TetraTTF-Calix[4]pyrrole: A Biomimmetic Receptor for Anions, Fullerenes and Electron-Deficient Planar Guests

Bähring, S. (Guest lecturer)

Activity: Talks and presentationsConference presentations

Description

In 2004 the groups of Sessler and Jeppesen reported of the first TetraTTF-calix[4]pyrrole (TTF-C[4]P), consisting of the strongly pi-electron-donating tetrathiafulvalene unit fused together with the pyrroles of the octamethyl-calix[4]pyrrole. This system was shown to complex both electron-deficient guests (1:2 Host:Guest) such as 1,3,5-trinitrobenzene (TNB) as well as anions (1:1) such as chloride (as its tetrabutylammonium salt). These complexation events take place via two different routes wherein the receptor TTF-C[4]P resides in two different conformations, the stronger complex being that of the anions which causes the formed complex with electron-deficient guests to collapse. This dual response behavior makes the receptor sensitive to its environment. Furthermore, when complexing anions in the cone conformation, the receptor is able to host [60]fullerene leading to a transient electron-transfer. Utilizing these three binding modes has led to new environmentally responsive system wherein electron-transfer processes can be modulated by different anionic- and cationic species.
This type of behavior is reminiscent of biological systems where allosteric modulators play a regulating role and the dual binding in the 1,3-alternate conformation follows a positive allosteric homotropic coopertivity similar to Hemoglobin binding of oxygen. The dual binding in the 1,3-alternate conformation has also led to the design of new supramolecular responsive polymer/oligomer systems based on TTF-C[4]P and electron-deficient planar bis-guests. These systems have been shown to function as sensing systems for TNB and chloride anion, and recently we reported the fluorescence turn-on when exposed to low levels of analytes.
The competition between anion-binding in the cone conformation versus binding of electron-deficient guests in the 1,3-alternate conformation has been a very uneven with anions winning the fight. Newly discovered binding of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), a precursor of NDA, has led to an unprecedented strong binding in the 1,3-alternate conformation and an anion-insensitive 1,3-alternate complex. This brings promise for new supramolecular polymers based on the NDA building block.
Period10. Jun 2017
Event titleGordon Research Seminar: Artificial Molecular Switches & Motors: null
Event typeSeminar
LocationHolderness, United States, New Hampshire
Degree of RecognitionInternational