Understanding the photophysical processes of organic materials is important for utilizing them as functional photonic materials. Typical photophysical processes include intersystem crossing, charge transfer (CT), symmetry-breaking charge separation (SB-CS), singlet fission (SF), etc. There are serval factors that can lead to different photophysical processes, such as the molecular energy levels, inter- and intramolecular interactions, solvent interactions, etc. Such factors can be adjusted by changing the forms of the materials or by synthetic approach. Especially for organic materials, there is more tunability by the synthetic approach. Transient absorption (TA) spectroscopy is one of the most popular and useful platforms to investigate photophysical processes, since it has spectral resolution to differentiate most of the transient species, with the time resolution various from femtosecond to microsecond. One can understand the excited-state dynamics by deconvoluting the TA spectra with a specific dynamic model. By using TA spectroscopy, and other ultrafast optical spectroscopies, we aim to enhance our fundamental understanding to the factors that can affect the photophysics. In this dissertation, we explore the SF and SB-CS processes for various materials in different forms, including solution, colloidal nanoparticle, polycrystalline thin film, single crystal. We also design and synthesize monomer, oligomer and donor-acceptor types of materials in order to further understand the structural-property relationship. In Chapter 2, we investigate the substituent effects on the SF of a bis(phenylethynyl) anthracene (BPEA) system in nanoparticles form. In Chapter 3, we investigate another blue-absorbing chromophore perylenemoniimide (PMI), and find SF in the single crystal and thin film. In Chapter 4, we move to the synthetic approach by synthesizing a perylenediimide (PMI) dimer and trimer, and investigate the effect of intramolecular coupling to coherent state mixing in the dimer and SB-CS in the trimer. Building on the results from Chapter 5, we further design and synthesize a perylene-di-perylenediimide system, and find the CT between the perylene and the PDI dimeric mixed-state. We hope the studies in this dissertation can not only improve the understanding of the photophysics of the organic chromophores, but also provide new directions on designing and characterizing photonic materials.

Creator

• Lin, Chenjian

DOI

• https://doi.org/10.21985/n2-jrhm-7n15

Subject

• Physical chemistry
• Chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_947331
• http://dissertations.umi.com/northwestern:16377

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright