The role of ruthenium and rhenium diimine complexes in conjugated polymersthat exhibit interesting opto-electronic properties

This paper reports the synthesis and opto-electronic properties of differen t conjugated polymers that contain the diimine complexes of ruthenium or rh enium. Conjugated poly(phenylene vinylene)s that contain aromatic 1,3,4-oxa diazole and 2,2'-bipyridine units on the main chain were synthesized by the palladium catalyzed olefinic coupling reaction. Other types of polymers ba sed on 1,10-phenanthroline bis(2,2-bipyridyl) ruthenium(n) or chlorotricarb onyl rhenium(I) complexes were also synthesized by the same reaction. In ge neral, these polymers exhibit two absorption bands due to the pi-pi* transi tion of the conjugated main chain and the d-pi* metal-to-ligand charge-tran sfer transition of the metal complex. As a result, the photosensitivity of the polymers beyond 500 nm was enhanced. Charge-carrier mobility measuremen ts showed that the presence of metal complexes could facilitate the charge- transport process, and the enhancement in carrier mobility was dependent on the metal content in the polymer. In addition, we have also demonstrated t hat the ruthenium complex could act as both photosensitizer and light emitt er. Photovoltaic cells were constructed, and they were subjected to irradia tion with a xenon arc lamp. Under illumination, the short circuit current a nd the open circuit voltage were measured to be 0.05 mAcm(-2) and 0.35 V, r espectively. The polymers were fabricated into single-layer emitting device s, and light emission was observed when the device was subjected to forward bias. The maximum luminance was determined to be 300 cd m(-2), and the ext ernal quantum efficiency was approximately 0.05 to 0.2%. Although the effic iency was relatively low when compared with other devices based on organic materials, we have demonstrated the first examples of using transition meta l complexes for both photovoltaic and light-emitting applications.