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This work exposes for the first time the remarkable influence of intramolecular group rotation on third‐order nonlinear optical (NLO) performance. In order to prove the role of group rotation, we designed and synthesized two photo‐response compounds tetramethyl 5,5′‐(((diazene‐1,2‐diylbis(4,1‐phenylene))bis(oxy))bis(methylene))diisophthalate (1) and 5,5′‐(((diazene‐1,2‐diylbis(4,1‐phenylene))bis(oxy))bis(methylene))diisophthalic acid (2) and investigated their NLO performance under different substituent (benzyloxy group) rotation states. 1 and 2 have dynamic benzyloxy group rotation in dilute solution and shows reverse saturated absorption (RSA). When the benzyloxy group rotation of 1 and 2 was restricted by PMMA, their NLO performance not only converted into saturated absorption (SA) and NLO refraction behaviours, but also hardly changed after isomerization. Interestingly, we also restricted the benzyloxy group rotation in solution to a certain extent through photo‐induced trans→cis isomerization, and found that the NLO performances of cis isomers of 1 and 2 exhibit SA and positive refraction and are similar to those of 1‐PMMA and 2‐PMMA. This work provides a new exploratory method for studying the influencing factors of third‐order NLO performance. [ABSTRACT FROM AUTHOR]

By utilizing Dy(hfac) 3 (H 2 O) 2 to react with enantiomerically pure tridentate N,N,N -pincer ligands, namely (-)/(+)-2,6-bis(4',5'-pinene-2'-pyridyl)pyridine (L R and L S ), respectively, homochiral Dy III enantiomeric pairs formulated as Dy(hfac) 3 L R /Dy(hfac) 3 L S ( R -1 / S -1 ) (hfac - = hexafluoroacetylacetonate) were achieved and structurally characterized. Meanwhile, their magnetic, photoluminescent (PL), and chiroptical properties were probed. The PL test results indicate that the precursor Dy(hfac) 3 (H 2 O) 2 only shows very weak emission, while R -1 exhibits characteristic Dy III f-f transition emission bands at room temperature. Furthermore, the nonlinear optical responses of Dy(hfac) 3 (H 2 O) 2 , L R /L S , and R -1 / S -1 were investigated in detail based on crystalline samples. The results reveal that L R and L S present the coexistence of second- and third-harmonic generation (SHG and THG) responses with more intense signals for SHG responses; and Dy(hfac) 3 (H 2 O) 2 merely displays weak THG responses, while R -1 and S -1 also only exhibit THG responses. However, the THG intensities of R -1 and S -1 are more than six times larger than that of Dy(hfac) 3 (H 2 O) 2 under the identical measurement conditions. These results demonstrate that introducing homochiral N,N,N -pincer ligands to replace two H 2 O molecules of Dy(hfac) 3 (H 2 O) 2 results in significant improvements of both PL performances and THG responses of resultant R -1 / S -1 enantiomers. R -1 and S -1 integrate PL, THG, and chiral optical activity in one molecule, suggesting their multifunctional merits. In particular, a convenient method is introduced to simultaneously test THG and SHG responses of molecular materials based on crystalline samples in this work.

This work exposes for the first time the remarkable influence of intramolecular group rotation on third-order nonlinear optical (NLO) performance. In order to prove the role of group rotation, we designed and synthesized two photo-response compounds tetramethyl 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalate (1) and 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalic acid (2) and investigated their NLO performance under different substituent (benzyloxy group) rotation states. 1 and 2 have dynamic benzyloxy group rotation in dilute solution and shows reverse saturated absorption (RSA). When the benzyloxy group rotation of 1 and 2 was restricted by PMMA, their NLO performance not only converted into saturated absorption (SA) and NLO refraction behaviours, but also hardly changed after isomerization. Interestingly, we also restricted the benzyloxy group rotation in solution to a certain extent through photo-induced trans→cis isomerization, and found that the NLO performances of cis isomers of 1 and 2 exhibit SA and positive refraction and are similar to those of 1-PMMA and 2-PMMA. This work provides a new exploratory method for studying the influencing factors of third-order NLO performance., (© 2021 Wiley-VCH GmbH.)