RESUMO
Organic molecules that undergo supercooling can provide the basis for novel stimuli-responsive materials, but the number of such compounds is limited. Results in this paper show that the stable organic radical 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (TEMPO) can form a stable supercooled liquid (SCL). Upon melting and cooling back to room temperature, the TEMPO SCL can persist for months, even after mild physical agitation. Its high vapor pressure can enable crystal growth at remote locations within the sample container over the course of days. Optical, electron paramagnetic resonance, and birefringence measurements show no evidence of new chemical species or partially ordered phases in the supercooled liquid. TEMPO's free radical character permits absorption of visible light that can drive photothermal melting to form the SCL, while a single nanosecond light pulse can initiate recrystallization of the SCL at some later time. This capability enables all-optical switching between the solid and the SCL phases. The physical origin of TEMPO's remarkable stability as an SCL remains an open question, but these results suggest that organic radicals comprise a new class of molecules that can form SCLs with potentially useful properties.
RESUMO
Ruthenium-catalyzed butadiene-mediated benzannulation enabled the first synthesis of 3,10-(di-tert-butyl)rubicene and its N-doped derivatives as well as preliminary studies on their photophysical properties. Unlike the parent rubicene and 3,10-(di-tert-butyl)rubicene, which adopt classical herringbone-type packing motifs in the solid state, the N-doped congener 7 b displayed columnar packing with an alternating co-facial arrangement of aromatic and heteroaromatic substructures.