Star-shaped small donor molecules based on benzotriindole for efficient organic solar cells: a DFT study

CONTEXT

The purpose of the S01-S05 series of end-capped modified donor chromophores is to amplify the energy conversion efficiency of organic solar cells. Using quantum chemical modeling, the photophysical and photoelectric characteristics of the S01-S05 geometries are examined.

METHOD

The influence of side chain replacement on multiple parameters, including the density of states (DOS), molecular orbital analysis (FMOS), exciton-binding energy (Eb), molecular electrostatic potential analysis, dipole moment (μ), and photovoltaic characteristics including open circuit voltage (VOC), and PCE at minimal energy state geometries, has been investigated employing density functional theory along with TD-DFT analysis. The molar absorption coefficient (λmax) of all the proposed compounds (S01-S05) was efficiently enhanced by the terminal acceptor alteration technique, as demonstrated by their scaling up with the reference molecule (SR). Among all molecules, S04 has shown better absorption properties with a red shift in absorption having λmax at 845 nm in CHCl3 solvent and narrow energy gap (EG) 1.83 eV with least excitation energy (Ex) of 1.4657 eV. All created donors exhibited improved FF and VOC than the SR, which significantly raised PCE and revealed their great efficiency as OSC. Consequently, the results recommended these star-shaped molecules as easily attainable candidates for constructing extremely efficient OSCs.

Theoretical design and evaluation of efficient small donor molecules for organic solar cells

CONTEXT

The development of high-efficiency photovoltaic devices is the need of time with increasing demand for energy. Herein, we designed seven small molecule donors (SMDs) with A-π-D-π-A backbones containing various acceptor groups for high-efficiency organic solar cells (OSCs). Molecular engineering was performed by substituting the acceptor group in the synthesized compound (BPR) with another highly efficient acceptor group to improve the photoelectric performance of the molecule.

METHOD

The photovoltaic, optoelectronic, and photophysical properties of the proposed compounds (BP1-BP7) were investigated in comparison to BPR using DFT and TD-DFT at MPW1PW91/6-311G(d,p) level of theory. All molecules we designed have red-shifted absorption spectra. The modification of the acceptor fragment of the BPR resulted in a reduced HOMO-LUMO energy gap; thus, the designed compounds (BP1-BP7) had improved optoelectronic responses as compared with the BPR molecule. Various key factors that are crucial for efficient SMDs such as exciton binding energy, frontier molecular orbitals (FMOs), absorption maximum (λmax), open circuit voltage (VOC), dipole moment (μ), excitation charge mobilities, and the transition density matrix of (BPR, BP1-BP7) have also been studied. Low reorganizational energy (holes and electrons) values provide high charge mobility, and all the designed compounds are efficient in this regard. Here, BP6 exhibits low excitation energy (1.66 eV), highest open circuit voltage (2.00 V), normalized VOC (77.23), and fill factor (0.931). Consequently, the superiority of the designed molecules advises experimenters to envision future developments in extremely effective OSC devices.

Synthesis of 1-(4-Bromobenzoyl)-1,3-dicyclohexylurea and Its Arylation via Readily Available Palladium Catalyst-Their Electronic, Spectroscopic, and Nonlinear Optical Studies via a Computational Approach

In this study, we reported the synthesis of 1-(4-bromobenzoyl)-1,3-dicyclohexylurea by the reaction of DCC (N,N'-dicyclohexylcarbodiimide) with 4-bromobenzoic acid. Subsequently, we further synthesized a new series of 1-(4-arylbenzoyl)-1,3-dicyclohexylurea (5a-g) derivatives using a Suzuki cross-coupling reaction between 1-(4-bromobenzoyl)-1,3-dicyclohexylurea (3) and various aryl/heteroaryl boronic acids (4). Thus, density functional theory (DFT) calculations have been performed to examine the electronic structure of the synthesized compounds (3, 5a-g) and to calculate their spectroscopic data. Moreover, optimized geometries and thermodynamic properties, such as frontier molecular orbitals (HOMO, LUMO), molecular electrostatic potential surfaces, and reactivity descriptors, were also calculated at the PBE0-D3BJ/def2-TZVP/SMD1,4-dioxane level of theory to validate the structures of the synthesized compounds.

