Proton induced tautomeric switching in N-rich aromatics with tunable acid-base character

Centore, Roberto; Manfredi, Carla; Fusco, Sabato; Maglione, Cira; Carella, Antonio; Capobianco, Amedeo; Peluso, Andrea; Colonna, Daniele; Carlo, Aldo Di

doi:10.1016/j.molstruc.2015.03.030

Cited by 13 publications

(18 citation statements)

References 31 publications

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“…Relevant chemical diagrams for the [1,2,4]triazolo [3,2-c][1,2,4]triazole system: the three tautomers of the neutral form (the adopted atom numbering of the heterobicycle is indicated only for the 2H-tautomer). respect to the 2H-tautomer, in the most favourable case) (Centore et al, 2015), the calculated energy of the 3Htautomer, in some cases, is greater than for the 2H-tautomer by only 1 kcal mol À1 or less (Centore et al, 2015). Despite this, the 3H-tautomer should be considered elusive, because it has not yet been observed in the solid state for any of the pure triazolotriazole compounds studied so far.…”

Section: Figurementioning

confidence: 89%

“…In the realm of fused-ring heteroaromatic systems that we have studied over the years (Centore et al, 1996(Centore et al, , 1999Ambrosanio et al, 1999), we have found in [1,2,4]triazolo [3,2-c]-[1,2,4]triazole a heterocyclic system with a rich tautomeric behaviour (Centore et al, 2013(Centore et al, , 2015(Centore et al, , 2017Fusco et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Stabilization of an elusive tautomer by metal coordination

Parisi¹,

Centore²

2021

Acta Crystallogr C

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The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol−1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr2 and ZnBr2, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C8H7N7)2(H2O)]Br·3H2O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr2(C8H7N7)2]·H2O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of CuII and ZnII. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

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Section: Figurementioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Stabilization of an elusive tautomer by metal coordination

Parisi¹,

Centore²

2021

Acta Crystallogr C

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“…As described in this paragraph, the anchoring group of the typical metal-free photosensitizer is a cyanoacrylic moiety which coincides with the electron acceptor part of the dye. Although many other anchoring groups have been tested, as pyridine, phosphonic acid, benzoic acid (Zhang and Cole, 2015 ) or tetrazole (Massin et al, 2014 ) and triazole derivatives (Centore et al, 2015 ), the best performing organic sensitizers, until recently, contained a cyanoacrylic-like anchoring group. In the last year, however, the Kakiage group investigated the alkoxysilyl moiety as a possible alternative anchoring group and prepared new photosensitizers with outstanding performances.…”

Section: Sensitizersmentioning

confidence: 99%

Research Progress on Photosensitizers for DSSC

2018

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Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, their peculiar optical and mechanical properties and the high indoor efficiency. Photosensitizers represent one of the most important components of a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to provide an overview of the three main classes of DSSC photosensitizers, namely ruthenium(II) polypyridyl complexes, Zn-porphyrin derivatives and metal-free organic dyes. After a brief introduction about the architecture and operational principles of a DSSC and the state of the art of the other main components of this type of device, we focused our discussion on photosensitizers. We have defined the numerous requirements DSSC photosensitizers should satisfy and have provided an overview of their historical development over the years; by examining specific dyes reported in the literature, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in real devices both in terms of efficiency (which recently reaches an outstanding 14.3%) and operational stability. Finally, we discussed, in the last section, the possible future developments of this intriguing technology.

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“…Knowledge of the tautomeric preferences in organic molecules, especially in tetrazoles and triazoles, is of importance since their functionality or physicochemical activity may be tautomer sensitive [14][15][16][17]. A number of papers have been published concerning different triazole tautomers, solvent effects on the equilibria between them [18][19][20][21] as well as the proton transfer phenomena in azole-based coordination polymers [22]. However, to the best of our knowledge, UV-induced proton transfer between azole tautomers was not reported.…”

Section: Introductionmentioning

confidence: 96%