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Synthesis, characterization, and investigation of photophysical and redox behaviors of a new class of homoand heterotrimetallic complexes of composition [(bpy/ phen) 2 Ru(dipy-Hbzim-tpy)M(tpy-Hbzim-dipy)Ru(bpy/ phen) 2 ] 6+ (M = Fe II , Ru II , and Os II ) derived from a conjugated heteroditopic bipyridine−terpyridine bridge were carried out in this work. Trimetallic RuZnRu complexes of composition [(bpy/phen) 2 Ru(dipy-Hbzim-tpy)Zn(tpy-Hbzim-dipy)Ru(bpy/phen) 2 ] 6+ were also synthesized in situ as their photophysical properties are of particular interest in demonstrating the absorption and emission spectra of the complexes in the presence of a metal (Zn 2+ ) that has neither metal-toligand charge transfer (MLCT) nor metal-centered ( 3 MC) states. Complexes display intense absorption bands spanning almost the entire UV and visible region. The complexes also exhibit rich electrochemical behaviors with a number of metal-centered reversible oxidation and ligand-centered reduction waves. All complexes are luminescent at room temperature, and timeresolved emission spectral studies indicate that peripheral Ru II -centered emissive 3 MLCT states are quantitatively quenched, by intramolecular energy transfer to the low lying 3 MLCT (for central Ru and Os) or 3 MC states of the Fe II center (nonluminescent). Interestingly, Fe(II) does not adversely deteriorate the photophysics of the RuFeRu assembly. Thus, multicomponent complexes in the present work can serve as well-organized light-harvesting antennas as the light absorbed by multiple chromophoric subunits is efficiently channeled to the distinct component having the lowest-energy excited state.

The coronavirus disease 2019 , which emerged from Wuhan, China, is now a pandemic, affecting across the globe. Government of different countries have developed and adopted various policies to contain this epidemic and the most common were the social distancing and lockdown. We proposed a SEIR epidemic model that accommodates the effects of lockdown and individual based precautionary measures and used it to estimate model parameters from the epidemic data up to 2nd April, 2020, freely available in GitHub repository for COVID-19, for nine developed and developing countries. We used the estimated parameters to predict the disease burden in these countries with special emphasis on India, Bangladesh and Pakistan. Our analysis revealed that the lockdown and recommended individual hygiene can slow down the outbreak but unable to eradicate the disease from the society. With the current human-to-human transmission rate and existing level of personal precautionary, the number of infected individuals in India will be increasing at least for the next 3 months and the peak will come in 5 months. We can, however, reduce the epidemic size and prolong the time to arrive epidemic peak by seriously following the measures suggested by the authorities. We need to wait for another one month to obtain more data and epidemiological parameters for giving a better prediction about the pandemic. It is to be mentioned that research community is working for drugs and/ or vaccines against COVID19 and the presence of such pharmaceutical interventions will significantly alter the results.

The Sagdeev potential technique has been employed to study the dust ion acoustic solitary waves and double layers in an unmagnetized collisionless dusty plasma consisting of negatively charged static dust grains, adiabatic warm ions, and isothermally distributed electrons and positrons. A

The purpose of this paper is to extend the recent work of Paul & Bandyopadhyay

A conjugated bis-terpyridine bridging ligand, 2-(4-(2,6-di(pyridin-2-yl)pyridin-4-yl)phenyl)-6-(2-(4-(2,6-di(pyridin-2-yl)pyridin-4-yl)phenyl)-1H-benzo[d]imidazol-6-yl)-1H-benzo[d] imidazole (tpy-BPhBzimH-tpy), was designed in this work by covalent coupling of 3,3'-diaminobenzidine and two 4'-(p-formylphenyl)-2,2':6',2″-terpyridine units to synthesize a new series of bimetallic Ru(II)-terpyridine light-harvesting complexes. Photophysical and electrochemical properties were modulated by the variation of the terminal ligands in the complexes. The new compounds were thoroughly characterized by H NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Absorption spectra of the complexes consist of very strong ligand-centered π-π* and n-π* transitions in the UV, metal-to-ligand, and intraligand charge transfer bands in the visible regions. Steady-state and time-resolved emission spectral measurements indicate that the complexes exhibit moderately intense luminescence at room temperature within the spectral domain of 653-687 nm having luminescence lifetimes in the range between 6.3 and 55.2 ns, depending upon terminal tridentate ligand and solvent. Variable-temperature luminescence measurements suggest substantial increase of the energy gap between luminescentmetal-to-ligand charge transfer state and nonluminescent metal centered in the complexes compared to the parent [Ru(tpy)]. Each of the three bimetallic complexes exhibits only one reversible couple in the positive potential window with almost no detectable splitting corresponding to simultaneous oxidation of the two remote Ru centers. All the complexes possess a number of imidazole NH protons, which became sufficiently acidic upon metal ion coordination. By utilizing these NH protons, we thoroughly studied anion recognition properties of the complexes in pure organic as well as predominantly aqueous media through multiple optical channels and spectroscopic methods. Finally computation investigations employing density functional theory (DFT) and time-dependent DFT were done to examine the electronic structures of the complexes and accurate assignment of experimentally observed optical spectral bands.

Postsynthesis halide treatment can brighten perovskite nanocrystals. While this has been recently explored for undoped nanocrystals having only the exciton emission, herein, the impact of halide-enriched and -deficient environments was studied for dual-emitting Mn­(II)-doped CsPbBr3 nanorods. This was performed by adopting a self-regulated approach where the nanorod solution reversibly switched the color brightness from blue to orange and vice versa by dilution and evaporation, respectively. With control experiments, it was established that the color switching was not due to a change in the rate of the exciton energy transfer from host to dopant energy states; rather, it was related to self-regulated fulfilling and again creating halide vacancies observed with variation of nanorod concentration. Being that the halide vacancy was established as one of the key factors for controlling the brightness of these nanocrystals, this reversible switching in doped CsPbBr3 adds new fundamental insight into controlling the photoluminescence of these emerging nanocrystals.

A theorem of Weil and Atiyah says that a holomorphic vector bundle E on a compact Riemann surface X admits a holomorphic connection if and only if the degree of every direct summand of E is zero. Fix a finite subset S of X, and fix an endomorphism A(x) ∈ End(E x ) for every x ∈ S. It is natural to ask when there is a logarithmic connection on E singular over S with residue A(x) at every x ∈ S. We give a necessary and sufficient condition for it under the assumption that the residues A(x) are rigid.Lemma 1.1. Let E be a simple holomorphic vector bundle on X. Then the following two statements are equivalent:(1) There is a logarithmic connection on E singular over S with residue A(x) for everyx ∈ S. (2) The collection of endomorphisms A(x), x ∈ S, satisfy the condition degree(E) + x∈S trace(A(x)) = 0 .Note that Lemma 1.1 holds for stable vector bundles because they are simple.