Datasets on multiparameter glacier change dynamics for the Jankar Chhu Watershed, Lahaul Himalaya, India

Characterization of glacier changes in the surface area, terminus, equilibrium line altitude (ELA), elevation, and velocity was worked out for the Jankar Chhu Watershed (JCW) of Lahaul Himalaya using freely available satellite remote sensing data and the limited number of field observations. We studied changes using Corona (1971), Landsat (1993‒2017), Sentinel 2A (2016), the SRTM Digital Elevation Model (DEM; 2000), and the global TanDEM‒X DEM (2014). Our results showed that changes in glacier area (‒14.7 ± 4.3 km²), terminus (‒4.7 ± 0.4 m a¯¹), and ELA (~ 20 m rise) between 1971 and 2016 are smaller than previously reported. Glacier lake area increased by ~0.3 km² during 1971‒2016. An intricate pattern of mass changes across the JCW was observed, with surface lowering on an average of ‒0.7 ± 0.4 m a¯¹ which equates to a geodetic mass balance of ‒0.6 ± 0.4 m w.e. a¯¹ during 2000‒14. The computed glacier surface velocities (1971‒2017)  reveal nearly stagnant debris-covered ablation zone but the dynamically active main trunk. The present study provides valuable insights into the recent multiparameter glacier variations, which are of critical importance to assess the future glacier dynamics on a regional scale in areas like the present one.</p

Direct Observation of Cascade of Photoinduced Ultrafast Intramolecular Charge Transfer Dynamics in Diphenyl Acetylene Derivatives: Via Solvation and Intramolecular Relaxation

Interaction of light with electron donor–acceptor π-conjugated systems leading to intramolecular charge transfer (ICT) plays an essential role in transformation of light energy. Here the cascade of photoinduced ICT processes is directly observed by investigating the excited state relaxation dynamics of cyano and mono/di methoxy substituted diphenyl acetylene derivatives using femtosecond pump–probe spectroscopy and nanosecond laser flash photolysis. The femtosecond transient absorption spectra of the chromophores upon ultrafast excitation reveal the dynamics of intermediates involved in transition from initially populated Frank–Condon state to local excited state (LE). It also provides the dynamic details of the transition from the LE to the charge transfer state yielding the formation of the radical ions. Finally, the charge transfer state decays to the triplet state by geminate charge recombination. The latter dynamics are observed in the nanosecond transient absorption spectra. It is found that excited state relaxation pathways are controlled by different stages of solvation and intramolecular relaxation depending on the solvent polarity. The twisted ICT state is more stabilized (978 ps) in acetonitrile than cyclohexane where major components of transient absorption originate from the S₁ state

Optical Investigation of Self-Aggregation of a Tetrazole-Substituted Diphenylacetylene Derivative: Steady and Excited State Dynamics in Solid and Solution State

Slow crystallization and fast precipitation of a tetrazole-substituted diphenylacetylene derivative (MPT) led to formation of solids with significantly different photoluminescence efficiencies of 0.06 and 0.33, respectively. A detailed study of the photophysical properties of solutions of MPT as a function of concentration and temperature indicated that the extent of formation of J- and H-aggregates played a significant role in determining the luminescence properties of these materials. Time-resolved emission spectroscopy showed that the lifetime of emission arising from the aggregated species was significantly higher than that of the monomer species. The long-lived emission might be due to the formation of excimer arising from the excitation of ground state J- and H-aggregates. The higher quantum yield of fluorescence in the solids obtained by fast precipitation could be attributed to the presence of increased amounts of J-aggregates similar to that observed in highly concentrated solutions (≥ 4.2 × 10–4 M). The photophysical studies of MPT in various concentrations indicate that J-aggregates are significantly more fluorescent than the H-aggregates. Transient absorption spectra measured by nanosecond laser flash photolysis indicated the formation of a triplet excited state with an absorption maximum of ∼490 nm and a quantum yield of 0.61

Tuning Microstructures in Organogels: Gelation and Spectroscopic Properties of Mono- and Bis-cholesterol-Linked Diphenylbutadiene Derivatives

The gelation and photophysical properties of mono- and bis-cholesterol derivatives linked to diphenylbutadiene have been investigated. Scanning electron microscopy of xerogels of the monocholesterol derivatives indicated that these molecules self-assemble into 3D networks consisting of helically twisted fibers. In contrast, the morphology of xerogels of the bis-cholesterol derivatives indicated agglomerated spheres. In concentrated solutions (>10−4 M), the self-assembled superstructure of the monocholesterol derivatives consists of helically twisted fibers whereas that of the bis-cholesterol derivatives indicated clustered spheres. An investigation of spectroscopic properties suggests that the morphology of the superstructures formed in these systems may be correlated to the nature of the molecular aggregates formed. Absorption and emission spectral studies as a function of concentration and temperature suggested the formation of predominantly J-type aggregates in the monocholesterol and H-type aggregates in the bis-cholesterol derivatives. It is proposed that the slipped stack arrangement within the J aggregates of the monocholesterol derivatives resulted in the formation of helically twisted fibers, whereas the cofacial arrangement in the H aggregates of the bis-cholesterol derivatives could prevent such fiber formation, resulting in the formation of the agglomerated spheres

Photochemical Phase Transition in Hydrogen-Bonded Liquid Crystals

Photochemical Phase Transition in Hydrogen-Bonded Liquid Crystal

Tuning Microstructures in Organogels: Gelation and Spectroscopic Properties of Mono- and Bis-cholesterol-Linked Diphenylbutadiene Derivatives

