| dc.description.abstract | With the advent of lasers in 1960, research on two-photon processes began to flourish, garnering significant interest in both biomedical and military fields. To apply these processes across various fields, we have focused on studying fluorescent dyes with dual-state emission and exploring their photophysical properties.
In this thesis, we have synthesized linear molecules based on a Donor-π bridge-Acceptor (D-π-A) structure. The first series is designed with N, N-dialkyl aniline as the electron-donating group, thiophene as the π-bridge, and sulfone as the electron-withdrawing group. We have developed compounds 1 and 2 with different alkyl groups attached to the donor. For the multi-branched molecules, we have used fused triazole and quinoxaline as the core, fluorene as the π-bridge, and diphenylamine as the electron-donating group, forming a multi-branched structure as the second series model compounds. Compounds 3 and 4 use C-C single and C-C triple bonds as the linkages and are designed to compare the impact caused by this structural variation. From the photophysical properties of these two series of model compounds, some features should be noted:
1. For the model compounds of the first series, it is found that whether using morpholine unit or (2-methoxyethoxy)ethane as the alkyl chain, the model compounds show nearly identical optical properties, indicating that the emission properties are not significantly affected by the type of alkyl chain. The only noticeable difference is in the solid-state fluorescence quantum yields, that is compound 1 shows nearly 20% higher solid-state fluorescence quantum yields compared to that of compound 2. This suggests that the morpholine unit offers better molecular segregation in the solid-state, leading to improved solid-state fluorescence quantum yields.
2. In the second series, optical data show that the compound 4 with triple bond as the extension of π-conjugation exhibits red-shifted fluorescence emission compared to that of compound 3. The red-shifted fluorescence emission accompanied by a decrease in emission intensity become more pronounced with increasing the solvent polarity. Similar behavior was reported by a literature (Mater. Adv., 2023, 4, 6612–6620) and it was postulated that in C-C triple bond as the linkage may cause the decline of intramolecular charge transfer and lead to the observed emission behavior.
3. Using C-C triple bond as the linkage has a pronounced promotion of the molecular two-photon absorptivity compared to that of using C-C single bond as the linkage, which is consistent with the experimental results observed by our former lab member′s (Mr. Bo-Kai Tsai) model system. | en_US |