Synthesis and Properties of Aromatic-Terminated Diacetylene Organogelators and Their Application to Photopatterning of Polydiacetylenes.

A series of simply structured diacetylene-diamide-based gelators (DAGs) with aromatic terminals were synthesized, and their gelation and subsequent photopolymerization abilities were analyzed. DAGs with an adequate spacer length (n) and tolyl terminals (DA-Tn) interacted with aromatic solvents, such as benzene and xylenes, at elevated temperatures. During the subsequent cooling process, the DAGs interacted with each other through CH-π interactions at their terminal positions. They also formed one-dimensional hydrogen bonding arrays through secondary amides, leading to stable organogels. These gels polymerized into π-conjugated polydiacetylenes (PDAs) under ultraviolet irradiation. In the p-xylene gels of DA-Tn, the spacer length exerted characteristic odd-even effects on the photopolymerization rates over a certain range (n = 3-6), which can be explained by periodic changes in the uniformity of the molecular packing modes. When the gelling solvent was changed to cyclohexane, the gelation and photopolymerization abilities were greatly improved because the DA-Tn gel networks became highly crystallized and transparent to ultraviolet light (254 nm). The ultimate conversion to PDA from DA-T8/cyclohexane gels was 45.2 wt %. Applying photolithographic techniques to the DAG with excellent photopolymerizability in the film state, we successfully fabricated microscale photopatterns of PDA. We also established a convenient removal process (development process) of DA monomers in unexposed areas. The resulting PDA patterns were quite stable to ambient light stimuli.