Synthesis of Functionalized Thiophene Based Pyrazole Amides via Various Catalytic Approaches: Structural Features through Computational Applications and Nonlinear Optical Properties

In the present study, pyrazole-thiophene-based amide derivatives were synthesized by different methodologies. Here, 5-Bromothiophene carboxylic acid (2) was reacted with substituted, unsubstituted, and protected pyrazole to synthesize the amide. It was observed that unsubstituted amide (5-bromo-N-(5-methyl-1H-pyrazol-3-yl)thiophene-2-carboxamide (7) was obtained at a good yield of about 68 percent. The unsubstituted amide (7) was arylated through Pd (0)-catalyzed Suzuki–Miyaura cross-coupling, in the presence of tripotassium phosphate (K₃PO₄) as a base, and with 1,4-dioxane as a solvent. Moderate to good yields (66–81%) of newly synthesized derivatives were obtained. The geometry of the synthesized compounds (9a–9h) and other physical properties, like non-linear optical (NLO) properties, nuclear magnetic resonance (NMR), and other chemical reactivity descriptors, including the chemical hardness, electronic chemical potential, ionization potential, electron affinity, and electrophilicity index have also been calculated for the synthesized compounds. In this study, DFT calculations have been used to investigate the electronic structure of the synthesized compounds and to compute their NMR data. It was also observed that the computed NMR data manifested significant agreement with the experimental NMR results. Furthermore, compound (9f) exhibits a better non-linear optical response compared to all other compounds in the series. Based on frontier molecular orbital (FMO) analysis and the reactivity descriptors, compounds (9c) and (9h) were predicted to be the most chemically reactive, while (9d) was estimated to be the most stable among the examined series of compounds.

Facile Synthesis of 5-Aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides via Suzuki Cross-Coupling Reactions, Their Electronic and Nonlinear Optical Properties through DFT Calculations

Synthesis of 5-aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides (4a–4n) by a Suzuki cross-coupling reaction of 5-bromo-N-(pyrazin-2-yl)thiophene-2-carboxamide (3) with various aryl/heteroaryl boronic acids/pinacol esters was observed in this article. The intermediate compound 3 was prepared by condensation of pyrazin-2-amine (1) with 5-bromothiophene-2-carboxylic acid (2) mediated by TiCl₄. The target pyrazine analogs (4a–4n) were confirmed by NMR and mass spectrometry. In DFT calculation of target molecules, several reactivity parameters like FMOs (E_HOMO, E_LUMO), HOMO–LUMO energy gap, electron affinity (A), ionization energy (I), electrophilicity index (ω), chemical softness (σ) and chemical hardness (η) were considered and discussed. Effect of various substituents was observed on values of the HOMO–LUMO energy gap and hyperpolarizability. The p-electronic delocalization extended over pyrazine, benzene and thiophene was examined in studying the NLO behavior. The chemical shifts of ¹H NMR of all the synthesized compounds 4a–4n were calculated and compared with the experimental values.

Is there a correlation between degree of viremia and liver histology in chronic hepatitis C?

OBJECTIVE

To determine the correlation between degree of histological liver damage and serum HCV RNA level in patients of chronic hepatitis C, in order to evaluate the usefulness of HCV RNA estimation as an alternate to liver biopsy.

METHODS

This non-interventional descriptive study, was carried out at the department of Pathology, Army Medical College, Rawalpindi, Pakistan between April and September 2002. Core needle liver biopsies of fifty five patients of chronic hepatitis C were evaluated according to Knodell's histological activity index system. The patients were categorized into four subgroups depending upon the grade and stage of disease according to Desmet's classification, and into three groups according to degree of viremia.

RESULTS

Five patients had mild viremia, 43 moderate and 7 had severe viremia. Seven patients had minimal disease, 9 mild, 22 moderate and 17 had severe chronic hepatitis. Eight patients had no fibrosis, 20 had fibrous portal expansion, 19 bridging fibrosis, and 8 patients had cirrhosis. No significant correlation was found between serum HCV RNA levels and grade or stage of the disease, with correlation coefficients of rs = -.054 and rs = .034 respectively. Moreover, no individual component of the HAI correlated with serum HCV RNA levels.

CONCLUSION

Serum HCV RNA level does not determine the degree of hepatic injury precisely and liver biopsy is necessary to accurately evaluate the extent of liver damage.

Morphological study of liver biopsy in Thalassaemia major

OBJECTIVE

To see the morphological changes in liver in transfusion dependent Thalassaemia major children undergoing bone marrow transplantation.

METHODS

This retrospective cross-sectional survey was conducted at Pathology department of Army Medical College and Paediatric department of Military Hospital, Rawalpindi from Jul 2000 to Aug 2003. Liver biopsies were done in 40 thalassaemic major children and histological changes including Knodell Histological activity index (HAI); grade, stage and score along with degree of haemosiderosis were noted. Serum ALT levels, ferritin assays and screening for HBsAg and Anti- HCV antibody were also carried out in these cases.

