Ultrafast symmetry-breaking charge separation in Perylenemonoimide-embedded multichromophores: impact of regioisomerism.

Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential to the latest generation of organic photovoltaics. However there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, it is reported herein, that ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit a larger bathochromic shift in the emission spectra and a significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display the strikingly different optical feature of SB-CS with a very fast charge separation rate (τCS = 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. The SB-CS for two dimers is well-supported by the formation of PMI˙+ and PMI˙- bands in the fs-TA spectra. Further analysis of fs-TA data revealed that, among the other multichromophores the trimer also exhibits a clear charge separation, whereas SB-CS signatures are less prominent, but can not be completely disregarded, for the meta- and para-dimers. Additionally, the charge separation dynamics of those above-mentioned PMI derivatives are devoid of a kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in the ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier (ΔG≠) of the derivatives in DMF are established from the Rehm-Weller equation and Marcus's theory, respectively. This work is an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining sustainable guidelines for using SB-CS.

Conformational Effect of Catechol-Terephthalonitrile Emitters Leading to Ambient Violet Phosphorescence.

Organic ambient violet phosphorescent (AVP) materials are of great interest due to their involvement of high energy and longer-lived triplet excitons. Here, we show three fused ring functionalized donor-acceptor-donor (D-A-D/D-A-D') emitters (BPT1-BPT3), in which two catechol-based donors (3,4-dihydroxybenzophenone, catechol, or 3,5-ditert-butylcatechol) are covalently fused to the terephthalonitrile acceptor via four O-C single bonds. Spectroscopic analysis revealed that all the molecules show AVP (∼390-394 nm, τAVP = 73-101 µs) with phosphorescence quantum yields (ϕP) of 1.8-27.4% due to low singlet-triplet gaps (0.036-0.046 eV) and conformational effects. BPT3 with bulky tert-butyl groups increases AVP (ϕP = 27.4%). Quantum chemistry calculations reveal flat (F1) and twisted (F2) conformers (ground state) with a low energy difference (∼4-5 kcal/mol) for all molecules; the F1 conformer is responsible for efficient AVP, while weak blue thermally activated delayed fluorescence with longer-lived delayed components is realized from the F2 conformer. This approach may provide important clues for the design of high-energy organic phosphorescent materials.

Spectral characteristics of the flavones and anthocyanins present in passionflower (Passiflora incarnata).

Rich in antioxidants with a variety of flavones and anthocyanins, passionflower/fruit has been extensively used in food, beverage, medicinal, and natural dyes industries. The individual components present in passionflower are identified by extracting them in methanol, partitioning them between ethyl acetate and aqueous layers, and recording their ESI mass spectrometric data. The steady-state absorption and fluorescence spectra of the extract in methanol and dimethyl sulfoxide are recorded and the lifetime of the fluorescing species is reported. The pH dependence of the absorption spectrum confirms the presence of the anthocyanins.

Inter-Network Charge-Transfer Excited State Formation Within a Two-fold Catenated Metal-Organic Framework.

Charge-transfer excited state (CTES) defines the ability to split photon energy into work producing redox equivalents suitable for photocatalysis. Here, we report inter-net CTES formation within a two-fold catenated crystalline metal-organic framework (MOF), constructed with two linkers, N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNDI) and 2,6-dicarboxynaphthalene (NDC). The structural flexibility puts two complementary linkers from two nets in a proximal position to interact strongly. Supported by the electrochemical and steady-state electronic spectroscopic data, this ground-state interaction facilitates forming CTES that can be populated by direct excitation. We map the dynamics of the CTES which persists over a few nanoseconds and highlight the utilities of such relatively long-lived CTES as enhanced conductivity of the MOF under light over that measured in dark and as a proof-of-the-principle test, photo-reduction of methyl viologen under white light.

Effect of Nanoscale Confinement on Ultrafast Dynamics of Singlet Fission in TIPS-Pentacene.

