Theoretical Investigations Of Photophysical Properties Of Common Metal Fe(?) Complexes And Their Application Prospect Analysis

As a kind of superior display screen,organic light-emitting diode?OLED?is more and more widely used because of their advantages such as wide angle of view,no backlight,thin thickness and applications in the curved bezel panel.At present,the guest doped luminescent materials used in OLED devices are mainly transition metal iridium?Ir?complexes and platinum?Pt?complexes.However,Ir and Pt with high pollution of relevant industries are rare and precious which results in the limit of their investigation and application.As the second most abundant metal element,Fe?II?is cheap and nontoxic with the 3d6 configuration like Ru?II??4d6?and Ir?III??5d6?.Therefore,Fe?II?is regarded as the ideal candidate of d6 metal complexes and the simple strategy is direct replacement of metal center.But there are no luminescent phenomenons on account of ultrafast nonradiative decay from metal-ligand charge transfer?MLCT?states to low-lying metal-centre charge transfer?MC?states originated from weak d orbital splitting.As a consequence,it is critical to explore how to increase the lifetimes of MLCT excited states.Two distinct strategies of increasing the lifetimes of MLCT states are proposed,one of which is enhancing the ligand field strength by the change of skeletons of ligands or the formation of ideal octahedral structures.The improvement of ligand field strength can promote the splitting of d orbitals which is benefit to suppress the nonradiative process by the lifting of MC states.And the opposite strategy by decreasing the ligand-field strength with different bulks of substituents results in more accessible high spin excited states like 5MLCT or 7MLCT,thus effectively increasing the rare high spin excited states lifetime.In this work,Density functional theory?DFT?and time-dependent density functional theory?TDDFT?are performed to establish a rapid qualitative evalution method which is used to study the influence on 3MLCT lifetime by two distinct ligand design strategies of Fe?II?complexes.This thesis is divided into five sections.The first section is the preamble which introduces the device structures and functions of OLED,the development of transition metal Ir and Pt complexes and the process of common metal replacement.The second chapter is the theoretical basis used in this thesis,including the foundation of quantum mechanics,the computational methods of quantum chemistry,the profile of relativistic effects,hole-electron analysis and electronic decay mechanism.From the third part to the fourth part,the qualitative and quantitative estimations on the photophysical properties of different Fe?II?complexes are presented.And the fifth chapter is the description of detection scheme of pollution caused by OLED related industries.We synthesize a water-soluble flurescent probe for multi-ion detection with the help of the experimental platform and the addition position and mechanism from CN-or HSO3-to the probe are ascertained by DFT and TDDFT.The details of researches are as follow:1.The strategy of increasing the excited states lifetime by reducing the ligand strength is carried out by the halogen substitution on the 6,6'' positions of terpyridine.[Fe?tpy?2]2+?tpy = 2,2?:6?,2?-terpyridine?is nonluminescent because of ultrafast nonradiative decay from MLCT states to the low-lying triplet metal centered states?3MC?or quintet metal centered states([Fe?tpy?2]²⁺).Through the halogen substituents on the 6,6'' positions of tpy,the derivates of [Fe?tpy?2]2+ own quintet ground states and rare high spin states lifetime.The reason is explored by the combination of electronic structures?singlet,triplet,quintet and septet states?,absorption properties,extended transition state coupled with natural orbitals for chemical valence?ETS-NOCV?,Laplacian bond order and potential energy curves?PECs?.We can find that different populations of multiple spin states of halogen-substituted [Fe?tpy?2]2+ are caused by different bulks of halogen atoms.Due to the deformation of structures originated from halogen atoms,the interactions between metal and ligands diminish and give rise to weaker d orbital splitting than that of [Fe?tpy?2]2+,but slightly impact the pairwise orbital characteristics.Moreover,the 3:97 population ratio of singlet ground state and quintet ground state of [Fe?dftpy?2]2+ is explained by the PECs.Small energy gap?about 11 kcal/mol?makes it available for the hopping from quintet ground state to singlet state at room temperature.2.Based on the exploration of the evalution method in the previous part,we study the photophysical process of Fe?II?complexes with stronger ligand field.More detailed theoretical investigation on the complexes of Fe?II?and Ru?II?containing NHC ligands is performed to expound the effect of the essential difference of metal center on the luminescence of the complexes.We hope to provide an evaluation method and theoretical basis for the design and synthesis of novel luminescent Fe?II?complexes.Ru BIP?BIP = 2,6-bis?imidazol-2-ylidene?pyridine?is theoretically established that the radiative decay lifetime of the second lowest triplet state is more consistence with experimental detection,which means its luminescence does not follow the Kasha's Rule.However,Fe BIP and Fe BIPC?Fe BIP with carboxyl groups?have no luminescent performance.According to the analysis of PECs,carboxyl groups are benefit for the increase of energy levels of 3MC states when diminishing the energy level of 3MLCT state.Nevertheless,the 3MC state is still low-lying.In conclusion,there is still a huge challenge for effective material replacement.More strong field ligands are urgent for emissive Fe?II?complexes.3.Phosphorescent materials such as Ir complexes are used in the experimental study of OLED devices.A large amount of waste liquid will be produced in the processes of metal mining and smelting.There are lots of cyanide and bisulfite and other pollutants in it.Cyanide and bisulfite are hypertoxic even in low concentration.The development of convenient methods of the detection of analyte is critically important.In this paper,the multiple-ion fluorescent probe CIM with superior water-solubility has been designed and synthesized.Modest p H moderation could be easily used to detect the CN-and HSO3-with different fluorescence wavelengths.The specific detection of naked eye recognition is not interfered with other potential coexisted species.The possible mechanism between probe and analytes is illustrated by theoretical calculations for clear theoretical explanation of the relevant mechanisms and basic research support on the environmental impact of heavy metal complexes industries.