FLUORESCENCE SPECTROSCOPY AND MICROSCOPY STUDIES OF CHROMOPHORE COUPLING IN ISOLATED SMALL MOLECULE NANOSTRUCTURES

My thesis focused on understanding the structural changes producing different spectral signatures seen in aggregates of 7,8,15,16- tetrazaterrylene (TAT). Recent work from our group showed crystallographically selective directional charge-separation within isolated extended TAT crystals without the need of an interface. Aggregates of different size not only exhibited different exciton recombination kinetics, but different spectral signatures. The motivation for understanding the change in the structural properties producing the unique spectral signatures is elucidating the mechanism of this directional charge-separation, intrinsic or extrinsic. In this case, an intrinsic mechanism means it is caused by molecular design and packing, and extrinsic mechanism means it is caused by grain boundaries or faults in stacking during the crystallization process. In pursuit of this question, two fundamental questions were investigated (1) What are the different stages of TAT crystal growth, and what is the dominant coupling at each one? (2) What is the underlying crystal structure of the small and large aggregates? (1) Investigation of different stages of TAT crystal growth and spectral signatures: Our initial hypothesis was TAT formed pristine nanoscale structures that had the same dominant intermolecular coupling. We based our theory on TAT\u27s molecular structure lacking substituents that could alter the molecular packing during solution-phase self-assembly. Our hypothesis was tested by sampling assemblies of different size aggregates and comparing their photoluminescence images and spectral signatures. Similar spectral signatures would indicate similar molecular packing and final exciton recombination pathway supporting an intrinsic mechanism. Different spectral signatures would suggest a different molecular packing and exciton recombination pathway. We found TAT could be isolated into assemblies of three different sizes and spectral signatures: small-clusters (\u3e250 nm, J-type), large-clusters (500 nm, HJ- type), and extended-crystals (microns, H-type). The dominant coupling was assigned based on a comparison of the 00/01 peak intensity ratio from the spectral signatures of the isolated monomer and assemblies. The spectrally resolved images of the large clusters showed the spectral signatures varied horizontally through the crystal, ranging from a peak intensity ratio of 1.4 to 0.5. The peak intensity ratio of 1.4 is similar to the single-molecule (1.43), and 0.5 is similar to the extended crystal. The transition in the observed spectral signatures from J \u3e monomer \u3c H as a result of transitioning from a small-cluster- large-cluster – extended-crystal indicated a naturally occurring exciton band inversion upon the assembly process. Typically, an exciton band inversion is caused by the manipulation of side chains to alter the molecular packing of the structure. Although the structural reason behind this naturally occurring exciton band inversion was unknown, this observation provided the opportunity during self-assembly to select for specific optical properties such as exciton recombination dynamics. (2) The underlying crystal structure for the small and large aggregates: To elucidate the structure producing the change in the spectral signatures, the aggregates growth process needed to be controlled to ensure the spectral signatures and photophysical properties could be correlated. Solvent vapor annealing was used to control the aggregation process. This method is widely used to induce aggregation by plasticizing the polymer matrix allowing for aggregation of the analyte to occur. Based on the concentrations used in the above study, we found we can isolate films of small-and large-cluster and extended-crystals. These aggregates have similar spectral signatures as that of the solution-grown aggregates but have higher polarization contrast parameter, M. The three-dimensional structure was probed using polarization anisotropy, defocused imaging, and TEM. The defocused imaging and polarization anisotropy showed the small-clusters were highly aligned linear dipoles. DFT calculations show cofacial dimer geometries that would have linear dipoles could range from a slip of 0.5-1.5 along the chromophore axis. TEM of the small-clusters and solution-grown crystals showed the same unit cell but grown along different crystallographic axis [011] vs. [010]. These findings suggest TAT initially forms in one crystallographic direction driven by N-H bonding and then along p-stacking direction when the -interactions become more dominant. Our hypothesis is the preservation of the unit cell at different stages of growth shows the J- to H-transition in TAT has little to do with the Coulombic coupling but is dependent on the charge-transfer interaction. Our findings also show for an unfunctionalized molecule, solvent vapor annealing is controlling more than just order of the chromophores, but the interference between the neighboring cofacial molecular orbitals. Our goal was to create design principles based on the effect molecular architecture has on chromophore coupling and resulting spectral signatures in TAT aggregates and nanowires. These paradigms would be applied for the advancement of using semiconductor nanowires as a route for directional control over energy and/or charge-transport. We probed isolated aggregates of TAT using photoluminescence spectroscopy and microscopy to understand the different interchromophore interactions present at different stages of growth. TEM, defocused imaging, and polarization anisotropy probed chromophore and crystalline structure within the aggregates. From my results three key findings can be made (1) exciton band inversion does not always need to be controlled by side chains (2) solvent vapor annealing can be used to control aggregate size and indirectly interchromophore interactions (3) Charge transfer interactions can experimentally be observed to have a profound impact on the spectral signatures of HJ aggregates. Ultimately, our vision is that these principles will be used to design new molecular systems that can be engineered to undergo singlet fission and incorporated into polarization control optical properties

