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Third-order NLO properties of ultrathin films containing cationic phthalocyanine and Keggin polyoxometalates fabricated using layer-by-layer deposition from aqueous solution

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Abstract

Composite films with alternating layers (PAH/PSS)3(AB/POM)n (PAH = polyallylamine hydrochloride, PSS = polystyrene sulfonate) derived from Alcian Blue-tetrakis(methyl-pyridinium) chloride (abbreviated as AB) and Keggin type polyoxometalates (POM = H4SiW12O40, H3PW12O40, H3PMo12O40, H5PMo10V2O40) have been fabricated and characterized. Under laser irradiation at 532 nm with a pulse duration of 6–7 ns, a repetition rate of 10 Hz and the intensity of the light at focus E0 being 10 μJ, the composite films exhibit self-defocusing behavior and saturated absorption effects, and the nonlinear optical absorption coefficient β (m W−1) and refractive index n2 (m2 W−1) of the films are 4–5 times larger than those of pure AB solution in view of their magnitude. Interestingly, it is found that third-order NLO susceptibilities χ(3) of films are in the order of χ(3)(AB/PSS) < χ(3)(AB/SiW12) < χ(3)(AB/PW12) < χ(3)(AB/PMo12) < χ(3)(AB/PMo10V2), which is reversed to the order of ELUMO(SiW12) > ELUMO(PW12) > ELUMO(PMo12) > ELUMO(PMo10V2), affirming that the incorporation of different Keggin type POMs of a lower LUMO energy level with phthalocyanine molecules into multilayers could tune the NLO responses of phthalocyanine films. It is concluded that the lower LUMO level of POM than that of the phthalocyanine can stimulate the easier transformation of excited electrons from AB to the POM within the donor–acceptor system (phthalocyanine molecules acted as an electron donor while POMs as an electron acceptor in the composite films) when flashed with the laser, which is thought to be accountable for the profound third-order optical nonlinearity of the composite films.

Graphical abstract: Third-order NLO properties of ultrathin films containing cationic phthalocyanine and Keggin polyoxometalates fabricated using layer-by-layer deposition from aqueous solution

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Publication details

The article was received on 26 Jul 2017, accepted on 21 Sep 2017 and first published on 21 Sep 2017


Article type: Research Article
DOI: 10.1039/C7QI00438A
Citation: Inorg. Chem. Front., 2017, Advance Article
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    Third-order NLO properties of ultrathin films containing cationic phthalocyanine and Keggin polyoxometalates fabricated using layer-by-layer deposition from aqueous solution

    H. M. Asif, N. Qu, Y. Zhou, L. Zhang, F. K. Shehzad, Z. Shi, Y. Long and S. U. Hassan, Inorg. Chem. Front., 2017, Advance Article , DOI: 10.1039/C7QI00438A

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