A dual emitting CsPbBr3/Eu-BDC composite as a ratiometric photoluminescent turn-on probe for aliphatic amine sensing.

The impressive photoluminescence properties of all inorganic cesium lead halide perovskite quantum dots (PeQDs) make them highly intriguing for fluorescence chemosensor applications. Herein, a ratiometric dual emitting perovskite-based sensor was designed by synthesizing fluorescent CsPbBr3 PeQDs in situ within a matrix of Eu-BDC (Eu(III) benzene-1,4-dicarboxylate). The results presented here establish the suggested sensor's quick and selective turn-on PL response to volatile primary aliphatic amine derivatives. In the presence of amines, the designed CsPbBr3/Eu-BDC sensor exhibits an enhancement of the PL signal of CsPbBr3 at 518 nm and the Eu-BDC signal at 615 nm served as a standard for constructing the ratiometric sensing system. Thereby, a visual color change from red to green was observed with the incremental addition of methylamine to the probe. A low detection limit of 0.083 ppm was determined for methylamine. In both the solution and vapor phases, this ratiometric sensor responds to a variety of primary aliphatic amines with very quick and strong fluorescence. Moreover, the sensor was effectively used for monitoring meat spoilage owing to the emission of biogenic amine vapor from meat products.

Prevalence of SARS-CoV-2 Infection among Children and Adults in 15 US Communities, 2021

During January-August 2021, the Community Prevalence of SARS-CoV-2 Study used time/location sampling to recruit a cross-sectional, population-based cohort to estimate SARS-CoV-2 seroprevalence and nasal swab sample PCR positivity across 15 US communities. Survey-weighted estimates of SARS-CoV-2 infection and vaccine willingness among participants at each site were compared within demographic groups by using linear regression models with inverse variance weighting. Among 22,284 persons >2 months of age and older, median prevalence of infection (prior, active, or both) was 12.9% across sites and similar across age groups. Within each site, average prevalence of infection was 3 percentage points higher for Black than White persons and average vaccine willingness was 10 percentage points lower for Black than White persons and 7 percentage points lower for Black persons than for persons in other racial groups. The higher prevalence of SARS-CoV-2 infection among groups with lower vaccine willingness highlights the disparate effect of COVID-19 and its complications.

CsPbBr3 perovskite quantum dot decorated ZIF-8 MOF: a selective dual recognition fluorometric visual probe for 4-nitroaniline and rhodamine blue.

The uses of highly luminescent perovskite quantum dots in real analytical detection were limited by their supersensitive nature. Here, we have designed a CsPbBr3 perovskite based fluorometric sensor by integrating them with a zeolitic imidazole framework (ZIF-8) via an in situ one step technique and established its stability in aqueous and other polar solvents. The CsPbBr3@ZIF-8 luminescence sensor functioned excellently for the trace detection of 4-nitroaniline and rhodamine blue dye molecules with a detection limit value of 8.367 ppb and 0.088 ppm, respectively. A comprehensive investigation found that the quenching of the fluorescence signal occurred via fluorescence resonance energy transfer (FRET) for rhodamine blue dye and a H-bonding interaction induced trap density mediated quenching mechanism was responsible for 4-NA detection. The potential of this suggested sensor as a cheap portable test paper probe for analyte detection was also explored. This study introduces CsPbBr3 as a cutting-edge sensing platform for industrial pollutants such as dye molecules and nitroaromatics.

Structural modulation of phenothiazine and coumarin based derivatives for high performance dye sensitized solar cells: a theoretical study.

