A remarkable study to unveil the relationship between fluorescence life time decay(ns) and nonlinear optical parameters of series of porphyrin and polyoxometalates hybrids

Relationship between excited state dynamics and nonlinear optical (NLO) parameters is very unique. Herein, three different polyoxometalates (POMs) namely WD-POM (Wells-Dawson POM) based porphyrin hybrids WDPOM3PyP, Trans-2WDPOM2PyP, and 3WDPOMPyP (having one, two, and three WD-POM respectively), and their porphyrin precursors with (Trishydroxyl amino methane) namely Tris3PyP, Trans-2Tris2PyP, and 3TrisPyP respectively have been used for the study. Fluorescence decay and Z-scan studies by using nanosecond (ns) time span conveys the corresponding lifespan for each excited state, along with the NLO analysis respectively. The calculated lifetime data were found in the range of 3WDPOMPyP (τ1 = 5.65 ns), Trans-2WDPOM2PyP (τ1 = 2.21 ns), and WDPOM3PyP (τ1 = 1.96 ns). Third order NLO measurements represented that WDPOM3PyP showed better NLO response (χ3 = 2.26 × 10-10esu and β = 1.54 × 10-5 esu) as compared to Trans-2WDPOM2PyP (χ3 = 1.73 × 10-10 esu and β = 1.53 × 10-5 esu), and 3WDPOMPyP (χ3 = 1.55 × 10-10 esu and β = 0.65 × 10-5 esu) obtained at wavelength of 532 nm. Electrochemical studies have shown that the minor energy differences between the singlet and triplet excited states are responsible for intercrossing system (ISC) that helps in the transfer of electrons from porphyrin moiety to WD-POM. By absorbing a photon, the excited species were produced causing an initial charge transfer. This charge transfer state undergoes an electron transfer decaying to the lowest triplet state, and singlet state causing an increase in NLO. The obtained results indicated potential uses in photonic and all-optical switching devices.

Designing diverse coordination modes for the covalent attachment of Wells-Dawson type polyoxometalate onto porphyrins

Five covalently bonded polyoxometalate (POM)-porphyrin hybrids were synthesized by reacting the Wells-Dawson type polyoxometalate [N(C4H9)4]5H4P2W15V3O62 with five tris-functionalized porphyrins containing different numbers of tris groups at different peripheral positions. These hybrids were thoroughly characterized using elemental analysis, NMR (1H, 31P, and 51V), mass spectrometry (ESI-MS, MALID-TOF-MS), FT-IR, UV-Vis, and fluorescence spectroscopies. The results proved that different quantities (one, two, and three) of the vanadium-capped Wells-Dawson type metal-oxide cluster P2W15V3O629- can be grafted onto a porphyrin moiety via covalent bonding with different orientations, depending on the number and position of peripheral functional groups on the porphyrin. Interestingly, remarkable fluorescence quenching (60% in 3Py-P@1POM, 75% in trans-2PyP@2POM, 80% in cis-2PyP@2POM, 85% in cis-2PhP@2POM, and 55% in 1Py-P@3POM, as compared to the fluorescence intensity of their corresponding porphyrin precursor) was observed under excitation (λexc = 328 nm), indicating electron transfer from the porphyrin moiety to the POM moiety through covalent linkage.

Porphyrins and Polyoxometalate Scaffolds

Polyoxometalates (POMs) can act as unique reservoirs for multiple electron transfers. As POMs display only weak absorption in the visible spectrum, they can be associated with chromophores such as porphyrins and porphyrin antennae. In this Minireview, the research dedicated to the combination of porphyrins and polyoxometalates is put in context and the state of the art identifying the challenges addressed in the optimization of hybrid materials for applications is detailed.

More Than 50-Fold Enhanced Nonlinear Optical Response of Porphyrin Molecules in Aqueous Solution Induced by Mixing Base and Organic Solvent

The difference absorption spectrum (DAS) of porphyrin molecules (tetraphenyl-porphyhrin sulfonic acid, TPPS) in aqueous solution induced by continuous wave laser irradiation has been reported previously. It was interpreted that the DAS was caused by the formation of TPPS aggregates induced by laser irradiation. However, transient spectra similar in their shape have already been reported and are attributed to the excited-state absorption and saturable absorption (SA) effects due to the triplet state formation in TPPS. In the present study, we investigated the triplet quenching effect by O2 on the DAS of TPPS aqueous solution and revealed that it originated from the triplet state formation. We also found that mixing the appropriate amount of MeOH and NaOH in TPPS aqueous solution increased its absorbance change by more than 50 times. This may be due to the decrease in dissolved oxygen concentration by mixing them. This result suggests the possibility of controlling the performance of NLO materials by adjusting the solvent mixture ratio and base/acid concentration.

