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Abstract On the basis of great diverse applications of nonlinear optical (NLO) materials, organometallic complexes have attracted considerable attention. In this paper, we present a detailed investigation on a series of Pt(II) dithienylcyclopentene(DTE)-based complexes via density functional theory method with the aim of evaluating their structures, electronic absorption spectra and first hyperpolarizabilities. The calculations demonstrate that the first hyperpolarizabilities can be enhanced by the introduction of quinolone into the complexes because of the enlarged spatial separation of electron density. However, Pt(II) complexes containing perfluorocyclopentene ring exhibit decreasing NLO response attributed to lower amount of charge transferred and short effective CT distance. The static first hyperpolarizabilities (β tot) of monometallic Pt(II) complexes are larger than those of bimetallic Pt(II) complexes due to correlative mixed charge-transfer patterns. More importantly, the closed-ring (1c) complex comprising DTE unit exhibits the largest β tot value approaching 144 × 10−30 esu, with the contrast over five times compared to corresponding open-ring due to the better π-conjugated delocalization and smaller HOMO and LUMO energy gap. In general, we envision our work will be beneficial for further rational design of DTE-containing Pt(II) complexes as high performance NLO materials. Graphical abstract Image 1 Highlights • Monometallic Pt(II) DTE-based complexes exhibit the largest β tot values. • The second-order NLO response of bimetallic Pt(II) complexes can be altered by various ligands. • The switching of NLO properties has been achieved by photoisomerization. [ABSTRACT FROM AUTHOR]

The iridium(III) complexes could be excellent second-order nonlinear optical (NLO) switch materials due to various advantages including abundant valence states, the diversity of coordination forms and rich electrochemical properties. In this work, the substituent effect and the multi-state switchable response of a series of novel Ir(CˆN) 2 ADC complexes (CˆN = cyclometalated ligands and ADC = diaminocarbene), induced by electrochemical behavior, have been calculated by density functional theory. The results show that the introducing strong electron-withdrawing groups on ADC ligands significantly enhanced the static first hyperpolarizabilities (β tot). Moreover, a distinct improvement of the β tot values can be found from the neutral complexes to the corresponding redox states. By this way, the remarkable multi-state NLO switch can be achieved. Remarkably, the β tot values of the one-electron-oxidized complex 1 + and the one-electron-reduced complex 1 - are ∼5.4 and ∼12.7 times larger than the corresponding neutral complex 1 , respectively. The larger β tot values are attributed to the lower transition energy and remarkable bathochromic shift of maximal absorption wavelength, which can be further illustrated by the separate distribution of β density. We envision that these studied iridium complexes can be seen as versatile and novel second-order NLO switching materials. The second-order NLO properties of the cyclometalated iridium(III) complexes were investigated by density functional theory (DFT) method, and the complexes 1 were promising to become novel redox-switchable NLO materials. Image 1 • The redox centers should take place preferentially at the CˆN ligands. • The introducing strong electron-withdrawing groups (NO 2) lead to the β tot values clearly enhanced. • Complexe 1 act as promising candidates for redox-switchable NLO materials. • There are clearly dependencies of β tot values on the transition energies. [ABSTRACT FROM AUTHOR]

Ru metal acetylide electron donor-acceptor complexes have important applications in the field of nonlinear optics. Herein, in this work, a series of half-sandwich ruthenium-based Cp*(dpe)Ru ([Ru*]) metal complexes with the dihydroazulene/vinylheptafulvene (DHA/VHF) have been investigated by density functional theory (DFT) calculations. The results showed that the position of the [Ru*] acetylide functionality, either para or meta on the phenylene ring to the DHA/VHF core ( 1c/1o and 2c/2o ), and additional a p -phenylene spacer ( 3c/3o ) had a great influence on the second-order nonlinear optical (NLO) responses. The systems 1 and 3 can significantly increased second-order NLO responses compared with system 2 . It was attributed to the more obvious charge transfer along y -axis, which is from [Ru*] acetylide functionality to DHA, accompanied by a significant decrease of the transition energy according electron density difference maps and time-dependent DFT calculations. The β vec values of the open-ring complexes were larger than the corresponding closed-ring complexes owing to the smaller HOMO−LUMO gap in the open-ring complexes. It was also because of the smaller BLA values in open-ring complexes, which had stronger π-conjugation. Especially, the change ratio of β vec value of system 2 was the largest due to the fact that their charge transfers degree varied greatly. In addition, the frequency-dependent NLO properties of the studied complexes were evaluated at 0.0239 a.u. and 0.0340 a.u. The calculation results demonstrated that the magnitude of the frequency-dependent first hyperpolarizability increased with the increasing frequency. We believe that our present work will be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) have been carried out to investigate the nine recently reported iridium (Ⅲ) complexes which substituted various cyclometalated ligands (CˆN) and aryl isocyanide ancillary ligands (CNAr). The aim of this paper is to study the substituents effect on geometrical structures, electronic and second-order nonlinear optical (NLO) properties, UV-vis absorption spectra. It is found that the first hyperpolarizabilities can be easily modulated by the introduction of different electron-withdrawing/donating ligands on CˆN and CNAr. Complexes with 2-benzothienylpyidine (btp) CˆN ligands or the substituents on CNAr are electron-withdrawing groups -NO 2 possess larger first hyperpolarizabilities values compared to remaining complexes. Significantly, the changes of the first hyperpolarizability can be qualitatively explained by means of the charge transfer pattern. It is anticipative that the theoretical investigation of these iridium complexes will be helpful for designing high-performance and versatile NLO materials. [ABSTRACT FROM AUTHOR]