Singlet fission (SF) is a phenomenon for the generation of a pair of triplet excitons from anexcited molecule in singlet electronic state interacting with another adjacent molecule in its ground electronic state. By increasing the effective number of charge carriers and reducing thermal dissipation of excess energy, SF is promised to enhance light-harvesting efficiency for photovoltaic applications. While SF has been extensively studied in thin films and crystals, the same has not been explored much within a confined medium. Here, we report the ultrafast SF dynamics of triisopropylsilylethynyl pentacene (TIPS-Pn) in micellar nanocavity of varying sizes (prepared from TX-100, CTAB, and SDS surfactants). The nanoparticles with a smaller size contain weakly coupled chromophores which are shown to be more efficient for SF followed by triplet generation as compared to the nanoparticles of larger size which contain strongly coupled chromophores which are less efficient due to the presence of singlet exciton traps. Through these studies, we delineate how a subtle interplay between short-range and long-range interaction among chromophores confined within nanoparticles, fine-tuned by the curvature of the micellar interface but irrespective of the nature of the micelle (cationic or anionic or neutral), play a crucial role in SF through and generation of triplets.

Comparison of the safety and efficacy of dexmedetomidine with midazolam for the management of paediatric dental patients: A systematic review.

BACKGROUND: Pain, fear, and anxiety have long been associated with pediatric dentistry. A child's cooperation with a dental.procedure.usually requires various behavioral management strategies conveyed by the entire dental team. The use of sedatives in dental clinics for providing analgesia and anxiolysis allows the patient to respond appropriately to verbal commands and light tactile stimulation., thus making dental treatment more patient friendly and effective. AIM: The aim of this study was to compare the safety and efficacy of dexmedetomidine versus midazolam for the management of pediatric patients in the dental clinic. MATERIALS AND METHODS: This systematic review was prepared according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Six articles were selected for this systematic review. Of them, only in four articles, homogeneous data were available which were subjected to meta-analysis. RESULTS: When compared with midazolam, premedication with dexmedetomidine resulted in much lower incidence of emergence delirium (odds ratio = 0.07, 95% confidence interval: 0.01-0.54, P = 0.01). No significant difference was observed with respect to satisfactory behavior of the child, successful parental separation, and satisfactory mask acceptance following sedation. CONCLUSION: Both dexmedetomidine and midazolam are equally effective for the management of pediatric patients in the dental clinic. In addition, dexmedetomidine premedication is associated with lower incidence of emergence delirium and has a better margin of safety.

Comparative Evaluation of Changes in Physiological and Psychomotor Effects in Pediatric Patients during Extraction under Different Concentrations of Nitrous Oxide-Oxygen Inhalation Sedation.

INTRODUCTION: Nonpharmacological behavioral management techniques are routinely used to create an environment that facilitates and builds a rapport between the child and the dentist to carry out procedures with minimal disruption. However, the discomfort associated with oral injections produces varying degrees of stress in all patients. Nitrous oxide (N2O)-oxygen (O2) inhalation sedation is one of the most widely used modalities for the management of fear and anxiety in children. OBJECTIVE: The objective was to evaluate changes in physiological and psychomotor effects in pediatric patients during extraction under different concentrations of N2O-O2 inhalation sedation. MATERIALS AND METHODS: A total of 300 healthy patients in the age range of 6-12 years (mean 8.9 years), who needed extraction of primary tooth, were included in the study. Pulse rate, SpO2, blood pressure (BP), and temperature were recorded at baseline, 30% N2O concentration, 50% N2O concentration, and again postoperatively. In addition, anxiety levels and neuromuscular coordination were recorded at the respective intervals. RESULTS: The results revealed a mean decrease in pulse rate and BP from baseline and an increase in temperature and O2 saturation during the sedation procedure. The findings were statistically significant. Significant impairment of coordination and psychomotor ability was seen at each step. Anxiety had significantly reduced after the onset of sedation due to the anxiolytic effect of N2O. CONCLUSION: N2O-O2 inhalation sedation under different concentrations reduces the anxiety of the patient and produces adequate sedation with vital signs within normal limits along with temporary impairment of psychomotor ability and coordination.

