A neutral mononuclear rhenium(I) complex with a rare in situ -generated triazolyl ligand for the luminescence "turn-on" detection of histidine.

A rare in situ -generated mononuclear rhenium complex [Re(bpt)(CO) ₃ (NH ₃ )] (1, bpt = 3,5-bis(2-pyridyl)-1,2,4-triazolate) can be used as a "turn-on" luminescent probe for selectively sensing L-histidine against other amino acids. Compound 1 was prepared by reacting Re ₂ (CO) ₁₀ , 2-cyanopyridine and hydrazine with an in situ formed bpt ligand through cyclization via C-N and N-N couplings with its single-side chelating mode arrayed with respect to the Re center. Compound 1 was highly stable and showed a green light MLCT emission in DMF solution at 507 nm upon excitation at 360 nm. Interestingly, the emission from 1 could be quenched by the addition of metal ions such as Ni ²⁺ and Cu ²⁺ but the emission efficiently recovered with the introduction of histidine. However, histidine could only be selectively detected when a combination of compound 1 and Ni ²⁺ was used. Therefore, the luminescence response of the Ni ²⁺ -modified compound 1 could be utilized as a "turn-on" probe for the selective detection of histidine. This work provides a simple method for developing new sensing platforms of a discrete metal complex based on rare in situ generation.