Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

Triazatriangulenium (TATA) and trioxatriangulenium (TOTA) ions are particularly suited systems to mount functional molecules onto atomically flat surfaces such as Au(111). The TATA and TOTA units serve as platforms that absorb onto the surface and form ordered monolayers, while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA’s are known to exhibit extremely fast cis→trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes (NBD) and quadricyclanes (QC) attached to TATA and TOTA platforms which can be used to check if these accelerated rates and the spin change mechanism also apply to [2 + 2] cycloreversions (QC→NBD).


Materials
Solvents for extraction and chromatography were technical grade. Most solvents used in reactions were extra dried (abs.) or used as received. Analytical TLC was performed with Polygeram ® SilG/UV254 (Macherey Nagel, 0.2 mm particle size) and visualization was accomplished by UV light. Flash chromatography was carried out using 0.040-0.063 nm silica gel (Merck). Reactions were carried out inert atmosphere using nitrogen (N2) as gas.

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 experiments. 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). Electrospray ionization (ESI) mass spectra were measured with a Thermo Scientific Q EXACTIVE.

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 self-built LED positioned at a distance of 1 cm from the sample.

VI. STM measurements
SAMs were prepared by immersing an Au(111) single crystal 3 hours in a 1-100 µM solution of 1 in toluene at room temperature. Afterwards the samples were rinsed with toluene and dried in the air. STM measurements were performed under ambient conditions, using a PicoPlus SPM (Agilent) and Pt/Ir tips.

VII. Calculations
General All geometry optimizations were carried out using density functional theory with the Minnesota functional M06-2X [8] in cooperation with Grimmes D3 [9] dispersion correction and the large triple zeta basis def2-TZVP [10]. This level performed well in Grimme's study on basic properties of a selected data base of structures [11]. The calculations were carried out with Turbomole7.2 [12], the m4 grid (in Turbomole nomenclature) and resolution-of-identity (RI) with multipole accelerated RI-J (marij). All stationary points were characterized by frequency calculations.