Molecular Design And Theoretical Study Of Organic Thermally Activated Delayed Fluorescent Materials Based On Diphenylsulphone And Triptycenes Derivatives

Triplet excitons can be fully converted to singlet ones by thermally activated delayed fluorescent(TADF)materials through thermal excitation.Thus,the internal quantum efficiency of TADF molecules can reach nearly 100% without employing noble metals,which makes it the third-generation organic electroluminescent material after the fluorescent and phosphorescent materials.Recently,the design and preparation of high efficient TADF organic molecules have attracted much attention.In this contribution,several TADF organic molecules with various structures and properties are designed,including diphenylsulphone derivatives and triptycenes.Moreover,their geometry structures,electronic properties,frontier molecular orbitals,emission wavelengths(?em)as well as singlet-triplet energy gaps(?EST)have been investigated on basis of density functionaltheory(DFT)and time-dependent density functionaltheory(TD-DFT).H/R substitution on the donor/acceptor moieties and “CH”/N substitution on the donor moieties were applied for the diphenylsulphone derivatives,and different donor fragmentswith various electron-donating strength were used for the triptycenes to investigate the relationship between the molecular emission properties and their geometries.Specifically,the main research contents include the following parts:A series of designed diphenylsulphone based thermally activated delayed fluorescent materials have been investigated using DFT and TD-DFTmethod at the PBE0/6-31G(d)theoretical level.We focused on the variation in electronic and optical properties as different substituents being introduced to the parent molecule.The calculated results show that the broad range emission wavelengths(352-731 nm)can be tuned via either H/R substitution on the donor/acceptor moieties or “CH”/N substitution on the donor moieties.The emission wavelengths are significantly bathochromic-shifted(15-252 nm)by introduction of electron-accepting groups(CN)on the acceptor fragment or electron-donating groups(CH3)on the donor fragments.While,“CH”/N substitution on the donor fragment results in hypochromatic shifts(10-127 nm).On basis of the hole-electron distributions analysis,the locally excited triplet states are close to or higher than the triplet intramolecular charge transfer state for most of the investigated molecules.Furthermore,the calculated singlet-triplet energy gap values of the designed four red emission molecules(0.007-0.014 eV),two green ones(0.010-0.013 eV)and a blue one(0.058 eV)are relatively small,indicating that these investigated derivatives are excellent thermally activated delayed fluorescent candidates.Our theoretical studies provide hints for the design of efficient broad emission thermally activated delayed fluorescent materials in the future.A series of donor-acceptor triptycenes have been designed on basis of the TADF material TPA-QNX-(CN)2.The influences of the different donor fragments with various electron-donating strength on the ?EST and ?em values are extensively investigated by employing DFT and TD-DFTtheory as well asthe optimal HF% method.The calculated results imply that,as the electron-donating strength of the donor fragment increases,the energy gap(?ES1-T1)between the lowest singlet excited state(S1)and the lowest triplet excited state(T1)decreases and the ?emis red shifted for the molecules using the same acceptor units.In addition,the energy splitting of the singlet and triplet intramolecular charge transfer states(?EST(CT))is also decreased by enlarge the twist angle(?1 and ?2)between the phenyl ring and the alternative fragment within the donor fragment.Therefore,efficient color tuning within a broad emission range(433-609 nm)as well as small ?EST(CT)values(0.01-0.05 eV)has been achieved via structural modification of the donor fragments.