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Shear-Triggered Crystallization and Light Emission of a Thermally Stable Organic Supercooled Liquid
Chung, Kyeongwoon,Kwon, Min Sang,Leung, Brendan M.,Wong-Foy, Antek G.,Kim, Min Su,Kim, Jeongyong,Takayama, Shuichi,Gierschner, Johannes,Matzger, Adam J.,Kim, Jinsang American Chemical Society 2015 ACS central science Vol.1 No.2
<▼1><P/><P>Thermodynamics drive crystalline organic molecules to be crystallized at temperatures below their melting point. Even though molecules can form supercooled liquids by rapid cooling, crystalline organic materials readily undergo a phase transformation to an energetically favorable crystalline phase upon subsequent heat treatment. Opposite to this general observation, here, we report molecular design of thermally stable supercooled liquid of diketopyrrolopyrrole (DPP) derivatives and their intriguing shear-triggered crystallization with dramatic optical property changes. Molten DPP8, one of the DPP derivatives, remains as stable supercooled liquid without crystallization through subsequent thermal cycles. More interestingly, under shear conditions, this supercooled liquid DPP8 transforms to its crystal phase accompanied by a 25-fold increase in photoluminescence (PL) quantum efficiency and a color change. By systematic investigation on supercooled liquid formation of crystalline DPP derivatives and their correlation with chemical structures, we reveal that the origin of this thermally stable supercooled liquid is a subtle force balance between aromatic interactions among the core units and van der Waals interactions among the aliphatic side chains acting in opposite directions. Moreover, by applying shear force to a supercooled liquid DPP8 film at different temperatures, we demonstrated direct writing of fluorescent patterns and propagating fluorescence amplification, respectively. Shear-triggered crystallization of DPP8 is further achieved even by living cell attachment and spreading, demonstrating the high sensitivity of the shear-triggered crystallization which is about 6 orders of magnitude more sensitive than typical mechanochromism observed in organic materials.</P></▼1><▼2><P>We investigate the molecular origin behind the shear-triggered crystallization with dramatic optical property changes of a thermally stable supercooled liquid.</P></▼2>
Bae, Min-Suk,Skiles, Matthew J.,Lai, Alexandra M.,Olson, Michael R.,de Foy, Benjamin,Schauer, James J. Elsevier 2019 Environmental pollution Vol.246 No.-
<P><B>Abstract</B></P> <P>Two hundred sixty-three fine particulate matter (PM<SUB>2.5</SUB>) samples were collected over fourteen months in Fresno and Bakersfield, California. Samples were analyzed for organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), and 160 organic molecular markers. Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF) source apportionment models were applied to the results in order to understand monthly and seasonal source contributions to PM<SUB>2.5</SUB> OC. Similar source categories were found from the results of the CMB and PMF models to PM<SUB>2.5</SUB> OC across the sites. Six source categories with reasonably stable profiles, including biomass burning, mobile, food cooking, two different secondary organic aerosols (SOAs) (i.e., winter and summer), and forest fires were investigated. Both the CMB and the PMF models showed a strong seasonality in contributions of some sources, as well as dependence on wind transport for both sites. The overall relative source contributions to OC were 24% CMB wood smoke, 19% CMB mobile sources, 5% PMF food cooking, 2% CMB vegetative detritus, 17% PMF SOA summer, 22% PMF SOA winter, and 12% PMF forest fire. Back-trajectories using the Weather Research and Forecasting model combined with the FLEXible PARTicle dispersion model (WRF-FLEXPART) were used to further characterize wind transport. Clustering of the trajectories revealed dominant wind patterns associated with varying concentrations of the different source categories. The Comprehensive Air Quality Model with eXtensions (CAMx) was used to simulate aerosol transport from forest fires and thus confirm the impacts of individual fires, such as the Rough Fire, at the measurement sites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comparison of Molecular marker CMB and PMF models to OC. </LI> <LI> Assessment of Forest Fire impacts on OC using PMF. </LI> <LI> Forest fire confirmation from CAMx simulations based on FLAMBE emissions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>