Oligo excimers

Similar results have been presented by Miller and co-workers, who capped the ends of oligo(dihexylfluorene)s and poly(dihexylfluorene)s with Frechet-type dendrons (Figure 7.17C) [73], Annealing experiments coupled with emission studies revealed that G-3 and G-4 dendrons were effective at preventing excimer formation, even when the poly(fluorene) spacer was 50-80 repeat units long. 

Conformations of oligo(pyridine-aA-pyrimidine)s 119 have been studied. On the basis of NMR analysis and the fluorescence spectrum in solution, the oligomers were found to take a helical conformation.203 The conformation was characterized by distinct chemical shifts (upheld shift), NOE effects, and excimer emission arising from the overlap of aromatic groups. The helical structure was confirmed for 120 in the... 

Cyano-substituted oligo(phenylenevinylene) dyes that are able to form excimers with terminal alkyl tails have been blended with fluorinated host polymers [163] that have a different crystallinity. 

Changes to the fluorescence properties of a probe due to stacking effects can also be exploited in piezochromic macroscopic sensors. One such example is based on the liquid crystalline molecule cyano-substituted oligo(p-phenylene vinylene) (OPV), which forms columnar crystal stacks with pronounced n-n interactions, leading to excimer fluorescence [42]. In the solid state, the monomer emission is observed as a structured band in the green (2em = 481 nm). On exposure to external pressure, such as grinding with a pestle and mortar, the emission band is red-shifted (Aem = 548 nm) and the vibrational stracture is lost. The emission properties can be reversed upon heating the sample at 130 °C. The choice of... 

Excimer emission of pseudo-geminal substituted [2.2]paracyclophanes (294) bearing oligo(phenylene vinylene) units were observed by n-n interaction (Scheme 63). ... 

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