Intramolecular delayed fluorescence as a tool for imaging science: Synthesis and photophysical properties of a first-generation emitter

The synthesis of a molecular dyad comprising two pyrene-based terminals covalently linked via a Hantzsch 1,4-dihydropyridine is described. The dyad is sufficiently flexible to allow the end groups to approach each other in fluid solution, as is evident from the appearance of excimer fluorescence. Transient absorption spectroscopy indicates that both intra- and intermolecular triplet-triplet annihilation (TTA) takes place at modest laser intensities and leads to delayed fluorescence. The spectral distribution of the delayed fluorescence signal matches that of the excimer. The kinetics of TTA and the overall yield of delayed fluorescence are considered in terms of the molecule adopting disparate conformations that interconvert slowly. Consideration is also given to the possible application of such delayed fluorescence in imaging technology.