OPTOELECTRONIC HYBRID INORGANIC-ORGANIC MATERIALS

OPTOELECTRONIC HYBRID INORGANIC-ORGANIC MATERIALS

Linear Optics vs Non Linear Optics Linear optics- Optics of weak light : Light is deflected or delayed but its frequency is unchanged. Non-Linear optics- Optics of intense light : We are concerned with the effects that light itself induces as it propagates through the medium.

Non-Linear optics produces many exotic events Nonlinear optics allows us to change the color of a light beam, to change its shape in space and time, to switch telecommunications systems, and to create the shortest events ever made by Man Ex: Sending infrared light into a crystal yielded this display of green light

A light wave acts on a molecule, producing an harmonic vibration of the electronic cloud which then emits its own light wave that interferes with the original light wave. In Linear optics

In Non-Linear Optics If irradiance is high enough the electronic cloud vibrates anharmonically so that new frequencies are produced corresponding to the energy difference between populated states.

Optical wave manipulation is one of the future technologies for optical processing. It has various applications in fiber-optic communications and optoelectronics which makes it an increasingly important topic among electrical engineers. Applications: Optical phase conjugation Optical parametric oscillators Optical computing Optical switching Importance of NLO Optical data storage

Polarization Linear r P r = ε χ E 0 Non-linear (1) (2) 2 (3) 3 P = ε 0 χ E+ χ E + χ E +... P: induced polarization of medium ε 0 : dielectric constant of vacuum E: electric field χ (i) : succeptibilities of i order ω ω χ (2) 2ω ω = electric field oscillation frequency χ (2) = second order susceptibility χ (2) = 0 for centrosymmetric solids

Phenomenon Associated With Non-linear Optics Second harmonic generation (ω + ω = 2ω). Sum frequency generation (ω 1 + ω 2 = ω 3 ). Difference frequency generation (ω 1 - ω 2 = ω 3 ). Optical parameter amplification (ω 1 + ω 2 = ω 3 ). N wave mixing (ω 1 + ω 2 + + ω n = ω n+1 ).

Future Scope The field of Nonlinear Optics today has grown into a vast enterprise with a considerable potential for technological applications. The nonlinear optical (NLO) materials needed for optimized components, however, have not yet been realized. New nonlinear optical materials and devices are in various stages of development. Inorganic-Organic nonlinear optical materials are thought to play a key role in the future of NLO. Purely optical information processing looms on the horizon.

NLO efficiency measured with respect to a standard THE KURTZ-PERRY METHOD ω laser Nd 3+ :YAG 1064 or 1907 nm χ (2) 0 Powdered Sample SHG (Second Harmonic Generation) 2ω with I 2 ω χ(2) Sample Holder Elliptical mirror Nd3+: YAG LASER 1.06 µm Raman Cell Filled with H 2 1.91 µm Lens Lens Photomultiplier Filters Computer

The acentricity requirement constitutes a major impediment when attempting to engineer materials with large χ (2). About 75% of organic molecules crystallizes in centrosymmetric space groups In salts, however, Coulombic interactions could overwhelm the unfavorable dipole-dipole interactions and allow noncentrosymmetric assembly of polar ionic moieties In fact: Marder et al., Chem. Mater, 1994, 6, 1137 [DAMS][pTS] SHG = 1000 U U = urea, Reference Standard where: [DAMS] + = H 3 C N + H C N CH 3 3 [pts] - = p-ch 3 C 6 H 4 SO 3 - trans-4-[-4-dimethylaminostyryl]-1-methylpyridinium

The search for new ionic materials has been recently focused on inorganic-organic hybrids, which properly combine the advantages of the organic species to those of the inorganic ones. The most common classes of hybrid material for second order NLO applications are those where the inorganic and organic components are organized in layered structures, each layer being of purely inorganic or organic nature.

Clément et al. [J. Am. Chem. Soc., 2000, 122, 9444] [DAMS-type cat.][mcr(c 2 O 4 ) 3 ] M = Mn, Fe, Co, Ni, Cu XRPD: layered structure SHG 0 for 2/3 of the compounds Side view of the structure of [DAPS][MnCr(C 2 O 4 ) 2 ] CH 3 CN [DAPS] + = H 3 C N + H C N CH 3 CH 3 CH 3 Clément et al. [Science, 1994, 263, 658; Chem. Mater., 1996, 8, 2153] [DAMS-type cat.]/[mps 3 ] M = Mn, Cd, Zn XRPD: intercalated structure For 2 compounds SHG =[DAMS][pTS]

In this field certainly fall our work on the NLO properties of a new family of layered compounds: Ugo et al. [Adv. Mater., 2001, 1665] CuI in KI aq + [DAMS]I in CH 3 CN [DAMS][Cu 5 I 6 ] SHG = [DAMS][pTS] Inorganic part Intensity 6 10 20 30 40 2θ Organic part Absorbance J aggregation of the organic cromophores High values of SHG λ (nm)

[DAMS] + organization into J-aggregates

A selective self-recognition process between host and guests can be assumed in the formation of the layered structures. The former, on the average centrosymmetric, should not promote the non-centrosymmetric arrangement of guests into J-aggregates. Probably, the non-centrosymmetric arrangement of the localized charge of the J-aggregates of [DAMS + ] cations could both enforce spontaneous poling within one guest layer and impart a definite order to the host Cu(I) vacancies, eventually determining the orientation of the nearby guest layer, i.e. the formation of a macroscopic organization.

