A class of organic light-emitting diodes (OLEDs) emit light tailored to the absorption spectra of growing plants. Upon photoexcitation, the OLEDs generate light in both the blue-green and red regions of the visible spectrum. A heavy metal atom present in the .pi.-conjugated polymer chain (such as platinum and/or iridium) acts via the spin-orbit coupling mechanism to cause an enhancement of the ratio of fluorescent to phosphorescent emission to be of approximately equal strength. These two emission bands overlap the absorption spectra of common plants grown under hydroponic conditions.
 Research carried out in connection with this invention was supported in part by National Science Foundation, Grant No. DMR-05-03172; and United States Department of Energy, Grant No. FG-04ER46109. Accordingly, the United States government may have certain rights in the invention.