Crystalline phase transitions caused by external stimuli have been used to detect physical changes in the solid-state properties. This study presents the mechanical switching of crystals of ferrocene-containing rotaxane controlled by focused laser light. The expansion and contraction of the crystals can be driven by turning on and off laser light at 445 nm. The irradiation-induced expansion of the crystal involves elongation along the a, b and c axes at 30 °C, whereas heating of the crystal at 105 °C causes the shortening of c axis. The expansions reversibly occur and have the advantage of a rapid relaxation (reverse) process. Single-crystal X-ray crystallography reveals the detailed structural changes of the molecules, corresponding to a change in the size of the crystals on laser irradiation. This molecular crystal behaviour induced by laser irradiation, is demonstrated for the remote control of objects, namely, microparticle transport and microswitching in an electric circuit.
A thermally crosslinkable poly(cyclopentadithiophene-alt-benzothiadiazole) (PCPDTBT) analogue copolymer with 2-ethylhexyl group and 5-hexenyl group on 4,4-positions of cyclopentadithiophene has been synthesised by palladium catalyzed Suzuki coupling reaction. Space-Charge Limited Current (SCLC) devices show hole mobility of up to 3 Â 10 À4 cm 2 V À1 s À1 . In addition, organic photovoltaics (OPVs) were fabricated using fullerene derivatives as acceptor materials. The best performing device exhibited Power Conversion Efficiency (PCE) at 2.0%, which could be improved to 3.7% after inclusion of dithiol additives. Most significantly, the lifetime of the OPV was enhanced by the crosslinking; when light soaked at 1 sun of irradiance, a half-life, t 1/2 ¼ 419 hours was measured, which is 51% improvement over an OPV using standard PCPDTBT. This higher stability is accounted for the crosslinkable structure of the polymer after annealing. The crosslinking reaction was confirmed by solubility tests, Fourier transform infrared spectroscopy and morphological analysis conducted by Atomic Force Microscopy and simultaneous synchrotron grazing-incidence small-/wide-angle X-ray scattering.
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