Synthesis of 13C-Labeled Aromatic Compounds

The compound with a ¹³C label in each position of the aromatic ring is prepared in a Friedel–Crafts acylation of ¹³C-labelled phenol with 2-bromoacetyl chloride,^{47 (link)} followed by reaction with NH₄SCN. The same reaction is used for the preparation of the derivative with a ¹³C label in the LG, using KS¹³CN instead. For synthesis and characterization details, see the ESI and Fig. S1–S7.† NMR, high resolution mass spectrometry (HRMS) and IR spectroscopy confirmed the isotope incorporation. For the laser experiments, the samples are dissolved in D₂O (Eurisotop) and acetonitrile (MeCN; Sigma-Aldrich), and dried with a molecular sieve before use.