The Chemistry of 5‐(Tetrazol‐1‐yl)‐2H‐tetrazole: An Extensive Study of Structural and Energetic Properties

5‐(Tetrazol‐1‐yl)‐2H‐tetrazole ( 1 ), or 1,5′‐bistetrazole, was synthesized by the cyclization of 5‐amino‐1H‐tetrazole, sodium azide and triethyl orthoformate in glacial acetic acid. A derivative of 1 , 2‐methyl‐5‐(tetrazol‐1‐yl)tetrazole ( 2 ) can be obtained by this method starting from 5‐amino‐2‐methyl‐tetrazole. Furthermore, selected salts of 1 with nitrogen‐rich and metal (alkali and transition metal) cations, including hydroxylammonium ( 4 ), triaminoguanidinium ( 5 ), copper(I) ( 8 ) and silver ( 9 ), as well as copper(II) complexes of both 1 and 2 were prepared. An intensive characterization of the compounds is given, including vibrational (IR, Raman) and multinuclear NMR spectroscopy, mass spectrometry, DSC and single‐crystal X‐ray diffraction. Their sensitivities towards physical stimuli (impact, friction, electrostatic) were determined according to Bundesamt für Materialforschung (BAM) standard methods. Energetic performance (detonation velocity, pressure, etc.) parameters were calculated with the EXPLO5 program, based on predicted heats of formation derived from enthalpies computed at the CBS‐4M level of theory and utilizing the atomization energy method. From the analytical and calculated data, their potential as energetic materials in different applications was evaluated and discussed.     

Oxidomolybdenum(VI) complexes with atrane-type [O3N] ligands

Dioxomolybdenum(VI) complex [MoO₂Cl₂(dmso)₂] reacts with a series of tetradentate O₃N-type aminoalcohol–bisphenol ligands to form oxomolybdenum(VI) complexes of type [MoOCl(Lⁿ)]. The reaction of H₃L¹ produces [MoOCl(L¹)] as two separable isomers, whereas the reaction of H₃L² or H₃L³ yields a single product. The X-ray analyses of cis- and trans-[MoOCl(L¹)] reveal that the complexes are formed of monomeric molecules. The ligands have tetradentate coordination through three oxygen donors and one nitrogen donor, which is located trans to the terminal oxo group. The sixth coordination site is occupied by a chloro ligand.     

From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task

Background  

Phase-locked gamma oscillations have so far mainly been described in relation to perceptual processes such as sensation, attention or memory matching. Due to its very short latency (≈90 ms) such oscillations are a plausible candidate for very rapid integration of sensory and motor processes.     

Memory-matches evoke human gamma-responses

Background  

Human brain activity in the gamma frequency range has been shown to be a correlate of numerous cognitive functions like attention, perception and memory access. More specifically, gamma activity has been found to be enhanced when stimuli are stored in or match with short-term memory (STM). We tested the hypothesis that gamma activity is also evoked when stimuli match representations in long-term-memory (LTM). EEG was recorded from 13 subjects performing a choice reaction task. Visual stimuli were either known real-world objects with a memory representation or novel configurations never seen before.     

Fundamental photoluminescence properties of pyrene carbonyl compounds through absolute fluorescence quantum yield measurement and density functional theory

We reviewed the photophysical properties of carbonyl-functionalized pyrene derivatives [i.e., pyrene with aldehyde (PA: 1-formylpyrene), ketone (PK: 1-acetylpyrene), carboxylic acid (PCA: 1-pyrenecarboxylic acid), and ester groups (PE: 1-methoxycarbonylpyrene)] using a measurement of absolute fluorescence quantum yield in various solvents and time-dependent density functional theory (TD-DFT) calculations. Here, we obtained new important data that fill in the gaps in existing datasets on these properties and help identify photoluminescence mechanisms. The results of the TD-DFT calculations were in agreement with the experimental results, and indicated that the low fluorescence of PA and PK is derived not only from intersystem crossing but also from internal conversion due to the proximity effect; this inference was also supported by the measurements of the photoluminescence spectra at low temperatures. In addition, factors leading efficiently to non-radiative processes were shown to be absent in PCA and PE. Thus, we successfully revised and systematized the photophysical properties of pyrene modified by carbonyl substitutes, including carboxamide groups, which were previously reported by us. Moreover, we showed that the photoluminescence properties of such compounds might be predictable by using TD-DFT calculations.     

Synthesis of highly soluble fluorescent π-extended 2-(2-thienyl)benzothiazole derivatives via oxidative cyclization of 2-thienylthioanilide as the key step

In this Letter, we synthesize highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and evaluate their photophysical properties. The key step is the synthesis of 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole (2) via oxidative cyclization of 2-thienylthioanilide using PhI(OAc)₂ as the oxidant. The target dyes could be easily synthesized by the Suzuki–Miyaura cross-coupling reaction of 2 and an appropriate π-donor. The photophysical properties of the 2-thienylbenzothiazole chromophore were controlled by the π-donor moiety. It was found that 2 exhibited large Stokes shifts (5345 cm⁻¹) and a high quantum efficiency for fluorescence (Φ_F = 0.94 in CH₂Cl₂). Therefore, it can be expected to be a useful photofunctional material in liquid crystal laser dyes and nonlinear optical materials.     

Design of Weak‐Donor Alkyl‐Functionalized Push–Pull Pyrene Dyes Exhibiting Enhanced Fluorescence Quantum Yields and Unique On/Off Switching Properties

We designed, synthesized, and evaluated environmentally responsive solvatochromic fluorescent dyes by incorporating weak push–pull moieties. The quantum yields of the push (alkyl)–pull (formyl) pyrene dyes were dramatically enhanced by the introduction of alkyl groups into formylpyrene (1‐formylpyrene: Φ_F=0.10; 3,6,8‐tri‐n‐butyl‐1‐formylpyrene: Φ_F=0.90; in MeOH). The new dyes exhibited unique sensitivity to solvent polarity and hydrogen‐bond donor ability, and specific fluorescence turn‐on/off properties (e.g., 3,6,8‐tri‐n‐butyl‐1‐formylpyrene: Φ_F=0.004, 0.80, 0.37, and 0.90 in hexane, chloroform, DMSO, and MeOH, respectively). Here, the alkyl groups act as weak donors to suppress intersystem crossing by destabilizing the HOMOs of 1‐formylpyrene while maintaining weak intramolecular charge‐transfer properties. By using alkyl groups as weak donors, environmentally responsive, and in particular, pH‐responsive fluorescent materials may be developed in the future.