Impact of Substitution Position on the Excited-State Dynamics and Nonlinear Optical Properties of Tetraphenylethylene-Corroles.

Abstract

Investigating the structure-property relationship in π-conjugated organic materials is crucial for designing efficient materials for diverse optoelectronic applications. Tailoring the molecular structure enables tuning the nonlinear optical (NLO) properties of π-conjugated systems. Herein, we report the synthesis, characterization, and photophysical properties of tetraphenylethylene (TPE)-substituted corroles in meso (meso-TPE-Cor) and beta position (β-TPE-Cor). The excited state dynamics, investigated using femtosecond transient absorption spectroscopy (fs-TAS) with excitation at the Soret band (400 nm), revealed an internal conversion in the 250-303 fs range, vibrational relaxation (VR) in 7.1-12.7 ps range, an intersystem crossing (ISC) in 0.94-1.05 ns range, and the triplet lifetime in 0.111-0.126 µs range. Comparatively, β-TPE-Cor exhibited faster ISC and VR than meso-TPE-Cor. Furthermore, the NLO properties of both the corroles were investigated using the femtosecond Z-scan technique. Both the corroles exhibited significantly strong NLO parameters, characterized by prominent three-photon absorption (3PA) coefficients (∼10^-4 cm³/GW²), high nonlinear refractive index (n₂ ∼10^-14 cm²/W), and hyperpolarizabilities (γ ∼ 10^-30 esu). We observed that substituting the same TPE substituent in the β position demonstrated better NLO properties. Furthermore, as a proof-of-concept application, we investigated the optical limiting onset threshold of both the corroles, which exhibited superior performance compared to previously reported organic materials, highlighting its application in various photonic devices.