Certain patterns of stripes are judged to be unpleasant to look at. They induce illusions of colour, shape and motion that are sometimes perceived predominantly to one side of fixation. People who suffer frequent headaches tend to report more illusions, and if the pain consistently occurs on the same side of the head the illusions tend to be lateralized. The parameters of the patterns that induce illusions (including their shape, spatial frequency, duty cycle, contrast and cortical representation) closely resemble those that elicit epileptiform electroencephalographic abnormalities in patients with photosensitive epilepsy. The viewing conditions under which such abnormalities are likely to appear are also those under which more illusions are seen.

Singlet fission is an excitation multiplication process in molecular systems that can circumvent energy losses and significantly boost solar cell efficiencies; however, the nature of a critical intermediate that enables singlet fission and details of its evolution into multiple product excitations remain obscure. We resolve the initial sequence of events comprising the fission of a singlet exciton in solids of pentacene derivatives using femtosecond transient absorption spectroscopy. We propose a three-step model of singlet fission that includes two triplet-pair intermediates and show how transient spectroscopy can distinguish initially interacting triplet pairs from those that are spatially separated and noninteracting. We find that the interconversion of these two triplet-pair intermediates is limited by the rate of triplet transfer. These results clearly highlight the classical kinetic model of singlet fission and expose subtle details that promise to aid in resolving problems associated with triplet extraction.

We compare the singlet fission dynamics of five pentacene derivatives precipitated to form nanoparticles. Two nanoparticle types were distinguished by differences in their solid-state order and kinetics of triplet formation. Nanoparticles that comprise primarily weakly coupled chromophores lack the bulk structural order of the single crystal and exhibit nonexponential triplet formation kinetics (Type I), while nanoparticles that comprise primarily more strongly coupled chromophores exhibit order resembling that of the bulk crystal and triplet formation kinetics associated with the intrinsic singlet fission rates (Type II). In the highly ordered nanoparticles, singlet fission occurs most rapidly. We relate the molecular packing arrangement derived from the crystal structure of the pentacene derivatives to their singlet fission dynamics and find that slip stacking leads to rapid, subpicosecond singlet fission. We present evidence that exciton delocalization, coincident with an increased relative admixture of charge-transfer configurations in the description of the exciton wave function, facilitates rapid triplet pair formation in the case of single-step singlet fission. We extend the study to include two hexacene derivatives and find that these conclusions are generally applicable. This work highlights acene derivatives as versatile singlet fission chromophores and shows how chemical functionalization affects both solid-state order and exciton interactions and how these attributes in turn affect the rate of singlet fission.

Bulky side chains promote a molecular packing and intermolecular coupling that effect high-efficiency singlet fission in amorphous solids of pentacene derivatives.

Solution-processable, crystalline material is found to be a promising target for quantitative, or lossless, singlet fission.

Perylene diimides (PDIs) are versatile n-type materials showing great promise in a number of optoelectronic applications. While the singlet manifold of PDI can be readily populated, triplet excited states are only accessible through complex multistep energy cascades or bimolecular sensitization. In this work, we have synthesized a series of thionated PDIs that display rapid intersystem crossing to triplet states. Significantly, the thionated PDIs are synthesized in one step from the parent compound using commercially available Lawesson's reagent. Electrochemical and steady state optical absorption measurements show that the electron affinity and ionization potentials can be systematically tuned through successive sulfur atom substitution. Thin-film optical absorption measurements show how the number and regiochemistry of the thiocarbonyl groups influence π−π interactions in the solid state. Ultrafast transient absorption spectroscopy reveals rapid triplet formation that is independent of the degree of thionation, highlighting this approach as a facile means of accessing the triplet manifold of PDI.

This study tested the efficacy of selected personality, behavioural, and social/organizational variables as predictors of adaptation to night work. Sixty female student nurses were studied during their first 15 months of shiftwork. Twenty-two worked on rotating day and afternoon shifts throughout, while the remaining 38 began regular night shifts after six months. Psychological symptoms were measured at baseline (Stage 1), six months (Stage 2) and 15 months (Stage 3). Repeated measures analysis of variance revealed a significant shift group x symptoms interaction (p less than 0.05) between Stages 2 and 3. Only the night workers displayed a significant increase (Tukey HSD: p less than 0.01) in symptoms between Stages 1 and 3. Multiple regression analysis revealed that neuroticism and perceived work/nonwork conflict predicted symptoms at Stage 2. Night work, social support from supervisors, and morningness were predictors at Stage 3. These results suggest that organisational, behavioural, and physiological factors moderate the impact of night work on psychological well-being, and personality factors do not.

Morningness scales have been translated into several languages, but a lack of normative data and methodological differences make cross-cultural comparisons difficult. This study examines the psychometric properties and factor structure of the Composite Scale of Morningness (CSM) in samples from five countries: France (n = 627), Italy (n = 702), Spain (n = 391), Thailand (n = 503), and Australia (n = 654). Strong national differences are identified. A quadratic relationship between age and CSM total score was apparent in the Australian data with a downward trend after age 35 yrs. There was no age effect in any sample in the range from 18 to 29 yrs. Factor analysis identified a three-factor solution in all groups for both men and women. Tucker's congruence coefficients indicate that: (1) this solution is highly congruent between sexes in each culture, and (2) a morning affect factor is highly congruent between cultures. These results indicate there are national differences in factorial structure and that cut-off scores used to categorize participants as morning- and evening-types should be established for different cultural and age groups.