Characteristic Excitation Wavelength Dependence of Fluorescence Emissions in Carbon "quantum" Dots

Carbon "quantum" dots (CDots), generally defined as small carbon nanoparticles with various surface passivation schemes, have emerged to represent a rapidly advancing and expanding research field. CDots are known for their bright and colorful fluorescence emissions, where the colorfulness is associated with the emissions being excitation wavelength dependent. In this work, CDots with 2,2′-(ethylenedioxy)bis(ethylamine) (EDA) for surface functionalization were studied systematically by using steady-state and time-resolved fluorescence methods. The observed fluorescence quantum yields are strongly excitation wavelength dependent, and the dependence apparently tracks closely the observed absorption profile of the EDA-CDots, whereas the excitation wavelength dependence of observed fluorescence lifetimes is much weaker, obviously decoupled from the quantum yields. Mechanistically, the presence of two sequential processes immediately following the photoexcitation of CDots leading to fluorescence is used to rationalize these effects, and the experimental results seem better explained by attributing one of the two processes to be primarily responsible for the characteristic excitation wavelength dependence. Significant implications of the mechanistic probing to the understanding of CDots as a new class of quantum dot-like fluorescent nanomaterials are discussed, and so are further challenges and opportunities

Abstract P151: Acculturation Predicts Activity-specific Parenting Practices In Hispanic/Latino Youth

Background: Hispanic youth are less physically active and more sedentary than non-Hispanic youth, contributing to relatively high rates of obesity among the nation’s largest ethnic minority group. Though parents can influence children’s behavior, it is unclear whether parenting practices related to the child’s physical activity are associated with activity in Hispanic/Latino youth, and whether cultural and environmental contexts predict the use of these parenting practices. Objective: We assessed 1) whether activity-specific parenting practices (ASPPs) are associated with moderate-to-vigorous physical activity (MVPA) and sedentary activity among Hispanic/Latino youth, and 2) if higher parental acculturation and greater perceived neighborhood-level socioeconomic challenges are associated with the use of less effective ASPP patterns. Methods: Youth from the Hispanic Community Children’s Health Study/Study of Latino Youth (SOL Youth; n=976) were examined. Activity was assessed using 7-day accelerometer data. ASPPs were identified from the Parenting strategies for Eating and Activity Scale (PEAS) using exploratory and confirmatory factor analysis of the ten items on activity. We used survey-weighted linear regression models to assess whether derived ASPPs predicted mean daily MVPA and sedentary time. K-means cluster analysis was used to group individuals based on ASPP use. Finally, we used survey-weighted multinomial logistic regression models to examine the association of parent acculturation-related measures and perceived neighborhood socioeconomic status and barriers to activity with ASPP cluster membership. Results: Factor analysis of the activity-specific PEAS items identified three ASPPs: Limit Setting, Discipline, and Monitoring/Reinforcement. Discipline predicted higher MVPA in females only (β 1.89 [95% CI 0.11-3.67]), and Monitoring/Reinforcement predicted higher MVPA in males only (β 4.71 [95% CI 0.68-8.74]). There was no association between Limit Setting and MVPA or any ASPPs and sedentary activity. K-cluster analysis revealed three ASPP patterns: Restrictive (high scores for Limit Setting and Discipline), Supportive (high scores for Limit Setting and Monitoring/Reinforcement) and Permissive (low score across ASPPs). Higher Anglo-orientation on the Brief ARSMA-II acculturation measure predicted membership in the Supportive compared to Permissive cluster (p= 0.03), while perceived neighborhood characteristics did not predict ASPP cluster membership. Conclusions: ASPPs are associated with MVPA in sex-specific ways but have no association with sedentary activity in Hispanic/Latino youth. Among acculturation and neighborhood characteristics, only Anglo-orientation predicted ASPPs patterns. More research is needed to understand how acculturation is influencing ASPPs and if ASPPs can be leveraged to change children’s activity

Cultural and neighborhood characteristics associated with activity-specific parenting practices in Hispanic/Latino youth: a secondary analysis of the Hispanic Community Children's health study/study of Latino youth

