On the way to supramolecular photochemistry at the single-molecule level

Abstract

Two examples of artificial supramolecular host-guest systems derived from resorc[4]arenes (calix[n]arenes based on resorcinol) and ammonium ions as guests have been studied by atomic force microscopy (AFM). For the first time, real single-molecule events have been determined for this type of supramolecular complexes and off-rates as well as molecular parameters of single-molecule aggregates such as the depths of the binding pocket (molecular length parameter) could be measured by applying the methods of dynamic force spectroscopy. In addition, this technique was also applied to differentiate between the two states (open and closed) of a photoswitchable resorc[4]arene-anthracene tweezer. An investigation of the exchange rates of various complexes in the gas phase by means of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry confirmed the results of the AFM study.

Optical switches with biplanemers obtained by intramolecular photocycloaddition reactions of tethered arenes

“…In previous years many publications on applications of the reversible reaction 1 $ 2 in supramolecular chemistry and materials science appeared. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In principle, such a switch can be monitored by any (physical) property which is sufficiently different for 1 and 2. An easy control is possible by measuring the absorbance of 1 and 2 at a certain excitation wavelength.…”

“…Mattay et al 11,12,15,16,[21][22][23] synthesized resorcin [4]arenes such as 43 and related compounds, which bear anthracene chromophores on opposite benzene rings. Irradiation at the anthracene absorption at 350 nm transforms 43a-e to the corresponding cycloisomers by intramolecular [4 + 4] cycloadditions; 43f shows a decomposition upon irradiation.…”

Functional characterization of a supramolecular affinity switch at the single molecule level

“…Although in some supramolecular systems like cyclodextrins, 14 hydrogen-bonded pyrimidine systems 19,18 or p-p-bridged systems, 21,22 fast complexation phenomena with quasi-equilibrium conditions could be observed, the host-guest-binding kinetics of most supramolecular systems can be quantitatively described within the framework of non-equilibrium conditions and the KBE-model. [15][16][17]19,23,25,26,44,45 Nevertheless, there are some deficiencies in the KBE-model, making it necessary to extend the current formalism. The HB-model accounts for the local statistical fluctuations that the molecular environment is subjected to, like variations in the ionic strength, pH, molecular structure or the direction of the externally applied force.…”

Photochromic resorcin[4]arenes: stabilization of intramolecular anthracene dimers in solution

“…Mp: 110-113 • C (lit. 14 (12), 194 (100), 193 (43), 176 (10), 166 (12), 165 (59), 164 (11), 163 (11), 150 (5), 139 (5), 96 (15), 89 (7), 88 (7), 70 (6), 45 (8), 43 (7), 41 (5), 27 (9).…”

“…4 In 2003, Kimura et al studied the photochromism and metal ion binding ability for chromenefunctionalized calixarenes 5 and two years later, Salzer et al used azobenzene as a photochromic unit on resorcin [4]arenes. 6 In our previous work, we presented a photoswitchable host system based on a resorcin [4]arene 7 and evaluated its complexing properties in the gas phase 8 and on a surface 9,10 using ammonium ions as guests. routes.…”