Chromophores emitting

Scheme 1-21. Synthesis of a blue-emitting copolymer with isolated chromophore by Wittig reaction a) base.

The optical properties can be tuned by variations of the chromophores (e.g. type of side-chains or length of chromophorc). The alkyl- and alkoxy-substituted polymers emit in the bluc-gnecn range of the visible spectrum with high photolu-inincsccncc quantum yields (0.4-0.8 in solution), while yellow or red emission is obtained by a further modification of the chemical structure of the chromophores. For example, cyano substitution on the vinylene moiety yields an orange emitter. 

Fluorescence probes possessing the PyU base 46 selectively emit fluorescence only when the complementary base is adenine. In this case, the chromophore of is extruded to the outside of the duplex because of Watson-Crick base pair formation, and exposed to a highly polar aqueous phase. On the contrary, the duplex containing a PyU/N (N = G, C and T) mismatched base pair shows a structure in which the glycosyl bond of uridine is rotated to the syn conformation. In this conformation, the fluorophore is located at a hydrophobic site of the duplex. The control of base-specific fluorescence emission is based on the polarity change in the microenvironment where the fluorophore locates are dependent on the l>yU/A base-pair formation. 

Like Raman scattering, fluorescence spectroscopy involves a two-photon process so that it can be used to determine the second and the fourth rank order parameters. In this technique, a chromophore, either covalently linked to the polymer chain or a probe incorporated at small concentrations, absorbs incident light and emits fluorescence. If the incident electric field is linearly polarized in the e direction and the fluorescent light is collected through an analyzer in the es direction, the fluorescence intensity is given by... 

---