Modulating the glassy and crystalline ordering of carbazole small molecules in bulk

Abstract

The mesoscopic assembly of functional π-conjugated molecules is known to influence the application of such systems. Carbazole is a widely utilized π-conjugated motif in construction of various electronically active compounds. Yet, the assembly of pristine carbazole molecules is seldom studied. Herein, we carried out a systematic structure-thermal phase behaviour study of alkyne bearing carbazoles with either ester or amide functionality on the nitrogen. The carbazole esters exhibit tunable glassy ordering due to conformational flexibility of n-alkyl chains and the lack of π-stacking, as evidenced by single crystal structures. However, the corresponding amide derivatives show crystalline ordering with enhanced thermal stability, driven by intermolecular hydrogen-bonding. Intriguingly, the ester and amide derivatives bearing chiral side chains show contrasting thin-film chiroptical properties. While the former shows no helical organization, the amides exhibit differential scattering of circularly polarized light arising from helical domains. This work underscores the importance of linker functionality in conjunction with alkyl chain length in dictating the bulk phase ordering of π-conjugated small molecules.