Tetrathiafulvalene (TTF)-Bridged Resorcin[4]arene Cavitands: Towards New Electrochemical Molecular Switches

Abstract

We report the synthesis of novel resorcin [4]arene-based cavitands featuring two extended bridges consisting of quinoxaline-fused TTF (tetrathiafulvalene) moieties. In the neutral form, these cavitands were expected to adopt the vase form, whereas, upon oxidation, the open kite geometry should be preferred due to Coulombic repulsion between the two TTF radical cations (Scheme 2). The key step in the preparation of these novel molecular switches was the P(OEt) 3 -mediated coupling between a macrocyclic bis(1,3-dithiol-2-thione) and 2 equiv. of a suitable 1,3-dithiol-2-one. Following the successful application of this strategy to the preparation of mono-TTF-cavitand 3 (Scheme 3), the synthesis of the bis-TTF derivatives 2 (Scheme 4) and 19 (Scheme 5) was pursued; however, the target compounds could not be isolated due to their insolubility. Upon decorating both the octol bowl and the TTF cavity rims with long alkyl chains, the soluble bis-TTF cavitand 23 was finally obtained, besides a minor amount of the novel cage compound 25a featuring a highly distorted TTF bridge (Scheme 6). In contrast to 25a, the deep cavitand 23 undergoes reversible vase ! kite switching upon lowering the temperature from 293 to 193 K (Fig. 1). Electrochemical studies by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) provided preliminary evidence for successful vase ! kite switching of 23 induced by the oxidation of the TTF cavity walls. The vase conformer is prevalent at room temperature at neutral pH, whereas the kite geometry is predominant at low temperatures ( 213 K) [1], upon protonation with acids such as CF 3 COOH (TFA) [4], or in the presence of Zn II ions [5]. At low temperature, solvation of the more extended surface stabilizes the kite geometry, whereas, at higher temperature, the entropic term TDS solv becomes unfavorable, and the vase conformation is dominant [1]. More recent investigations also showed that suitably sized solvent molecules (such as small benzene derivatives) favorably solvate (stabilize) the vase form and reduce the propensity for vase ! kite transition [6]. On the other hand, the kite conformation is additionally stabilized by solvents with substantial H-bonding acidity: weak H-bonding interactions between the mildly basic quinoxaline N-atoms, and solvent molecules are more efficient in the open kite than in the closed vase form [6b]. Acid-induced switching from the vase to the kite

An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene‐Fused Dipyridophenazine Molecule

“…All calculations were performed with the Gaussian 03 program system. [31] 5,6-Diaminobenzene-1,3-dithiole-2-thione (2): The reported procedure [32] was modified as follows: 1,2-diaminobenzene-4,5-bis(thiocyanate) (2.44 g, 11 mmol) was added to a degassed solution of Na 2 S·9 H 2 O (8.71 g, 36 mmol) in water (135 mL), and the mixture was heated to 70 8C for 1 h to produce a clear brownish solution. The mixture was cooled to 50 8C, and CS 2 (1.4 mL, 23.2 mmol) was slowly added dropwise.…”

Complexation and Dynamic Switching Properties of Fluorophore‐Appended Resorcin[4]arene Cavitands

“…Selective functionalization of the rim of resorcin[4]arene cavitands, by attaching long rigid arms bearing terminal chromophores to two wall flaps in the anti-orientation, generates molecular switches featuring large, geometrically well defined contraction/expansion motions. [14][15][16] In the vase conformation, the chromophores are located in close proximity to each other, whereas in the kite conformation they are several nanometers apart. Different interchromophoric interactions in the two states translate into different physical properties that can be utilized to quantify the switching processes.…”

A Novel Poly(aryleneethynylene) with Tetrathiafulvalene (TTF) Side Chains: Synthesis, Self‐Assembly, and Electroactive Property

“…The starting materials, 1, 3, 5, and another monomer 7 were synthesized according to the literature. [7][8][9][10] Compound 2 was obtained by modifying the reported procedure (yield 48%). [8] By a phosphite-mediated crosscoupling reaction of 2 with 3, the diamine TTF 4 could be obtained (yield 35%).…”