Tetrathiafulvalene (TTF)-Annulated Calix[4]pyrroles: Chemically Switchable Systems with Encodable Allosteric Recognition and Logic Gate Functions

Abstract

Molecular and supramolecular systems capable of switching between two or more states as the result of an applied chemical stimulus are attracting ever-increasing attention. They have seen wide application in the development of functional materials including, but not limited to, molecular and supramolecular switches, chemosensors, electronics, optoelectronics, and logic gates. A wide range of chemical stimuli have been used to control the switching within bi- and multiple state systems made up from either singular molecular entities or supramolecular ensembles. In general, chemically triggered switching systems contain at least two major functional components that provide for molecular recognition and signal transduction, respectively. These components can be connected to one another via either covalent or noncovalent linkages. Of particular interest are switchable systems displaying cooperative or allosteric features. Such advanced control over function is ubiquitous in nature and, in the case of synthetic systems, may allow the capture and release of a targeted chemical entity or permit the transduction of binding information from one recognition site to another. Allosterically controlled complexation and decomplexation could also permit the amplification or deamplification of analyte-specific binding affinity, lead to nonlinear binding characteristics, or permit a magnification of output signals. Our own efforts to develop chemically driven supramolecular switches, advanced logic gates, and multifunction cascade systems have focused on the use of tetrathiafulvalene (TTF) annulated calix[4]pyrroles (C4Ps). These systems, TTF-C4Ps, combine several orthogonal binding motifs within what are conformationally switchable receptor frameworks. Their basic structure and host-guest recognition functions can be controlled via application of an appropriate chemical stimulus. Homotropic or heterotropic allosteric molecular recognition behavior is often seen. This has allowed us to (1) produce self-assembled structures, (2) control switching between bi- and multistate constructs, (3) generate chemical logic gates performing chemical-based Boolean logic operations, (4) create ionically controlled three-state logic systems that release different chemical messengers and activate disparate downstream reactions, and (5) encode a variety advanced functional operations into what are relatively simple molecular-scale devices. Looking to the future, we believe that exploiting allosteric control will expand opportunities for supramolecular chemists and allow some of the complexity seen in biology to be reproduced in simple constructs. Of particular appeal would be a capacity to release chemical messengers at will, perhaps after a prior capture and chemical modification step, that then encode for further downstream functions as seen in the case of the small molecules, such as neurotransmitters and pheromones, used by nature for the purpose of intraentity communication. Molecular scale logic devices with allosteric functions are thus the...

New dimensions in calix[4]pyrrole: the land of opportunity in supramolecular chemistry

“…52 In this context, Sessler's group attached the TTF moiety at the bpositions of C4P to generate diverse TTF-C4Ps (29, 31, and 33), as shown in Schemes 3 and 4. [53][54][55][56][57]…”

The Redox Coupling Effect in a Photocatalytic RuII‐PdII Cage with TTF Guest as Electron Relay Mediator for Visible‐Light Hydrogen‐Evolving Promotion

“…TTF is known as aredox-active and electron donor molecule synthesized artificially forty years ago, [43] which is facile to be oxidized to radical-cation species via one-electron process. [44] Thehydrophobic innerspace makes MOC-16 ready to capture TTF guests in aqueous medium; [42,45] therefore,e lectron transfer might occur when TTF is coalesced and interacted with photoredox MOC-16 host, [46][47][48][49] thus enabling TTF to serve as aregulator to tune photo-electronic activity of MOC-16 ( Figure 1).…”

The Redox Coupling Effect in a Photocatalytic RuII‐PdII Cage with TTF Guest as Electron Relay Mediator for Visible‐Light Hydrogen‐Evolving Promotion

“…TTF is known as a redox‐active and electron donor molecule synthesized artificially forty years ago, which is facile to be oxidized to radical‐cation species via one‐electron process . The hydrophobic innerspace makes MOC‐16 ready to capture TTF guests in aqueous medium; therefore, electron transfer might occur when TTF is coalesced and interacted with photoredox MOC‐16 host, thus enabling TTF to serve as a regulator to tune photo‐electronic activity of MOC‐16 (Figure ).…”