Heavy atom effect on nonlinear absorption and optical limiting characteristics of 5,10,15,20-(tetratolyl) porphyrinato phosphorus (V) dichloride

Abstract

Optical limiting performance and third-order nonlinearity X⁽³⁾ are investigated in 5,10,15,20-(tetratolyl) porphyrinato phosphorus (V) dichloride ([(TTP)P^VCl₂]⁺). Heavy atom effect exerted by the two axial chlorides is found to result in low fluorescence yield (ø_fl), shorter lifetimes of S₁,T₁ and faster intersystem crossing (ISC), leading to larger excited state absorption (ESA) from T₁→T_n. This phenomenon is found to lower the limiting threshold by 30 times and increase the second hyperpolarizability by one and three orders in ps and ns time regimes, respectively.