Photoinduced charge carriers in conjugated polymer-fullerene composites studied with lightinduced electron-spin resonance Dyakonov, V.; Zoriniants, G.; Scharber, M.C.; Brabec, C.J.; Janssen, R.A.J.; Hummelen, Jan Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Detailed studies on photoinduced spins in conjugated polymer/fullerene composites using ͑cw͒ light-induced electron-spin-resonance ͑LESR͒ technique are reported. Two overlapping LESR lines are observed, from positive polarons on the polymer chains and negative charges on the fullerene moieties. Microwave power saturation studies show different relaxation times for these two spins, ruling out spin-exchange correlations, giving clear evidence of independent spins. The unusually high relaxation rate of the fullerene monoanionic spins is of intrinsic origin, and discussed in terms of a splitting of the T 1u level by a Jahn-Teller-type distortion as proposed in the literature. Further, we observed two distinct contributions to LESR signals: a prompt one and a persistent one. The excitation light intensity dependence of the prompt contributions into the P ϩ and C 60 Ϫ ESR signals is of bimolecular type (I 0.5

Substantial fluctuations of the fluorescence intensity have been detected for single clusters of poly(phenylenevinylene) containing more than 75 polymer chains or 30,000 monomer units. To the best of our knowledge, this is the first time such fluctuations (which resemble the "blinking" effect in single-molecule fluorescence) have been reported for such a large molecular ensemble containing several macromolecules. Together with the distinct jumps, smooth fluctuations of the fluorescence intensity, with characteristic times from milliseconds to seconds, were observed. This fact distinguishes the fluorescence behaviour of the polymer clusters from that of other multichromophoric systems such as the single chains of conjugated polymers reported in the literature. The consecutive or simultaneous switching of one or several emitting sites from the "on" to "off" state does not explain the character of the fluctuations observed. We suggest that the quenching of the light-emitting exciton by a long-lived species, such as, for example, polarons, plays an important role in these unusual fluctuations. Electric field induced fluorescence quenching differs significantly for different clusters. It is proposed that this fluorescence was mainly quenched by polarons injected from the electrodes in the presence of an electric field. The specific behaviour of each cluster is explained by suggesting a different position of the clusters with respect to the electrodes.

We have used directed two‐component self‐assembly to “pattern” organic monolayers on the nanometer scale at the liquid/solid interface. The ability of the scanning tunneling microscope to investigate structural details in these adlayers was used to gain insight into the two‐component two‐dimensional phase behavior. The components are symmetrically alkylated bisurea derivatives (R1‐urea‐spacer‐urea‐R2; R1, R2=alkyl, spacer=alkyl or bisthiophene). The bisthiophene unit acts as a marker and its bisurea derivative (T2) is a component in all the mixtures investigated. By varying the position of the hydrogen‐bond forming urea groups along the molecule and the length of the alkyl chains of the other components, the effect of 1) hydrogen bonding, 2) molecule length, 3) odd–even effects, and 4) shape complementarity on the two‐dimensional phase behavior was investigated. Insight into the effect of these parameters leads to the control of the two‐dimensional patterning: from randomly intermixed systems to phase separation.

Nanoparticles have attracted enormous attention for biomedical applications as optical labels, drug delivery vehicles, and contrast agents in vivo. In the quest for superior photostability and bio-compatibility, nanodiamonds (NDs) are considered one of the best choices due to their unique structural, chemical, mechanical, and optical properties. So far, mainly fluorescent NDs have been utilized for cell imaging. However, their use is limited by the efficiency and costs in reliably producing fluorescent defect centers with stable optical properties. Here, we show that single non-fluorescing NDs exhibit strong coherent anti-Stokes Raman scattering (CARS) at the sp3 vibrational resonance of diamond. Using correlative light and electron microscopy, the relationship between CARS signal strength and ND size is quantified. The calibrated CARS signal in turn enables the analysis of the number and size of NDs internalized in living cells in situ, which opens the exciting prospect of following complex cellular trafficking pathways quantitatively.

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