Photofunctional materials : photochromism, thermally activated delayed fluorescence and room temperature phosphorescence

Novel photofunctional molecules have been designed, synthesized and characterized. Their interactions with light are categorized into three types: photochromism, thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). It is shown in this thesis that these properties can be tuned and manipulated by rational molecular design. A series of Cu(I) complexes bearing dithienylethene backbones show tunable photoreaction quantum yield by altering the ancillary ligand while a phosphine-oxide containing organic compound synthesized from one of the Cu(I) precursors is found to exhibit turn-on aggregation-induced emission. Their photochemical and photophysical properties are analyzed by UV-Vis and photoluminescence spectroscopy in addition to computational simulations. Using simple synthetic modifications such as oxidation and methylation, three structurally similar quinolinium-containing diarylethene compounds give rise to various photochemical and photophysical properties including turn-on fluorescence, red-green-blue emission switching and RTP, respectively. UV-Vis and photoluminescence spectroscopy as well as lifetime measurements are employed to study these properties. Potential applications in cellular imaging and super-resolution imaging are demonstrated. Pyridinium and quinolinium salts are designed to show TADF and RTP in the solid state with different counter anions. An iodide compound only shows low-temperature phosphorescence and bromide salts are found to exhibit TADF with RTP contributions and. However, compounds with other anions only display RTP. By using steady-state and time-resolved photoluminescence spectroscopy at variable temperatures, these properties are probed in depth. Three sulfur-bridged carbazole compounds were synthesized, to gain an understanding of electronic effects on RTP. The oxidation state at the sulfur center can be changed to modulate the phosphorescence efficiency in the solid state, in addition to fluorescence properties in the solution state.Science, Faculty ofChemistry, Department ofGraduat