The preparation and optical characterization of a novel PPV derivative displaying reversible tunable photophysical and electrophysical properties, poly-(5-vinylene-5'- (vinylene-1,4-phenylene)-2,2'-bipyridine), p-BVP, (1), is reported and its application in the preparation of tunable organic electroluminescent devices is described. The photophysical properties of the new polymer, such as its absorption, emission and electroluminescence are sensitive to the present of even minute traces of vapors of different acids and bases such as ammonia, formic acid and haloacids. The acid/base vapor induced optical changes are reversible and can be repeated many times without any significant degradation of the optical and mechanical properties of the films. Intermediate spectra can be generated simply by controlling the exposure time of the films to acidic or basic vapors. Similar effects were observed for two other polymers, poly-(5-vinylene-5'-tri(vinylene-1,4- phenylene)-2,2'-bipyridine), p-BTVP, (2), and its random analog p-BRTVP, (3). The tunability of the photo- and electrophysical properties of the polymers originates probably from structures changes associated with protonation-deprotonation processes and aggregation phenomena.