In:
New Journal of Chemistry, Royal Society of Chemistry (RSC), Vol. 47, No. 39 ( 2023), p. 18359-18373
Abstract:
The effect of hydrogen bonds on the NLO properties was not considered as essential, in particular in pyridine hydrazone systems. Yet, we show in the present study that a control of these photoswitches depends on the strength of hydrogen bonds. In this study, we investigate a selection of 18 E / Z pyridine hydrazone photoswitch molecules to explore the impact of resonance-assisted hydrogen bond (RAHB) on the NLO properties in the E / Z isomers. Using quantum calculations at the ωB97XD/6-311+g(d) level of theory, we determine various electronic parameters, reactivity descriptors, bond length alternation (BLA) values, nuclear independent chemical shift (NICS) aromaticity indices, QTAIM topology, energy of hydrogen bond ( E HB ), RAHB, and linear and nonlinear optical properties for these molecules. The agreement between the quantum calculations and experimental spectra is illustrated through TD-DFT calculations, showing small deviations. Contrary to conventional expectations, our findings demonstrated that the delocalization strength of the electrons and NLO properties of the Z isomers are significantly enhanced by the presence of a resonance-assisted hydrogen bond. The Z -isomer exhibited a lower excited state energy, weaker energy gap, smaller BLA value, larger dipole moment variations for the first excited state, higher Φ E → Z , and electron delocalization at the quasi-cycle closed (RAHB) compared to the E -isomer. Furthermore, we find that the hyperpolarizability value of the title photoswitches increases as the wavelength of the incident light decreases, i.e. , β(695) 〉 β(1064) 〉 β(1340) 〉 β(∞), and the dispersion has less effect at λ = 1064 and 1340 nm. Additionally, we observe a strong relation between the photoisomerization quantum yield ( Φ E ⇄ Z ) and static hyperpolarizability (β) of the first and second isomer, where Φ E ⇄ Z is proportional to β of the second isomer and inversely proportional to b of the first isomer. This inverse trend between static hyperpolarizability and photoisomerization quantum yields is attributed to the electron-withdrawing character of substituents on the Ar ring. Our research provides valuable insights into optimizing the 2nd-order NLO properties of pyridine hydrazone photoswitch molecules. By understanding the influence of hydrogen bonding on the delocalization strength of the electrons (RAHB) and the shape-dependent NLO performance, we gain the ability to design and synthesize novel photoswitch molecules with enhanced NLO characteristics.
Type of Medium:
Online Resource
ISSN:
1144-0546
,
1369-9261
Language:
English
Publisher:
Royal Society of Chemistry (RSC)
Publication Date:
2023
detail.hit.zdb_id:
1472933-7
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