The influence of UV irradiation in inert atmosphere on the emission. spectrum of fluorene containing poly[9,9-bis(2-ethyl)hexylfluorene] (PF2/6) has been. investigated by means of -optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross-linking of the films. FTIR measurements show no reduction of the C=O stretching mode, upon irradiation, and, moreover, the degree of cross-linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence. of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer on to ketonic defect sites. The found result enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000cd M-2 at 7 V) two-color OLEDs.