Charge-Transfer States Determine Iron Porphyrin Film Third-Order Nonlinear Optical Properties in the near-IR Spectral Region

Abstract

Femtosecond degenerate four-wave mixing (DFWM) was used to study third-order nonlinear optical properties of electropolymerized Fe(III) tetrakis(p-hydroxyphenyl)porphyrin films. Third-order nonlinear susceptibility χ 1111 (3) (-ω;ω,ω,-ω) was determined at 760-1350 nm. Susceptibility χ (3) values for a 500 nm thick porphyrin film ranged between (2-15)×10 -20 m 2 V -2 ((1.4-10.7)×10 -12 esu). The time response of electronic nonlinearities was faster than 120 fs. The sum-over-states model was applied to determine real and imaginary components for χ (3) and molecular second hyperpolarizability, γ. At wavelengths <800 nm, porphyrin film χ (3) is enhanced due to the 700 nm one-photon charge-transfer (CT) band. Nonlinear properties at longer wavelengths are determined by a two-photon resonance with a 17 400 cm -1 state. This state was not observed for other porphyrins and is attributed to a two-photon CT transition. Due to the resonance with the twophoton state, porphyrin Im χ (3) and two-photon absorption cross-section δ increased about 10 times when compared to values in the long-wavelength limit. Because of the contributions of the two-photon state, real component Re χ (3) had a negative sign in the near-IR spectral range; Re χ (3) ≈ -6×10 -20 m 2 V -2 at 9000-13 000 cm -1 . Results suggest that transition metal CT states can improve third-order nonlinear properties of organic materials.

Excited-state absorption and ultrafast relaxation dynamics of protoporphyrin IX and hemin

“…Moreover, the increased density of vibronic states reduces the lifetime of substituted porphyrins relative to porphine, increasing the width of the absorption bands. 50,51 Finally, in a nearly saturated hemin solution it has been possible to observe a broad band, extending from 800 to 1400 nm and centered at around 1000 nm (see the inset in Fig. To the best of our knowledge, free hemin in water solution occurs as a pentacoordinate high spin complex, 48,49 where water/hydroxyl appears as the fifth coordination ligand.…”

Thermal Behavior of Free‐Base and Core‐Modified Bicyclo[2.2.2]octadiene‐Fused Porphyrins

“…The inner mixture was concentrated, and the residue was chromatographed on silica gel (10 % EtOAc/hexane) to give 20. 2,6 ]undec-8-en-3-one (9.01 g, 50.0 mmol) in dry THF (130 mL) was slowly added a solution of LDA (2.0  in THF, 30.0 mL, 60.0 mmol) at -78°C under an atmosphere of nitrogen, and the mixture was stirred for 20 min at the same temperature. To this mixture was added a solution of PhSeBr (14.16 g, 60.0 mmol) in dry THF (30 mL) with stirring.…”

“…For example, porphyrinoids utilized for photodynamic therapy (PDT) of tumors [1] are desired to have strong absorption bands in the red region (over 650 nm) for light transparency in living cells, in addition to the ability to generate singlet oxygen by light irradiation, [2] tumor-tissue selectivity, [3] and nontoxic nature in the dark. [4] Requisites of a large absorption cross section for multiphoton absorbing materials [5] and of a large χ 3 coefficient for third-harmonic generation [6] are other examples. Tuning of their molecular electronic structures is mainly achieved by the following methods: introduction of electron-withdrawing and electron-donating groups, [7] deformation of the porphyrin ring by bulky substituents, [8] dissymmetrization of the π-electron system by partial breakage of the extra π bonds, [9] expansion of the porphyrin π system, [10] and substitution of the porphyrin core nitrogen atoms by other atoms involving oxygen, sul-rin derivative preferentially existed.…”

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

“…Materials with nonlinear optical (NLO) properties and fast response to laser irradiation, as well those as with merits such as small optical loss, high optical quality, good stability, low cost and ease of preparation, have attracted increasing attention owing to their potential applications in ultrafast optical switching, optical communication, optical modulators, and optical limiting . The chemist's goal in this work is to design molecules and materials with high nonlinear coefficients and develop models that can predict these characteristics from the molecular structure . Discovering organic molecules with large nonlinear responses is an active pursuit, and properties are often manipulated by making structural modifications to donor and acceptor building blocks, as well as to conjugated linking π‐units …”