Cucurbit[8]uril-induced diarylethene thermally activated delay fluorescence supramolecular switch for sequential energy transfer

Constructing molecular switches based on supramolecular assembly strategy is a research hotspot. In this work, we constructed an all visible-light-regulated supramolecular photo-switch based on pyridinium-modified diarylethene derivative (DTE-Me) and cucurbit[8]uril (CB[8]). CB[8] not only accelerated the photochromic process under 365 nm ultraviolet light but also shifted the absorption of open formed DTE-Me to the visible region, which led to efficient photocyclization under 450 nm visible light irradiation, while DTE-Me and DTE-Me/CB[7] remained unchanged under the same irradiating condition. Moreover, the complexation with CB[8] could induce the strong thermally activated delayed fluorescence (TADF) of guest molecular at 550 nm, which further shifted to 670 nm through two-step sequential energy transfer with sulforhodamine B (SRB) and Cy5. This energy transfer process could also be regulated with visible light, and the application for information encryption was also demonstrated. This assembly provides a convenient approach to construct all visible light-regulated TADF photo-switch.     

The Chemical Bond: When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength

We have quantum chemically analyzed element−element bonds of archetypal H_nX−YH_n molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g., from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance.     

Tetrasubstituted Peropyrenes Formed by Reductive Aromatization: Synthesis,Functionalization and Characterization

The chromophore class of 1,3,8,10-tetrasubstituted peropyrenes was effectively synthesized from peropyrenequinone via a Zn-mediated reductive aromatization approach. In one step, a symmetric functionalization of the peropyrene backbone introducing silylethers ( 2 , 3 ), pivaloyl ( 4 ), triflyl ( 5 ) and also phosphinite ( 6 ) groups was established. Furthermore, the potential of using 4 and 5 in transition metal catalysed cross couplings was explored leading to 1,3,8,10-tetraaryl ( 8 - 11 ) and tetraalkynyl ( 7 ) peropyrenes. The influence of various substituents on the optoelectronic properties of these π-system extended peropyrenes was investigated in solid state by means of X-ray crystallography, in solution by means of UV-Vis and fluorescence spectroscopy and by their redox properties studied via cyclic voltammetry. By comparison with DFT and TD-DFT calculations, it could be elucidated that introduction of a broad variety of substituents in such versatile one or two step procedures leads to peropyrenes with easily tunable HOMO and LUMO energies ranging in a gap window of 0.8 eV. The frontier molecular orbital energies identify the target molecules as promising candidates for hole transporting semiconductors.     

Lateral Metallation and Redistribution Reactions of Sodium Ferrates Containing Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilide Ligands

Alkali-metal ferrates containing amide groups have emerged as regioselective bases capable of promoting Fe−H exchanges of aromatic substrates. Advancing this area of heterobimetallic chemistry, a new series of sodium ferrates is introduced incorporating the bulky arylsilyl amido ligand N(SiMe₃)(Dipp) (Dipp=2,6-iPr₂-C₆H₃). Influenced by the large steric demands imposed by this amide, transamination of [NaFe(HMDS)₃] (HMDS=N(SiMe₃)₂) with an excess of HN(SiMe₃)(Dipp) led to the isolation of heteroleptic [Na(HMDS)₂Fe{N(SiMe₃)Dipp}]_∞ ( 1 ) resulting from the exchange of just one HMDS group. An alternative co-complexation approach, combining the homometallic metal amides [NaN(SiMe₃)Dipp] and [Fe{N(SiMe₃)Dipp}₂] induces lateral metallation of one Me arm from the SiMe₃ group in the iron amide furnishing tetrameric [NaFe{N(SiCH₂Me₂)Dipp}{N(SiMe₃)Dipp}]₄ ( 2 ). Reactivity studies support that this deprotonation is driven by the steric incompatibility of the single metal amides rather than the basic capability of the sodium reagent. Displaying synergistic reactivity, heteroleptic sodium ferrate 1 can selectively promote ferration of pentafluorobenzene using one of its HMDS arms to give heterotrileptic [Na{N(SiMe₃)Dipp}(HMDS)Fe(C₆F₅)]_∞ ( 4 ). Attempts to deprotonate less activated pyridine led to the isolation of NaHMDS and heteroleptic Fe(II) amide [(py)Fe{N(SiMe₃)Dipp}(HMDS)] ( 5 ), resulting from an alternative redistribution process which is favoured by the Lewis donor ability of this substrate.     

A Comprehensive Study on the Full Series of Alkali-Metal Selenocyanates AI[SeCN] (AI=Li−Cs)

The full series of quasibinary alkali-metal selenocyanates was synthesized either by oxidation of the respective cyanides (A=Li−Rb) or by metathesis (A=Cs). For Li[SeCN] only ball-milling and subsequent annealing led to the isolation of the quasibinary selenocyanate. Their structures were refined from single-crystal and powder X-ray data. The respective solid-state IR and Raman spectra were interpreted with the aid of solid-state quantum-mechanical calculations and DSC-TGA measurements allowed for extraction of melting points. Only for Li[SeCN] a possible phase transition was observed that is discussed on the basis of VT-PXRD experiments. It is also the only quasibinary selenocyanate to form a hydrate (Li[SeCN] ⋅ 2H₂O).     

Improving stability and thermal properties of TiO2-based nanofluids for concentrating solar energy using two methods of preparation

Journal of Thermal Analysis and Calorimetry - Nanofluids are considered a promising alternative to the classic fluids used in heat transfer processes. One interesting application of nanofluids is...     

Calorimetric (DSC) and dielectric (TSDC) investigation on the thermal behavior and molecular mobility in the supercooled liquid and glassy states of bifonazole and lamotrigine

Journal of Thermal Analysis and Calorimetry - The thermal behavior of the two glass-forming drugs bifonazole and lamotrigine was studied by differential scanning calorimetry (DSC); we reported a...     

An unsteady thermal investigation of a wetted longitudinal porous fin of different profiles

Journal of Thermal Analysis and Calorimetry - The unsteady thermal behavior of a porous longitudinal fin in a fully wet circumstance in the existence of convection as well as radiation effect is...     

Efficiency analysis of thermosyphon solar flat plate collector with low mass concentrations of ND–Co3O4 hybrid nanofluids: an experimental study

Journal of Thermal Analysis and Calorimetry - In the present study, the thermal efficiency, convective heat transfer and friction factor analysis are investigated for a flat plate solar collector...