Theoretical Study On The Switchable Second-order Nonlinear Responses Of Series Ru Complexes

With the rapid development of the molecular switches,seeking excellent nonlinear optical(NLO) materials of the molecular switches has attracted a lot of interests. Compared with the inorganic and organic molecules, organometallic molecules have the unique structural and electronic characteristics. What’s more, organometallic complexes often have large NLO responses, and also offer the greate design flexibility. The switchable NLO behaviors of the organometallic complexes could be obtained by oxidation/reduction of central metal or organic ligand and the photoisomerization and protonation/deprotonation of ligand. The metal Ru is easy to form the six coordination because of the characteristic of the outermost layer. It also has good metal-ligand charge transfer character and the lower transition energy. The second-order NLO properties of a series of Ru complexes have been studied by using quantum chemical calculations. The obtained results are as follows:1. The second-order NLO properties and absorption spectrum of a series of Ru-coordinated DTE complexes have been investigated by density functional theory(DFT) and time-dependent DFT(TDDFT). On the basis of the invertible photoisomerization, redox and protonation, 2o has been adopted as an example to modulate the second-order NLO responses. The main conclusions are as follows:(1) After the photoisomerization process, the DTE forms a relevant good plane, which significantly improves the second-order NLO responses. Particularly, 2c displays the largest βvec value, about 52.7 times as large as that of 2o, because of the DTE π-π* charge transfer.(2) The oxidization process not only changes vector direction of the βvec but also changes the βvec values, which is due to the charge contribution from the x- and z-polarized transitions.(3) The protonation reaction has an influence on tuning the second-order NLO responses, to a certain extent. For example, 1c further decreases the charge transfer transition from x- and z-axis, which is as low as one-sixth of 2c.2. The second-order NLO properties of a series of ruthenium complexes of 9-oxidophenalenone were investigated by DFT and TDDFT, and the conclusions are as follow:(1) The coordination bond lengths are hardly affected by changing the species of the ancillary ligands. However, when a ancillary ligand displaces a main ligand, the coordination bond length shows an enhanced tendency.(2) With respect to 2a, the molecular charge transfer is more obvious than 1a, which results in an increase of the βtot value. While for 3a and 4a, vector directions of the charge transfer are oppositely along the y-axis.(3) The redox of NLO responses of eigenstates has been studied based on the good invertible redox property. The calculated results reveal that oxidation process change transition feature. The βtot values of 3b and 4b are ~12 and 25 times as large as 3a and 4a, respectively. This indicates that the βtot values of 3a and 4a can be efficiently modulated in oxidized reaction, and will become potentially excellent redox-switchable NLO molecular materials.(4) For systems with the reduced species, however, the reduction processes no longer bring about effective redox switching. With the injection of an electron, the βtot values of 1c and 2c decrease. By contrast, the βtot values of the reduced species 3c and 4c greatly enhance. This implies that the reduction processes alter the electron-attracting ability of acceptor and electron-donating ability of donor and affect the degree of the charger transfer, which leads to the different βtot values.In summary, the above conclusions will provide valuable information for scientists to design the potential materials of NLO switches of these Ru complexes.