A multitechnique investigation of the second order NLO response of a 10,20-diphenylporphyrinato nickel(II) complex carrying a phenylethynyl based push-pull system in the 5- and 15-positions

Abstract

A multitechnique investigation of the determination of the order of magnitude of the second and third order NLO response of [5-[(4-dimethylaminophenyl)ethynyl]-15-[(4nitrophenyl)ethynyl]-10,20-diphenylporphyrinato]nickel(II) (1) is reported with the aim to produce self consistent evidence for a significant NLO response of this kind of push-pull porphyrin chromophore. The experimental multitechnique approach is based on the EFISH technique, working with a nonresonant incident wavelength of 1.907 μm, on the solvatochromic method and finally on a vibrational method, avoiding any fluorescence or resonance interference. A theoretical MNDO-TDHF evaluation of the zero-frequency quadratic and cubic hyperpolarizabilities of an ab initio optimized planar structure is also reported. The order of magnitude of the quadratic hyperpolarizability of (1) at zero frequency (β 0 ), was found to be significantly lower than that reported for the corresponding Cu(II) or Zn(II) complexes with the same push-pull porphyrin chromophore.

Porphyrins for Second Order Nonlinear Optics (NLO): An Intriguing History §

“…An exceptionally high quadratic hyperpolarizability β was reported by Therien et al [10,11] for the Cu II (2) (β = 1501 × 10 −30 esu) and particularly for the Zn II (3) (β = 4933 × 10 −30 esu) complexes ( Figure 1) measured by the HRS technique with a resonant incident wavelength of 1064 nm. Later the β value of 3, deduced by absorption and electroabsorption data (Stark effect), was reported to be lower (1710 × 10 −30 esu) [11] and lower values for the Ni II porphyrin 1 (β about 80-100 × 10 −30 esu) were measured also by the EFISH technique working in CHCl3 with a non-resonant incident wavelength of 1907 nm [13].…”

“…For this reason, in the particular case of electronically complex chromophores such as porphyrins, showing a strong absorption B band (Soret) at 400-500 nm and two or more Q bands between 600 nm and 700 nm, the discussion and the comparison of results obtained using a single technique or under different experimental conditions can be misleading, as was reported by some of us in 2004 [13]. In order to avoid these drawbacks, we have always measured the second order NLO response of our porphyrin chromophores by the EFISH technique, working with a non-resonant incident wavelength of 1907 nm.…”

“…Among the many examples reported in the literature [6,7], 2D architectures based on π-delocalized macrocycles such as porphyrins and metal porphyrins [8][9][10][11][12][13] have attracted great attention due to their thermal and chemical stability, their good solubility, and their potential processability as layers [14]. Moreover, through their polarizable π-conjugated ring, acting as a linker, they can induce a facile electronic exchange within a push-pull system, as required for large second order NLO response [15].…”

“…In addition, the architectural flexibility of porphyrins allows a large number of structures reported in the literature, as well as a large variety of substituents to be attached at the meso or β-pyrrolic positions of the porphyrin ring [10][11][12][13]16] or to the axial position of a metal porphyrin [17].…”

“…The correct determination of the quadratic hyperpolarizability of asymmetric porphyrins and metal porphyrins is of major importance. In fact, β can be measured by many different techniques, such as HRS (Hyper Rayleigh Scattering) [10], Stark effect [11], EFISH (Electric Field Second Harmonic Generation), and solvatochromic analysis [8,9,12,13,19]. Depending on the incident wavelength, these measurements can be affected by resonance [8,9] and in the case of the HRS technique, also by a fluorescent contribution to the second harmonic emission [10].…”