Towards More Photostable,Brighter, and Less Phototoxic Chromophores: Synthesis and Properties of Porphyrins Functionalized with Cyclooctatetraene

Free base and zinc porphyrins functionalized with cyclooctatetraene (COT), a molecule known as a good triplet-state quencher, have been obtained and characterized in detail by structural, spectral, and photophysical techniques. Substitution with COT leads to a dramatic decrease of the intrinsic lifetime of the porphyrin triplet. As a result, photostability in oxygen-free solution increases by two to three orders of magnitude. In non-degassed solutions, improvement of photostability is about tenfold for zinc porphyrins, but the free bases become less photostable. Similar quantum yields of photodegradation in free base and zinc porphyrins containing the COT moiety indicate a common mechanism of photochemical decomposition. The new porphyrins are expected to be much less phototoxic, since the quantum yield of singlet oxygen formation strongly decreases because of the shorter triplet lifetime. The reduction of triplet lifetime should also enhance the brightness and reduce blinking in porphyrin chromophores emitting in single-molecule regime, since the duration of dark OFF states will be shorter.     

Thermal and Photophysical Properties of Highly Quadrupolar Liquid-Crystalline Derivatives of the [closo-B12H12]2− Anion

Two series of 1,12-bis-zwitterionic derivatives of the [closo-B₁₂H₁₂]²⁻ anion ( B ), containing either two 4-alkoxypyridinium groups ( 1B[n]-p ) or one 4-alkoxypyridinium and one 4-pentylthianium groups ( 2B[n]-p ), were prepared and their structural (XRD, DFT), thermal, and photophysical properties were compared with those of the analogous derivatives of the [closo-B₁₀H₁₀]²⁻ anion ( 1A[n]-p and 2A[n]-p ). Some 1,7-derivatives of B were isolated and investigated. Both series 1[n] and 2[n] exhibit nematic and crystalline polymorphism; the 12-vertex derivatives ( B ) have higher transition temperatures than those of the 10-vertex analogues ( A ). All compounds fluoresce with quantum yields higher for 1B (Φ_F=0.37 for 1B[7]-p and Φ_F=0.27 for 2B[7]-p ) than those for the 10-vertex analogues (Φ_F=0.04 for 2A[5]-p ). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, β_(−ω,ω,0), for 2B[7]-p than that for the 10-vertex analogue 2A[7]-p (1.7×10⁻³⁰ vs. 18.9×10⁻³⁰ esu at ω=0).     

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

The properties of the intramolecular hydrogen bonds of doubly ¹⁵N‐labeled protonated sponges of the 1,8‐bis(dimethylamino)naphthalene (DMANH⁺) type have been studied as a function of the solvent, counteranion, and temperature using low‐temperature NMR spectroscopy. Information about the hydrogen‐bond symmetries was obtained by the analysis of the chemical shifts δ_H and δ_N and the scalar coupling constants J(N,N), J(N,H), J(H,N) of the ¹⁵NH¹⁵N hydrogen bonds. Whereas the individual couplings J(N,H) and J(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum |J(N,H)+J(H,N)| generally represents a measure of the hydrogen‐bond strength in a similar way to δ_H and J(N,N). The NMR spectroscopic parameters of DMANH⁺ and of 4‐nitro‐DMANH⁺ are independent of the anion in the case of CD₃CN, which indicates ion‐pair dissociation in this solvent. By contrast, studies using CD₂Cl₂, [D₈]toluene as well as the freon mixture CDF₃/CDF₂Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroacetate perturbed the hydrogen bond, the large noncoordinating anion tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate B[{C₆H₃(CF₃)₂}₄]^? (BARF^?), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high‐field shifts of the hydrogen‐bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates.     

The influence of external uniaxial stretching on the electromigration and diffusion of hydrogen in iron

Electromigration and diffusion of hydrogen in iron, depending on unit elongation, were investigated. The resistivity method was applied in the investigations. It was found that the obtained experimental results cannot be described by means of a single flux of hydrogen, which diffuses in the electric field. In order to explain the obtained results, we assumed the existence of the following two fluxes of hydrogen in the stretched metal: migration, according to the interstitial mechanism, and migration according to the interstitial-defective mechanism. The dependence of effective valences and diffusion coefficients for both mechanisms were determined.     

Enthalpic interaction coefficients of NaI–alkanediol pairs in methanol and in water

The dissolution enthalpies of NaI in the mixtures of methanol with 1,2-alkanediols (1,2-propanediol, 1,2-butanediol, 1,2-pentanediol) and with ??,??-alkanediols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol), as well NaI in the mixtures of water with 1,3-propanediol and 1,2-pentanediol, were determined at 298.15?K. The energetic effect of interactions between the investigated alkanediols and NaI in methanol and in water was calculated using the enthalpic pair interaction coefficients (h _xy ) model. These results along with the other data concerning the NaI?Cnon-electrolyte pairs taken from our earlier reports and from the literature were analyzed with respect to the effect of the non-electrolyte properties on the variations of the h _xy values. The group contributions illustrating the interactions of NaI with selected functional groups in non-electrolyte (alkanediol and alkanol) molecules, namely: CH₂ and OH groups were calculated and discussed.     

