbalances the dimer‐radical equilibrium. [ABSTRACT FROM AUTHOR]

In the scientific literature, the term aqueous environment is loosely employed as it encompasses a broad range of different buffering agents. While there is an increasing number of experimental evidence that point toward specific buffer effects extending far beyond pH, the impact of the chemical nature of the buffering ions is often disregarded, especially in photochemical studies. Herein, we highlighted the importance of buffer specific effects on both the photobleaching and the singlet oxygen quantum yields of a dye in aqueous environments. For this study, we chose erythrosine B (EB) as our model photosensitizer as its photochemistry and photobleaching are well documented in the literature. We followed EB's photobleaching via absorption spectroscopy in four different aqueous solvents, including pure water, phosphate, Tris and HEPES buffer. These buffer systems were selected because they are commonly used in biochemical and biological applications. Our results show that specific buffer effects cannot be neglected. Indeed, the singlet oxygen quantum yield for EB is significantly different in HEPES compared to the other solvents. Furthermore, we showed that EB's photoproduct is highly dependent on the nature of the chemical buffer being used. [ABSTRACT FROM AUTHOR]

In the scientific literature, the term aqueous environment is loosely employed as it encompasses a broad range of different buffering agents. While there is an increasing number of experimental evidence that point toward specific buffer effects extending far beyond pH, the impact of the chemical nature of the buffering ions is often disregarded, especially in photochemical studies. Herein, we highlighted the importance of buffer specific effects on both the photobleaching and the singlet oxygen quantum yields of a dye in aqueous environments. For this study, we chose erythrosine B (EB) as our model photosensitizer as its photochemistry and photobleaching are well documented in the literature. We followed EB's photobleaching via absorption spectroscopy in four different aqueous solvents, including pure water, phosphate, Tris and HEPES buffer. These buffer systems were selected because they are commonly used in biochemical and biological applications. Our results show that specific buffer effects cannot be neglected. Indeed, the singlet oxygen quantum yield for EB is significantly different in HEPES compared to the other solvents. Furthermore, we showed that EB's photoproduct is highly dependent on the nature of the chemical buffer being used. [ABSTRACT FROM AUTHOR]

A study is conducted to characterizes that (ferrocenoyl) Fc-labeled (double stranded)ds-DNA can form reproducible monolayers on Au (gold) surfaces. In this a comparison of two configurations is made which differ only in the Fc attachment point.

Abstract: Herein, we report the synthesis, electrochemical, and computational evaluation of six 2‐substituted imidazolium bromides and six 2‐substituted imidazolium triflates. All final compounds were obtained in 2 or fewer synthetic steps from inexpensive starting materials and display a single, irreversible electrochemical reduction. The reduction potentials span a range greater than 1 V depending on the electron withdrawing power of the 2‐substituent. Imidazolium bromides such as Bn2(H)ImBr reduce with E1/2 = −2.70 V vs Fc/Fc+, whereas the electron‐withdrawing Br‐containing analog Bn2(Br)ImBr reduces at only −1.58 V vs Fc/Fc+. The reduction potential of imidazolium bromides obeys a linear free energy relationship to σm Hammett constants, whereas imidazolium triflates correlate better with the σp Hammett constants. These results indicate that the stabilizing effect of the 2‐substituent is anion‐sensitive, changing from induction to resonance upon exchanging bromide for triflate. Predicted electron affinities from density functional theory–optimized structures of imidazolium cations and reduced species more closely match experimental data for the triflates, suggesting that a triflate anion does not electronically perturb the imidazolium core as much as a bromide. Taken together, these data highlight the dual modularity of imidazolium salts by changing both 2‐substituent and anion. [ABSTRACT FROM AUTHOR]