The exponential growth of utilizing synthetic organic molecules in optoelectronic applications poses strong demands for rational control over the excited states of the materials. The manipulation of excited states through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colors, high quantum efficiencies and efficient energy/charge transfer processes. Recently, a significant breakthrough in lifetime tuning of excited states has been made;the purely organic molecules were found to have ultralonglived excited state under ambient conditions with luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores. Given the conceptual advance in understanding the fundamental behavior of excited state tuning in organic luminescent materials, the investigations of organic ultralong room-temperature phosphorescence(OURTP) should provide new directions for researches and have profound impacts on many different disciplines. Here, we summarized the recent understandings on the excited state tuning, the reported OURTP molecules and their design considerations,the spectacular photophysical performance, and the amazing optoelectronic applications of the newly emerged organic optoelectronic materials that free of heavy metals.
We develop high efficiency solution-processed pure green organic light-emitting devices using a starburst molecule 7,7′,7″-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(4-(4-(9H-carbazol-9-yl)phenyl)benzo[c][1,2,5]thiadiazole)(TRcz)doped 2-methyl-9,10-di(2-naphthyl)anthracene(MADN)as the emitting layers.The electroluminescence properties of the devices with different doping concentrations are investigated.With the increasing doping concentration from 0.5wt%to 5wt%,the maximum efficiency changes from 4.8cd/A to 8.4cd/A.Under the optimal concentration of 4wt%,the device shows pure green emission at 516nm with a chromaticity coordinate of(0.30,0.59)as well as a high brightness of 19900cd/m^(2)and a high efficiency of 10.1cd/A,which are better than 11490cd/m^(2)and 4.2cd/A obtained in the undoped device.