Time to restart: A comparative compilation of triage recommendations in dentistry during the Covid -19 pandemic.

BACKGROUND: The novel coronavirus (COVID-19) pandemic has become a enormous challenge for the health care facilitators. It has significantly affected the dental professionals in their clinical practices, hospitals and even dental schools. Due to the risk of cross - infection involved within in the dental setting, the dental professional is even scared to provide emergent treatment for a patient. AIM: The aim of this comparative review is to throw light on the essential knowledge that a clinician must acquire before triaging a patient, understanding the case definition of COVID-19 and preparedness required before planning to re-open the dental practices. METHODOLOGY: The updated database obtained from various governmental and non-governmental official webpages were rapidly analysed up till May 31, 2020. CONCLUSION: This compilation of recommendations and guidance laid by various authorities across the world will function as a foundation for safer dental practice within the future.

Unravelling the Role of Water in Ultrafast Excited-State Relaxation Dynamics within Nano-Architectures of Chlorophyll a.

Water plays a pivotal role in structural stability of supramolecular pigment assemblies designed for natural light harvesting (for example, chlorosome antenna complex) as well as their artificial analogs. However, the dynamic role of water in the context of excite-state relaxation has not been explored till date, which we report here. Using femtosecond transient absorption spectroscopy, we investigate the excited-state dynamics of two types of nano-scale assemblies of chlorophyll a with different structural motifs, rod-shaped and micellar assemblies, that depend on the water content. We show how water participates in excess energy dissipation by vibrational cooling of the non-thermally populated Qy band at different rates in different types of clusters but exhibits no polar solvation dynamics. For the micelles, we observe a bifurcation of stimulated emission line shape, whereas a positive-to-negative switching of differential absorption is observed for the rods; both these observations are correlated with their specific structural aspects. Density functional theory calculations reveal two possible stable ground state geometries of dimers, accounting for the bifurcation of line shape in micelles. Thus, our study elucidates water-mediated structure-function relationship within these pigment assemblies.

Reliability of Sawai's classification for dental cervical abrasions: A pilot study.

AIM: To test the reliability of the Sawai's classification for dental cervical abrasions. METHODS: Intraoral photographs of 70 teeth from 23 patients with tooth abrasions were taken by the first examiner MS. The teeth were marked and the photos were maintained in a soft copy sequentially. Two other examiners FA and SC were trained in the use of the classification and any clarifications needed were provided at the beginning of the study. Each examiner was then given the soft copy of the complied photographs and was asked to classify the dental cervical abrasion according to their understanding of the Sawai's classification. They were given sheets to write their responses for every marked tooth. All the examiners were blinded to each other's observations which were then tested for inter-rater agreement among the three examiners. RESULTS: The 70 teeth with tooth abrasions from 23 patients were examined by 3 investigators (MS, FA and SC) to test the reliability of the Sawai's classification system for tooth abrasion. Each examiner marked their responses in separate sheets which were blinded to each other. The kappa statistics were performed for inter-rater agreement among the three examiners. The level of agreement was evaluated according to the six-level nomenclature given by Landis and Koch. ICC and 95%CI between two examiners, i.e., the inter-rater agreement among 1st examiner (MS) and 2nd examiner (FA) was 0.89. The inter-rater agreement among 1st examiner (MS) and 3rd examiner (SC) was 0.89. And the inter-rater agreement among 2nd examiner (FA) and 3rd examiner (SC) was 0.83. All the three comparisons show an almost perfect agreement between them. CONCLUSION: There is an almost perfect agreement between multiple observers for classifying dental cervical abrasions using Sawai's classification. Hence, this classification is reliable.