Evaluation of the parameters of 1:1 charge transfer complexes from spectrophotometric data by non-linear numerical method

Abstract

The non-linear numerical method for evaluation of equilibrium constants and molar extinction coefficients of molecular complexes from a spectrophotometric experiment is described, which in contrast to linear models has no limitations with respect to concentrations of the components. The proposed procedure is applied to donor–acceptor interaction in solution between N-ethyl carbazole (EtCz) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or n-hexyl 2,5,7-trinitro-9-dicyanomethylenefluorene-4-carboxylate (HexDTFC) to evaluate the method and to obtain the parameters of charge transfer complexes (CTCs) formation. Association constants ( K) and molar extinction coefficients ( ε) of CTCs derived from non-linear approach (EtCz–TCNQ: K=2.49±0.19 M −1; ε=2950±160 M −1 cm −1. EtCz–HexDTFC: K=12.1±0.3 M −1; ε=1335±24 M −1 cm −1) are close to that from linear models but show lower standard errors in parameter estimations.