Photochemical Sciences Ph.D. Dissertations

Title

Synthesis and photophysical property investigation of beads on a chain (BoC) silsesquioxane hybrid oligomers: probable pseudo conjugation

Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Joseph Furgal (Committee Chair)

Second Advisor

Robyn Miller (Other)

Third Advisor

H. Peter Lu (Committee Member)

Fourth Advisor

Xiaohong Tan (Committee Member)

Abstract

Our overall goal here in this dissertation is to develop silicon-based hybrid materials that are potential high stability materials replacements for those in current electronics systems. To design the hybrid structures, a unique class of silicon-based compounds, silsesquioxanes (SQ) was used as the building block. SQs are three dimensionally compact Si-O bonded, cage-type compounds that can be synthesized to contain a variety of functional groups on each of the cage vertices. They offer useful properties such as thermal and photo stability, a high degree of functionalization, solution processability, and facile synthesis. The works in this dissertation focus on mixed functional (vinyl/phenyl) SQs of different sized cages containing 8, 10, and 12 silicon atoms. They are synthesized by fluoride catalyzed rearrangement reaction in a statistically controlled manner to achieve the desired vinyl groups for oligomerization. Spectroscopic measurements in picosecond/subpicosecond timeframes were performed before evaluating their potential applications. In chapter 2, vinyl/phenylSQs are cross-coupled by 4-di-bromo-aromatic linkers: Benzothiadiazole (BT), Phenanthrenequinone (PQ), Ethyl-carbazole (EC) and Phenyl-carbazole (PC). To compare photophysical properties between caged and non-caged structures, bis-tri-alkoxysilyl (linker) model compounds are synthesized. Luminescence quantum yields for oligomers are generally lower than the corresponding model compounds (except for PQ) which denotes non-radiative energy transfer possibility in oligomer. In addition, rapid transient absorption anisotropy decay (10’s ps in oligomers) provide signatures for excitation energy transfer between linker chromophores in oligomers. In chapter 3, we have designed hybrid oligomers with a vinyl/phenylSQ cage backbone linked with cross-linkers including 2,7-dibromo-9-fluorenone, 2,7-dibromo-9,9-dimethylfluorene, 1,4-dibromo-2,5-dimethoxybenzene, 2,5-dibromopyridine, 2,6-dibromopyridine, 2,3-dibromothiophene, 2,5-dibromothiophene, and 2,5- dibromothieno[3,2-b]thiophene and assess their photophysical properties in the steady state absorption and emissionrealms. Each of these oligomers exhibits a wide array of fluorescence quantum yield and shifts in the absorption and emission spectra dependent on the variations in substitution position. The 4th chapter addresses material development by incorporating unique azo-group compounds and a near-IR absorbing dye to the vinyl/phenylSQs. The presence of vinyl/phenylSQs in these compounds have bolstered their stability along with improved photon absorptivity in UV-visible and near-IR regions. Further prospectus will be given on using these materials towards multi-purpose applications.

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