Structure and Properties of Functionalized Bithiophenesilane Monodendrons

This study reports a focal group modification of bithiophenesilane monodendrons and its effect on their molecular ordering in solution, bulk, and surface. We investigated hydrophobic M Dn monodendrons and COOH-functionalized MDn-COOH monodendrons with generations, n = 0, 1, and 3. We observed that increasing the number of branches led to the progressive blue shift, indicating distorted packing of branched thiophene fragments of M Dn. In contrast, MDn-COOH monodendrons showed I progressive red shift with the increasing generation number, indicating gradual domination of sigma-pi interactions. Moreover, the introduction of a focal carboxylic group resulted in the formation of a highly crystalline state for the linear MD0-COOH compound with separated alkyl tail-thiophene packing, which limits;pi-pi interactions. Increasing branching in the COOH-containing monodendrons resulted in a hydrophobichybrophilic balance sufficient to form stable and uniform Langmuir monolayers at the air-water at I modest surface pressure ( < 10 mN/m), easily transferrable to a solid substrate. However, a further increase in the thickness of the surface layers from tens to hundreds of nanometers via Langmuir-Blodgett (LB) deposition or spin casting is limited by the formation of globular surface aggregates because Of strong intermolecular interactions. A modest red shift observed for condensed langmuir monolayers indicates densification of thiophene branches and limited intramonolayer crystallization, which preserves photoluminescence. In contrast, thicker surface films showed a significant red shift confirming a dense molecular packing with strong pi-pi interactions. which results in photoluminescence quenching.