Design, synthesis and nonlinear optical characterization of novel mixed ligand ruthenium metal-organic complex

doi:10.1016/j.optmat.2020.110068

Optical Materials

Volume 107, September 2020, 110068

https://doi.org/10.1016/j.optmat.2020.110068 Get rights and content

Highlights

•
Successfully designed and synthesized mixed-ligand ruthenium metal-organic complex.
•
Fabricated low optical loss metal-organic/PMMA films for solid-state optical limiters.
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Optical limiting clamping as low as 38 μJ was displayed by the complex.
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High optical nonlinearity in the complex is due to excellent charge communication between various groups.

Abstract

In the present study, novel mixed ligand ruthenium metal-organic complex (RuThAP) was designed and synthesized. The chemical structural analysis was performed using NMR, UV–Vis and FTIR spectroscopy. RuThAP/Poly(methylmethacrylate) (PMMA) films were successfully fabricated by homogeneously embedding RuThAP in optically inactive PMMA using spin-coating. Third-order nonlinear optical coefficients of RuThAP in liquid and solid phase were determined by Z-scan technique with nanosecond laser beam. RuThAP molecule exhibited strong reverse saturable absorptive (β_eff = 8.81 ± 0.88 x10⁻⁹ m/W) and negative refractive (n₂ = −5.47 ± 0.55 x10⁻⁹ esu) optical nonlinearity at 532 nm. The RuThAP molecule also demonstrated strong optical limitation with optical limiting clamping level as low as 38 μJ due to large absorptive optical nonlinearity. These results pave the platform for high efficient metal-organic/PMMA films based solid-state optical limiters with low cost, flexible, dependable and low optical loss.

Graphical abstract

Introduction

Laser technology has been extensively employed in wide civilian and military applications including optical limiting, optical information processing, industrial processing, etc [1,2]. Optical limiting (OL) systems are vital in safeguarding sensitive optical devices against harsh laser light [[1], [2], [3], [4], [5]]. Developing OL materials is one of the key areas of nonlinear optics (NLO). Strong absorptive nonlinearity and quick response time are critical to developing competent OL materials [3,4]. For this intent, different material systems have been developed which cover small and large organic molecules, inorganic materials, etc [[1], [2], [3], [4], [5], [6], [7]]. Currently, organometallics or coordination complexes or metal-organics received great interest for NLO because in this system optical nonlinearity synergistically improves with the insertion of metal ion and/or organic moiety [[8], [9], [10], [11], [12], [13], [14], [15]]. These systems earned much attraction due to its specific advantages, large absorptive and refractive nonlinearity, stability, transmittance, ease in chemical structure modifications, simple synthetic procedure, etc. Also, the strength of optical nonlinearity can be changed by altering the metal ion and organic moiety [[16], [17], [18]].

Metal-organic complexes with sulfur-comprising ligands attract significant interest due to superior physiochemical properties. Among them, dithiolato ligands have been investigated widely, they give rise to the corresponding complexes with various metals (Scheme 1) [19]. Oxidation of dianionic complexes [M(S₂C₂R¹R²)₂]^2–directs to neutral complexes [[20], [21], [22]], in which sulfur-comprising ligands may contain dithiocarbonyl or dithiolate structure, while the metal atom may occur in different oxidation states. The presence of a phosphine group adds to the high scale of electron density delocalization, strong ligand and metal orbital interactions, and the metal-organic complexes capable to stabilize different oxidation states (including radical anion species). At present, studies are performed on different applications of dithiolene metal-organic complexes, which include magnetic, conducting, electrochemical, electrocatalytic, nonlinear optical properties, superconductivity, and liquid crystalline properties [ [19,[23], [24], [25], [26], [27], [28]]]. Apart from nickel, palladium, and platinum complexes, coordination compounds of metals with various electronic structures (Mⁿ, Scheme 1), including complexes with extra ligands (Cp, Cp*, etc.) are extensively studied.

The σ-donating phosphine group tethered to dithiolene group adds importance to the ligand design. Primarily, the phosphine is expected to bind strongly to the transition metals. Besides, the rigidity of the ring would fix the chelating ring size and highly support ligand lability at the position trans. Above all, dithiolene and phosphine are known as strong trans effect/influence ligands, so they would be competent to activate/labilize groups coordinated in a position trans to them. Since tertiary phosphines (PR₃) and dithiolene each have many advantageous properties such as a large trans effect or influence respectively (but different donor/coordination properties), combined properties should be effective in enhancing migratory reactions of base molecules coordinated in trans positions, which make them desirable as novel ligands. There is also an interest in the bonding properties of ligands that must bind mutually cis sites since these would require remaining reactive sites to be mutually cis to each other (ideal for migration reactions) as well as simultaneously trans to the dithiolene's trans-influence or the phosphine's trans-effect.

