Polyelectrolytes- Excimer Formation

A number of reviews of interest have appeared of both a specific and general nature. These include photoresponslve polymers with the main emphasis on phase transitions, memory and shape retention 2 , the kinetics of polyelectrolyte formation , molecular modelling for excimer formation , luminescent probes and molecular dynamics . The uses of thermally stimulated emission for monitoring radical decay and chemiluminescence of polymers... 

Section 2.2.1.1 highlighted how the vibrational fine structure of pyrene, when dispersed under relatively dilute conditions, in the absence of excimer formation, can be used to reveal the pH-dependent response of PMAA. An alternative approach has used the occurrence of intermolecular excimer formation between dispersed pyrenyl probes under relatively concentrated conditions to monitor the conformational switch of the polymer [6,71]. When dispersed in PMAA, at concentrations higher than its solubility limit in water, partitioning of the probe between the hydrophobic polymer coil and the aqueous phase results [6,71]. Dependent on the pH of the solution and consequently the conformational state of the polyelectrolyte, the balance between these two distinct populations can be affected. For example, Fig. 2.7 shows the fluorescence emission spectra for the probe l,3-bis(l-pyrenyl)propane (1,3PP) when dispersed in aqueous solutions of PMAA [71]. At low pH, an emission spectrum consistent with that of monomeric unassociated pyrene is observed centered around... 

The complexity observed in polymer fluorescence decay kinetics is further exacerbated when fluorescent polyelectrolytes are dissolved in aqueous media [29,30,33,35,37,43,120,122,128-132] segregation of the macromolecular structure into hydrophobic and hydrophilic-rich domains results in differing degrees of water penetration which further complicates the time-resolved fluorescence [26]. Within this context, more recent attempts to describe time-resolved polymer photophysical data include use of the blob model [133,134], which accounts for the range of environments encountered in heterogeneous systems by invoking a distribution of rate constants for excimer formation. 

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