Functionalized derivatives of the saddle-shaped molecule tetrabenzo[8]circulene were successfully synthesized through a Diels-Alder/oxidative cyclodehydrogenation approach. This methodology improves on our previously reported synthesis, affording products containing both electron-rich and electron-poor functional groups from readily available starting materials in a more efficient manner. The optoelectronic effects that result from the introduction of this functionality are presented and briefly discussed.

The dynamics of proton transfer to the aprotic solvent 1-methylimidazole (MeIm, proton acceptor) from the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) was investigated using fast fluorescence measurements. The closely related molecule, 8-methoxypyrene-1,3,6-trisulfonic acid trisodium salt (MPTS), which is not a photoacid, was also studied for comparison. Following optical excitation, the wavelength-dependent population dynamics of HPTS in MeIm resulting from the deprotonation process were collected over the entire fluorescence emission window. Analysis of the time-dependent fluorescence spectra revealed four distinct fluorescence bands that appear and decay on different time scales. We label these four states as protonated (P), associated I (AI), associated II (AII), and deprotonated (D). We find that the simple kinetic scheme of P → AI → AII → D is not consistent with the data. Instead, the kinetic scheme that describes the data has P decaying into AI, which mainly goes on to deprotonation (D), but AI can also feed into AII. AII can return to AI or decay to the ground state, but does not deprotonate within experimental error. Quantum chemistry and excited state QM/MM Born–Oppenheimer molecular dynamics simulations indicate that AI and AII are two H-bonding conformations of MeIm to the HPTS hydroxyl, axial, and equatorial, respectively.

We report the dynamics of concentrated lithium chloride aqueous solutions over a range of moderate to high concentrations. Concentrations (1−29 to 1−3.3 LiCl−water) were studied in which, at the highest concentrations, there are far too few water molecules to solvate the ions. The measurements were made with optically heterodyne-detected optical Kerr effect experiments, a non-resonant technique able to observe dynamics over a wide range of time scales and signal amplitudes. While the pure water decay is a biexponential, the LiCl−water decays are tetra-exponentials at all concentrations. The faster two decays arise from water dynamics, while the slower two decays reflect the dynamics of the ion-water network. The fastest decay (t 1 ) is the same as pure water at all concentrations. The second decay (t 2 ) is also the same as that of pure water at the lower concentrations, and then, it slows with increasing concentration. The slower dynamics (t 3 and t 4 ), which do not have counterparts in pure water, arise from ion-water complexes and, at the highest concentrations, an extended ion-water network. Comparisons are made between the concentration dependence of the observed dynamics and simulations of structural changes from the literature, which enable the assignment of dynamics to specific ion-water structures. The concentration dependences of the bulk viscosity and the ion-water network dynamics are directly correlated. The correlation provides an atomistic-level understanding of the viscosity.

The ultrafast dynamics of acrylamide monomers (AAm), polyacrylamide (PAAm), and polyacrylamide hydrogels (PAAm-HG) in water were studied using optical heterodynedetected optical Kerr effect (OHD-OKE) spectroscopy. Previous ultrafast infrared (IR) measurements of the water dynamics showed that at the same concentration of the acrylamide moiety, AAm, PAAm, and PAAm-HG exhibited identical water dynamics and that these dynamics slowed with increasing concentration. In contrast to the IR measurements, OHD-OKE experiments measure the dynamics of both the water and the acrylamide species, which occur on different time scales. In this study, the dynamics of all the acrylamide systems slowed with increasing concentration. We found that AAm exhibits tetraexponential decays, the longest component of which followed Debye−Stokes−Einstein behavior except for the highest concentration, 40% (w/v). Low concentrations of PAAm followed a single power law decay, while high concentrations of PAAm and all concentrations of PAAm-HG decayed with two power laws. The highest concentrations, 25% and 40%, of PAAm and PAAm-HG showed nearly identical dynamics. We interpreted this result as reflecting a similar extent of chain− chain interactions. At low concentrations, PAAm displays non-Markovian, single-chain dynamics (single power law), but PAAm displays entangled chain−chain interactions at high concentrations (two power laws). PAAm-HG has chain−chain interactions at all concentrations that arise from the cross-linking. At high concentrations, the dynamics of the entangled of PAAm become identical within error as those of the cross-linked PAAm-HG.

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In six of seven cases, direct anodic oxidation of the ethynyl group of an ethynylphenylderivatized free-base porphyrin gave modified glassy carbon electrodes in which the porphyrin was strongly surface-bound, most likely in a perpendicular geometry through covalent attachment of the ethynyl group to a surface carbon atom. The porphyrins each contained an ethynylphenyl group in one meso position and varied in the groups present in the other three meso positions. Electrografted 5,10,15,20-tetrakis(ethynylphenyl)porphyrin, H21, which has ethynyl moieties in all four meso positions, has well-defined surface voltammetry and grows to multi-layer levels upon repeated cyclic voltammetry (CV) deposition scans. Multi-layering was not observed to the same degree for mono-ethynylphenyl-substituted porphyrins, and became progressively less for porphyrins having groups in the 15-meso position that were more protective against ethynyl radical attack. Clean molecular monolayer-level coverage was observed for 5-ethynylphenyl-10,20-bis(3-methoxyphenyl)-15-hexylporphyrin, H25. Owing to the fact that the ethynyl oxidation potential (1.1 to 1.5 V vs ferrocene) is more positive than that of the second macrocycle oxidation, the longevities and follow-up reactions of the porphyrin dications were also studied by CV, chemical oxidation, and optical spectroscopy in homogeneous solution. The primary follow-up products of the doubly oxidized porphyrins, whether surface-bound or in solution, were pyrrole-protonated species that were easily reduced back to the neutral porphyrin.

The electrochemical oxidation of the chemotherapeutic anti-cancer agent tamoxifen, 1, was studied by voltammetry and electrolysis. Three successive one-electron anodic reactions were observed for 1 in dichloromethane containing weakly-coordinating [B(C 6 F 5) 4 ]as the supporting electrolyte anion. The first (totally irreversible) oxidation (ca 0.64 V vs ferrocene) occurs at the tertiary amine, giving a putative amine radical cation 1 +• that abstracts a hydrogen atom, most likely from solvent, to give the corresponding ammonium ion 1-H +. The latter is responsible for the two further one-electron oxidations, which take place at the triarylethynyl part of the molecule (E 1/2 values of 0.94 V and 1.33 V vs ferrocene). Bulk oxidation of 1 at E appl = 0.6 V produces the ammonium ion 1-H + , which can be cathodically reduced back to neutral tamoxifen in an overall chemically reversible process. The present findings are not consistent with the mechanism described in previous literature for the anodic oxidation of tamoxifen.