Excimer formation molecular weight effects

Despite the technical problems in the latter film study, we conclude that there is no intramolecular excimer formation in the compounds of Richards et al.143, and probably little intermolecular excimer formation in the pure films. The absence of an effect of solvent power 25) on the possible excimer fluorescence of the R = CH3 polymer may not be significant, since little change in the coil dimensions would be expected for the short ( 300 backbone atoms) polymers 143> which were studied. Additional work is needed on the fluorescence of such polymers having higher molecular weights, different aryl substituents (R = 2-naphthyl, for example), and fewer adventitious impurities. 

Pyrene excimer fluorescence was used as a sensitive proximity probe in the intermolecular complex system. Upon addition of PAA solution, the intramolecular mobility of the PEG chain was suppressed resulting in decreased intramolecular excimer formation. Simultaneously, the local concentration of PEG is increased in the vicinity of PAA. The excimer formation seems to result from the arrangement of pyrene groups which is already pre-formed in the ground state. The effect of complexation is observed to be more pronounced in the PEG-PAA with a higher molecular weight of PAA. A more complete account of this work will appear elsewhere. (16,17)... 

This concept has several benefits. On the one hand, the perpendicular arrangement of the two molecular halves leads to a high steric demand of the resulting rigid structure. This structural feature efficiently diminishes molecular interactions between the 7r-systems, which leads to a higher solubility of the spiro-linked compounds compared to the non-spiro-Unked parent compounds. The unwieldy structure of fluorescent emitters based on the spiro concept also suppresses very effective excimer formation frequently observed in the solid state of many fluorescent dyes, and the emission properties are thereby stabilized. On the other hand, the doubling of the molecular weight in combination with the cross-shaped molecular structure and the... 

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