Theoretical Study Of The Effect From Embedded O-carborane Ligand To The Photophysical Property Of A Cyclometalated Pt(?) Complex

In recent years,luminescence materials especially organic light-emitting diodes?OLEDs?have attracted considerable attention for their advantages of flexibility in full-color displays and low energy consumption in white-light illumination.Organometallic complexes,which contain a centered heavy metal atom?e.g.iridium,gold and platinum?that brings strong spin-orbit coupling?SOC?effect,have short excited-state lifetime,wide color tunability and high emission quantum yields.Among all the organometallic complexes,the cyclometalated Pt-based counterpart is most widely utilized.In cyclometalated Pt?II?complexes,the ligands can be bidentate,terdentate and tetradentate.Compared with the other two,the complex with terdentate ligand has better structural planarity and luminescent behaviorThe research object involved in this paper is a series of cyclometalated Pt?II?complex with embedded o-carborane ligand.These traditional Pt?II?complexes?C,N,C-cyclometalated Pt?II?complex?with a terdentate ligand consisting of the N-coordinating pyridine and two cyclometalating fragments:p-anisole and benzene,and t-butylisonitrile.Throughout this work,four o-carboranes(C₂B₈H₁₀,C₂B₁₀H₁₂,C₂B₁₁H₁₃ and C₂B₁₂H₁₄)are selected to be introduced into the C,N,C-cyclometalated Pt?II?complex through structural matching and stability analysis,named 2,3,4,5,respectively,aiming to find effect of o-carborane on these molecules.And a comparative traditional cyclometalated Pt?II?complex 1 is also included in this work.Their electronic structure,absorption and emission properties of these complexes are determined using the density functional theory and time-dependent density functional theory method.The effects of o-carborane on the photophysical properties and quantum efficiency are elucidated,such as molecular orbital,configuration,spin-orbit coupling and vibrational modes.For the first time,we have comprehensively investigated in radiative and non-radiative processes of these complexes,trying to figure out the effect of different size o-carborane on molecular rigidity,energy level and normal mode displacement.Meanwhile,we expected to find a phosphorescent molecule with ideal luminescent color and high efficiency.Our research indicates that in their geometrical structures,the carborane makes a powerful contribution to the molecular rigidity and effectively prevention of Pt-Pt contact formation.The absorption and emission wavelengths of 2,3 and 5 are blue-shifted compared with original compound 1 due to the increasing gap between HOMO and LUMO levels.Meanwhile,the carborane introduced a concentrated distribution of energy level of excited states,which is positive to increase the probability of ISC.The charge transfer states of these Pt?II?complexes with o-carborane are always localized on the?-conjugation part of terdentate ligand.It is beneficial to the improvement of phosphorescence intensity.In addition,the introduction of o-carborane affects the interaction strength of C1-C2,which influences the conjugated structure and vibrational modes of the tridentate ligands in these Pt?II?complexes concomitantly.All the discussion of nonradiative decay rate indicates that complex with a high symmetry carborane is superior to low symmetry.Considering the results of emission wavelengths,k_r and k_nr above,it is believed that5 has the best performance and can be used as a high efficiency phosphorescent material.We sincerely hope our theoretical calculation can provide the most accurate guidance for the design of phosphorescent compounds which unravels new prospect in photoelectric functional materials.