Fluorescence of Polymers in Gel State

Excimer formation can be explained in terms of a combination of local rotational isomeric and longer range diffusional motions of the chain. In polymer solution we observed and discuss the role of both in solid film any type of movement is generally restricted, and the mobility of a polymer in a gel state is rather between the solution and soUd, a more precise description of which was published by de Gennes [50]. 

The freely-rotating chain of a polymer in dilute solution is represented by a statistical distribution of conformational structures of the chain. The resultant excimer fluorescence emission is a broad Gaussian band. The excimer fluorescence spectrum from a solid polymer results in a very broad spectrum which is characteristic of the distribution of conformations adopted by the polymer in the preparation process. This distribution depends upon the thermal history of the sample and the conditions used for the casting these dependencies were presented by Frank and co-workers [26]. The complexity of photophysical processes accompanying the excimer formation and the inherent complexity 

The lifetime data of PS differ from laboratory to laboratory, because the fluorescence decay curve reflects not only the polymer type and solvent, but the processes of preparation, i.e., temperature, quality of the solvent, etc. 

Basically, in the extended conformation as well as in the three-fold helical conformation of the iPS chain, the phenyls do not form excimer states, because the distance between parallel phenyls in the three-fold helical conformation is 0.665 nm, as reported by Natta [62] and Sundararajan and co-workers [54]. This distance is too large for excimer formation of the sandwich type (which have a distance of 0.3-0.35 nm). In this situation, the excimer can be formed only outside the crystalline region, e.g., in the region of the lamellar borders, because in these areas some deformation of the helical conformation of the PS chain makes the excimer structure formation more probable. The excitation energy can effectively migrate along the helical structure [60, 63] to the lamellar border, where 

The phase separation process was observed in iPS gel [66, 67]. The gel was formed by cooling a solution of iPS in BA (0%-20% w/w) from a temperature of 443 K, in which clear solution is obtained, to 273 K, at a maximum cooling rate of 0.42 K s, which lead 

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