Bis(dicyanomethylene)squarate squaraines in their 1,2- and 1,3-forms: Synthesis, crystal structure and spectroscopic study of compounds containing alkali metals and tetrabutylammonium ions

Squaraine-Based Optical Sensors: Designer Toolbox for Exploring Ionic and Molecular Recognitions

“…Several solvent systems, typically at elevated temperatures, have been utilized. However, the most commonly used solvents are as follows: (a) mixtures of aromatic hydrocarbons (typically toluene or benzene) and alcohols (typically n-butanol), with the azeotropic removal of water (this is, by far, the most prevalent system) [12][13][14]; (b) alcohols, in the presence of trialkylorthoformates, which are used as dehydrating agents [15][16][17]; (c) typical molecular organic solvents, such as dimethylformamide [18][19][20]. Non-conventional types of media, such as deep eutectic solvents, have been recently shown to be suitable for the synthesis of squaraine dyes [21].…”

Vibrational Spectroscopic Analysis of 1,3-Dianiline Squarate: Infrared, Normal Raman, Surface-Enhanced Raman Scattering, and Density Functional Theory Calculations

“…It is composed of a highly electron-deficient central core (from the oxocarbon squarate, SQ, 2 ), surrounded by two opposite “aniline” ligands, electron-rich donating species, forming a trans -zwitterionic structure with important spectroscopic implications. SQ is powerful electrophilic species and reacts easily with aromatic amines yielding deeply colored condensation products. , DSQ has been commonly used as an intermediary reactant aiming to obtain 1,3-( R 1 R 2 )-squarate derivatives. − However, its specific potential applications have been underexplored despite some studies dating back to 1975, possibly due to its solubility issues. , There are not many studies available in the literature about its physical–chemical properties, and only a few characterization data can be found. ,, …”

“…29,30 There are not many studies available in the literature about its physical− chemical properties, and only a few characterization data can be found. 24,25,31 Although the practical uses of DSQ and DSQ-based dyes have been sparse, in the last few years, there has been increasing attention to their applications as photosensitizers. 11,32,33 Due to their strong light absorption in the blue region, these squaraines have been used as visible light photoinitiators in photopolymerization reactions.…”

Squaraines: Crystal Structures and Spectroscopic Analysis of Hydrated and Anhydrous Forms of Squaric Acid-Isoniazid Species

“…1,2 Such systems possess interesting structural features such as flat cyclic structures, high molecular symmetry (D nh ) and an extensive π electron delocalization. 2−4 The partial or total substitution of the oxygen atoms by other groups originates systems named pseudo-oxocarbons, 5,6 and the oxygen(s) substitution(s) in the squaric acid (H 2 Sq, n = 4) by nitrogenous groups engenders the so-called squaraines, 5,7 see Figure 1a.…”

“…Oxocarbons are an important class of anionic molecules formed by “ n ” carbon and oxygen atoms with general formula (C n O n ) 2– , where “ n ” varies from 3 to 6 for deltate, squarate, croconate, and rhodizonate, respectively. , Such systems possess interesting structural features such as flat cyclic structures, high molecular symmetry ( D nh ) and an extensive π electron delocalization. − The partial or total substitution of the oxygen atoms by other groups originates systems named pseudo-oxocarbons, , and the oxygen(s) substitution(s) in the squaric acid (H 2 Sq, n = 4) by nitrogenous groups engenders the so-called squaraines, , see Figure a.…”