Photo-Stimulated Polychromatic Room Temperature Phosphorescence of Carbon Dots

Single-component multicolor luminescence, particularly phosphorescence materials are highly attractive both in numerous applications and in-depth understanding the light-emission processes, but formidable challenges still exist for preparing such materials. Herein, a very facile approach is reported to synthesize carbon dots (CDs) (named MP-CDs) that exhibit multicolor fluorescence (FL), and more remarkably, multicolor long-lived room temperature phosphorescence (RTP) under ambient conditions. The FL and RTP colors of the CDs powder are observed to change from blue to green and cyan to yellow, respectively, with the excitation wavelength shifting from 254 to 420 nm. Further studies demonstrate that the multicolor emissions can be attributed to the existence of multiple emitting centers in the CDs and the relatively higher reaction temperature plays a critical role for achieving RTP. Given the unique optical properties, a preliminary application of MP-CDs in advanced anti-counterfeiting is presented. This study not only proposes a strategy to prepare photo-stimulated multicolor RTP materials, but also reveals great potentials of CDs in exploiting novel optical materials with unique properties

Visible-Light-Excited Room Temperature Phosphorescent Carbon Dots

Carbon dots (CDs) with a room temperature phosphorescent (RTP) feature have attracted considerable interest in recent years due to their fundamental importance and promising applications. However, the reported matrix-free RTP CDs only show short-wavelength (green to yellow) emissions and have to be triggered by ultraviolet (UV) light (below 400 nm), limiting their applications in certain fields. Herein, visible-light-excited matrix-free RTP CDs (named AA-CDs) with a long-wavelength (orange) emission are reported for the first time. The AA-CDs can be facilely prepared via a microwave heating treatment of L-aspartic acid (AA) in the presence of ammonia and they emit unique orange RTP in the solid state with visible light (420 nm) excitation just being switched off. Through the studies of the carbonization process, the C=O and C=N containing moieties in the AA-CDs are confirmed to be responsible for the observed RTP emission. Finally, the applications of AA-CDs in information encryption and anti-counterfeiting were preliminarily demonstrated

Rich Variety of Three-Dimensional Nanostructures Enabled by Geometrically Constraining Star-like Block Copolymers

The influence of star-like architecture on phase behavior of star-like block copolymer under cylindrical confinement differs largely from the bulk (i.e., nonconfinement). A set of intriguing self-assembled morphologies and the corresponding phase diagrams of star-like (AB)_<i>f</i> diblock copolymers with different numbers of arms <i>f</i> (i.e., <i>f</i> = 3, 9, 15, and 21) in four scenarios (ϕ_A = 0.3 and <i>V</i>₀ > 0; ϕ_A = 0.3 and <i>V</i>₀ < 0; ϕ_A = 0.7 and <i>V</i>₀ > 0; and ϕ_A = 0.7 and <i>V</i>₀ < 0 (where ϕ_A is the volume fraction of A block) and <i>V</i>₀ < 0 and <i>V</i>₀ > 0 represent that the pore wall of cylindrical confinement prefers the inner A block (i.e., A-preferential) and B block (i.e., B-preferential), respectively) were for the first time scrutinized by employing the pseudospectral method of self-consistent mean-field theory. Surprisingly, a new nanoscopic phase, that is, perforated-lamellae-on-cylinder (denoted PC), was observed in star-like (AB)₃ diblock copolymer at ϕ_A = 0.3 and <i>V</i>₀ > 0. With a further increase in <i>f</i>, a single lamellae (denoted L₁) was found to possess a larger phase region. Under the confinement of A-preferential wall (i.e., <i>V</i>₀ < 0) at ϕ_A = 0.3, PC phase became metastable and its free energy increased as <i>f</i> increased. Quite intriguingly, when ϕ_A = 0.7 and <i>V</i>₀ > 0, where an inverted cylinder was formed in bulk, the PC phase became stable, and its free energy decreased as <i>f</i> increased, suggesting the propensity to form PC phase under this condition. Moreover, in stark contrast to the phase transition of C₁ → L₁ → PC (C₁, a single cylindrical microdmain) at ϕ_A = 0.3 and <i>V</i>₀ > 0, when subjected to the A-preferential wall (ϕ_A = 0.7), a different phase transition sequence (i.e., C₁ → PC → L₁) was identified due to the formation of a double-layer structure. On the basis of our calculations, the influence of star-like architecture on (AB)_<i>f</i> diblock copolymer under the imposed cylindrical confinement, particularly the shift of the phase boundaries as a function of <i>f</i>, was thoroughly understood. These self-assembled nanostructures may hold the promise for applications as lithographic templates for nanowires, photonic crystals, and nanotechnology