From Simplicity to Complexity in Grafting Dawson-Type Polyoxometalates on Porphyrin, Leading to the Formation of New Organic-Inorganic Hybrids for the Investigation of Third-Order Optical Nonlinearities

Four new organic-inorganic hybrids, [N(C₄H₉)₄]₅H[{HNC₂O(CH₂O)₃P₂V₃W₁₅O₅₉}C₄₄N₄H₂₉O₃] (TPPOH-1POM), [N(C₄H₉)₄]₁₀H₂[{HNC₂O(CH₂O)₃P₂V₃W₁₅O₅₉}₂C₄₄N₄H₂₈O₂] (TPPOH-2POM trans), [N(C₄H₉)₄]₁₀H₂[{HNC₂O(CH₂O)₃P₂V₃W₁₅O₅₉}₂C₄₄N₄H₂₈O₂] (TPPOH-2POM cis), and [N(C₄H₉)₄]₁₅H₃[{HNC₂O(CH₂O)₃P₂W₁₅V₃O₅₉}₃C₄₄N₄H₂₇O] (TPPOH-3POM), have been synthesized by covalently grafting the Dawson-type polyoxometalate (POM) [N(C₄H₉)₄]₅[H₄P₂W₁₅V₃O₆₂] onto new porphyrins N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]-4-[10,15,20-tris(4-hydroxyphenyl)porphyrin-5-yl]benzamide (TPPOH-1Tris), 4,4'-[5,15-bis(4-hydroxyphenyl)porphyrin-10,20-diyl]bis[ N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide] (TPPOH-2Tris trans), 4,4'-[10,15-bis(4-hydroxyphenyl)porphyrin-5,20-diyl]bis[ N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide] (TPPOH-2Tris cis). and 4,4',4″-[20-(4-hydroxyphenyl)porphyrin-5,10,15-triyl]tris[ N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide] (TPPOH-3Tris), respectively, in N, N-dimethylacetamide under nitrogen. The hybrid compounds were thoroughly characterized by elemental analysis, FT-IR, NMR (¹H, 2D NOESY, ³¹P, and ⁵¹V), ESI-MS, MALDI-TOF-MS, UV-vis, and fluorescence spectroscopy. All porphyrins and their corresponding hybrids exhibited remarkable third-order nonlinear-optical responses under laser irradiation, with the intensity of light at focus E₀ being 4.2 μJ at wavelength 532 nm, pulse duration τ = 6 ns, and repetition rate 10 Hz. The molecular second hyperpolarizability (γ) values of the hybrids (TPPOH-1POM, TPPOH-2POM trans, TPPOH-2POM cis, TPPOH-3POM) were calculated to be 8.48 × 10^-28 esu, 8.94 × 10^-28 esu, 10.16 × 10^-28 esu, and 8.93 × 10^-28 esu, while the molecular second hyperpolarizability (γ) of their corresponding porphyrin precursors (TPPOH-1Tris, TPPOH-2Tris trans, TPPOH-2Tris cis, and TPPOH-3Tris) were 7.19 × 10^-28 esu, 8.09 × 10^-28 esu, 9.07 × 10^-28 esu, and 7.24 × 10^-28 esu, respectively. The γ values of the cis forms were found to be superior to those of all other compounds, indicating the significant role of the greater dipole moment and low symmetry of the cis form compared to other compounds. It was also found that the fluorescence intensity was decreased by 81.52%, 90.37%, 93.93%, and 84.62% for the hybrids TPPOH-1POM, TPPOH-2POM trans, TPPOH-2POM cis, and TPPOH-3POM with respect to their corresponding precursors, respectively, which reveals the Dawson-type POM as a strong quencher. This quenching phenomenon not only indicates again unequivocally the formation of hybrid compounds but also may imply a photoinduced electron/energy-transfer process favored from a porphyrin moiety to a Dawson-type POM moiety.

