“…The families of hydroxy carboxylic acids that have been exploited as proton transfer systems are hydroxyl-benzoic acids and esters [ 34 , 35 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ], hydroxynaphthoic acids [ 71 , 72 , 73 , 74 , 75 ] and anthranilic acid and its esters [ 76 , 77 , 78 , 79 , 80 , 81 ]. Besides carboxylic acids, other compounds belonging to hydroxyflavones [ 82 , 83 , 84 ], quinoline family and anthraquiniones [ 85 , 86 , 87 ,…”