title: Structure and properties of functionalized bithiophenesilane monodendrons.
abstract: 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 MDn monodendrons and COOH-functionalized MDn-COOH monodendrons with generations, n=0, 1, 2, and 3. We observed that increasing the number of branches led to the progressive blue shift, indicating distorted packing of branched thiophene fragments of MDn. In contrast, MDn-COOH monodendrons showed a 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 hydrophobic-hybrophilic balance sufficient to form stable and uniform Langmuir monolayers at the air-water at a 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.
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA.
authors.forename: Ray
authors.initials: R
authors.lastname: Gunawidjaja
authors.forename: Yuriy N
authors.initials: YN
authors.lastname: Luponosov
authors.forename: Feifei
authors.initials: F
authors.lastname: Huang
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Ponomarenko
authors.forename: Aziz M
authors.initials: AM
authors.lastname: Muzafarov
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Tsukruk