ABSTRACT Hydrogen‐bonded organic salts are versatile supramolecular materials whose architecture can be tuned through co‐former selection. Here, we report two multicomponent crystals of the azobenzene polycarboxylic acid 4,4′‐(diazene‐1,2‐diyl)bis(3,5‐dicarboxybenzoic acid) ( DADIA ): one with imidazole ( DADIA:IMD2 ) and one with N ‐methylimidazole ( DADIA:MeIMD ). Both were prepared by mechanochemical grinding followed by recrystallization from methanol. In each case, proton transfer from the carboxylic acid groups to the imidazole nitrogen gives charge‐assisted N + –H···O − hydrogen bonds, so the materials are best described as organic salts. Single‐crystal x‐ray diffraction shows that DADIA:IMD2 crystallizes in a monoclinic ( C2/c ) and DADIA:MeIMD in a triclinic ( P‐1 ), both forming two‐dimensional HOF‐like architectures. In DADIA:IMD2 , protonated imidazole acts as an active network node, generating channels occupied by disordered solvent. In DADIA:MeIMD , the 2D sheet is stabilized by O–H···O bonding between DADIA host molecules, with protonated N ‐methylimidazole housed in the pores as a passive guest. The compounds were further characterized by 1 H NMR, FT‐IR, PXRD, and TGA. These results show how a single N ‐methyl substituent switches the co‐former between the network node and the guest, with implications for gas storage, separation, and drug delivery.
ABSTRACT Peptide‐ and peptoid‐based biomimetic hierarchical materials have received significant attention as their structure and functionality can be precisely programmed by molecular design and self‐assembly. Although numerous reviews have highlighted their synthesis, self‐assembly behavior, and applications, the fundamental roles of noncovalent and covalent cross‐linking in governing their hierarchical organization, stability, and functionality have not been systematically examined from a physical organic chemistry perspective. This mini review discusses how molecular recognition, reaction kinetics, reaction mechanisms, and thermodynamics govern hierarchical self‐assembly and postassembly cross‐linking of peptide‐ and peptoid‐based hierarchical materials.
ABSTRACT An investigation into the photophysical effects of a series of 10 bis(phenolate) aza‐GaDIPYs with regioselective substitution on the 4,4′‐ and 5,5′‐positions of the phenolate rings was conducted. Computational and experimental data confirmed that installation of strong π‐electron donors on the 5,5′‐positions provided maximized bathochromic shifts in both absorption and emission spectra as well as larger Stokes shifts when compared to the 4,4′‐isomers. This can be rationalized by how the 5,5′‐positions interact strongly with the HOMO and weakly with the LUMO, thus narrowing the HOMO‐LUMO gap. Combined, these data demonstrate that judicious functionalization of the phenolate rings represents a reliable strategy to achieve absorption and emission maxima above 800 nm.
ABSTRACT Small molecule organic fluorophores have provided utility across several fields. Existing dyes have been used to make responsive materials, detect diseases and quantify analytes in various media and in many other applications. Although there are excellent molecules for many of these applications, most of the existing fluorophore moieties have limitations such as small Stokes shifts, low brightness, or poor stability. To address this challenge, researchers have developed several hybrid dyes, where two or more fluorescent molecules are covalently bonded together. The dyes augment each other's photophysical properties, often leading to application‐specific improvements. This study presents the synthesis and characterization of the first phosphaquinolinone (PN)–nitrobenzoxadiazole (NBD) hybrid fluorophore. Through the combination of these two groups, the resultant molecule exhibits excellent Stokes shifts and shows promise as a building block towards more functionalized PN‐containing hybrid fluorophores.
In this review, we highlight experimental studies of gas‐phase nucleophilic aromatic substitution (SNAr). SNAr is a reaction of great utility and import, and studies in the gas phase present a unique opportunity to ferret out intrinsic reactivity. The literature in this field spans over 50 years. This review provides historical context from which to assess findings and possible future directions in the field.
