*2.1. General*

Theophylline, Squaric acid, Tetrahydrofurane (THF), Diethyl Ether, and Ethanol were used as received from MERCK-Sigma Aldrich (Taufkirchen, Germany, EU). Solvents were commercially available and used without any other purification. Water was used after filtration with MilliQ Advantage A10 technology from Millipore (MERCK-Sigma Aldrich (Darmstadt, Germany)).
