Theoretical Studies On The Optoelectronic Properties Of Re(Ⅰ) Complexes Containing Quinonoid

In the past two decades,transition metal complexes have attracted extensive concerns because of their promising applications such as highly efficient electroluminescent（EL）emitters in organic light-emitting diodes（OLEDs）,dye-sensitized solar cells（DSSCs）,luminescence probes.Among various investigated transition metal complexes,those from Re（Ⅰ）carbonyl receive attention increasingly since Wrighton reported the luminescence and the electron transfer properties in the excited state of[fac-Re（CO）₃LCl]（L=1,10-phenanthroline）.Rhenium（I）complexes with promising performance such as high PL quantum yield,satisfying excited state lifetime,along with the potentiality of achieving an internal quantum efficiency of 100%.The photophysical,photochemical,and electrochemical properties of Re（Ⅰ）complexes can be effectively controlled by selecting the suitable ligands.For Re（Ⅰ）complexes,N^N type ligands,such as 2,2’-bipyridine,1,10-phenanthroline and their derivatives as well as other heterocyclic ligands containing nitrogen atom are most frequently chosen.Re（Ⅰ）complexes owing the N^O type ligand with donating oxygen atom were rarely concerned to date.This situation leaves a void for exploring the photoelectric material.In this work,a series of Re（Ⅰ）complexes with the bidentate N^O type ligand have been investigated by means of the density functional theory（DFT）in combination with time-dependent DFT（TDDFT）to explore their geometry structures,electronic structures,spectroscopic properties and other correlative properties as dyes in dye-sensitized solar cells（DSSCs）.This work aims at revealing the correlation of Re（Ⅰ）complexes with the bidentate N^O type ligand between their electronic structures and luminescence performance.Through adjusting the molecular structures of the complexes,their photoelectric properties should be improved,and then some useful information for designing new photoelectric materials with the practical application perspective can be obtained.This work contains three parts as follow:Inthefirstpart,wetookdinuclear[Re₂（CO）₆（N^O）L₂]（N^O=2,5-bis（4’-（isopropyl）-anilino）-1,4-benzoquinone,L=4-dimethylaminopyridine）as parent model（complex 1）to theoretically design three types of mononuclear Re（Ⅰ）complexes（a,b,and c types）containing the quinone ligand.The three types of model complexes can be described as[Re（CO）₃（N^O）L]（L=4-dimethylaminopyridine,a1;4-carboxylicpyridine,a2;ethynyl,b1;phenol,b2）and[Re（CO）₂（N^O）L]c1（L=4,4?-dicarboxyl-2,2?-bipyridine（N^N））.The geometry structure optimization results in the ground state at PBE1PBE/[LanL2DZ,6-311G（d）]level revealed that Re（Ⅰ）in all the model complexes exhibited the distorted octahedral coordination conformation.The frontier molecular orbitals of the complexes were effectively tuned on the energy level and energy gaps through introducing the ligands or ancillary group with differentπ-donating ability.TD/DFT calculations uncovered that a1/a2 and b1/b2 displayed absorptions between 350-800 nm and emissions in the visible light region of 700-760 nm with the lifetime of 50-80 ns,while c1 emits in the infrared region with the lifetime of microsecond magnitude.For all the complexes,the lowest energy absorption and emission are all originated from ILCT electron transition.The comprehensive results including ionization potential（IP）and electron affinity（EA）along with the reorganization energy（λ）properties indicated that a2 and c1had the advantage to act as the charge transfer material.In the second part,we theoretically design five mononuclear Re（Ⅰ）complexes[Re（CO）₃（N^O）L]（L=acetonitrile,N^O=2,5-bis（4?-（hydroxyl）anilino）-1,4-benzoquinone,d1;2,5-bis-anilino-1,4-benzoquinone,d2;2,5-bis（4?-（carboxyl）-anilino）-1,4-benzoquinone,d3;2,5-bis（4?-（sulfonyl hydroxide）-anilino）-1,4-benzoquinone,d4;2,5-bis（4?-（nitro）-anilino）-1,4-benzoquinone,d5）,containing the quinone with different substituent on the para-position of aniline.Studies have shown that to change the substituent group with different electron-donating properties on the N^O ligands can adjust the electronic structure of complexes and further affect the electron absorption as well as the emission properties.The energy levels of HOMO and LUMO of the five model complexes decrease gradually from d1 to d5.The five complexes all show absorptions between 350-800 nm and emit in the area of red light with the lifetime of 50-140ns.Not only the electronoic structures but also the spectroscopic properties of the complexes are adjusted due to the decoration to the N^O ligand.In the third part,we examine three Re（Ⅰ）complexes a2,c1,and the conformational isomer of c1,c2,as dyes in DSSC.Some important parameters to evaluate the performance of DSSC have been calculated.Three dye molecules can be adsorbed on the（TiO₂）₁₆6 surface.Studies have shown that the HOMO of the adsorption models are occupied by the components of dye,while the LUMO are dominated by the semiconductor.The fitted absorption spectra for adsorption systems in acetonitrile media resemble those of respective isolated dyes in profile just with slight red-shifts.These features verify that the three complexes can act as the dyes in DSSC.The calculation results of-ΔGⁱnjectnject and LHE means that c2 should display better performancein DSSC than a2 and c1.