Emissive Substoichiometric Covalent Organic Frameworks for Water Sensing and Harvesting.

Emissive covalent organic frameworks (COFs) have recently emerged as next-generation porous materials with attractive properties such as tunable topology, porosity, and inherent photoluminescence. Among the different types of COFs, substoichiometric frameworks (so-called Type III COFs) are especially attractive due to the possibility of not only generating unusual topology and complex pore architectures but also facilitating the introduction of well-defined functional groups at precise locations for desired functions. Herein, the first example of a highly emissive (PLQY 6.8%) substoichiometric 2D-COF (COF-SMU-1) featuring free uncondensed aldehyde groups is reported. In particular, COF-SMU-1 features a dual-pore architecture with an overall bex net topology, tunable emission in various organic solvents, and distinct colorimetric changes in the presence of water. To gain further insights into its photoluminescence properties, the charge transfer, excimer emission, and excited state exciton dynamics of COF-SMU-1 are investigated using femtosecond transient absorption spectroscopy in different organic solvents. Additionally, highly enhanced atmospheric water-harvesting properties of COF-SMU-1 are revealed using FT-IR and water sorption studies.The findings will not only lead to in-depth understanding of structure-property relationships in emissive COFs but also open new opportunities for designing COFs for potential applications in solid-state lighting and water harvesting.

A covalent organic polymer as an efficient chemosensor for highly selective H2S detection through proton conduction.

A hydrazide based covalent organic polymer (COP) with pyridine functionalities has been synthesized and used to fabricate an efficient chemosensor for the detection of gaseous H2S at 25 °C through a proton conduction process. The gas sensing behavior of the COP has been measured in a dynamic flow-through resistance measurement system. The COP fabricated sensor shows a lower response time of 9 s with a recovery time of 12 s, when the experiment is performed with a H2S concentration of 200 ppm at 25 °C. It also shows high selectivity to H2S gas compared to other gases such as CO2, NH3, CO and NO2.

Benzoselenadiazole-Based Conjugated Molecules: Active Switching Layers with Nanofibrous Morphology for Nonvolatile Organic Resistive Memory Devices.

In this work, two symmetrical donor-acceptor-donor (D-A-D) type benzoselenadiazole (BSeD)-based π-conjugated molecules were synthesized and employed as an active switching layer for non-volatile data storage applications. BSeD-based derivatives with different donor units attached through common vinylene linkers showed different electrical and optical properties. 4,7-Di((E)-styryl)benzo[c][2,1,3]selenadiazole (DSBSeD) and 4,7-bis((E)-4-methoxystyryl)benzo[c][2,1,3]selenadiazole (DMBSeD) are sandwiched between gallium-doped ZnO (GZO) and metal aluminum electrodes respectively through solution-processed spin-coating method. The solution-processed nanofibrous switching layer containing the DMBSeD-based memory device showed reliable memory characteristics in terms of write and erase operations with low SET voltage than the random-aggregated DSBSeD-based device. The nanofibrous molecular morphology of switching layer overcomes the interfacial hole transport energy barrier at the interface of the DMBSeD thin-film and the bottom GZO electrode. The memory device GZO/DMBSeD/Al based on nanofibrous switching layers shows switching characteristics at compliance current of 10 mA with Vset =0.79 V and Vreset =-0.55 V. This work will be beneficial for the rational design of advanced next-generation organic memory devices by controlling the nanostructured morphology of active organic switching layer for enhanced charge-transfer phenomenon.

Insights into the Aggregation Behaviour of a Benzoselenadiazole-Based Compound and Generation of White Light Emission.

We have designed and synthesized the benzoselenadiazole (BDS) based donor-acceptor-donor (D-A-D) π-conjugated compound 4,7-di((E)styryl)benzo[2,1,3]selenadiazole (1). A single-crystal study of 1 shows J-type molecular aggregation in the solid state. The crystal packing of 1 shows head-to-head dimeric intermolecular assembly via Se⋅⋅⋅N interactions while staircase-type interlock molecular packing has occurred via Se⋅⋅⋅π interaction. The staircase-type interlock packing of dimeric molecular arrangement induces sheet-type, herringbone type architecture along crystallographic a axis and ab plane via CH⋅⋅⋅π interactions. Interestingly, the J-type aggregation of 1 in solid state changes to H-type aggregation upon UV-irradiation. Moreover, our spectroscopic findings in solution state reveal H-type of aggregation of 1 in 90 % aqueous THF. We have further demonstrated white light emission in the binary mixture of 1 and 1-pyrenemethanol (2) in 90 % aqueous THF. Our study reveals solvent specific co-assembly of H-aggregated 1 and 2 in 90 % aqueous THF solution, which shows white light emissive properties with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (0.32, 0.31). The observed white light emission arises mainly due to the combination of red light from H-aggregated 1, blue light from monomeric 2 and green light from excimers of 2.

Redox-Active Dynamic Self-Supporting Thixotropic 3D-Printable G-Quadruplex Hydrogels.

Redox-active G-quadruplex hydrogels were prepared by dynamic boronate ester formation between ferroceneboronic acid and guanosine. Dynamic boronate esters imparted thixotropic and 3D-printability to the hydrogel. Initially, the ferrocene moiety was oxidised to produce a weaker ferrocenium-based green hydrogel. However, the less stable ferrocenium converted into more stable ferrocene to produce a hydrophobic, water-stable and robust hydrogel.

Understanding the conformational analysis of gababutin based hybrid peptides.

Constrained γ-amino acid gababutin (Gbn) based peptides that form different conformations have been synthesized. Striving to rationalize the impact of side chain orientations framing tetrapeptide-based supramolecular organic frameworks and morphological entities, Gbn incorporated hybrid peptides Boc-Gbn-Aib-Aaa-Aib-OMe (where Aaa = Phe(F) for peptide 1, Leu(L) for peptide 2 and Tyr(Y) for peptide 3) were synthesized by changing the amino acid at the third position. The solution state dual folded conformation (C12/C10 H-bonded) is probed by 2D NMR spectroscopy in support of a DMSO-d6 titration and VT NMR experiments. Peptides 1-3 adopt a C12/C10 type H-bonded dual folded conformation in the crystal state. In addition, distinct supramolecular frameworks result from the modification and orientation of the third residue side chain of peptides 1-3. A solvent induced morphological diversity of peptides 1-3 is attained by modifying the side chain backbone of the tetrapeptides, which are investigated by various microscopic (SEM and AFM) studies. Gbn-based peptides 1-3 show significant morphological and supramolecular packing properties, which are fairly different from those of their gabapentin (Gpn) based analogue peptides.

Redox-Active Peptide-Functionalized Quinquethiophene-Based Electrochromic π-Gel.

An electrochromic system based on a self-assembled dipeptide-appended redox-active quinquethiophene π-gel is reported. The designed peptide-quinquethiophene consists of a symmetric bolaamphiphile that has two segments: a redox-active π-conjugated quinquethiophene core for electrochromism, and peptide motif for the involvement of molecular self-assembly. Investigations reveal that self-assembly and electrochromic properties of the π-gel are strongly dependent on the relative orientation of peptidic and quinquethiophene scaffolds in the self-assembly system. The colors of the π-gel film are very stable with fast and controlled switching speed at room temperature.