Tunable conversion from saturable absorption to reverse saturable absorption in poly (pyrrole methine) derivatives

Abstract

Four kinds of poly (pyrrole methine) derivatives were synthesized. Nonlinear optical absorption studies of these polymers are investigated at 800 nm with the Z-scan technique and femtosecond laser pulses. These derivatives show tunable conversion from saturable absorption (SA) to reverse saturable absorption (RSA). The conversion from SA to RSA depends on not only the intensity but also the polymer structure. Electronic donor methyl groups in the pyrrole methine chain enhance the electron density distribution in the backbone of the polymer, and electron-rich thienyl group improves electron transition. These groups lead to a red shift in linear absorption, a reduction of E_g and an improvement of electron transition and nonlinear absorption coefficient β.