3-Alkynyl-substituted terthiophenes and polythiophenes were synthesized, and their properties and behavior toward hydroboration with Mes(2)BH were investigated. The alkynyl-substituted terthiophene was found to crystallize in an intriguing layered structure that mimics an interdigitated polymer wherein the terthiophenes form tightly pi-stacked linear pseudopolymer strands. The heptynyl side chains of neighboring stacks interlock ideally, almost completely filling the void in-between substituents and thus allowing for minimal spacing between neighboring pseudopolymer strands. Poly(3-alkynylthiophene)s were accessed through Grignard metathesis polymerization (GRIM) of 2,5-dibromo-3-heptynylthiophene, which yielded polymers of moderate molecular weights (M-n = 6.3; PDI = 1.73) in yields of up to 82%. Further modification by hydroboration with Mes2BH resulted in a material that is partially functionalized with vinylborane groups and as a result exhibits charge transfer bands in the UV-vis spectra. A single-crystal X-ray structure of the corresponding hydroborated terthiophene species shows extensive intermolecular interactions, resulting in pi-stacks of pi-dimers, despite the steric bulk of the dimesitylborane moieties.