Side-group fluorescence

Energy transfer in polymers has been studied in the pure solid state, in heterogeneous systems (e.g. polymer blends), in liquid solutions and in solid solutions. The last case, which will be considered here, provides relatively simple and clear experimental conditions since interactions between the macromolecules can be excluded by dilution and molecular movement is severely restricted by low temperature and rigid environment. Thus, excitonic energy transfer can be studied without competing molecular movement. The luminescence of dilute, solid solutions of aromatic polymers is not dominated by excimers - in sharp contrast to the other modes of observation - so that side group fluorescence and phosphorescence can be observed. This does not mean, however, that exciton trapping processes are absent in these systems. 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

All the above compounds yield excimer fluorescence when excited in room-temperature solution. However, because the rotational potential of the C—X bond and the nonbonded interactions of the substituents of the X atom differ from those of the C—C bond 126), the amount of excimer fluorescence from R(C—X—C)R differs from that of R(C—C—C)R. The heteroatom X can also influence the rotational state of the side groups R, as illustrated by the formation of the anti-photodimer in bis(l-naphthylmethyl)ether u2), but not in l,3-bis(l-naphthyl)propane 10). Finally, compounds having n 3 may exhibit excimer fluorescence, if the linkage contains one or more heteroatoms. For example, the—C—O—C—C— linkage in a,to-bis(2-naphthyl) compound allows excimer fluorescence to be observed in room-temperature solution39). 

Duportail,G., Froelich,D., Weill, G. Fluorescence quenching as a tool in the study of the distribution of local concentrations in polymer solutions. I. Polymers bearing quenching side groups. European Polymer J. 7,977-987 (1971). 

The spectral behavior and quantum yields of an ESDPT molecule [2,2 -bipyridyl]-3,3 -diol [BP(OH)2] (54) in sol-gel glasses modified by organic side groups were studied with the properties of BP(OH)2 in solutions, in a plain sol-gel glass and in PMMA [148], The fluorescence intensity of the dye in a fresh sol-gel glass is similar to that in water, whereas the corresponding blue shift is smaller and... 

Polythiophenes 126 and 127 having chiral side groups have been synthesized, and their conformation has been studied by means of CD absorption and fluorescent spectra.214 215 For example, polymer 126... 

Similar studies in aqueous solutions of polyCacrylic acid), PAA, i.e., variation of vs, pH are shown in Figure 3B. A smaller increase in with Au 0 fluorescence was observed around pH 3-4 than in the case of PMA, however, it is still 6-7 times larger than that in water. The data again indicate that due to the lack of methyl side groups i.e. lack of hydrophobic interaction PAA forms much looser coils at low pH than PMA, with smaller effects of the conformational transition on the photophysics of Au 0. 

If some of the side groups are substituted by dyes or fluorescent molecules, the display may work without polarizers. It is expected that large screen ferroelectric liquid crystalline polymer displays will come out in the near future. 

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