| Synthesis of novel spiropyrans (SPs) functionalized with N-indolino chelating groups (SO3--, COO-- and COOH) and their irradiation afforded a family of bi-dentate merocyanine (MC) ligands capable of complexing a series of divalent metal ions (Zn2+ , Cu2+, Ni2+, Co2+, Fe 2+, Ca2+, Mg2+). A structure-property relationship study was undertaken to examine the effects of ligand, tether chain length and nature of metal on the thermal reversion of the ring-opened MC to the SP form. In the absence of metals, the thermal reversion rate was affected by electrostatic repulsion between the anionic chelating functionality and the phenoxide moiety. Irradiation in the presence of Zn2+, Cu2+ and Fe2+ produced the transient cis-MC-metal complex and a geometrical isomeric transoid-MC-metal complex, which were completely stable to thermal reversion. The other metals (Ni2+, Co 2+, Ca2+ Mg2+) formed stable complexes only with the trans-MAC form. The thermal reversion rate of the trans-MC-metal complex was sensitive to the ligand and the tether chain length, as stabilization of the merocyanine (MC) from thermal reversion was observed to be most effective for the anionic ligands. Fluorescence measurements revealed an enhanced quantum yield associated with MC-metal complexation, and reversion back to the SP form occurred on exposure to 520 nm light, signifying that the switch is photo-reversible. These results demonstrated that a novel dual-wavelength photo-activated molecular switch with applications to 3-D Optical Data Storage technology has been developed.; The aggregation behavior of symmetrical anilino-based squaraines with varying N-groups (n-butyl, n-octyl and n-dodecyl, benzyl) was examined in DMSO/water mixtures. Self-assembly was assessed through UV/Vis spectroscopic and Dynamic Light Scattering (DLS) studies with quantitative interpretation based on exciton theory. Anilinosquaraines formed two distinct solution aggregates, Type J and Type H, depending on the composition of the DMSO-water medium and the N-group. DLS measurement of squaraines that exhibited the Type J and Type H morphologies showed that: (a) the particle diameter increased with increasing hydrophobicity; (b) solvent composition has a large effect on the Type J aggregate size; and (c) Type J aggregates are of equal dimensions with Type H aggregates. It is proposed that the dynamic conversion (J → H) results from intra-molecular re-organization of individual molecules within the aggregate. |