Studies on the construction and operation of miniaturized potentiometric biosensors

This study aims at presenting the studies on construction and operation of solid-state miniaturized biosensor with potentiometric detection. The performance of sensors with layer which consisted of mixture of aliphatic thiols and thiols containing ferrocene terminal groups or the conductive polymer layer obtained by electrochemical polymerization of 3,4-ethylenedioxythiophene was compared. Both of the applied modifications proved to significantly affect the sensors’ performance, influencing the stability of their working parameters in time. Wherein, the greatest improvement in planar sensors’ operating parameters was achieved by applying conductive polymer layer. Subsequently, a system creating universal platform for the construction of a biosensor, dedicated to almost any analyte determination, depending on the composition of the affinity proteins used in the receptor layer, was developed. For the construction of proposed biosensor, alkaline phosphatase was chosen as a model enzyme, assuming either the role of direct component of receptor layer or a label in affinity biosensor. The affinity biosensor structure was characterized by a sandwich assay, using a highly specific interaction occurring between streptavidin and biotin. Aside from optimization of various components of the constructed sensor, the most adequate analysis conditions were designated in the course of presented research. As it turned out, the composition of buffer solution used has a significant influence on the activity of the applied enzyme as well as on the working parameters of the sensor. Tris buffer was, therefore, found as the one ensuring the best performance of sensors utilizing alkaline phosphatase.     

1H/2H NMR studies of geometric H/D isotope effects on the coupled hydrogen bonds in porphycene derivatives

The 1H and 2H NMR spectra of porphycene (1), 2,3,6,7,12,13,16,17-octaethylporphycene (2), 2,7,12,17-tetra-n-propylporphycene (3), and 2,7,12,17-tetra-(tert-butyl)-3,6-13,16-dibenzo[cde;mno]porphycene (4) partially deuterated in the mobile proton sites are reported. These compounds exhibit two intramolecular NHN hydrogen bonds of increasing strength representing models of the concerted HH transfer in the parent compound, porphycene. The 1H chemical shifts of the mobile protons are correlated with the difference of the energies of the amino- and imino-N1s orbitals reported by Ghosh A.; Moulder J.; Br?ring M.; Vogel E. Angew. Chem., Int. Ed. 2001, 113, 445-448. The chemical shifts of 4 indicate a reduced contribution of the aromatic ring current as compared to the other compounds which is associated to the nonplanarity of this molecule. The primary H/D isotope effects on the chemical shifts give information about the primary, secondary, and vicinal geometric isotope effects of the two inner hydrogen bonds of porphycenes. The vicinal effects indicate a cooperative coupling of the two hydrogen bonds which may favor a concerted double proton-transfer mechanism.     

Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives

Novel aluminum(III)- and zirconium(IV)-tetraphenylporhyrin (TPP) derivatives are examined as fluoride-selective ionophores for preparing polymer membrane-based ion-selective electrodes (ISEs). The influence of t-butyl- or dichloro-phenyl ring substituents as well as the nature of the metal ion center (Al(III) versus Zr(IV)) on the anion complexation constants of TPP derivative ionophores are reported. The anion binding stability constants of the ionophores are characterized by the so-called “sandwich membrane” method. All of the metalloporphyrins examined form their strongest anion complexes with fluoride. The influence of plasticizer as well as the type of lipophilic ionic site additive and their amounts in the sensing membrane are discussed. It is shown that membrane electrodes formulated with the metalloporphyrin derivatives and appropriate anionic or cationic additives exhibit enhanced potentiometric response toward fluoride over all other anions tested. Since selectivity toward fluoride is enhanced in the presence of both anionic and cationic additives, the metalloporphyrins can function as either charged or neutral carriers within the organic membrane phase. In contrast to previously reported fluoride-selective polymeric membrane electrodes based on metalloporphyrins, nernstian or near-nernstian (−51.2 to −60.1 mV decade⁻¹) as well as rapid (t < 80 s) and fully reversible potentiometric fluoride responses are observed. Moreover, use of aluminum(III)-t-butyltetraphenylporphyrin as the ionophore provides fluoride sensors with prolonged (7 months) functional lifetime.     

Polymer Inclusion Compounds by Polymerization of Monomers in β-Cyclodextrin Matrix in DMF Solution

The investigations of the synthesis of polyrotaxanes by the radical polymerization of monomers (vinylidene chloride, methyl acrylate, styrene, and methacrylonitrile) in DMF in the presence of β-cyclodextrin have been carried out. The possibility of formation β-cyclodextrin inclusion compounds with some vinyl monomers or some other organic substances in DMF solution has been established. We assume that the inclusion in presence of the solvent is related to the unusual phenomenon of β-cyclodextrin crystallization in hot DMF solutions. The polymerization of vinyl monomers in DMF solution at increased temperatures in the presence of β-cyclodextrin leads to compounds containing a great amount of cyclic compounds (up to 80%). Similar results have been obtained for monomers introduced as previously prepared adducts with β-cyclodextrin. Stable compounds of polymer and β-cyclodextrin have been obtained in the case of vinylidene chloride. The lack of carbohydrate moieties in the product obtained by polymerization of vinylidene chloride in the presence of linear dextrin suggest the inclusion character of the linkage between polymer and β-cyclodextrin molecules. The structure of a topological compound of polyrotaxane type is most feasible after dehydrochlorination.