We examined sub-nanosecond timescale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7-10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors. The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the bestperforming blends, the presence of crystalline acceptor domains was also established.

We report on the dependence of time-resolved photoluminescence (PL) and photocurrent in small-molecule bulk heterojunctions on the donor–acceptor (D/A) LUMO offset, D/A separation, and acceptor domain structure. We chose a high-performance functionalized fluorinated anthradithiophene (ADT) derivative, ADT-TES-F, as the donor and two other fluorinated ADT derivatives, ADT-R-F (where R is a variable side group), as well as two functionalized fluorinated pentacene (Pn) derivatives, Pn-R-F8, as acceptors. The choice of ADT and Pn acceptors enabled us to separate the effects of the D/A LUMO offset, which was approximately zero in the case of ADT acceptors and ∼0.55 eV in the case of Pn acceptors, from those of molecular packing on the optoelectronic properties. The acceptor side groups R were chosen based on (i) packing motifs in the solid state and (ii) size, to achieve different D/A separations at the D/A interface. Addition of an ADT-R-F acceptor to the ADT-TES-F donor introduced disorder, which resulted in increased PL emission, depending on the acceptor’s packing motif, and in reduced photocurrents. In ADT-TES-F/Pn-R-F8 films, charge transfer from ADT-TES-F to Pn-R-F8 was observed with an acceptor packing-dependent formation of an exciplex, which dissociated under applied electric field, contributing to charge carrier photogeneration. However, this contribution was not sufficient to compensate for a photocurrent reduction due to an increased disorder at Pn-R-F8 concentrations of 7 wt % and above, regardless of the acceptor’s R-groups and packing motifs.

BackgroundFacebook, a popular social networking site, has been used by people of different ages and professions for various purposes. Its use in the field of medical education is increasing dramatically. At the same time, the pros and cons of facebook use among the health science students has attracted the attention of educators. The data regarding its use and the effect on the life of Nepalese health science students has not yet been documented. Therefore, this study is carried out to evaluate the effect of facebook use on social interactions, behaviour, academics, and the health of students in a medical college of Nepal.ResultsA cross-sectional descriptive study conducted among medical, dental, nursing and allied health science students using self-administered questionnaire. The study showed that 98.2 % of participants were facebook users. Among 452 respondents, 224 and 228 were male and female respectively, with a mean age of 20.2 ± 1.2 years. The main reason for using facebook was to remain in contact with family and friend (32 %), while its use for the academic purpose was only 5 %. However, 80.8 % of students acknowledged ease in acquiring academic materials from others, through facebook. One-fourth of the students acknowledged that they are using facebook late at night on a regular basis, while surprisingly 4.2 % of the students admitted accessing facebook during the classroom lectures. Almost two-third of the users, further admitted that facebook has had a negative impact on their studies. Burning eyes (21 %), disturbed sleep (19 %), and headache (16 %) were the most common adverse health effects reported by the facebook users. Many students (71.4 %) tried and most of them (68.7 %) succeeded, in reducing time spent on facebook, to allow for increased time devoted to their studies.ConclusionThe widespread use of facebook among the health science students, was found to have both positive and negative effects on their academics, social life, and health.

No abstract

The newly developed regression equations are more accurate for prediction of width of unerupted permanent teeth in a Nepalese population. Further studies are required based on larger sample size, to confirm the applicability of the new regression equations proposed.