Hydrogen-bonding-based thermochromic phenol-amine complexes

Abstract

Variable-temperature UV-vis, 13 C NMR and IR studies showed that proton-transferred complexes were formed between phenols and amines in apolar solvents at low temperature. Upon cooling a solution of pnitrophenol and diisopropylamine in toluene, the colour of the solution changed from colourless to yellow. This thermochromism was ascribed to the proton transfer in the hydrogen-bonding complex. Under UV-vis conditions, butylamine and imidazole also caused similar thermochromism upon complexation with p-nitrophenol, while triethylamine, quinuclidine and pyridine did not. The thermochromic behaviour was particularly dependent on the stoichiometry of the amine and the phenol: a solution of 3,3'-dibromo-5,5'-dinitro-2,2'-biphenyldiol and diisopropylamine with a molar ratio of 1:1 showed no thermochromism, while solutions with 1:2 or higher ratios showed thermochromism, indicating that excess amine is required to obtain the proton-transferred species. These results revealed that the proton-transferred species forms in apolar solvents at low temperature if an appropriate hydrogen-bonding network between the phenol and the amine can stabilize it.

Determination of thermodynamic properties for protonation equilibrium between isomeric cresols and N,N-dimethylaniline in n-hexane medium

“…There are reports that the binary systems of isomeric cresols form hydrogen bonded complexes with 1-alkanols, dimethylsulfoxide, N,N-dimethylformamide and cyclohexanone [12][13][14][15]. Variable-temperature UV-vis, 13 C NMR and IR studies have been carried out in different solvents at a low temperature and the color change in ternary mixtures of phenols and amines in non-polar solvents was attributed to the proton transfer followed by the formation of hydrogen bonded complex [16]. Similar behavior is shown by both aniline-water and aniline-methanol clusters with very similar intermolecular interactions and equilibrium geometry.…”

Ultrasonic and spectral studies on charge transfer complexes of anisole and certain aromatic amines

“…The solvent n-hexane used was spectral grade Aldrich sample. The purity of these chemicals was ascertained by comparing the measured densities and ultrasonic velocity (Table 1) at the investigated temperatures with the reported literature values [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. The liquid mixtures of required concentrations were prepared by weighing appropriate amounts of pure liquids and mixed in airtight stopper bottles to minimize evaporation losses.…”

4-Dimethylaminopyridinium picrate: supramolecular aggregation through extensive N—H...O and C—H...O interactions

“…The linkage could involve not only electrostatic interactions, but also the formation of molecular complexes (Zaderenko et al, 1997). It has been reported that proton-transferred thermochromic complexes are formed between phenols and amines in apolar solvents at low temperature if an appropriate hydrogen-bonding network between phenols and amines can stabilize it (Mizutani et al, 1998). Pyridinium picrate has been reported in two crystalline phases, and it occurs in both phases as an internally linked hydrogen-bonded ion pair; both phases are regarded as molecular crystals rather than salts, based on their structural arrangements (Botoshansky et al, 1994).…”