A family of “two-in-one” dual-emissive complexes, [Mn(L)₃]MnHal₄, containing octahedral and tetrahedral Mn²⁺ ions in the single structure, is introduced.

More rigid μ₂-N,S coordination of 2-(alkylsulfanyl)pyrimidine ligands in copper(i) iodide coordination polymers leads to a much more efficient emission in comparison with N-monodentate coordination.

Silver(I) complexes with 2-amino-4-phenyl-6-methylpyrimidine (L), [Ag₃L₂(H₂O)_0.55(NO₃)₃]_n (1) and [Ag₂L₂(PPh₃)₂(NO₃)₂] (2), have been synthesized and structurally characterized. In the solid state the free ligand L demonstrates dual fluorescence: a high energy band at 375 nm is the emission of the monomer L while a low-energy band at 450 nm can be attributed to the emission of the tautomeric dimer, L₂-imino, formed in the excited state double proton transfer (ESDPT) process. In the solid state the complexes demonstrate excitation wavelength dependent photoluminescence originating from three emission mechanisms (hereafter abbreviated as A, B and C for complex 1; A′, B′ and C′ for complex 2). The spectroscopic and computational results reveal that these emission mechanisms can be assigned to metal + nitrate anion to ligand L charge transfer phosphorescence (mechanisms A and A′), excimer ¹π–π* fluorescence (mechanism B), fluorescence of L₂-imino dimeric units formed due to ESDPT (mechanism B′) and ligand-centered ¹π–π*/¹n–π* fluorescence (mechanisms C and C′). The luminescence of complex 1 at λ_ex = 340 nm shows thermochromic behavior; the emission color dramatically changes from blue-green at 77 K to yellowish green at 175 K and white at 300 K.

The emission of ESIPT-fluorophores is known to be sensitive to various external and internal stimuli and can be fine-tuned through substitution in the proton-donating and proton-accepting groups. The incorporation of metal ions in the molecules of ESIPT fluorophores without their deprotonation is an emerging area of research in coordination chemistry which provides chemists with a new factor affecting the ESIPT reaction and ESIPT-coupled luminescence. In this paper we present 1-hydroxy-5-methyl-4-(pyridin-2-yl)-2-(quinolin-2-yl)-1H-imidazole (HL^q) as a new ESIPT-capable ligand. Due to the spatial separation of metal binding and ESIPT sites this ligand can coordinate metal ions without being deprotonated. The reactions of ZnHal₂ with HL^q afford ESIPT-capable [Zn(HL^q)Hal₂] (Hal = Cl, Br, I) complexes. In the solid state HL^q and [Zn(HL^q)Hal₂] luminesce in the orange region (λ_max = 600–650 nm). The coordination of HL^q by Zn²⁺ ions leads to the increase in the photoluminescence quantum yield due to the chelation-enhanced fluorescence effect. The ESIPT process is barrierless in the S₁ state, leading to the only possible fluorescence channel in the tautomeric form (T), S₁ ^T → S₀ ^T. The emission of [Zn(HL^q)Hal₂] in the solid state is blue-shifted as compared with HL^q due to the stabilization of the ground state and destabilization of the excited state. In CH₂Cl₂ solutions, the compounds demonstrate dual emission in the UV (λ_max = 358 nm) and green (λ_max = 530 nm) regions. This dual emission is associated with two radiative deactivation channels in the normal (N) and tautomeric (T) forms, S₁ ^N → S₀ ^N and S₁ ^T → S₀ ^T, originating from two minima on the excited state potential energy surfaces. High energy barriers for the GSIPT process allow the trapping of molecules in the minimum of the tautomeric form, S₀ ^T, resulting in the possibility of the S₀ ^T → S₁ ^T photoexcitation and extraordinarily small Stokes shifts in the solid state. Finally, the π-system of quinolin-2-yl group facilitates the delocalization of the positive charge in the proton-accepting part of the molecule and promotes the ESIPT reaction.