Investigate The Mechanism Of Heteroatom Effect In Diradical And Their Optoelectronic Devices

In recent years,organic molecules which containing unpaired electrons have attracted more attention from scientists due to their unique properties such as low energy band gap and strong intermolecular spin interactions.In the application of organic electronics and spintronics would be the perfect platform to reach their full potentials.Due to the inherent instability of diradical compounds,the electronic applications of such compounds are still limited.In general,the electronic structure of the ground state of diradicals can be quantified by a characteristic parameter?y₀?.The value of y₀ ranges from 0?closed-shell state?to 1?open-shell state?.Until now,researchers have proposed several methods for adjusting the characteristics of diradicals,such as adjusting the conjugate length of a molecule,substitution by donor or acceptor groups,etc.However,a non-destructive method is required to study the relationship between the physical properties and diradical character.Inspired by heteroatom-substituted organic semiconductors,we have synthesized stable diradicals which were based on diketopyrrolopyrrole?DPP?core and phenoxyl radical center.The effects of heteroatom substitution were fully studied in term of absorption,energy gap and electronic devices.The main content of this thesis includes the following two aspects:1.With DPP as the acceptor center,phenoxy radicals are introduced at both ends,and the radicals delocalize to the entire molecule through the strong electron-withdrawing ability of the DPP core.Also,the introduction of heteroatom substituted five-membered rings ensure the planarity of the molecule between the core and phenoxyl,leads to better conjugation length and adjustable diradical character.The synthesized molecules were fully characterized.2.As the currently synthesized phenoxyl based diradicals have almost no application in electronic devices due to their poor stability.Since our DPP based diradicals possess outstanding chemical stability,we have applied them into organic electronics.In organic field-effect transistor,our diradicals show n-type transport properties and the electron mobility reaches to 4.0×10^-3 cm²v^-1 s^-1.In photodetector,due to the narrow absorption band in the near infrared region,they respond to light at 650,780 and 808 nm with a maximum current of 35?A.