Investigation of ultrafast carrier dynamics in curcumin dye for environment friendly dye-sensitized solar cell.

Natural dyes have been widely employed in the fabrication of dye-sensitized solar cells (DSSCs). DSSCs are favored for their cost-effective, and simple fabrication process relies on metal-based and organic dyes. The choice of dyes greatly affects the performance of DSSCs. DSSCs have found a lot of applications in indoor, solar power gadgets with reasonable efficiency up to 13%. Nonetheless, despite advances in DSSC technology, the complex photophysics and excited state dynamics associated with natural dyes employed in DSSCs remain elusive and have not been adequately investigated. This information gap emphasizes the need for more study and analysis into the behavior of these dyes, since understanding their underlying principles might lead to major improvements in DSSC performance and efficiency. In this work, we have investigated the fundamental characteristics and excited-state carrier dynamics of natural dye curcumin using ultrafast transient absorption (TA) spectroscopy technique. The curcumin dye shows delay time-dependent positive and negative signals in the TA spectra, which are related to excited state absorption and stimulated emission. We also found that hydrogen bonding and polarity effect of solvent significantly influence the carrier dynamics of curcumin. Ultrafast lifetime component indicates that hydrogen-bond rearrangements are involved in the kinetics of the relaxation process of the S1 state of curcumin photo-sensitizer.

A GPS Data-Based Index to Determine the Level of Adherence to COVID-19 Lockdown Policies in India.

The growth of COVID-19 cases in India is scaling high over the past weeks despite stringent lockdown policies. This study introduces a GPS-based tool, i.e., lockdown breaching index (LBI), which helps to determine the extent of breaching activities during the lockdown period. It is evaluated using the community mobility reports. This index ranges between 0 and 100, which implies the extent of following the lockdown policies. A score of 0 indicates that civilians strictly adhered to the guidelines while a score of 100 points to complete violation. Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) is modified to compute the LBI. We considered fifteen states of India, where the spread of coronavirus is relatively dominant. A significant breaching activity is observed during the first phase of lockdown, and the intensity increased in the third and fourth phases of lockdown. Overall breaching activities are dominant in Bihar with LBI of 75.28. At the same time, it is observed that the majority of the people in Delhi adhered to the lockdown policies strictly, as reflected with an LBI score of 47.05, which is the lowest. Though an average rise of 3% breaching activities during the second phase of lockdown (L2.0) with reference to the first phase of lockdown (L1.0) is noticed in all the states, a decreasing trend is noticed in Delhi and Tamil Nadu. Since the beginning of third phase of lockdown L3.0, a significant rise in breaching activities is observed in every state considered for the analysis. The average LBI rise of 16.9% and 27.6% relative to L1.0 is observed at the end of L3.0 and L4.0, respectively. A positive spearman rank correlation of 0.88 is noticed between LBI and the cumulative confirmed cases. This correlation serves as evidence and enlightens the fact that the breaching activities could be one of the possible reasons that contributed to the rise in COVID-19 cases throughout lockdown.

Divergent reactivity of a new dinuclear xanthene-bridged bis(iminopyridine) di-nickel complex with alkynes.

The reaction of a dinucleating bis(iminopyridine) ligand L bearing a xanthene linker (L = N,N'-(2,7-di-tert-butyl-9,9-dimethyl-9H-xanthene-4,5-diyl)bis(1-(pyridin-2-yl)methanimine)) with Ni2(COD)2(DPA) (COD = cyclooctadiene, DPA = diphenylacetylene) leads to the formation of a new dinuclear complex Ni2(L)(DPA). Ni2(L)(DPA) can also be obtained in a one-pot reaction involving Ni(COD)2, DPA and L. The X-ray structure of Ni2(L)(DPA) reveals two square-planar Ni centers bridged by a DPA ligand. DFT calculations suggest that this species features NiI centers antiferromagnetically coupled to each other and their iminopyridine ligand radicals. Treatment of Ni2(L)(DPA) with one equivalent of ethyl propiolate (HCCCO2Et) forms the Ni2(L)(HCCCO2Et) complex. Addition of the second equivalent of ethyl propiolate leads to the observation of cyclotrimerised products by 1H NMR spectroscopy. Carrying out the reaction under catalytic conditions (1 mol% of Ni2(L)(DPA), 24 h, room temperature) transforms 89% of the substrate, forming primarily benzene products (triethyl benzene-1,2,4-tricarboxylate and triethyl benzene-1,3,5-tricarboxylate) in 68% yield, in a ca. 5 : 1 relative ratio. Increasing catalyst loading to 5 mol% leads to the full conversion of ethyl propiolate to benzene products; no cyclotetramerisation products were observed. In contrast, the reaction is significantly more sluggish with methyl propargyl ether. Using 1 mol% of the catalyst, only 25% conversion of methyl propargyl ether was observed within 24 h at room temperature. Furthermore, methyl propargyl ether demonstrates the formation of cyclooctatetraenes in significant amounts at a low catalyst concentration, whereas a higher catalyst concentration (5 mol%) leads to benzene products exclusively. Density functional theory was used to provide insight into the reaction mechanism, including structures of putative dinuclear metallocyclopentadiene and metallocycloheptatriene intermediates.

Carbon disulfide binding at dinuclear and mononuclear nickel complexes ligated by a redox-active ligand: iminopyridine serving as an accumulator of redox equivalents for the activation of heteroallenes.

The dinuclear complex Ni(2)L(1)(η(2)-CS(2))(2) (2), featuring iminopyridine ligation, is prepared by COD substitution from Ni(2)L(1)(COD)(2) (1). Spectroscopic, structural, and theoretical data reveals significant activation of the metal-bound C-S bonds, as well as the different oxidation states of the iminopyridine in (1-) and (0).

Flavin as a photo-active acceptor for efficient energy and charge transfer in a model donor-acceptor system.

A donor-acceptor dyad model system using a flavin moiety as a photo-active acceptor has been synthesized for an energy and photo-induced electron transfer study. The photophysical investigations of the dyad revealed a multi-path energy and electron transfer process with a very high transfer efficiency. The photo-activity of flavin was believed to play an important role in the process, implying the potential application of flavin as a novel acceptor molecule for photovoltaics.