Self-assembly of a series of thiocyanate complexes with high two-photon absorbing active in near-IR range and bioimaging applications

• The first systematic study of the transition metal complexes.
• Transition metal ions serve as multidimensional templates to control structure.
• The functionalized complexes exhibit much larger σ2PA and higher quantum yield.
• Hetero-metal complexes present much higher σ2PA than homo-metal complexes.
• 1 offers a potential application in two-photon fluorescence imaging.

A series of novel complexes bearing high fluorescence quantum yields and showing the peak two-photon absorption (2 PA) cross-sections in the near-infrared region, Zn(SCN)2L2(1), [Cd(SCN)2L2]n(2), Co(SCN)2L4(3), Ni(SCN)2L4(4), [CdHgL2(SCN)4]n(5) and [MnHg(SCN)4L2]n(6), containing functional chromophore (L = (E)-(4-diethyl anilinostyryl)pyridine), were synthesized in high yields. Crystal structures of all the complexes were confirmed. Hetero-metal complexes (5, 6: L:M = 1:1) present much higher two-photon absorption (2 PA) cross-sections (σ) in comparison with those of the homo-metal complexes (L:M = 4:1 in 3 and 4, L:M = 2:1 in 1 and 2) and the free ligand (L) which may due to the fact that the hetero-metal complexes have more bridged anions (SCN−), conjugated subunits –[Hg(SCN)2M]– and –[Hg2(SCN)4M2]–. In addition, the results revealed that 2 PA response was much enhanced for the Zn(SCN)2L2 and two-photon fluorescence cell imaging experiment proved its potential application.

It is the first systematic study of the transition metal complexes. The results exhibit that the transition metal ions serve as multidimensional templates to control the crystal structures and further tailor the fluorescence quantum yields and 2 PA cross-sections. Zn(SCN)2L2 displays much lower toxicity and brighter two-photon fluorescent bioimaging than its free ligand, which make it successfully applied to a two-photon fluorescent probe.Figure optionsDownload as PowerPoint slide