DescriptionIn 2004 the groups of Sessler and Jeppesen reported of the first TetraTTF-calixpyrrole (TTF-CP), consisting of the strongly pi-electron-donating tetrathiafulvalene unit fused together with the pyrroles of the octamethyl-calixpyrrole. 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-CP 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 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-CP 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.
|Period||10. Jun 2017|
|Event title||Gordon Research Seminar: Artificial Molecular Switches & Motors|
|Location||Holderness, United States, New Hampshire|
|Degree of Recognition||International|