Poly(arylene ether)s with aromatic azo-coupled cobalt phthalocyanines in the side chain: synthesis, characterization and nonlinear optical and optical limiting properties

A novel poly(arylene ether) with azo-coupled cobalt phthalocyanine in the side chain (PAE-azo-CoPc) was prepared by 1,2-benzodinitrile, anhydrous cobaltous chloride and a novel azobenzene-containing poly(aryl ether) (PAE-azo-DCN) via a nucleophilic substitution polycondensation based on a novel bisfluoro monomer, 4-[(3,4-cyanophenyl)diazenyl]phenyl-2,6-difluorobenzoate. The obtained polymers were characterized and evaluated by FT-IR, ¹H NMR, DSC and TGA. PAE-azo-CoPc exhibited higher glass transition temperature and better thermal stability than PAE-azo-DCN because of the introduction of cobalt phthalocyanine groups. The results of Z-scan measurements demonstrated that PAE-azo-CoPc showed reversible saturable absorption and positive refraction, and PAE-azo-DCN showed saturable absorption and negative refraction. By calculation, PAE-azo-CoPc exhibited larger third-order nonlinear optical susceptibilities than that of PAE-azo-DCN. The results of optical limiting measurements demonstrated that the PAE-azo-CoPc exhibited an excellent optical limiting response.

A novel poly(arylene ether) with azo-coupled cobalt phthalocyanine in the side chain was prepared by 1,2-benzodinitrile, anhydrous cobaltous chloride and a novel azobenzene-containing poly(aryl ether).

Functional polyoxometalates from solvothermal reactions of VOSO4 with tripodal alkoxides – a study on the reactivity of different “tris” derivatives

A facile synthetic procedure for functional polyoxovanadates is reported. Furthermore, this study shows different possible binding modes of amino functionalised tris(hydroxymethyl)methane derivatives on polyoxovanadates.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Application of Near-IR Absorption Porphyrin Dyes Derived from Click Chemistry as Third-Order Nonlinear Optical Materials

Recently, third‐order nonlinear properties of porphyrins and porphyrin polymers and coordination compounds have been extensively studied in relation to their use in photomedicine and molecular photonics. A new functionalized porphyrin dye containing electron‐rich alkynes was synthesized and further modified by formal [2+2] click reactions with click reagents tetracyanoethylene (TCNE) and 7, 7, 8, 8‐tetracyanoquinodimethane (TCNQ). The photophysical properties of these porphyrin dyes, as well as the click reaction, were studied by UV/Vis spectroscopy. In particular, third‐order nonlinear optical properties of the dyes, which showed typical d‐π‐A structures, were characterized by Z‐scan techniques. In addition, the self‐assembly properties were investigated through the phase‐exchange method, and highly organized morphologies were observed by scanning electron microscopy (SEM). The effects of the click post‐functionalization on the properties of the porphyrins were studied, and these functionalized porphyrin dyes represent an interesting set of candidates for optoelectronic device components.

Chiral polyoxomolybdate-based hybrid compounds obtained by spontaneous resolution: syntheses, structures and non-linear optical properties

By spontaneous resolution, two chiral hybrid 2D architectures [MMo₆O₂₁(glycine)₃]²⁻ (M = Te 1, Se 2) were obtained, which show an SHG efficiency of about 3.5 and 3.7 × KDP.

Lanthanide-supported molybdenum–vanadium oxide clusters: syntheses, structures and catalytic properties

Three new species, originating from β-[Mo₆V₂O₂₆]⁶⁻ polyoxoanion and lanthanides, as heterogeneous catalysts exhibit good catalytic activities toward the cyanosilylation reaction.

Structures and third-order nonlinear optical properties of two three-dimensional Cd(ii) coordination polymers with trinodal (3, 4, 5) and dinodal (4, 5) connected network topologies

We reported two Cd(ii) coordination polymers with trinodal (3, 4, 5) and dinodal (4, 5) connected network topologies. Two compounds exhibit very strong NLO absorption in thin films and solution.

Fabrication and optical nonlinearities of composite films derived from the water-soluble Keplerate-type polyoxometalate and chloroform-soluble porphyrin

Porphyrin–POM composite films fabricated using a LBL approach show notable nonlinear saturated absorption and self-defocusing effects.