Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials.

Alessandra Forni,Gabriele Di Carlo,Francesca Tessore,Francesca Limosani,Pietro Tagliatesta

doi:10.3390/ma14164404

Abstract

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence.

Highlights

In the last two decades, many organic and organometallic molecular chromophores have attracted attention in the scientific community for their significant second-order nonlinear optical (NLO) properties, mainly arising from push–pull structures as donor—π-delocalized spacer— acceptor systems [1,2]
In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P, carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer
Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for porphyrin–C60 dyads (P-C60) dyads and Fc-P-C60 triads, our electric-field-induced second-harmonic generation (EFISH) results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence

Summary

Introduction

In the last two decades, many organic and organometallic molecular chromophores have attracted attention in the scientific community for their significant second-order NLO properties, mainly arising from push–pull structures as donor—π-delocalized spacer— acceptor systems [1,2]. The four meso, the eight β-pyrrolic, and the two axial positions allow a wide variety of chemical functionalizations, so that many different substituents can be linked to the core and to the metal center. By changing the metal center, its oxidation state, the type of the axial ligands, the nature of the substituents at the periphery of the macrocycle, the flexibility of the synthetic process and of structural diversification can be exploited to achieve a fine-tuning of the electronic properties and a large second-order NLO response [3]. The non-negligible role of third-order contributions to the quadratic hyperpolarizability of A4 β-substituted ZnII porphyrins was highlighted [17]

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Conclusion