Formation of persistent ordered lamellar mesophases in azobenzene-containing silver thiolates and their application in the controlled synthesis of silver nanomaterials

Abstract

Metal thiolates have aroused intensive interest mainly due to their precursor-based preparation of nanostructured metal or metal chalcogenides. In this paper, a series of azobenzene-containing thiol ligands with different length alkoxy tails and their corresponding silver thiolates AgS–C₁₀H₂₀–Ph–NN–Ph–OC_nH_2n+1 with n = 1, 6, 8, 12, have been successfully synthesized, and their thermal properties and phase behavior have been systematically investigated by differential scanning calorimetry (DSC), variable-temperature SAXS/WAXS and temperature dependent FTIR. By introducing azobenzene mesogen for the first time into the silver thiolates, ordered lamellar liquid crystalline mesophases persisting throughout a higher temperature have been achieved derived from their specific orthorhombic crystalline structures, which are in sharp contrast to the micellar or hexagonal columnar mesophases reported for silver alkane thiolates with a longer aliphatic alkyl chain AgSC_mH_2m+1 (m ≥ 12) owing to the interplay of azobenzene mesogen π–π stacking and the inorganic skeleton binding of a Ag–S slab. Furthermore, the intermediate nanoparticles formation and silver nanodisks preparation through an in situ thermolytic reaction based on such mesogenic precursors have been demonstrated in principle. As a kind of functional metallomesogen precursor the silver mesogenic thiolates with persistent ordered lamellar mesophases provide an ideal two-dimensional (2D) confined environment for the investigation of a layered-precursor-to-lamellar-nanomaterial (LPLM) mechanism of solventless thermolysis and the fascinating controlled preparation of variant 2D shaped metal or metal sulfide nanomaterials.