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The substitution of heteroatoms and the expansion of π‐conjugated units have significant effects on the photoelectric properties of polycyclic aromatic hydrocarbons (PAHs). In this study, based on the experimental molecule PBC, 10 acene derivatives containing the pyrrole group were designed by three strategies: (1) changing the connection position of the pyrrole group, (2) exchanging the position of the N atom, and (3) increasing the length of the π‐linker. Density functional theory (DFT) was used to optimize the molecular geometric structure. Time‐dependent density functional theory (TD‐DFT) was used to calculate the relevant parameters of the excited states. The results show that both of the pyrrole group and the N atom in the para‐position, and the addition of the π‐linker can reduce the energy gap, cause redshift of the linear absorption peak, and increase the two photon absorption (TPA) cross‐section. The analyses of the charge density difference (CDD) and the charge‐transfer matrix (CTM) proved that the electron transfer is mainly concentrated in the π‐linker. Moreover, the participation of the multi‐ring skeleton on both sides decreases gradually with the increase of the length of the π‐linker. The length of the π‐linker changes the dominant transition channel and intramolecular charge‐transfer (ICT) characteristics of TPA, thus affecting the transition dipole moments and nonlinear absorption properties. The second hyperpolarizability of the designed molecule PBI5‐p5 is also significantly superior to that of similar materials reported. It is expected that the above molecular design strategies and comprehensive analysis of nonlinear optical (NLO) properties could provide theoretical support for the research on acene derivatives. [ABSTRACT FROM AUTHOR]

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]

The ground-state structures and absorption spectra of three dyes, carbazole, phenothiazine and diphenylamine, were studied by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The strong absorption peak, electron transition as well as the energy levels of molecular orbitals were obtained and compared in the gas and solvent phase. Furthermore, we further calculated the effect of the expanding conjugated bridge on the absorption spectra and the energy levels of molecular orbitals. Visualized method of charge difference density (CDD) was used to show the direction of charge transfer in the molecules of interest during photo-excitation. The energy levels of dyes (CBZ, WD-5 and DTA) and expanding bridge dyes (C-b1, W-b1 and D-b1) were shown. LUMO level of six dyes is in this order DTA > D-b1 ≈ CBZ > WD-5 > C-b1 > W-b1. The introduction of the benzene ring into the bridge space widens the absorption range, however, the ability of electron injection and recovery is indeed depressed. [ABSTRACT FROM AUTHOR]

Closely contacted Pd nanoparticles with average size of 8 nm are uniformly deposited on quartz. The ageing, hydriding, hydriding and then ageing of the nanoparticles are characterized by the transmission electron microscopy, optical extinction spectrum, and X-ray photoelectron spectroscopy, which show little chemical and crystallographic change. The contact between the nanoparticles and quartz and contacts among the nanoparticles are investigated by the pump-probe technique. The contact between nanoparticles and quartz looses with the ageing, hydriding, hydriding and then ageing of the nanoparticles, and the contacts among nanoparticles loose with the ageing whereas compresses with the hydriding. [ABSTRACT FROM AUTHOR]

Pd nanoparticles are deposited on one surface of a quartz sheet. Their optical nonlinearity and ultrafast dynamics in air and in hydrogen environment are investigated. The Pd nanoparticles exhibit self focusing and saturable absorption in air. In hydrogen environment with increasing hydrogen, the NPs maintain self focusing, however their nonlinear refraction index increases; and their nonlinear absorption changes from saturable absorption to reverse saturable absorption. In hydrogen environment, the acoustic breathing movement of these NPs damps more obviously and the contact between the NPs and quartz sheet is looser, comparing to that in air. [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.)

The third order non-linear optical response of a dicyanomethylene dihydrofuran compound (DCDHF-2V) was investigated using a Z-scan technique in picosecond and nanosecond time regimes. The results show that DCDHF-2V has excellent excited state non-linear refraction properties on both time regimes, and the non-linear refraction index is also solvent-dependent in the nanosecond regime. The excited state relaxation dynamics of DCDHF-2V were demystified via femtosecond transient absorption spectroscopy. The TA spectra reveal that the solvent viscosities have a substantial impact on the excited state relaxation of DCDHF-2V. The exotic photophysical phenomena in DCDHF-2V reported herein can shed new light on future development of small organic non-linear optical materials with large non-linear coefficients and fast response., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Yang, Li, Wei, Zhou, Li, Fang and Song.)