A series of dyes with the D-π-A architecture has been designed and studied for dye sensitized solar cells (DSSCs). We have used phenothiazine (PTZ) and coumarin (COU) derivatives as the donor unit and benzopyrrole (BTZ) and 2-methyl-2H-isoindole-1,3-(3aH,7aH)-diene (IND) as the acceptor unit along with the azomethine group and thiophene ring as the π-spacer unit. Three electron donating groups viz. -CH3, -NH2, and -OH and four electron withdrawing groups viz. -CF3, -COCl, -F and -NO2 have been attached at the donor and the acceptor units respectively of the four unsubstituted dyes COU-BTZ, PTZ-BTZ, COU-IND and PTZ-IND. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods have been employed to investigate the structural, electronic and photochemical properties of these dyes. The study reveals that the unsubstituted dye PTZ-BTZ possesses the lowest value of ΔH-L. Our study also reveals that attachment of the -NO2 group at the acceptor unit lowers the ΔH-L values of all the dye molecules. We have observed that the excited state oxidation potential (ESOP) of all the dyes lies above the conduction band of the TiO2 semiconducting surface. However, the ground state oxidation potential (GSOP) of most of the dyes belonging to the COU-BTZ and COU-IND groups lies below the redox potential of the I-/I3- redox couple. The total reorganization energy (λtot) values of the COU-BTZ and COU-IND groups of dyes are observed to be low compared to the other groups of dyes. The study of the charge transport properties of the dyes confirms that the designed dyes will act as electron transport materials. The absorption properties of the dyes show that the COU-BTZ group of dyes possesses the maximum values of the absorption wavelength (λmax values) and attaching the -NO2 group at the acceptor unit shifts the λmax values of all the dyes to the longer region. From the study of the electronic properties of the dye-TiO2 complexes it has been observed that the performance of the dyes has been enhanced compared to the isolated dye molecules.

Characterization of Human Immunodeficiency Virus (HIV) Infection in Cisgender Men and Transgender Women Who Have Sex With Men Receiving Injectable Cabotegravir for HIV Prevention: HPTN 083.

BACKGROUND: The HIV Prevention Trials Network (HPTN) 083 trial demonstrated that long-acting cabotegravir (CAB-LA) was more effective than tenofovir disoproxil fumarate-emtricitabine (TDF/FTC) in preventing human immunodeficiency virus (HIV) in cisgender men and transgender women who have sex with men. We characterized HIV infections that occurred in the blinded phase of HPTN 083. METHODS: Retrospective testing included HIV testing, viral load testing, quantification of study drugs, and HIV drug resistance testing. RESULTS: Fifty-eight infections were evaluated, including 51 incident infections (12 in CAB arm and 39 in TDF/FTC arm). In many cases (5 in CAB arm and 37 in TDF/FTC arm), infection was associated with low or unquantifiable study drug concentrations. In 4 cases, infection occurred with on-time CAB-LA injections and expected plasma CAB concentrations. CAB exposure was associated with prolonged viral suppression and delayed antibody expression. In some cases, delayed HIV diagnosis resulted in CAB provision to participants with undetected infection, delayed antiretroviral therapy, and emergence of drug resistance; most of these infections would have been detected earlier with viral load testing. CONCLUSIONS: Early detection of HIV infection and prompt antiretroviral therapy initiation could improve clinical outcomes in persons who become infected despite CAB-LA prophylaxis. Further studies are needed to elucidate the correlates of HIV protection in persons receiving CAB-LA.

End-capped group manipulation of non-fullerene acceptors for efficient organic photovoltaic solar cells: a DFT study.

A series of acceptors, S1-S5, has been designed based on the acceptor-π-donor-π-acceptor (A-π-D-π-A) architecture by incorporating a phenothiazine unit as the central donor unit. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods have been employed to study the effect of various end-capped groups on the geometric, electronic, optical and charge transport properties of the designed acceptor molecules. The results reveal that on increasing the electron-withdrawing nature of the end-capped groups, the performance of the acceptor molecules increases. It is also observed that on increasing the flexibility of the end-capped groups, the planarity of the molecules gets destroyed and, as a result, the performance of the acceptor molecules decreases. The investigated molecules exhibit high electron affinity (EA) and low reorganization energy for electrons (λ-), indicating the electron acceptor nature of the designed molecules. The absorption properties of the molecules manifest that compounds S2-S4 possess high values of the maximum wavelength (λmax) of absorption. We have also studied the properties of a D/A active layer by considering PffBT4T-2OD as the electron donor and arranging PffBT4T-2OD/S1-S5 molecules in a face to face manner. Properties of the D/A blend indicate that molecules S2-S4 have capacity to promote charge carrier separation at the D/A active layer. Our results provide guidelines for further designing of acceptors to enhance the performance of organic solar cells (OSCs).

