In this communication, preparation of graphene quantum dots (GQDs) with size about 10 nm by vigorous oxidation of graphite is reported. Thus obtained GQDs exhibit good physiological solubility, high photostability, low cytotoxicity, and yellow-green fluorescence with quantum yield about 7%. Furthermore, the feasibility of the GQDs for cell imaging application is demosntrated.

Green tea polyphenols, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), all showed antioxidative effect in liposomes for lipid oxidation initiated in the lipid phase (antioxidant efficiency EC > EGCG > ECG > EGC) or in the aqueous phase (EC ≫ EGC > EGCG > ECG) as monitored by the formation of conjugated dienes. For initiation in the lipid phase, β-carotene, itself active as an antioxidant, showed antagonism with the polyphenols (EC > ECG > EGCG > EGC). The Trolox equivalent antioxidant capacity (TEAC EGC > EGCG > ECG > EC) correlates with the lowest phenol O-H bond dissociation enthalpy (BDE) as calculated by density functional theory (DFT). Surface-enhanced Raman spectroscopy (SERS) was used to assess the reducing power of the phenolic hydroxyls in corroboration with DFT calculations. For homogeneous (1:9 v/v methanol/chloroform) solution, the β-carotene radical cation reacted readily with each of the polyphenol monoanions (but not with the neutral polyphenols) with a rate approaching the diffusion limit for EC as studied by laser flash photolysis at 25 °C monitoring the radical cation at 950 nm. The rate constant did not correlate with polyphenol HOMO/LUMO energy gap (DFT calculations), and β-carotene was not regenerated by an electron transfer reaction (monitored at 500 nm). It is suggested that the β-carotene radical cation is rather reacting with the tea polyphenols through addition, as further evidenced by steady-state absorption spectroscopy and liquid chromatography-mass spectroscopy (LC-MS), in effect preventing regeneration of β-carotene as an active lipid phase antioxidant and leading to the observed antagonism.

Solution-phase conformations and charge photogeneration dynamics of a pair of low-bandgap copolymers based on benzo[1,2-b:4,5-b(')]dithiophene (BDT) and thieno[3,4-b]thiophene (TT), differed by the respective carbonyl (-C) and ester (-E) substituents at the TT units, were comparatively investigated by using near-infrared time-resolved absorption (TA) spectroscopy at 25 °C and 120 °C. Steady-state and TA spectroscopic results corroborated by quantum chemical analyses prove that both PBDTTT-C and PBDTTT-E in chlorobenzene solutions are self-aggregated; however, the former bears a relatively higher packing order. Specifically, PBDTTT-C aggregates with more π-π stacked domains, whereas PBDTTT-E does with more random coils interacting strongly at the chain intersections. At 25 °C, the copolymers exhibit comparable exciton lifetimes (~1 ns) and fluorescence quantum yields (~2%), but distinctly different charge photogeneration dynamics: PBDTTT-C on photoexcitation gives rise to a branching ratio of charge separated (CS) over charge transfer (CT) states more than 20% higher than PBDTTT-E does, correlating with their photovoltaic performance. Temperature and excitation-wavelength dependent exciton∕charge dynamics suggest that the CT states localize at the chain intersections that are survivable up to 120 °C, and that the excitons and the CS states inhabit the stretched strands and the also thermally robust orderly stacked domains. The stable self-aggregation structures and the associated primary charge dynamics of the PBDTTT copolymers in solutions are suggested to impact intimately on the morphologies and the charge photogeneration efficiency of the solid-state photoactive layers.

In this study, we developed a nanosystem based on upconversion nanoparticles (UCNPs) coated with a layer of polyaniline nanoparticles (PANPs). The UCNP induces upconversion luminescence for imaging and photothermal conversion properties are due to PANPs. In vitro experiments showed that the UCNPs-PANPs were nontoxic to cells even at a high concentration (800 µg mL −1 ). Blood analysis and histological experiments demonstrated that the UCNPs-PANPs exhibited no apparent toxicity in mice in vivo. Besides their efficacy in photothermal cancer cell ablation, the UCNP-PANP nanosystem was found to achieve an effective in vivo tumor ablation effect after irradiation using an 808 nm laser. These results demonstrate the potential of the hybrid nanocomposites for use in imaging-guided photothermal therapy.

Primary charge photogeneration dynamics in neat and fullerene-blended films of a pair of alternating benzo[1,2-b:4,5-b(')]dithiophene (BDT) and thieno[3,4-b]thiophene (TT) copolymers are comparatively studied by using near-infrared, time-resolved absorption (TA) spectroscopy under low excitation photon fluence. PBDTTT-E and PBDTTT-C, differed merely in the respective TT-substituents of ester (-E) and carbonyl (-C), show distinctly different charge photogeneration dynamics. The pair of neat PBDTTT films show exciton lifetimes of ∼0.1 ns and fluorescence quantum yields below 0.2%, as well as prominent excess-energy enhanced exciton dissociation. In addition, PBDTTT-C gives rise to >50% higher P(•+) yield than PBDTTT-E does irrespective to the excitation photon energy. Both PBDTTT-E:PC61BM and PBDTTT-C:PC61BM blends show subpicosecond exciton lifetimes and nearly unitary fluorescence quenching efficiency and, with respect to the former blend, the latter one shows substantially higher branching ratio of charge separated (CS) state over interfacial charge transfer (ICT) state, and hence more efficient exciton-to-CS conversion. For PBDTTT-C:PC61BM, the ultrafast charge dynamics clearly show the processes of ICT-CS interconversion and P(•+) migration, which are possibly influenced by the ICT excess energy. However, such processes are relatively indistinctive in the case of PBDTTT-E:PC61BM. The results strongly prove the importance of ICT dissociation in yielding free charges, and are discussed in terms of the film morphology and the precursory solution-phase macromolecular conformation.