Exploring Long-Lived Luminescence in Supramolecular Constructs

This thesis investigates sustaining long-lived luminescence in a supramolecular construct, which is Small-Molecule Ionic Isolation Lattices (SMILES), through two key strategies. Firstly, exploring the reinstatement of triplet emission from phosphorescent dyes when embedded in SMILES. Secondly, exploring the generation of electronic donor-acceptor systems within SMILES by energetically activating Cyanostar (CS), the macromolecule unit constructing SMILES, and result in charge-transfer emission with prolonged lifetimes.

In Part I, fundamental investigations were performed to focus on the bimolecular interactions between cyanostar (CS) and mono-cationic phosphorescent dyes, particularly PtTA complexes. Stern-Volmer experiments elucidate the triplet energy transfer between PtTA complexes and CS, indicating methods to prevent efficient triplet energy transfer to CS for phosphorescent chromophores. The performances of three PtTA complexes in SMILES solid emitters align with the triplet energy matching criterion, leading to the successful generation of Pt3-SMILES crystals and nanoparticles with enhanced emission and prolonged lifetime. Investigations on the enhanced phosphorescence in Pt3-SMILES suggest the effectively circumvented non-radiative deactivation pathways, hereby the phosphorescent SMILES strategy has been fundamentally established.

Part II extends the exploration to multi-cationic metalloporphyrin dyes, specifically Por4, aiming to amplify phosphorescence within SMILES structures. The efficiency of SMILES in boosting Por4 phosphorescence is demonstrated, with Por4-SMILES crystals and nanoparticles emitting red phosphorescence with millisecond-range lifetimes. These findings highlight the potential of SMILES as an alternative to cryogenic conditions for achieving strong phosphorescence in metalloporphyrin dyes, by sufficiently suppressing the non-radiative pathways.

Part III shifts focus to exciplex formation in SMILES solids, as a method to extend fluorescence lifetimes within SMILES. By measuring solid samples with varying molar ratios of CS and fluorophore (TPT), the long-lived excited state arising from the charge-transfer mechanism is validated. This approach offers a promising method for fluorophores to prolong luminescence lifetimes in SMILES-based structures.

In summary, this thesis offers a comprehensive exploration of strategies to achieve long-lived luminescence in SMILES-based supramolecular structures. By elucidating fundamental bimolecular interactions, enhancing phosphorescence from phosphorescent dyes, and leveraging the formation of charge-transfer transition, significant achievements have been made towards extending luminescence lifetimes in SMILES materials, laying the groundwork for diverse applications in luminescent materials and beyond.