Exploration of the Luminescence Properties of Organic Phosphate Salts of 3‐Quinoline‐ and 5‐Isoquinolineboronic Acid

3‐Quinoline‐ and 5‐isoquinolineboronic acids (3QBA and 5IQBA) were combined with 1‐naphthyl and diphenyl phosphate (1NP and DPP) to give three crystalline molecular salts of 1:1 stoichiometric composition, viz., 3QBA‐1NP, 5IQBA‐1NP and 3QBA‐DPP. The products were characterized by elemental analysis, single‐crystal X‐ray diffraction studies, IR spectroscopy, luminescence spectroscopy and TG‐DSC measurements. The analysis of the solid‐state structures revealed that the molecular components are linked by strong charge‐assisted hydrogen bonds forming heterodimeric synthons of the type B(OH)2···–O2P and N+–H···O(P). In addition, the hydrogen phosphate salts derived from 1NP exhibit the homodimeric P(O)OH···O(HO)P synthon. The aggregates formed through the above‐mentioned hydrogen bonding motifs are further connected through π···π interactions, which involve mainly the aromatic rings of the quinolinium/isoquinolinium cations. The crystal structure analyses were accomplished by Hirshfeld surface analyses and the associated 2D fingerprint plots, illustrating the similarities and differences of the three salts more concisely. Solid‐state photoluminescence spectroscopy of the title compounds showed emission in the blue region with an extraordinary high quantum yield (Φf = 98 %) for compound 3QBA‐DPP.