Directional Charge Separation in Isolated Organic Semiconductor Crystalline Nanowires

One of the fundamental design paradigms in organic photovoltaic device engineering is based on the idea that charge separation is an extrinsically driven process requiring an interface for exciton fission. This idea has driven an enormous materials science engineering effort focused on construction of domain sizes commensurate with a nominal exciton diffusion length of order 10 nm. Here, we show that polarized optical excitation of isolated pristine crystalline nanowires of a small molecule n-type organic semiconductor, 7,8,15,16-tetraazaterrylene, generates a significant population of charge-separated polaron pairs along the π-stacking direction. Charge separation was signalled by pronounced power-law photoluminescence decay polarized along the same axis. In the transverse direction, we observed exponential decay associated with excitons localized on individual monomers. We propose that this effect derives from an intrinsic directional charge-transfer interaction that can ultimately be programmed by molecular packing geometry

Sex Offenders’ Perceptions of the Police and Courts:Are There Spill-Over Effects?

Individuals convicted of sexual offenses are rarely asked their views of the police and courts. The aims of this study were to examine the impact of feelings of guilt on perceptions of the police and police interview outcomes and spill-over effects from perceptions of the police to perceptions of the courts. Participants were 116 adult males incarcerated for sexual offenses who were invited to report their perceptions of police interviewers, feelings at the time of interview, interview outcomes, and perceptions of the court process. Feelings of guilt were related to perceptions of the police. Both feelings of guilt and perceptions of the police were associated with interview outcomes. Spill-over effects were found as perceptions of the police were directly related to perceptions of the courts. The findings highlight the important role of police officers as gatekeepers to the criminal justice system, with associated implications for police officers’ training and practice

Impact of COVID-19 lockdown on the incidence and mortality of acute exacerbations of chronic obstructive pulmonary disease: national interrupted time series analyses for Scotland and Wales

The COVID-19 pandemic and ensuing national lockdowns have dramatically changed the healthcare landscape. The pandemic’s impact on people with chronic obstructive pulmonary disease (COPD) remains poorly understood. We hypothesised that the UK-wide lockdown restrictions were associated with reductions in severe COPD exacerbations. We provide the first national level analyses of the impact of the COVID-19 pandemic and first lockdown on severe COPD exacerbations resulting in emergency hospital admissions and/or leading to death as well as those recorded in primary care or emergency departments

Effect of oxygen on the expression of renin-angiotensin system components in a human trophoblast cell line

During the first trimester, normal placental development occurs in a low oxygen environment that is known to stimulate angiogenesis via upregulation of vascular endothelial growth factor (VEGF). Expression of the placental renin-angiotensin system (RAS) is highest in early pregnancy. While the RAS and oxygen both stimulate angiogenesis, how they interact within the placenta is unknown. We postulated that low oxygen increases expression of the proangiogenic RAS pathway and that this is associated with increased VEGF in a first trimester human trophoblast cell line (HTR-8/SVneo). HTR-8/SVneo cells were cultured in one of three oxygen tensions (1%, 5% and 20%). RAS and VEGF mRNA expression were determined by qPCR. Prorenin, angiotensin converting enzyme (ACE) and VEGF protein levels in the supernatant, as well as prorenin and ACE in cell lysates, were measured using ELISAs. Low oxygen significantly increased the expression of both angiotensin II type 1 receptor (AGTR1) and VEGF (both P < 0.05). There was a positive correlation between AGTR1 and VEGF expression at low oxygen (r = 0.64, P < 0.005). Corresponding increases in VEGF protein were observed with low oxygen (P < 0.05). Despite no change in ACE1 mRNA expression, ACE levels in the supernatant increased with low oxygen (1% and 5%, P < 0.05). Expression of other RAS components did not change. Low oxygen increased AGTR1 and VEGF expression, as well as ACE and VEGF protein levels, suggesting that the proangiogenic RAS pathway is activated. This highlights a potential role for the placental RAS in mediating the proangiogenic effects of low oxygen in placental development