Hispanic/Latino youth are less physically active than non-Hispanic/Latino youth. We assessed whether activity-specific parenting practices relate to moderate-to-vigorous physical activity (MVPA) and sedentary behavior among Hispanic/Latino youth, and whether cultural (acculturation) and neighborhood characteristics (perceived barriers to activity) relate to the use of parenting practice patterns. Using the Hispanic Community Children's Health Study/Study of Latino Youth (SOL Youth, n=976 8-16-year-olds), we modeled linear regression associations between parenting practices and mean daily MVPA and sedentary behavior. Parenting practice patterns were then developed using k-means cluster analysis, and regressed on parental acculturation and neighborhood characteristics. Discipline predicted higher MVPA in females (beta 1.89 [95% CI 0.11-3.67]), while Monitoring/Reinforcement predicted higher MVPA in males (beta 4.71 [95% CI 0.68-8.74]). Three patterns were then identified: Negative Reinforcement (high Limit Setting and Discipline use), Positive Reinforcement (high Limit Setting and Monitoring/Reinforcement use), and Permissive Parenting (low parenting practice use). Higher acculturation predicted use of Positive Reinforcement. Activity-specific parenting practices are associated with activity in sex-specific ways among Hispanic/Latino youth, and cultural factors predict the use of parenting practices

An ordered, self-assembled nanocomposite with efficient electronic and ionic transport

Mixed conductors-materials that can efficiently conduct both ionic and electronic species-are an important class of functional solids. Here we demonstrate an organic nanocomposite that spontaneously forms when mixing an organic semiconductor with an ionic liquid and exhibits efficient room-temperature mixed conduction. We use a polymer known to form a semicrystalline microstructure to template ion intercalation into the side-chain domains of the crystallites, which leaves electronic transport pathways intact. Thus, the resulting material is ordered, exhibiting alternating layers of rigid semiconducting sheets and soft ion-conducting layers. This unique dual-network microstructure leads to a dynamic ionic/electronic nanocomposite with liquid-like ionic transport and highly mobile electronic charges. Using a combination of operando X-ray scattering and in situ spectroscopy, we confirm the ordered structure of the nanocomposite and uncover the mechanisms that give rise to efficient electron transport. These results provide fundamental insights into charge transport in organic semiconductors, as well as suggesting a pathway towards future improvements in these nanocomposites

An ordered, self-assembled nanocomposite with efficient electronic and ionic transport

Mixed conductors-materials that can efficiently conduct both ionic and electronic species-are an important class of functional solids. Here we demonstrate an organic nanocomposite that spontaneously forms when mixing an organic semiconductor with an ionic liquid and exhibits efficient room-temperature mixed conduction. We use a polymer known to form a semicrystalline microstructure to template ion intercalation into the side-chain domains of the crystallites, which leaves electronic transport pathways intact. Thus, the resulting material is ordered, exhibiting alternating layers of rigid semiconducting sheets and soft ion-conducting layers. This unique dual-network microstructure leads to a dynamic ionic/electronic nanocomposite with liquid-like ionic transport and highly mobile electronic charges. Using a combination of operando X-ray scattering and in situ spectroscopy, we confirm the ordered structure of the nanocomposite and uncover the mechanisms that give rise to efficient electron transport. These results provide fundamental insights into charge transport in organic semiconductors, as well as suggesting a pathway towards future improvements in these nanocomposites

Functionalization of Carbon Nanoparticles and DefunctionalizationToward Structural and Mechanistic Elucidation of Carbon “Quantum” Dots

Small carbon nanoparticles were functionalized by low-molecular weight amino compound 3-ethoxypropylamine (EPA) for ultracompact carbon dots of bright fluorescence emissions. The results from solution-phase NMR characterization support the expected dot structure of carbon nanoparticles surface-attached with EPA species. The optical properties of the EPA-carbon dots share many features with those found in carbon dots of other surface functionalities, but there is an extra absorption shoulder in the blue spectral region, into which the excitation results in much enhanced green fluorescence emissions. The EPA-carbon dots were defunctionalized by gradually removing the EPA species from the carbon nanoparticles, along with spectroscopic characterizations on the samples of different degrees of defunctionalization. The outcomes further confirm the critical role of surface functionalization in the superior optical properties of carbon dots. Results from systematic measurements of fluorescence quantum yields and decays at different excitation wavelengths for the EPA-carbon dots and their gradually defunctionalized samples are presented, and their mechanistic implications are discussed