The N-alkyl derivatisation and photochemical dimerisation of 3 o-, m-, and p-nitro substituted 4-azachalcones (1-3) yielded 3 new o-, m-, and p-nitro substituted (E)-N-decyl-4-azachalconium bromides, (2E)-1-(2-nitrophenyl)-3-(N-decyl-4-pyridinium bromide)-2-propen-1-one (4), (2E)-1-(3-nitrophenyl)3-(N-decyl-4-pyridinium bromide)-2-propen-1-one (5), and (2E)-1-(4-nitrophenyl)-3-(N-decyl-4-pyridinium bromide)-2-propen-1-one (6), and 3 new dimers in solution, (1 beta,2 alpha)-di-(3-nitrobenzoyl)-(3 beta,4 alpha)-di(4-pyridinyl)cyclobutane (7), (1 beta,2 alpha)-di-(4-nitrobenzoyl)-(3 beta,4 alpha)-di-(4-pyridinyl)cyclobutane (8a), and (1 beta,2 beta)-di-(4-nitrobenzoyl)-(3 beta,4 alpha)-di-(4-pyridinyl)cyclobutane (8b), stereoselectively. The monomeric compounds showed good antimicrobial activity against test micro-organisms. The most sensitive microorganisms were Gram-positive bacteria. The monomers also showed high antioxidant activity, while the dimerisation products 7-8a,b were less active. Compound 6 was found to have similar or even higher activity when compared to the standard antioxidants Trolox((R)) and vitamin C, respectively. The possible dimerisation products of compounds 1-3 were calculated theoretically. Experimental and theoretical calculations showed that delta-truxinic type dimer is the most stable isomer.