Similar layered compounds are obtained but the strength of SHG is controlled by the organic chromophore: [DAMS(2//)]I in CH 3 CN + CuI in KI aq [DAMS(2//)][Cu 5 I 6 ] [DAMS(2//)] + = H 3 C N H 3 C + N CH 3 XRPD Intercalated Structure UV J aggregates SHG = 10 UREA [DAZOP] + = [DAZOP]I in CH 3 CN + CuI in KI aq H 3 C N N + H 3 C N N CH 3 [DAZOP][Cu 5 I 6 ] XRPD Intercalated Structure UV J aggregates SHG = 0.4 [DAMS][pTS] The synthesis is not always reproducible. The intercalate is strongly contaminated by centrosymmetric [DAZOP][Cu 2 I 3 ]. [DAES]I in CH 3 CN + CuI in KI aq [DAES][Cu 5 I 6 ] [DAES] + = H 3 C H 3 C N N + CH 2 CH 3 XRPD Intercalated Structure UV NO J aggregates SHG = 0.25 UREA

When the chromophore is [DIBAMS] +, the steric hindrance of the butyl doesn t allow the formation of the inorganic layer and of J- aggregates leading to a centrosymmetric structure. CuI solid + [DIBAMS]I in CH 3 CN [DIBAMS][Cu 4 I 5 ] [DIBAMS] + = N + N CH 3

Ag(I) hybrid inorganic-organic materials [DAMS]I in CH 3 CN + AgI in KI aq [DAMS][Ag 2 I 3 ] Probably centrosymmetric SHG = nihil However, using a heterogeneous synthetic route: [DAMS]I in CH 3 CN + AgIsolid [DAMS][Ag 5 I 6 ] XRPD Intercalated Structure UV J aggregates SHG = [DAMS][pTS] Contaminated by 5% of a not yet characterized species

Prompted by the recent publications on organic and metalcoordination mechanochemical reactions in the absence of a solvent, we have investigated the solid state synthesis of the Ag(I) intercalated compound Ball milling [DAMS]I + 5AgI [DAMS][Ag 5 I 6 ] 9 h at r.t. low cristallinity Intensity (Counts, a.u.) After 9 h After 7 h After 4 h After 2.5 h 7 14 2Theta (deg) 21 27 Manually mixed reactants

XRPD Intercalated Structure [DAMS][Ag 5 I 6 ] Prepared by 9 h ball milling Abs 400 500 600 700 800 UV Wavelength[nm] J Aggregates BUT SHG = 0.5 UREA

The apparent disagreement between NLO efficiency and presence of J aggregates can be rationalized considering that: NLO: Necessitating a macroscopic polarity, solid state second order NLO is sensitive to both intraand inter-layer guests (organic chromophores) ordering XRPD: Only detects host structural organization (inorganic slabs) UV: Evidences just guests intra-layer disposition (J aggregation)

Our results indicate that: Presence of J aggregates intra-layer guests ordering has already taken place Poor SHG response inter-layer ordering: i) Has still to be completely accomplished ii) Is somehow contrasted by a prolonged mechanical treatment iii) Necessitates a successive thermal treatment In fact: [DAMS]I + 5 AgI ball milling 30 min. [DAMS][Ag 5 I 6 ] 160 C 3h SHG = [DAMS][pTS] Intensity (Counts, a.u.) After 9 h ball-milling After heating 7 14 2Theta (deg) 21 27

Stimulated by these results we have applied the same synthetic route to [DAZOP] + and [DAES] + chromophores with Cu(I) and Ag(I) : ball milling 30 [DAZOP]I + 5 MI [DAZOP][M 5 I 6 ] 160 C 3h ball milling 30 UV J aggregates SHG = 0.4 [DAMS][pTS] [DAES]I + 5 MI [DAES][M 5 I 6 ] M = Ag, Cu 160 C 3h UV NO J aggregates SHG = 0.25 UREA The mechanochemical synthesis, reproducible, is the only appliable one to prepare pure [DAZOP][Cu 5 I 6 ] and [DAES][Ag 5 I 6 ]. It seems that, in the case of both Cu(I) and Ag(I) the ethyl group of [DAES] + hampers the organization of chromophores into J aggregates, with concomitant low NLO activity.

In conclusion We have prepared a new family of layered hybrid materials characterized by giant second order NLO properties. We have also successfully applied, for the first time, a solid state synthetic route for these materials. We have conveyed spectroscopic, SHG and structural evidences that, in the chromophore self-organization process, intra-layer ordering precedes inter-layer one, i.e. that a step-by-step organisation occurs. In addition, this self-assembling process is highly influenced by the steric hindrance of the organic chromophore itself.