Abstract
Nonlinear optical (NLO) properties of organic and metal-organic materials are of considerable interest to emerging optoelectronic and photonic technologies. Much work has been carried out on the former materials but the latter ones have received less attention till date. Herein, a density functional theory (DFT) study on the combined effects of transition metal chelation and solvent polarity on the first hyperpolarizability (βtot) of 4-methoxyacetophenone thiosemicarbazone (MAPTSC) is reported. MAPTSC exhibits a tautomeric form with higher optical nonlinearity rendering its NLO response in polar solvents potentially switchable. Our results have revealed significant modifications of the first hyperpolarizability of MAPTSC upon complexation with different transition metal chlorides in the presence of solvents with varying dielectric constants. Therefore, its second-order NLO response is highly tunable by the synergy of transition metal chelation and solvent polarity. MAPTSC and its Zn(II) and Pt(II) chloride complexes are promising NLO materials because their gas-phase βtot values are larger than those of the prototype push-pull molecules, para-nitroaniline (PNA) and urea, by factors of about 1.40–1.76 and 19.57–37.24, respectively; these factors greatly increase in polar solvent medium. Moreover, they possess high optical transparencies in the visible region of the electromagnetic spectrum which mitigate transparency/nonlinearity trade-offs, thereby increasing the likelihood of broad band NLO response.
Highlights
Nonlinear optical (NLO) materials have recently received considerable attention because of their potential applications in the optoelectronic and all-optical devices of telecommunication, optical switching, optical signal processing, optical transmission, optical data storage, optical computing, and so forth, [1, 2]
Much attention in this paper has been focused on the thione tautomer of methoxyacetophenone thiosemicarbazone (MAPTSC) and its complexes because the thione tautomer is the predominant form of thiosemicarbazones [28]
Strong absorption of light in the visible region of the EM spectrum restricts the NLO applications of materials [39] due to significant transparency/nonlinearity trade-offs that often lead to lower device efficiency and reduced photostability
Summary
Nonlinear optical (NLO) materials have recently received considerable attention because of their potential applications in the optoelectronic and all-optical (photonic) devices of telecommunication, optical switching, optical signal processing, optical transmission, optical data storage, optical computing, and so forth, [1, 2]. Transition metal complexes containing π-conjugated organics are less explored in this area despite their potentials of combining the high optical nonlinearity and chemical flexibility of organic materials with the physical ruggedness of inorganic materials. In an effort to bridge this gap, the impact of metal complexation on the NLO responses of purely organic push-pull systems is currently being investigated. In this perspective, we chose 4-methoxyacetophenone thiosemicarbazone (MAPTSC) as our organic push-pull system because thiosemicarbazones and their metal complexes are notable materials for SHG and, as such, are highly applicable in the field of nonlinear optics [16]. The DFT is very instrumental in designing molecules for NLO applications [14] because of its remarkable accuracy/computational-time ratio, coupled with the fact that it takes good account of electron correlation effects in calculations
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