Novel ditopic 2-mercaptothiazoles and their sodium salts: synthesis, structural diversity and luminescence

Abstract

A set of novel bis-(2-mercaptothiazoles) has been synthesized. 4,5-Difluorobenzo[1,2-d:3,4-d′]bisthiazole-2,7-dithiol (1), 4,8-difluorobenzo[1,2-d:5,4-d′]bisthiazole-2,6-dithiol (2), 4,4′,5,5′,7,7′-hexafluoro-[6,6′-bibenzo[d]thiazole]-2,2′-dithiol (3) and naphtho[1,2-d:5,6-d′]bis(thiazole)-2,7-dithiol (4) were obtained by condensation of halogenated aromatic diamines or dinitro compounds with potassium ethylxanthate or CS₂ while the synthesis of benzo[1,2-d:4,5-d′]bis(thiazole)-2,6-dithiol (5) was performed starting from a centrosymmetric benzodiaminedithiol. The disodium salts of new bisthiazoles 1–5 as well as previously known benzo[1,2-d:5,4-d′]bisthiazole-2,6-dithiol (H₂(dmbt)) with a formula Na₂Lx(DME)₄ (L = 1–3, 5, dmbt) were synthesized from sodium sylilamide NaN(SiMe₃)₂ and respective bisthizoles in DME media. X-Ray srtuctural analysis revealed that the salts of bisthiazoles 2, 5 and dmbt are molecular complexes in which bisthiazoles act as ditopic ligands coordinating two sodium atoms. A similar reaction of 4 and NaN(SiMe₃)₂ in DME media results in a formation of 2D coordination polymer [Na₂L⁴(DME)₂]_n which shows an intense photoluminescence (PL) at room temperature and 77 K. Solvent replacement in [Na₂L⁴(DME)₂]_n with THF results in a formation of novel 2D coordination polymer [Na₂L⁴(THF)₄]_n which turned out to be non-luminescent. Time-resolved PL spectroscopy revealed that the low temperature PL of the disodium salts consists of fluorescent and phosporescent components. Based on the phosphorescence spectra the triplet levels of the bisthizoles were found to be 21 400, 21 400, 21 500, 21 600, 18 900 and 21 200 cm⁻¹ for bithiazoles 1–5 and dmbt respectively.