Solvent Effects on the Photophysical Properties of a Donor-acceptor Based Schiff Base.

In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.

Impact of Air Pollution on Allergic Rhinitis and Asthma: Consensus Statement by Indian Academy of Pediatrics.

JUSTIFICATION: Rising air pollution is an ever-growing threat to many human diseases. Poor air quality has been directly correlated with respiratory allergies with a disproportionate affection among the pediatric age group. A clear understanding of common air pollutants and their potential contribution in allergic rhinitis and asthma is lacking. OBJECTIVE: To formulate a consensus statement for appropriate understanding among pediatricians and general practitioners about the effects of air pollution on respiratory allergies and their prevention. PROCESS: A group of experts (Pediatric pulmonologists and allergy specialists) from across India were appointed by the Indian Academy of Pediatrics (IAP) to formulate a consensus statement on 'Allergy and Air pollution'. A virtual meeting was conducted on 6th April 2020 to discuss in detail regarding various issues related to the subject and a writing committee was formed with broad consensus. After extensive literature review and multiple virtual sessions, the current document was prepared and circulated via email to the representatives from central IAP and IAP environment chapter. All the experts approved the consensus with minor modifications after a detailed discussion on 29th September 2020 on a virtual platform. RECOMMENDATIONS: Air pollution is the emerging contributor to respiratory allergies due to various mechanisms including oxidative stress and compromised mucociliary clearance. Children are more vulnerable to both outdoor and indoor pollution, due to their unique physiological characteristics. Knowledge about pollutant particle size and air quality index will help in demarcating level and extent of airway involvement. Relevant environmental history in difficult allergic rhinitis and asthma cases, along with conventional pharmacological measures, is warranted. Multipronged approach, targeted at community, physician and individual levels, needs to be emphasized to improve air quality and reduce economic and psychological burden of respiratory allergies.

Theoretical study of electronic transport through P-porphyrin and S-porphyrin nanoribbons.

Electronic transport through P-porphyrin and S-porphyrin nanoribbons have been studied by using nonequilibrium Green's function formalism (NEGF) combined with density functional theory (DFT) method. Band structure of both nanoribbons shows metallic behavior and bands near the Fermi level contain π character contributed by py orbital. Both nanoribbons exhibit metal-like conduction at extreme low bias. A remarkable negative differential resistance (NDR) effect is observed for both nanoribbons which is further explained with the evolution of transmission peak within energy bias window (EBW), and overlap of energy states of left and right electrodes. The low bias NDR phenomena of our proposed devices could be used in designing NDR devices including frequency multipliers, memory, and fast switches.

The spin filtering effect and negative differential behavior of the graphene-pentalene-graphene molecular junction: a theoretical analysis.

Density functional theory (DFT) combined with nonequilibrium Green's function (NEGF) formalism are used to investigate the effects of substitutional doping by nitrogen and sulfur on transport properties of AGNR-pentalene-AGNR nanojunction. A considerable spin filtering capability in a wide bias range is observed for all systems, which may have potential application in spintronics devices. Moreover, all model devices exhibit a negative differential effect with considerable peak-to-valley ratio. Thus, our findings provide a way to produce multifunctional spintronic devices based on nitrogen and sulfur doped pentalene-AGNR nanojunctions. The underlying mechanism for this interesting behavior was exposed by analyzing the transmission spectrum as well as the electrostatic potential distribution. In addition, a system doped with an odd number of dopant shows a rectifying efficiency comparable to other systems. The above findings strongly imply that such a multifunctional molecular device would be a useful candidate for molecular electronics. Graphical abstract The graphene-pentalene-graphene molecular junction.

Electronic and optical properties of C24, C12X6Y6, and X12Y12 (X = B, Al and Y = N, P).

Utilizing first-principles calculations, we studied the electronic and optical properties of C24, C12X6Y6, and X12Y12 fullerenes (X = B, Al; Y = N, P). These fullerenes are energetically stable, as demonstrated by their negative cohesive energies. The energy gap of C24 may be tuned by doping, and the B12N12 fullerene was found to have the largest energy gap. All of the fullerenes had finite optical gaps, suggesting that they are optical semiconductors, and they strongly absorb UV radiation, so they could be used in UV light protection devices. They could also be used in solar cells and LEDs due to their low reflectivities. Graphical abstract Possible applications of doped C24 fullerene.