Synthesis And Photophysics Of Platinum(Ⅱ) 2,2’-Bipyridine Complexes And Iridium(Ⅲ)Complexes

With the development of laser technology,various laser sources have brought revolutionary changes and essentially improvement to the scientific community,industrial world and our social life.Recently,lasers are used extensively in photonic,medical and military field.However,there is an urgent need for protection human to against lasers.Reseachers have found that reverse saturable absorption of some organic dyes under strong laser shown potential application in optical limiting.The organic molecules which based on nonlinear optical effect may develop into good optical limiting materials.In order to explore the relationship between the structure and photophysical properties,we report the design,synthesis and characterization of five new Pt(Ⅱ)complexes and two Ir(Ⅲ)complexes.Firstly,fluorene as starting material,designed and synthesized two acetylene ligands with varied numbers of repeating fluorene units,and two corresponding Pt(Ⅱ)complexes Pt-1 and Pt-2 by a series of Sonogashira Coupling reactions,Pt-1 has two repeating units on the acetylide ligands,while Pt-2 has three repeating fluorene units on the acetylide ligands.The photophysical properties of these two complexes were investigated via UV-vis absorption,transient absorption(TA),and emission spectroscopic techniques.Additionally,the nonlinear transmission was demonstrated at 532 nm for ns laser pulses.The UV-vis absorption spectra of Pt-1 and Pt-2 show that with the extending of π-conjugation on the acetylide ligands,the molar extinctions of the absorption bands become larger,but the energies of the absorption bands do not exhibit substantial changes.This result indicates that extending the π-conjugation of the acetylide ligands does not change the optical window for reverse saturable absorption very much.However,it significantly increases the lifetimes of the lowest triplet excited state and causes a bathochromical shift of the TA band.Consequently,both complexes exhibit a strong reverse saturable absorption at 532 nm for ns laser pulses.Secondly,fluorene as starting material,designed and synthesized three complexes Pt-1,Pt-2 and Pt-3 with different electron-donating substituents by nitration,aminating,alkylation,reduction and Sonogashira Coupling reactions.Their UV-vis absorption spectra show that with the increased electron-donating ability of the terminal substituent,the π-π*transition bands are distinctly blue-shifted,but the energies of the MLCT(metal-to-ligand charge transfer)/LLCT(ligand-to-ligand charge transfer)transitions are essentially the same.Due to the strong electron-donating ability of the terminal substituent,the lowest-triplet excited states of these conplexes are short-lived,which prevents us observing the triplet excited-state absorption.However,all three complexes still exhibit strong reverse saturable absorption at 532 nm for ns laser pulses.Thirdly,fluorene as starting material,designed and synthesized two new 2-(2-quinolinyl)quinoxaline substituted N^N ligands,and their dinuclear corresponding Ir(Ⅲ)complexes by a series of Sonogashira Coupling and Suzuki Coupling reactions.The UV-vis absorption spectra of the complexes show that the extended π-conjugation of the diimine ligand only increase the molar extinction of the major absorption bands and causes a red-shift of these bnads but does not affect the energy or the intensity of the MLCT/LLCT transitions.The TA study shows that both of the complexes exhibit a moderate triplet quantum yield and a structurless positive TA band at 500-650 nm.However,extending the π-conjugation of the diimine ligand decreases the triplet quantum yield and the triplet lifetime of the Ir(Ⅲ)complex.Both complexes exhibit moderately strong reverse saturable absorption at 532 nm for ns laser pulses.At last,we do optical limiting test for all the complexes.With the increasing of incident energy,the transmittances of all the samples decrease.This suggests that the reverse saturable absorption happened at 532 nm and these complexes can serve as good optical limiting materials.