Self-Assembly of Miktoarm Star-Like AB_<i>n</i> Block Copolymers: From Wet to Dry Brushes

Self-assembly of miktoarm star-like AB_<i>n</i> block copolymer in both selective solvent (A- or B-selective) and miscible homopolymer matrix (A or B homopolymer), that is, formation of micelles, was for the first time investigated by theoretical calculations based on self-consistent mean field theory. Interestingly, the calculation revealed that the size of micelles in solvent was smaller than that in homopolymer under the same conditions. In B-selective solvent, with increasing number of B blocks <i>n</i> in miktoarm star-like AB_<i>n</i> block copolymer at a fixed volume fraction of A block, the micellar size decreased gradually. In stark contrast, when miktoarm star-like AB_<i>n</i> block copolymer dissolved in B homopolymer matrix at molecular weight ratio of B homopolymer to AB_<i>n</i> block copolymer <i>f</i>_H = 0.30, the overall micellar size decreased nonmonotonically as the number of B blocks <i>n</i> in AB_<i>n</i> block copolymer increased. The largest micelle was formed in AB₂ (i.e., <i>n</i> = 2). This intriguing finding can be attributed to a wet-to-dry brush transition that occurred from <i>n</i> = 1 to <i>n</i> = 2 in the micellization of miktoarm star-like AB_<i>n</i> block copolymer. Moreover, the micellization behaviors of miktoarm star-like AB_<i>n</i> block copolymer in A-selective solvent and A homopolymer matrix were also explored, where the overall micellar size in both scenarios was found to decrease monotonically as <i>n</i> in AB_<i>n</i> block copolymer increased. These self-assembled nanostructures composed of miktoarm star-like AB_<i>n</i> block copolymers may promise a wide range of applications in size-dependent drug delivery and bionanotechnology

Epidural Labor Analgesia Is Associated with a Decreased Risk of the Edinburgh Postnatal Depression Scale in Trial of Labor after Cesarean: A Multicenter, Prospective Cohort Study

Postpartum depression is a disabling mental disorder commonly seen in parturients under trial of labor after cesarean, which causes serious harm to the parturients. The etiology is unclear. We hypothesized that epidural labor analgesia can reduce the incidence rate of postpartum depression. Enrolled multiparas were divided into the epidural labor analgesia group (n = 263) or nonanalgesia group (n = 160) according to their own request. Edinburgh Postnatal Depression Scale was used to assess their mental status at 48 hours and 42 days after delivery. Relative perinatal variables were collected and further analyzed using univariate analysis and multivariate logistic regression analysis to assess the relation of epidural analgesia with the occurrence of postpartum depression under trial of labor after cesarean. The Edinburgh Postnatal Depression Scale score 48 hours ≥ 10 in the no epidural analgesia group was 26.42% while the epidural analgesia group was 8.49% (OR, 0.209; 95% CI, 0.096–0.429; P<0.001). The Edinburgh Postnatal Depression Scale score 42 day ≥ 10 in the no epidural analgesia group was 25.16% while the epidural analgesia group was 6.59% (OR, 0.235; 95% CI, 0.113–0.469; P<0.001). The incidence of postpartum depression was significantly lower in the epidural labor analgesia group at 48 hours and 42 days. There was also a significant relation between the Edinburgh Postnatal Depression Scale scores at 48 hours and 42 days after delivery. Epidural analgesia, discomfort within 42 days, and self-rating anxiety scale are independent predictors of postpartum depression for trial of labor after cesarean in 42 days. Epidural labor analgesia is associated with a decreased risk of postpartum depression. Further study with a large sample size and more centers is needed to evaluate the impact of epidural analgesia on the occurrence of postpartum depression. Chinese Clinical Trial Register, ChiCTR-ONC-17010654