Rational design of BODIPY-carbazole analogues in the context of D-π-A approach for facile charge transport: A DFT/TD-DFT study.

In this paper, we have examined the influence of torsional rigidity on the optoelectronic properties by imposing furan, pyrrole and thiophene unit on the BODIPY-carbazole based donor-acceptor systems employing density functional theory (DFT) formalism. We have designed 12 small conjugated molecules based on the donor (carbazole)-acceptor (BODIPY) approach using furan, pyrrole and thiophene unit as the bridging units. To study the torsional rigidity imparted by the bridging units we have performed potential energy surface (PES) analysis. Our study explores that among the bridging units furan and thiophene impart maximum and minimum rigidity on the systems respectively. Different parameters viz. distortion energy (ΔEdis), HOMO-LUMO gap (ΔH-L values), ionization potential (IP), electron affinity (EA), bond length alteration (BLA) parameters, dipole moment values, reorganization energies for holes (λh) and electrons (λe), electronic coupling matrix element (V), charge transfer rate (kct), hopping mobility (µhop), radiative decay rate (kr) etc. have been calculated. The absorption and emission spectra of the BODIPY based compounds have been studied using TD-DFT. NTO analysis have also been performed for the dominant electronic transitions. Our calculations predict that compounds possessing pyrrole unit as the bridging unit and compounds in which BODIPY unit is meso substituted with pyrrole unit possesses greater amount of conjugation and as a result exhibit facile charge transport.

Rational Design of Bay-Annulated Indigo (BAI)-Based Oligomers for Bulk Heterojunction Organic Solar Cells: A Density Functional Theory (DFT) Study.

In this paper, we have designed a series of oligomers based on the donor-acceptor concept. Here, acceptor bay-annulated indigo (BAI) dye and donor N-methyl-4,5-diazacarbazole (DAC) are joined by a thiophene linkage. We have substituted the 5th and 5'th positions of the acceptor unit and the 2nd position of the donor unit with various electron-withdrawing and electron-donating groups to study various structural and electronic properties of the compounds. In this regard, we have calculated the dihedral angle, distortion energy, bond length alteration (BLA) parameters, bang gap (Δ H - L ) values, partial density of states (PDOS), electrostatic potential (ESP) surface analysis, reorganization energy, charge transfer rates, hopping mobility values, and absorption spectra of the compounds. The ESP plots of the compounds indicate significant charge separation in the studied compounds. Our study manifests that the designed compounds are prone to facile charge transport.

Charge transport in isoindigo-dithiophenepyrrole based D-A type oligomers: A DFT/TD-DFT study for the fabrication of fullerene-free organic solar cells.

In this paper, we have designed a series of isoindigo-dithiophenepyrrole based oligomers with donor-acceptor architecture. The donor and acceptor units are joined by a thiophene linkage. We have substituted the 5,5'-positions of the isoindigo acceptor unit with different +I groups, viz., -CH3, -NH2, -SH, -OH, -OCH3, and -CH=CH2, and -I groups, viz., -F, -NO2, -CN, -COCH3, -COOH, and -CF3. We have studied the structural, charge injection, and transport properties employing the density functional theory (DFT) formalism. Our study explores that the presence of bulky substituents adversely affects these properties. Values of frontier orbital energies, ionization potentials, and electron affinities are calculated for each compound to predict the ease of charge injection from metal electrodes to these compounds. Most of our compounds show the ease of hole injection ability and show a large electron injection barrier. Computation of reorganization energies followed by the charge transfer integral and charge transfer rate have also been performed. Our findings reveal that compounds substituted with +I groups possess larger hole mobilities than the compounds with -I groups. Substitution of a dimer of compound 9 with -NO2 leads to the highest hole and electron mobility. Dipole moment values have also been calculated to study the charge transport properties. We have also computed the absorption properties of the compounds using the time-dependent DFT method. Our study indicates that absorption properties are changed by the attachment of substituents and can be tuned according to the requirements. Among the studied compounds, the -OCH3 substituted dimer (dimer 6) exhibits the largest bathochromic shift with a λ max of 554 nm. From this study, we can infer that our designed compounds are promising candidates for fabrication of optoelectronic devices.