Thenil and furil-imidazole-based efficient ionic green emitters with high color purity for non-doped light-emitting electrochemical cells

Abstract

Future artificial lighting devices ought to be efficient, economical, environmentally benign and free of rare metals like iridium. In this regard, we report the design and fabrication of a non-doped light-emitting electrochemical cell (LEC or LEEC) featuring two new donor (D)–acceptor (A) type ionic green-emitting materials, namely thenil (ThAz) and furil (FuAz) imidazole-coupled triazines. These emitters exhibited good solubility in common organic solvents, excellent thin-film-forming ability, thermal stability and, more importantly, strong luminescence both in the solution and solid-state. Green LEEC devices fabricated with a single component active layer of both the green emitters presented similar photophysical properties; however, thenil imidazole-triazine exhibited better performance in devices than its furil counterpart. These ThAz- and FuAz-based non-doped LEECs revealed emission at 525 and 540 nm with excellent green CIE coordinates (0.23, 0.69) and (0.26, 0.67), respectively, which are very close to those of pure green emission. Moreover, the ThAz and FuAz devices delivered maximum brightness values of 1556 and 1173 cd m⁻² along with maximum current efficiencies of 3.77 and 2.80 cd A⁻¹ and power efficiencies of 1.31 and 1.12 lm W⁻¹, respectively.