Triarylmethanes, compounds in which the central carbon atom is attached to three aryl rings, have a wide variety of photophysical properties which are utilized in the dye industry and also in the development of novel fluorescent tags and biomarkers. The aryl rings attached to the central carbon atom of the parent molecule triphenylmethane can freely rotate. Bridging the aryl rings of triarylmethanes with heteroatoms or through bonds decreases the conformational flexibility enjoyed by the parent molecules. Conformationally restricted triarylmethane (CRT) molecules like 9‐arylxanthenes (oxygen bridging), 9‐arythioxanthenes (sulfur bridging), 9,10‐dihydro,9‐arylacridines (nitrogen bridging), and 9‐arylfluorenes (bridging through C–C bond) have decreased conformational flexibility and display amphihydric behavior which results in benzenoid structure and quinoid structure of these molecules. The quinoid form of these molecules displays very rich photophysical properties which are the subject of this review. These molecules also have widespread utility, and over the last decade, a number of studies have been focused on the synthesis, photophysical properties, and applications of molecules derived from this core structure. Through this review, we intend to give the readers an outlook on the different strategies employed to synthesize these molecules and also provide a broader perspective on the various intriguing properties of these molecules. The applications of these classes of molecules in diverse fields like photocatalysis, chemical biology, pharmaceutical chemistry, and bio‐imaging are discussed. Also, the areas that need to be further developed are highlighted, which may provide a further impetus in the development of this class of molecules.
Selective formation of positional isomers and accordingly tuning the physicochemical properties of small conjugated organic molecules through structural isomers is an effective crystal engineering for a fascinating successful delivery of thermally stable and photophysically exciting compounds. By small structural skeleton changes, the single crystal of the naphthalenemaleonitrile isomers is found to exhibit a drastic change in crystal packing array, which in turn is found to tune the thermal and physicochemical properties. The α-isomer (A) forms the "herringbone packing" (HP) due to peri-interaction-sensitive C−H•••(Ar)π (Ar = naphthalene ring) interactions, and the β-isomer (B) forms the "bricklayer packing" (BP) due to π(CN)•••π(Ar) stacking interactions. These two positional isomers have revealed insight of molecular packing-dependent structure−property relationship. In this report, we show that a simple modification of relatively less common weak interactions, such as C−H•••π(Ar) ↔ π(CN)•••π(Ar), through the preparation of isomers, can lead to a drastic change in crystal packing (HP ↔ BP). Also, this report demonstrates that by a small structural diversity, one can obtain significant changes in the physicochemical properties like melting behavior, enthalpy, entropy, and electrical properties in the solid state. Therefore, it transpires from this study that structural isomer provides a useful complement to intermolecular nonbonding interactions as a tool to design new promising materials.
By proper choice of substituents on the aldehyde and amine, the nature of Schiff base formed (fully condensed or half condensed) could be tuned by the templating effect of the metal ion. Condensation of 5-chlorosalicylaldehyde with ethylene diamine in the presence of Co(II) or Cu(II) and azido anions have afforded two new half condensed Schiff base metal complexes [CuL(µ1,1-N 3)] 2 (1) and [CoL 2 ]N 3 •H 2 O (2), where L = (E)-2-((2-aminoethyl)methyl)-4chlorophenol that were structurally characterized by X-ray analysis, IR and UV spectra. Complex 1 is an asymmetric µ-1,1 azide bridged dimer displaying weak antiferromagnetic interactions (J =-2.93 ± 0.03 cm-1), in agreement with the axial-equatorial N 3-linkage between the two copper centers. Complex 2 is a monomer of low spin Co(III).
Naphthalenemaleonitrile positional isomers, (1N: 2-amino-3-(((E)-naphthalene-1-ylmethylene)amino)maleonitrile) and (2N: 2-amino-3-(((E)-naphthalene-2-ylmethylene)amino) maleonitrile) were synthesized and studied comparatively here. Their molecular configurations exhibit an extraordinary ability to affect photophysical properties like Aggregation Induced Emission...
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