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

Abstract

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.