RESULTS

Forty children 1.5-10.5 years of age (mean 6.1 years) with a male to female ratio of 1.2:1 were included in the study. According to Knodell HAI scoring, 24 (60%) cases had Knodell HAI score between 13/22 to 18/22 and 18 patients (45%) in grade 9-12/18. Six children had fully developed cirrhotic changes whereas 22 and 12 patients showed stage 3 and 1 respectively. Twenty eight (70%) patients had grade 3-4 haemosiderosis. HBsAg was positive in 6 and anti- HCV antibody in 14 patients. Serum ferritin and ALT levels were markedly raised in most of the patients.

CONCLUSION

Seventy percent patients had moderate to severe haemosiderosis and high Knodell HAI score was found in children with severe haemosiderosis, raised ALT and Ferritin levels and with positive serology for HBsAg and anti- HCV antibody. Liver biopsy is useful in thalassaemic children to assess the stage of liver disease and selection of suitable cases for bone marrow transplantation (BMT).

Efficacy of bronchial wash cytology and its correlation with biopsy in lung tumours

OBJECTIVE

To evaluate bronchial wash cytology with histology in our set up.

METHODS

Seventy three specimens were obtained by flexible fiberoptic bronchoscope at pulmonology department of Military Hospital Rawalpindi. All the preserved samples were processed under standard conditions. The slides were stained with Papanicolaou and Haematoxylin and Eosin stains.

RESULTS

A total of 73 patients were studied. The age range was 21 to 80 years. Male to female ratio was 8:1. Complete cytological and biopsy consensus was found in 55 (77.4%) cases. Cytology revealed 24 cases as malignant and nine as atypical/suspicious. Benign and inadequate were 29 and 2 respectively. Histopathology of these cases confirmed 24 (32.9%) as malignant and 29 (39.8%) as benign. True positive alongwith suspicious/atypical were 33 and true negative cases were 29. False positive was one case only whereas false negative cases were eight. The bronchial wash cytology showed sensitivity (80.5%), specificity (96.6%) and accuracy (87.3%). Positive predictive value and negative predictive value were 97% and 78.4% respectively. The commonest types of tumours were squamous cell carcinoma and small cell carcinoma.

CONCLUSION

It is concluded that bronchial wash cytology is a valuable tool and yields almost same information as biopsy. It is useful in patients with evidence of obstruction or risk of haemorrhage.

An autopsy study of hypertrophic cardiomyopathy

OBJECTIVE

To see the pathological features of this disease in our set up and to emphasise the importance of morphological examination in making the diagnosis of hypertrophic cardiomyopathy (HCM) especially in cases of sudden cardiac death.

METHODS

A retrospective, descriptive study of 15 autopsies of this particular disease was carried out at the Armed Forces Institute of Pathology (AFI) Rawalpindi during the period from 1990 to 1995. The hearts along with blood vessels were fixed in 10% formalin and were dissected according to the modified Virchow's method for eliciting the gross appearance of cardiac chambers and valves. Representative sections were taken for histological examination.

RESULTS

All the cases were young adult males. The age range was from 17-34 years (mean, 26-6 years). Ten cases died suddenly and five cases had an evidence of moderate to severe exertion preceding their death. Symmetrical as well as asymmetrical hypertrophy was noted in this study. The thickness of inter ventricular septum (mean 20 mm) and left ventricular wall (mean 22.5 mm) was increased. All the specimens revealed disarray of hypertrophic myocardial fibres and patchy interstitial fibroses.

CONCLUSION

Sudden death is usually the first manifestation of disease. The hearts showed asymmetric as well as concentric hypertrophy. Myofibre hypertrophy and disarray was an important pathological findings in our cases. While carrying out post-mortem examination of a case of sudden cardiac death one should also keep in mind the possibility of this disease.

A comparative investigation of dental and medical student's motivation towards career choice

OBJECTIVE

A number of recent studies have investigated the motivations underlying the career choice of dental and medical students, suggesting that they may be very different. However, as yet, no studies have been conducted which provide a direct comparison of dental and medical students studying in the same place. Accordingly, the aim of this investigation was to conduct a survey which directly compared the motivation of a selection of dental and medical students at Manchester University.

