Photoresponsive iodine-bonded liquid crystals based on azopyridine derivatives with a low phase-transition temperature

<p>Halogen bonding interactions in the formation of liquid crystalline phases have been recognised in recent years. Here, we report a novel series of iodine-bonded liquid crystals using 1,2-diiodotetrafluorobenzene (1,2-DITFB) and azopyridine derivatives (AnAzPy), showing a smectic A phase and concurrent photoresponsive behaviour. These were characterised by using a polarising optical microscope, differential scanning calorimetry and UV-vis absorption spectroscopy. The formation of iodine bonding in the complexes was confirmed by X-ray photoelectron spectroscopy and Raman spectroscopy. Importantly, these iodine-bonded complexes demonstrated a low liquid crystal temperature range (30–50°C) among those reported for photoresponsive halogen-bonded liquid crystals. The molar ratio of the iodine-bonded donor and acceptor was 1:1 upon the self-assembly of the supramolecular complex molecule, as indicated by 1D-WAXD experiments of mixed samples of 1,2-DITFB and AnAzPy with different molar ratios. This study offers a new family of photoresponsive halogen-bonded liquid crystals and broadens the potential applications in their associated systems.</p

Changes in temperature, precipitation, and fertilizer application crop growth period during 1980–2010.

<p>* Represents the 5% level of significance.</p><p>** Represents the 1% level of significance.</p><p>Changes in temperature, precipitation, and fertilizer application crop growth period during 1980–2010.</p

The study region.

<p>The semiarid area of northern China (the filled area) and the distribution of the thirty-eight meteorological stations including Wuchuan and Guyuan in the semiarid area of northern China.</p

Responses of Crop Water Use Efficiency to Climate Change and Agronomic Measures in the Semiarid Area of Northern China

<div><p>It has long been concerned how crop water use efficiency (WUE) responds to climate change. Most of existing researches have emphasized the impact of single climate factor but have paid less attention to the effect of developed agronomic measures on crop WUE. Based on the long-term field observations/experiments data, we investigated the changing responses of crop WUE to climate variables (temperature and precipitation) and agronomic practices (fertilization and cropping patterns) in the semi-arid area of northern China (SAC) during two periods, 1983–1999 and 2000–2010 (drier and warmer). Our results suggest that crop WUE was an intrinsical system sensitive to climate change and agronomic measures. Crops tend to reach the maximum WUE (WUEmax) in warm-dry environment while reach the stable minimum WUE (WUEmin) in warm-wet environment, with a difference between WUEmax and WUEmin ranging from 29.0%-55.5%. Changes in temperature and precipitation in the past three decades jointly enhanced crop WUE by 8.1%-30.6%. Elevated fertilizer and rotation cropping would increase crop WUE by 5.6–11.0% and 19.5–92.9%, respectively. These results indicate crop has the resilience by adjusting WUE, which is not only able to respond to subsequent periods of favorable water balance but also to tolerate the drought stress, and reasonable agronomic practices could enhance this resilience. However, this capacity would break down under impact of climate changes and unconscionable agronomic practices (e.g. excessive N/P/K fertilizer or traditional continuous cropping). Based on the findings in this study, a conceptual crop WUE model is constructed to indicate the threshold of crop resilience, which could help the farmer develop appropriate strategies in adapting the adverse impacts of climate warming.</p></div

Relationship of crop WUE and Tmax, Tmin, precipitation, and fertilizer during 1983–2010 in the SAC.

<p>A, C and E is the relationship of WUE and Tmax, precipitation and fertilizer in Wuchuan, respectively. B, D and Fis the relationship of WUE and Tmin, precipitation, and fertilizer in Guyuan, respectively. The insets illustrate the change of WUE with elevated temperature and fertilizer usage (within the threshold). <i>P</i><0.01 represents the 1% level of significance; <i>P</i><0.05 represents the 5% level of significance.</p

Changes of WUEs of spring wheat (W, black), naked oat (N, red), potato (P, blue), and maize (M, yellow) in Wuchuan and Guyuan from 1983 to 2010, respectively.

<p>P<0.01 represents the 1% level of significance; P<0.05 represents the 5% level of significance. A and B refer to the change trend of crop WUE from 1983–2010 at Wuchuan and Guyuan, respectively; C and D refer to the discrete level of WUE at Wuchuan and Guyuan, respectively. In the Fig C and D, “Minimum value”, “1/4 percentile value”, “Median (spot)”, “3/4 percentile value”, “Maximum value” are presented from bottom to top, which is the same case throughout this study. Numbers above box plots are coefficient of variation (CV) of WUE of different crop during the 1980s, the 1990s and the 2000s. I means the period of 1983–1999; II means the period of 2000–2010.</p

Estimated crop yield changes.

<p>Crop yield changes of spring wheat, naked oat, potato, and maize by two panel regression models (PRM) for 1°C increase in temperature (A) and 10% decrease in precipitation (B) during crop growing season in Wuchuan and Guyuan from 1983–2010.</p

The difference of water use efficiency (millet, rape, and potato) in rotation and continuous cropping during 2008–2010.

<p>SM means soil moisture;</p><p>SMI means soil moisture before sowing;</p><p>SMII means soil moisture in harvest period;</p><p>P means precipitation;</p><p>WC means water consumption;</p><p>Y means yield;</p><p>WUE means water useefficiency;</p><p>R means rotation cropping;</p><p>C means continuing cropping.</p><p>The difference of water use efficiency (millet, rape, and potato) in rotation and continuous cropping during 2008–2010.</p

Impact of the warming-drying trend (WDT) and the amount of fertilizer on water use efficiency in wetter and drier years in different periods in semiarid area of northern China (SAC).

<p>I means the years of 1983–1999; II means the years of 2000–2010. Columns labeled with the different letter are significantly different (<i>P</i><0.05).</p><p>Impact of the warming-drying trend (WDT) and the amount of fertilizer on water use efficiency in wetter and drier years in different periods in semiarid area of northern China (SAC).</p

Temporal changes in average temperature (a, °C), minimum temperature (b, °C), maximum temperature (c, °C), precipitation (d, mm), Palmer Drought Severity Index (e), and the fertilization (f, kg ha^-1) during 1980–2010 in semiarid area of northern China (SAC).

<p>The inset in f illustrates differences of fertilizer in spring wheat, naked oat, potato and maize in Wuchuan (W) and Guyuan (G) in stage I and stage II. Columns labeled with the different letter are significantly different (P<0.05). P<0.01 represents the 1% level of significance; P<0.05 represents the 5% level of significance.</p