Considerably more interesting, therefore, may be metal complex with chelating sulfur-containing ligands along with phosphine ligands. From the viewpoint of potential application as materials for electronics, complex (Fig. 1) offers a number of important advantages: (1) the metal oxidation state is determined by ligands X, and it can change in a predictable mode; (2) weaker binding of ligand provides the possibility for reversible dissociation and substrate coordination.

By considering above points, we synthesized novel mixed metal-organic complex of ruthenium triphenylphosphine complex containing C₃S₅ and acetylacetonato group, which acts as a neutral ligand (Scheme 2) and studied third-order optical nonlinearity in liquid and solid phase with Z-scan process and extracted the nonlinear absorption coefficient (β_eff), imaginary NLO susceptibility (Imχ³), nonlinear refraction index (n₂) and real NLO susceptibility (Reχ³). The OL activity of Ruthenium complex, RuThAP complex also studied.

Section snippets

Materials and methods

Research grade chemicals were used for the synthesis. The standard procedure adopted to purify and dry the solvents [29]. RuCl₃.3H₂O was procured from Loba Chemie and used as it is. [RuCl₃(PPh₃)₃] was prepared by refluxing RuCl₃·3H₂O and triphenylphosphine in methanol for 4 h [[30], [31], [32]].

The electronic absorption spectrum of the metal-organic complex was collected using UV–Vis double beam spectrophotometer (GBC Cintra 101) in DMSO solution (λ = 200–800 nm). FT-IR spectrum was obtained

Synthesis of complex

The complex was tested for its solubility and was found to be soluble in DMF and DMSO solutions. The melting point of [RuCl(C₃S₅)(acac)(PPh₃)₂] was found to be 195°.

The IR spectrum (Fig. 2) of complex shows an intense band around 2014 cm⁻¹, which is ascribed to dicarbonyl vibration [[35], [36], [37]]. The band at 1572 cm⁻¹ suggests the vibration of ν(C=C). The band near 744 cm⁻¹ is due to the vibration of ν(C–S) in the C₃S₅ group is altered in the complex [36]. The band at523 cm⁻¹ is due to the

Conclusions

Mixed ligand (dmit and acetylacetonato) ruthenium metal complex was successfully synthesized and characterized. The third-order NLO parameters were determined using the Z-scan process. The presence of different organic moieties around the metal ion, enhances the covalent character of the complex and in turn makes the complex more photo stable due to higher conjugation. Metal-organic complex exhibited strong absorptive optical nonlinearity due to RSA and negative refractive optical nonlinearity

CRediT authorship contribution statement

K.B Manjunatha: Investigation, Formal analysis, Writing - original draft, Writing - review & editing. Dileep Ramakrishna: Methodology, Formal analysis, Writing - original draft, Writing - review & editing. B.J. Rudresha: Formal analysis, Validation. Albin Antony: Methodology, Investigation. P. Poornesh: Conceptualization, Supervision, Project administration.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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¹: Authors contributed equally.

View full text

Design, synthesis and nonlinear optical characterization of novel mixed ligand ruthenium metal-organic complex

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Synthesis of complex

Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Opt. Mater.

Opt. Mater.

Opt. Mater.

Opt. Mater.

Chem. Phys. Lett.

Coord. Chem. Rev.

Inorg. Nucl. Chem. Lett.

J. Inorg. Nucl. Chem.

Opt. Mater.

Polyhedron

Optic Commun.

Optik

Dyes Pigments

Org. Electron.

Mater. Chem. Phys.

Optic Commun.

Dyes Pigments

Chem. Rev.

Nature

Dalton Trans.

Chem. Commun.

Adv. Optic Photon

Dalton Trans.

Chem. Commun. (J. Chem. Soc. Sect. D)

Opt. Quant. Electron.

Chem Plus Chem

ChemPhysChem

Phys. Chem. Chem. Phys.

Dalton Trans.

J. Phys. Chem. B

J. Am. Chem. Soc.

J. Am. Chem. Soc.