STUDY DESIGN

A questionnaire was developed for this study on the basis of previous surveys investigating the motivations of dental and medical students towards career choice. Six dimensions were covered in the questionnaire including: status and security; the nature of the occupation; career opportunities; patient care and working with people; use of personal skills; and interest in science. In addition, students were asked about the role of work experience in either dentistry or medicine. The questionnaire was distributed to 80 medical students and 80 dental students chosen from a random selection of lecture slots.

RESULTS

The results were analysed using the Mann-Whitney U test. Statistically significant differences were revealed in all six areas of career choice motivation. For instance, dental students were significantly more likely to be motivated by factors relating to status and security and the nature of their occupation (eg regular working hours, self employment and independence). By contrast, medical students were significantly more likely to be motivated by factors relating to career opportunities, patient care and working with people, use of personal skills, and interest in science. Work experience was a strong motivating factor in the case of both dental and medical students (though especially for dental students).

CONCLUSIONS

In comparison with dental students, medical students manifested a more professional attitude in which altruism and intellectual challenge constituted central motivating factors. By contrast, dental students demonstrated more of a commitment to personal and financial gain. The paper queries how useful such attitudes are to a re-oriented dental profession whose aspiration is to provide more accountable and community oriented services.

Clonal hematopoiesis as defined by polymorphic X-linked loci occurs infrequently in aplastic anemia

We evaluated the methylation status of the X-linked gene phosphoglycerate kinase (PGK1) and the DXS 255 locus detected by probe M27 beta to study clonality in acquired aplastic anemia (AA). A total of 30 females were suitable for clonal analysis of peripheral blood polymorphonuclear cells (PMN) and mononuclear cells using a polymerase chain reaction-based procedure in 24 patients and Southern blotting in 9. Overall, 10 of 30 patients exhibited an imbalanced X-inactivation pattern. However, in 4 patients, analysis of constitutional DNA suggested a skewed methylation pattern and 2 further cases had to be excluded because of the lack of an appropriate control. A truly clonal pattern was thus established in 4 of 30 (13%) patients. In 7 patients who later developed clonal disorders of hematopoiesis, X-inactivation analysis did not predict this event in any case. In patients with a paroxysmal nocturnal hemoglobinuria phenotype, there was no correlation between the proportion of phosphatidylinositol glycan anchored protein (PIG-AP)-deficient blood cells and the corresponding X-inactivation pattern. X-inactivation analysis detected clonal hematopoiesis in only 3 of 10 patients with a deficiency in PIG-AP in the cell population under study, but sorting of nucleated cells on the basis of PIG-AP expression showed the clonal nature of PIG-AP-deficient cells. We conclude that the majority of patients with AA show polyclonal hematopoiesis using X-linked clonal analysis, but that minor clonal populations, such as PIG-AP-deficient cells, may not be detected unless sorted cell populations are separately analyzed.

Hepatitis C as a cause of chronic liver disease in northern Pakistan

The antibodies to hepatitis C virus (HCV) were tested in 45 histologically confirmed cases of chronic liver disease. Twelve cases had chronic hepatitis, 24 cirrhosis and 9 hepatocellular carcinoma. Anti-HCV was detected in 6 patients. Two (16.67%) were suffering from chronic hepatitis, 3 (12.5%) had cirrhosis and one (11.11%) hepatocellular carcinoma. None of the anti-HCV positive cases had past history of blood transfusion. The patients of chronic liver disease in this study had a much higher prevalence of HBV infection which indicates that in northern Pakistan hepatitis C virus infection is not a common cause of chronic liver disease whereas HBV infection plays an aetiological role in a much larger number of these cases.

Fatal amoebic liver abscess: an autopsy study

An autopsy study of 20 cases is presented. The mean age was 32 years (range: 14-45). Four cases (20%) presented with jaundice. Another four (20%) had continuous fever with abdominal pain. Six had loose motions with blood and mucus in the stools. The mean duration of illness was 7.2 days. All cases were thin and emaciated. Liver was grossly enlarged (mean weight: 2680 g). The abscess was single in all cases except one. The right lobe was involved in 15 cases, the left in four and both in one. The average size of abscess was 13 cm. The abscess had ruptured in the abdomen in 3 patients, for which laparotomy was performed. Pulmonary involvement was seen in 3 cases. Colon showed ulceration in half the patients. In 2 cases perforation was also present. No cerebral involvement was present. A number of interesting features emerged from this study. Although amoebic liver abscess is a common disease, its diagnosis can be missed due to unusual presentation. In the present study, diagnosis of viral hepatitis, carcinoma lung, bacillary dysentery and enteric fever with perforation were made, which probably contributed materially to fatal outcome.