Facile dione protection to benzo[1,2-b:6,5-b']dithiophene-4,5-dione (BDTD) in triggering ultraviolet emission - A new member of the emissive 3,3′-bridged dithiophenes

To date, 3,3 '-bridged dithiophenes with bridges developed from the first period elements (either pristine or oxidised) are non emissive. Benzo[1,2-b:6,5-b']dithiophene-4,5-dione (BDTD) is a typical 3,3 ' fused-dithiophene with a dione bridge. It is a critical building block for semiconducting materials, and it is non emissive. We serendipitously discovered that by protecting the diketone of BDTD with ethylene glycol, two isomers (BDTD-5 and 6) were obtained and both compounds effectively emit UV light in solution. Their maximum emission (382 and 375 nm for BDTD-5 and 6, respectively) are independent of the type of solvent. Both compounds exhibited fluorescence intensity enhancement in DMF-H2O with the increase of water fraction from 0-90%. BDTD-6 can also effectively emit in its crystalline state with a quantum yield (QY) of 14% and an average fluorescence lifetime of 1.6 ns. X-ray crystallographic analysis indicates that BDTD-6 possesses a 3D C-(HO)-O- horizontal ellipsis interaction structure which produced its effective emission in the crystalline state. These two isomers not only have enlarged the emissive members of the 3,3 '-fused dithiophene family, but also expand the emission boundary of emitters in this category to the UV area.

Automated summary

We found that by protecting the diketone of BDTD, two isomers were obtained, and both compounds effectively emit UV light in solution. BDTD-6 can also effectively emit in its crystalline state with a quantum yield of 14% and an average fluorescence lifetime of 1.6 ns. These two isomers not only expand the emissive members of the 3,3'-fused dithiophene family, but also extend the emission boundary of emitters in this category to the UV area.