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Hean, Duane

University of British Columbia

Novel solid state photofunctional materials have been designed, and their structure-properties relationships are investigated. This thesis focuses on two distinct photofunctional properties: generating photomechanical motion in photoswitch-based crystals and ‘afterglow’ emission from organic alloy crystals and novel organic emitters. A novel hemithioindigo (HTI) photoswitch is functionalized with an anthracene group, and its photophysical properties are investigated in the solution and solid state. When irradiated with light, the photoswitch exclusively undergoes photoisomerization. In the crystalline state, E- isomer crystals isomerize and undergo a photosalient effect upon exposure to green light, while the Z- isomer undergoes a thermosalient event when heated. [2+2] Photodimerization is also employed to generate photomechanical motion in hemithioindigo photoswitch analogs. Hemithioindigo can undergo solid state reactions generating photoproducts not observable in solution. Three hemithioindigo photoswitch analogs are designed and used to elicit photomechanical motion in the crystalline state. Additionally, further mechanical motion is observed when previously irradiated crystals are heated. Crystallography and 1H NMR spectroscopy were used to provide insights into the mechanism of photomechanical motion. These proof-of-concept photomechanical responses in crystalline hemithioindigo photoswitches demonstrate their potential use as light-driven microactuators. The facile synthesis of HTIs enables tuning the photomechanical system based on the desired application. Solid state host-guest chemistry is employed to produce a series of seven organic alloys of two organic emitters with contrasting photophysical properties. One emitter has a long lifetime with ‘afterglow’ emission, while the other has a high photoluminescence efficiency. By carefully tuning the composition of the components between 30% - 100%, interesting photophysical properties emerge in addition to the fine-tunability of the system, which are probed using steady-state and time-resolved photoluminescence spectroscopy at variable temperatures. This provides a new perspective of the rules established for developing organic long-lived emissive materials for host-guest doped systems. Finally, novel organic carbazole-thiophene-based organic emitters are designed, synthesized, and characterized. The repositioning of the carbazole around the thiophene as well as introducing a secondary carbazole moiety results in solid state thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP).

Text; Still Image

2022-11-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/80161

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/