Strategy for Enhancing Second-Order Nonlinear Optical Properties of the Pt(II) Dithienylethene Complexes: Substituent Effect, π-Conjugated Influence, and Photoisomerization Switch

Abstract

The second-order nonlinear optical (NLO) properties of a series of Pt(II) dithienylethene (DTE) complexes possessing the reversible photochromic behavior have been investigated by density functional theory (DFT) combined with the analytic derivatives method. The results show that the calculated static first hyperpolarizabilities (βtot) of the open-ring and closed-ring systems significantly increase in the range of 2.1-4.5 times through strengthening of the electron-withdrawing ability of the substituent R (R = H, CF3, NO2) and an increase of the number of thiophene rings. Moreover, there is a large enhancement of the βtot values from the open-ring systems to the corresponding closed-ring systems. This efficient enhancement is attributed to the better delocalization of the π-electron system, the more obvious degree of charge transfer, and the larger f(os)/E(gm)(3) (f(os) is the oscillator strength, and E(gm) is the transition energy between the ground and the excited states) values in the closed forms according to the bond length alternation (BLA) and time-dependent density functional theory (TDDFT) calculations. In addition, the dispersion has less influence on the frequency-dependent first hyperpolarizabilities (βtot(ω)) of the studied systems at the low-frequency area ω (0.000-0.040 au). Our present work would be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes.

Theoretical Study of the Substituent Effects on the Nonlinear Optical Properties of a Room‐Temperature‐Stable Organic Electride

“…NH 2 , CH 3 , F, CN, and NO 2 ) on the NLO properties of Na@(TriPip222). Different from a previously reported case, in which donor/acceptor substituents were introduced into a conjugated complexant of an NLO molecule, the TriPip222 complexant in Na@(TriPip222) is nonconjugated, and the intramolecular charge‐transfer (ICT) processes occur mainly through a novel kind of “through‐space” electronic interactions instead of a π‐conjugate bridge. Considering that all the complexants in previous synthetic organic electrides were nonconjugated crown ethers and azacryptands, we expected that this work could provide additional knowledge about the substituent effects on the NLO response and could also offer an effective method to tune the NLO properties of known electrides.…”

“…The substitution of different donor/acceptor groups has a substantial effect on the NLO response of a molecule, and hence, substituent effects were successfully utilized to modulate the NLO properties of different NLO molecules . Recently, we investigated the substituent effects of several donor and acceptor groups on the NLO properties of Li + (calix[4]pyrrole)Li − alkalide .…”

Third order NLO properties of corannulene and its Li-doped dimers: effect of concave–convex and convex–convex structures

“…17 The obvious CT properties can cause a large difference between the ground and excited state dipole moments and low-energy CT transitions, 18,19 which thus causes the organic molecules to exhibit considerably large nonlinear optical (NLO) activities. [20][21][22][23][24] Therefore, the p-p intermolecular interactions, signicantly connecting with obvious CT properties, are found to strongly affect the NLO properties. In view of this, buckybowls involving p-p interactions offer exciting future opportunities for designing novel smart NLO materials.…”

Exploring Second-Order Nonlinear Optical Properties and Switching Ability of a Series of Dithienylethene-Containing, Cyclometalated Platinum Complexes: A Theoretical Investigation

“…Qiu et al studied the strategy for enhancing the second-order NLO properties in these systems by theoretical method. 38 By increasing the thiophene rings of the C ∧ N (cylometalating 2-(2′-thienyl)pyridyl (thpy)) ligand, and introducing stronger electron-withdrawing substituents on pyridyl ring, the β values of both open-forms and closed-forms have several times enlargement. However, from the viewpoint of designing second-order NLO switches, such results are unsatisfactory, because we find that, with the enlargement of the β values, the contrasts (define as the ratio of β tot values of closed-forms over open-forms) are decreased.…”