A highly contorted push–pull naphthalenediimide dimer and evidence of intramolecular singlet exciton fission

Singlet fission is a process by which two molecular triplet excitons are generated subsequent to the absorption of one photon. Molecules that enable singlet fission have triplet state energy at least half of the bright singlet state energy. This stringent energy criteria have challenged chemists to device new molecular and supramolecular design principles to modulate the singlet–triplet energy gap and build singlet fission systems from a wide range of organic chromophores. Herein, we report for the first time intramolecular singlet fission in the seminal naphthalenediimide (NDI) scaffold constrained in a push–pull cyclophane architecture, while individually the NDI chromophore does not satisfy the energy criterion. The challenging synthesis of this highly contorted push–pull cyclophane is possible from the preorganized pincer-like precursor. The special architecture establishes the shortest co-facial NDI⋯NDI contacts (3.084 Å) realized to date. Using broadband femtosecond transient absorption, we find that the correlated T–T pair forms rapidly within 380 fs of photoexcitation. Electronic structure calculations at the level of state-averaged CASSCF (ne,mo)/XMCQDPT2 support the existence of the multi-excitonic T–T pair state, thereby confirming the first example of singlet exciton fission in a NDI scaffold.

We report for the first-time intramolecular singlet fission (SF) in the naphthalenediimide (NDI) scaffold constrained in a cyclophane architecture, while individually the NDI units does not satisfy the requisite energy criterion for SF.     

Calculations predict rapid tunneling by carbon from the vibrational ground state in the ring opening of cyclopropylcarbinyl radical at cryogenic temperatures

B3LYP/6-31G(d) calculations have been performed on the ring opening of cyclopropylcarbinyl radical 1 to 3-buten-1-yl radical 2. The dynamics of the reaction have been computed with canonical variational transition state theory (CVT), both with and without inclusion of small-curvature tunneling (SCT). The CVT + SCT calculations predict that 1 should undergo rapid and temperature-independent ring opening to 2 at cryogenic temperatures, by tunneling from the lowest vibrational level of 1.     

Aromatic superclusters from all-metal aromatic and antiaromatic monomers, [Al4]2- and [Al4]4-

Calculations on the structures of dimers of all-metal aromatic and anti-aromatic molecules such as (Al4(2-)) and (Al4(4-)) reveal that, unlike their organic counterparts such as benzene and cyclobutadiene which form pi-stacked complexes, these molecules form new clusters with no reminiscence of the original units. These clusters have a very large binding energy and can be further stabilized through charge-balance by counterions and solvents.     

Miniature Non-thermal Plasma Induced Cell Cycle Arrest and Apoptosis in Lung Carcinoma Cells

Plasma Chemistry and Plasma Processing - Non-thermal plasma has been a promising new cancer treatment modality in plasma oncology field. It generates extracellular and intracellular reactive...     

Non-minimally coupled scalar fields, Holst action and black hole mechanics

The paper deals with the extension of the Weak Isolated Horizon (WIH) formulation of black hole horizons to the non-minimally coupled scalar fields. In the early part of the paper, we introduce an appropriate Holst type action to incorporate scalar fields non-minimally coupled to gravity and construct the covariant phase space of the theory. Using this phase space, we proceed to prove the laws of black hole mechanics. Further, we show that with a gauge fixing, the symplectic structure on the horizon reduces to that of a U(1) Chern–Simons theory. The level of the Chern–Simons theory is shown to depend on the non-minimally coupled scalar field.     

Precise frequency measurements of atomic transitions by use of a Rb-stabilized resonator

We demonstrate a technique for frequency measurements of atomic transitions with a precision of 30 kHz. The frequency is measured with a ring-cavity resonator whose length is calibrated against a reference laser locked to the D2 line of 87Rb, the frequency of which is known with 10-kHz accuracy. We have used this method to measure the hyperfine structure in the 5P(3/2) state of 85Rb. We obtain precise values for the hyperfine constants, A = 25.041(6) MHz and B = 26.013(25) MHz, and a value of 77.992(20) MHz for the isotope shift in the D2 line.     

Wormhole supported by dark energy admitting conformal motion

In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed.     

Rational Design of Biaxial Tensile Strain for Boosting Electronic and Ionic Conductivities of Na2MnSiO4 for Rechargeable Sodium-Ion Batteries

Using first-principles calculations, biaxial tensile (ϵ=2 and 4 %) and compressive (ϵ=−2 and −4 %) straining of Na₂MnSiO₄ lattices resulted into radial distance cut offs of 1.65 and 2 Å, respectively, in the first and second nearest neighbors shell from the center. The Si−O and Mn−O bonds with prominent probability density peaks validated structural stability. Wide-band gap of 2.35 (ϵ=0 %) and 2.54 eV (ϵ=−4 %), and narrow bandgap of 2.24 eV (ϵ=+4 %) estimated with stronger coupling of p–d σ bond than that of the p–d π bond, mainly contributed from the oxygen p-state and manganese d-state. Na⁺-ion diffusivity was found to be enhanced by three orders of magnitude as the applied biaxial strain changed from compressive to tensile. According to the findings, the rational design of biaxial strain would improve the ionic and electronic conductivity of Na₂MnSiO₄ cathode materials for advanced rechargeable sodium-ion batteries.     

Cooperative interactions in supramolecular aggregates: linear and nonlinear responses in calix[4]arenes.

The linear and nonlinear optical polarizabilities of donor-acceptor (D-pi-A) chromophores in confined geometries of calix[4]arenes are investigated through a model for interacting polar-polarizable molecules. Both the linear polarizability (alpha) and the first hyperpolarizability (beta) decrease with increasing the interdipolar angle, as expected in the oriented-gas picture. However, within the polar-polarizable model we predict deviations from the additive result, irrespective of the interdipolar angle. Depending on the nature of the chromophore, electrostatic intermolecular interactions between polar and polarizable chromophores lead to cooperative damping or enhancement of the optical responses. Specifically, for chromophores whose ground state is dominated by the neutral D-pi-A structure both alpha and beta are suppressed with respect to the prediction of the oriented-gas model, whereas the opposite holds true for chromophores whose ground state is dominated by the zwitterionic D(+)-pi-A(-). These results explain recent experimental data on a calix[4]arene functionalized with a donor-acceptor dye for nonlinear optical applications. Density functional theory calculations on the relevant crystal structure further support our interpretation.     

Stable transition metal complexes of an all-metal antiaromatic molecule (Al4Li4): role of complexations

We propose for the first time a few examples of stable transition metal complexes of an all-metal antiaromatic molecule Al4Li4. We demonstrate that these all-metal species can be stabilized by complexation with 3d transition metals very similar to their organic counterpart, C4H4. Complexation to transition metal ions reduces the frontier orbital energies and introduces aromatic charactersitics. We consider a series of such complexes: [eta4-(Al4Li4)-Fe(CO)3, eta2,sigma2-(Al4Li4)-Ni, and (Al4Li4)2Ni] and compare and contrast their energetics with their organometallic counterparts. Fragmentation energy, orbital correlation energy analysis, and the nucleus-independent chemical shift (NICS) values support the complexation-induced stabilities in these systems.