Determination of the quadratic hyperpolarizability of trans-4-[4-(dimethylamino)styryl]pyridine and 5-dimethylamino-1,10-phenanthroline from solvatochromism of absorption and fluorescence spectra: a comparison with the electric-field-induced second-harmonic generation technique

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

“…The parallel use of absorption and emission solvatochromism does not require the direct evaluation of the radius of the cavity a occupied by the solute in the solvent which, when calculated empirically or even from known structures of structurally related compounds, may be the origin of major discrepancies [11].…”

“…Since A and C, like B and D, are constant for a specific absorption transition of a given molecule, assuming in first approximation μ e -μ g as a constant independent from the solvent, a suitable fitting of experimental data to Equations 2 and 3 yields both B and D, thus allowing an estimate of Δμ eg = μ e -μ g by a two-equation system [11]. In this way an empirical evaluation of a, which is usually the source of large errors, is not required.…”

“…The value of the ground state dipole moment μ is relevant for the determination of the quadratic hyperpolarizability by the most used experimental methodologies (Stark effect [6], EFISH [7,10] solvatochromic method [11]). However we were unable to measure experimentally the dipole moment of (1) in CHCl 3 solution following the Guggheneim method [19] due to the lack of reproducibility of the measurements as already reported for other push-pull porphyrinic systems [10].…”

“…Therefore the solvatochromic investigation of (1), which allows determination of the charge transfer quadratic hyperpolarizability β CT along the direction of the major contributing charge transfer transitions [11], should give values of β CT comparable, as order of magnitude, to EFISH β 1.907 , being the dipole moment direction quite coincident with the major charge transfer axis [6].…”

“…1) using the EFISH technique, working with a non-resonant incident wavelength of 1.907 μm. In parallel we have used also the solvatochromic method [11] and a vibrational method [12] not affected by fluorescence or resonance interferences. The investigation was carried out on the Ni(II) (1) complex because the only EFISH investigation reported working with a non-resonant incident wavelength of 1.907 μm, for the determination of the quadratic hyperpolarizability of similar push-pull porphyrin chromophores, was carried out on Ni(II) complexes [7].…”