Synthesis, Crystal Structures, Fluorescence and Quantum Chemical Investigations of some Multi-Substituted Quinoline Derivatives

Starting from eugenol (4-allyl-2-methoxyphenol) three new quinoline derivatives, namely 5-bromo-7-(carboxymethoxy)-6-hydroxy-1-methylquinolin-1-ium-3-sulfonate (Q2, C 12 H 10 BrNO 7 S), 5-amino-7-(carboxymethoxy)-6-hydroxyquinolin-1-ium-3-sulfonate (Q4, C 11 H 10 N 2 O 7 S) and 7-(carboxymethoxy)-5,6-dihydroxylquinolin-1-ium-3-sulfonate (Q6, C 11 H 9 NO 8 ), have been synthesized and crystallised as dihydrate. The best planes through the quinoline ring and the carboxymethoxy substituent is 6.60 (14), 7.28 (6) and 4.73 (7)° for Q2, Q4 and Q6, respectively. The crystal packing of Q2 is characterised by O-H…O, π …π and Br …pyridine interactions. The two water molecules bridge three sulphate groups. Infinite chains of Q4 running in the direction [021] are formed by O/N-H …O hydrogen bonds at both ends of the molecule. Parallel chains interact by O/N-H…O hydrogen bonds and π…π and C=O…phenyl stacking. The -NH 2 substituent bridges two sulphate groups, while the two water molecules bridge the other functional groups. The packing of Q6 consists of sheets of molecules interaction through O/N-H…O hydrogen bonds while the two water molecules bridge all function groups present. Parallel sheets interact through π…π and C=O…pyridine stacking. An aqueous solution of Q2 and its precursor 7-(carboxymethoxy)-6-hydroxyquinolin-1-ium-3-sulfonate (Q) exhibits fluorescence which is pH dependent. The fluorescence intensity of a 10 μM solution of Q containing Zn 2+ reaches its maximum for a [Zn 2+ ]:[Q] ratio of 1:1. The fluorescence properties of Q, Q2, Q4 and Q6 were further investigated by DFT calculation methods.