Synthesis and Chiroptical Properties of Bithiophene-Functionalized Open and Methylene-Bridged Binaphthyl Derivatives

Abstract

Thiophene-based π-conjugated compounds are one of the most important classes of organic materials for optoelectronic applications. In this context, herein we report the synthesis of two enantiopure binaphthyl systems: an open and a methylene-bridged 1,1′-bi-2-naphthol (BINOL) derivative, functionalized at the C6/C6′ positions with lateral 2,2′-bithiophen-5-yl moieties (compounds (aR)-3 and (aR)-6, respectively). Both final products were subjected, together with their synthetic precursors (i.e., the corresponding unsubstituted and 6,6′-dibrominated BINOL derivatives), to UV–vis absorption and electronic circular dichroism (ECD) investigation in solution and thin films. A computational analysis based on density functional theory (DFT) and time-dependent DFT (TD-DFT) allowed us to gain physical insight into the observed (chiro)optical properties, emphasizing the crucial role of thiophene rings as C6/C6′ substituents. Moreover, the occurrence of induced ECD and circularly polarized luminescence (CPL) signals was observed in preliminary tests of chiroptical induction, performed for thin films of achiral benzothiadiazole (BTD) dye 7 in the presence of small percentages (0.5–5.0 mol %) of the methylene-bridged target molecule (aR)-6 as chiral inducer.