Journal of Photochemistry and Photobiology A: Chemistry 131 (2000) 55–60 Radiochemiluminescence of carboxyquinolines K. Papadopoulos a , T. Triantis b , D. Dimotikali b , J. Nikokavouras a,∗ a Institute of Physical Chemistry, NRCPS “Demokritos”, 15310 Ag. Paraskevi Attikis, Athens, Greece b Chemical Engineering Department, NTU Athens, Iroon Polytechniou 9, 15780 Zografou, Athens, Greece Received 22 November 1999; accepted 26 November 1999 Abstract Carboxyquinolines, specifically 2-carboxyquinoline (quinaldic acid), 4-carboxy-2-hydroxyquinoline (kynurenic acid), 2-carboxy-4- hydroxyquinoline, 4,4 ′ -dicarboxy-2,2 ′ -biquinoline and 2,2 ′ -biquinoline-4,4 ′ -dicarboxylic acid dipotassium salt in dialkylated amides are radiolyzed to novel 1,4-dihydroquinolines which emit light on addition of bases in the presence of oxygen giving rise to quinolinones. The overall quantum yields (radiolysis and chemiluminescence) are as high as 2.4×10 −5 einstein mol −1 . The radiolysis and chemiluminescence mechanisms are discussed. The radiochemiluminescence reactions constitute prospective radiation dosemeters and can be used for analytical applications. ©2000 Elsevier Science S.A. All rights reserved. Keywords: Chemiluminescence; Radiolysis; Carboxyquinolines; Dihydroquinolines; Quinolinones; Radiochemiluminescence 1. Introduction We have recently reported that exposure of de-aerated acridone and acridine derivatives in N,N-dialkylated amides even to the diffuse light of the laboratory or to -irradiation results in photolysis or -radiolysis, while subsequent ad- dition of strong bases to said spent mixtures gives rise to very efficient chemiluminescence (CL) [1,2]. In the present work we wish to report the radiochemiluminescence — a term that we have coined to describe a radiolysis pro- cess leading to chemiluminescent products and subsequent CL — of carboxyquinolines such as 2-carboxyquinoline (quinaldic acid, 1a), 2-carboxy-4-hydroxyquinoline (1b), 4-carboxy-2-hydroxyquinoline (kynurenic acid, 1c), 4,4 ′ -dicarboxy-2,2 ′ -biquinoline (1d) and 2,2 ′ -biquinoline-4, 4 ′ -dicarboxylic acid dipotassium salt (1e) in N,N-dimethyl- formamide (DMF) in the presence of oxygen with bases such as sodium hydride, aqueous alkalies or tetraalkylammonium hydroxides (see Table 1). The title compounds are used in many analytical and medicinal applications. Quinaldic acid (1a) is used for the determination of many transition metals [3–5], while kynurenic acid (1c) is referred over 100 times in the last 5 years in medicinal applications. The dipotas- sium salt of 2,2 ′ -biquinoline-4,4 ′ -dicarboxylic acid (1e) is referred for automatic sugar chromatography and for the de- tection of reducing sugars in borate complex ion-exchange ∗ Corresponding author. chromatography [6,7] as well as for protein determination [8] and for the spectrophotometric determination of copper [9,10]. Although in common with biacridinium salts and biacridylidenes the CL of bis-isoquinolinium salts with hy- drogen peroxide in alkaline solutions and their reduction products with singlet oxygen has been recently reported [11,12], the radiochemiluminescence of carboxyquinolines has never been reported. 2. Experimental techniques 2.1. Reagents 2-Carboxyquinoline (quinaldic acid, 1a), 2-carboxy-4- hydroxyquinoline (1b), 4-carboxy-2-hydroxyquinoline (kynurenic acid, 1c), 4,4 ′ -dicarboxy-2,2 ′ -biquinoline (1d), 2,2 ′ -biquinoline-4,4 ′ -dicarboxylic acid (1e), 2,4-dihydroxy- quinoline and 4,4 ′ -dihydroxy-2,2 ′ -biquinoline were pur- chased from Fluka and Aldrich and were used without further purification. The purity of all compounds used was checked by NMR, UV and fluorescence spectroscopy. N,N-dimethylformamide was purified and dried by the stan- dard procedure [13]. Sodium hydride was purchased from Aldrich as powder and used without further purification. Lithium, sodium, potassium and tetramethylammonium hy- droxides were used as 0.1M solutions. Working solutions were freshly made. 1010-6030/00/$ – see front matter ©2000 Elsevier Science S.A. All rights reserved. PII:S1010-6030(99)00243-9