Distinct bulk emission properties of the hexacatenar molecules by varying the polarity of peripheral chains

Abstract

In this study, we explored the distinct emission properties of two hexacatenar molecules 1 and 2 with an identical intramolecular charge transfer (ICT) chromophore in the bulk state, influenced by the type of peripheral chain. Their chromophore comprises an electron acceptor (A) composed of naphthalene-conjugated 1,3,4-oxadiazoles, and an electron donor (D) composed of 3,4,5-alkoxybenzene. The nonpolar decyl and polar tri(ethylene oxide) (TEO) chains are the peripheral chains for 1 and 2, respectively. 1 exhibits a crystalline (Cry) to a liquid crystalline (LC), and then to a liquid (Liq) state as the temperature increases, but 2 exists in a Liq state at room temperature (RT). The morphological analysis of 1 in the LC phase suggests a hexagonal columnar structure where the stacking distance between chromophores is 3.4 Å. In the solution state, 1 and 2 strongly reveal ICT emission properties with increasing solvent polarity, consistent with DFT simulations. Remarkably, the bulk samples of 1 and 2 display distinct emission colors at RT, which blue-shift with increasing temperature. The complex temperature-dependent emission properties of 1 and 2 are associated with their molecular dynamic motions, characterized by dielectric relaxation spectroscopy (DRS) studies. The emission differences between bulk 1 and 2 are attributed to the degree of stabilization of the ICT state, by varying the type of non-emissive peripheral chains. This study demonstrates that the emission properties of the same chromophore can be engineered by the polarity of the peripheral chains in the bulk state.