Femtosecond nonlinear optical properties of polycyclic aromatic hydrocarbon-based Benzo[e]pyrene derivatives

Abstract

We herein report our results on the nonlinear optical (NLO) properties of three polycyclic aromatic hydrocarbons (PAHs) based benzo[e]pyrene derivatives namely 10-phenylbenzo[e]pyrene (BP1), 13-fluoro-10-(4-fluorophenyl)benzo[e]pyrene (BP2), and 13-methoxy-10-(4 methoxyphenyl)benzo[e]pyrene (BP3). Using experimental techniques such as UV–Visible absorption, Z-scan technique, and theoretical time-dependent density functional theory (TDDFT), we have investigated the linear absorption, NLO coefficients, second hyperpolarizability, and optical limiting onset of these molecules. The ultrafast nonlinear Z-scan experiment was performed using ∼70 fs pulsed laser with 800 nm as central wavelength. Using the three-level model analysis based on rate equations, the contribution of different nonlinear processes contributing to nonlinear absorptions in these molecules is elucidated. All three molecules exhibited strong reverse saturable absorption due to mixed contribution of two-photon absorption (2PA) and three-photon absorption (3PA) with 2PA and 3PA coefficients of (1.26–1.79) × 10−11 cm/W and (6.23–7.39) × 10−5 cm3/GW2, respectively. The closed-aperture Z-scan data for all the examined molecules depicted valley-peak signature, which indicated a positive refractive index. The second hyperpolarizability was calculated with magnitude observed ∼10−32 esu. Using the TDDFT calculation, the complete optimization of the individual structure of molecules was achieved and the results matched with experimental observations.