The gelation and photophysical properties of mono- and bis-cholesterol derivatives linked to diphenylbutadiene have been investigated. Scanning electron microscopy of xerogels of the monocholesterol derivatives indicated that these molecules self-assemble into 3D networks consisting of helically twisted fibers. In contrast, the morphology of xerogels of the bis-cholesterol derivatives indicated agglomerated spheres. In concentrated solutions (>10−4 M), the self-assembled superstructure of the monocholesterol derivatives consists of helically twisted fibers whereas that of the bis-cholesterol derivatives indicated clustered spheres. An investigation of spectroscopic properties suggests that the morphology of the superstructures formed in these systems may be correlated to the nature of the molecular aggregates formed. Absorption and emission spectral studies as a function of concentration and temperature suggested the formation of predominantly J-type aggregates in the monocholesterol and H-type aggregates in the bis-cholesterol derivatives. It is proposed that the slipped stack arrangement within the J aggregates of the monocholesterol derivatives resulted in the formation of helically twisted fibers, whereas the cofacial arrangement in the H aggregates of the bis-cholesterol derivatives could prevent such fiber formation, resulting in the formation of the agglomerated spheres

Spatially heterogeneous glacier elevation change in the Jankar Chhu Watershed, Lahaul Himalaya, India derived using ASTER DEMs

This study investigates elevation change (dh) and geodetic mass budget of glaciers in the Jankar Chhu Watershed (JCW), Lahaul Himalaya, India, based on the difference in ASTER DEMs during 2002–2018. Glacier-wide spatially heterogeneous dh patterns were evaluated in the context of morphological and topographical settings. During 2002–2018, glaciers show a mean annual elevation change rate (dh/dt) of −0.38 ± 0.10 m a−1, resulting in a specific mass budget of −0.32 ± 0.09 m w.e.a−1, close to the previously reported estimates in western Himalaya. Nearly stagnant thick debris-covered tongue (>10% debris cover) characterized by melt hotspots exhibits maximum dh at up-glacier instead of the terminus. Debris-free glaciers (dh near the terminus. Spatially heterogeneous dh under varying debris cover is interpreted as an insulating effect of debris thickness as validated by field measurements. We suggest that elevation change of debris-covered glaciers cannot be generalized and glacier-wide spatially detailed mapping of dh is necessary to better understand the control of different surface morphology under warming climatic conditions in the western Himalayas. We present a spatially heterogeneous elevation change rate of 33 glaciers (150.9 km2) in the Jankar Chhu Watershed (JCW), Chandrabhaga basin, Western Himalaya based on the differences of ASTER digital elevation models (DEMs).We estimate the altitude-dependent elevation change of glaciers under varying debris thickness and surface morphology.Glaciers in the JCW show mean dh/dt of –0.38 ± 0.10 m a−1, resulting in a specific mass budget of –0.32 ± 0.09 m w.e.a−1, close to the previously reported estimates in western Himalaya.Debris-covered ice exhibits higher elevation change than debris-free ones.Thick debris-covered tongues show maximum surface lowering at up glaciers while debris-free tongue exhibits maximum lowering near the terminus.Debris thickness controls the altitude-wise spatial elevation change pattern in the JCW. We present a spatially heterogeneous elevation change rate of 33 glaciers (150.9 km2) in the Jankar Chhu Watershed (JCW), Chandrabhaga basin, Western Himalaya based on the differences of ASTER digital elevation models (DEMs). We estimate the altitude-dependent elevation change of glaciers under varying debris thickness and surface morphology. Glaciers in the JCW show mean dh/dt of –0.38 ± 0.10 m a−1, resulting in a specific mass budget of –0.32 ± 0.09 m w.e.a−1, close to the previously reported estimates in western Himalaya. Debris-covered ice exhibits higher elevation change than debris-free ones. Thick debris-covered tongues show maximum surface lowering at up glaciers while debris-free tongue exhibits maximum lowering near the terminus. Debris thickness controls the altitude-wise spatial elevation change pattern in the JCW.</p

Asymmetric Squaraine Dyes: Spectroscopic and Theoretical Investigation

A joint experimental and theoretical study is presented of two asymmetric squaraine dyes and their parent symmetric dyes. The definition of reliable essential-state models for asymmetric squaraines sheds light on the intriguing spectroscopic behavior of this class of molecules, showing inverted and normal solvatochromism in absorption and emission, respectively. This behavior is related to charge redistribution in the excited state, with important implications for optimal design of asymmetric dyes for solar cell applications

Correlation between Solid-State Photophysical Properties and Molecular Packing in a Series of Indane-1,3-dione Containing Butadiene Derivatives

The solid-state photophysical and photochromic properties and the molecular packing in single crystals of a series of donor−acceptor-substituted butadiene derivatives with alkoxy groups as donor and indane-1,3-dione as acceptor are reported. These materials showed significant enhancement and red-shift in fluorescence in the solid state compared to that in solution. The single crystal analysis of these derivatives indicated that these effects could be attributed to both improved intramolecular charge transfer due to planarization of the molecules and to intermolecular exciton coupling between adjacent molecules leading to aggregate fluorescence. The character of the aggregate formed (H- or J-type) and extent of aggregation were strongly dependent on the length of the alkyl substituent, and these differences could be correlated to variations in the molecular packing observed in their single crystals. Some of the derivatives could be super cooled to a metastable glassy state with significantly different optical properties. Transformation from crystalline to a highly stable glassy form could also be induced by light, making these materials useful for recording optical images

Zwitterionic Dye-Based Conducting Polymers. Synthesis and Optical Properties of Pyrrole-Derived Polysquaraines

Zwitterionic Dye-Based Conducting Polymers. Synthesis and Optical Properties of Pyrrole-Derived Polysquaraine