Factors influencing terrestriality in primates of the Americas and Madagascar

Among mammals, the order Primates is exceptional in having a high taxonomic richness in which the taxa are arboreal, semiterrestrial, or terrestrial. Although habitual terrestriality is pervasive among the apes and African and Asian monkeys (catarrhines), it is largely absent among monkeys of the Americas (platyrrhines), as well as galagos, lemurs, and lorises (strepsirrhines), which are mostly arboreal. Numerous ecological drivers and species-specific factors are suggested to set the conditions for an evolutionary shift from arboreality to terrestriality, and current environmental conditions may provide analogous scenarios to those transitional periods. Therefore, we investigated predominantly arboreal, diurnal primate genera from the Americas and Madagascar that lack fully terrestrial taxa, to determine whether ecological drivers (habitat canopy cover, predation risk, maximum temperature, precipitation, primate species richness, human population density, and distance to roads) or species-specific traits (body mass, group size, and degree of frugivory) associate with increased terrestriality. We collated 150,961 observation hours across 2,227 months from 47 species at 20 sites in Madagascar and 48 sites in the Americas. Multiple factors were associated with ground use in these otherwise arboreal species, including increased temperature, a decrease in canopy cover, a dietary shift away from frugivory, and larger group size. These factors mostly explain intraspecific differences in terrestriality. As humanity modifies habitats and causes climate change, our results suggest that species already inhabiting hot, sparsely canopied sites, and exhibiting more generalized diets, are more likely to shift toward greater ground use.Fil: Eppley, Timothy M.. San Diego Zoo Wildlife Alliance; Estados Unidos. Portland State University; Estados UnidosFil: Hoeks, Selwyn. Radboud Universiteit Nijmegen; Países BajosFil: Chapman, Colin A.. University of KwaZulu-Natal; Sudáfrica. Wilson Center; Estados Unidos. Northwest University; China. The George Washington University; Estados UnidosFil: Ganzhorn, Jörg U.. Universitat Hamburg; AlemaniaFil: Hall, Katie. Sedgwick County Zoo; Estados UnidosFil: Owen, Megan A.. San Diego Zoo Wildlife Alliance; Estados UnidosFil: Adams, Dara B.. Humboldt State University; Estados Unidos. Ohio State University; Estados UnidosFil: Allgas, Néstor. Asociación Neotropical Primate Conservation Perú; PerúFil: Amato, Katherine R.. Northwestern University; Estados UnidosFil: Andriamahaihavana, McAntonin. Université D'antananarivo; MadagascarFil: Aristizabal, John F.. Universidad Autónoma de Ciudad Juárez; México. Universidad de los Andes; ColombiaFil: Baden, Andrea L.. City University of New York; Estados Unidos. New York Consortium In Evolutionary Primatology; Estados UnidosFil: Balestri, Michela. Oxford Brookes University (oxford Brookes University);Fil: Barnett, Adrian A.. University Of Roehampton; Reino Unido. Universidade Federal de Pernambuco; BrasilFil: Bicca Marques, Júlio César. Pontificia Universidade Católica do Rio Grande do Sul; BrasilFil: Bowler, Mark. University Of Suffolk; Reino Unido. San Diego Zoo Wildlife Alliance; Estados UnidosFil: Boyle, Sarah A.. Rhodes College; Estados UnidosFil: Brown, Meredith. University of Calgary; CanadáFil: Caillaud, Damien. University of California at Davis; Estados UnidosFil: Calegaro Marques, Cláudia. Universidade Federal do Rio Grande do Sul; BrasilFil: Campbell, Christina J.. California State University Northridge (calif. State Univ. Northridge);Fil: Campera, Marco. Oxford Brookes University (oxford Brookes University);Fil: Campos, Fernando A.. University of Texas at San Antonio; Estados UnidosFil: Cardoso, Tatiane S.. Museu Paraense Emílio Goeldi; BrasilFil: Carretero Pinzón, Xyomara. Proyecto Zocay; ColombiaFil: Champion, Jane. University of Calgary; CanadáFil: Chaves, Óscar M.. Universidad de Costa Rica; Costa RicaFil: Chen Kraus, Chloe. University of Yale; Estados UnidosFil: Colquhoun, Ian C.. Western University; CanadáFil: Dean, Brittany. University of Calgary; CanadáFil: Kowalewski, Miguel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Estación Biológica de Usos Múltiples (Sede Corrientes); Argentin