Diazocine-functionalized TATA platforms

Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a platform (triazatriangulenium (TATA)) which adsorbs on the gold surface, with an acetylene spacer standing upright, like a post in the middle of the platform and the azobenzene unit mounted on top. The rate acceleration is due to a very peculiar thermal singlet–triplet–singlet mechanism mediated by bulk gold. To investigate this mechanism further and to examine scope and limitation of the “spin-switch catalysis” we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis-configuration. Upon irradiation with light of 405 nm the cis-configuration isomerizes to the trans-form, which slowly returns back to the stable cis-isomer. To investigate the thermal trans→cis isomerization as a function of the conjugation to the metal surface, we connected the acetylene spacer in meta (weak conjugation) and in para (strong conjugation) position. Both isomers form ordered monolayers on Au(111) surfaces.


NMR Spectroscopy
NMR spectra were measured in deuterated solvents (Deutero). All compounds were characterized using 1 H and 13 C NMR spectroscopy. The signals were assigned using 2D spectroscopy. For 1 H and 13 C NMR assignment we performed HSQC and HMBC. The degree of deuteration is given in parentheses. 1

IR spectroscopy
Infrared spectra were measured on a Perkin-Elmer 1600 Series FT-IR spectrometer with an A531-G Golden-Gate-Diamond-ATR-unit. Signals were abbreviated with w, m, s and for weak, medium and strong intensities. Broad signals are additionally labeled with br.

Mass spectrometry
The high resolution (HR) mass spectra were measured with an APEX 3 FT-ICR with a 7.05 T magnet by co. Bruker Daltonics. Electron impact (EI).
After stirring for 5 min, the reaction was poured onto ice/water (500 mL). The solution was S7 extracted with dichloromethane (3 × 300 mL) and the combined organic layers were washed with saturated sodium thiosulfate solution and saturated sodium chloride solution and then dried over magnesium sulfate. The solvent was removed under reduced pressure and the crude product was purified via column chromatography (silica gel, cyclohexane/ethyl acetate, 2/1) to obtain a beige solid (817 mg, 2.50 mmol, 10%).

IV.1 Methods
UV-Vis spectra were recorded on a PerkinElmer Lambda 650 Photospectrometer in a 1 cm path length quartz cuvette. Irradiation of UV-vis samples were carried out at 25 °C using a custom-made LED positioned at a distance of 1 cm from the sample.

VI. Calculations
The geometry optimizations were carried out using density functional theory with the Minnesota functional M06-2X [4] including Grimmes D3 [5] dispersion correction and the large triple zeta basis def2-TZVP [6]. This theoretical level performed well in Grimme's latest study on basic properties of a large set of organic molecules [7]. The calculations were performed with Turbomole7.2 [8], including the m4 grid (in Turbomole nomenclature) and resolution-of-identity (RI) with multipole accelerated RI-J (marij) to speed up the calculations. All stationary points are characterized by frequency calculations.