*2.4. Formation Constant*

The formation constant of the investigated CT complexes was determined using the modified Benesi–Hildebrand method [19] using the following Equation (1):

$$\mathbf{I}\left[\mathbf{A}\_{0}\right]/\text{A}=\mathbf{1}/\text{c}^{\text{AD}}+\mathbf{1}/\mathbf{K}\_{\text{c}}\cdot\mathbf{c}\times\mathbf{1}/\mathbf{D}\_{0}\tag{1}$$

where '[Ao]' is the molar concentration of the acceptor ChA or DDQ, 'Do' is the molar concentration of the donor (PA); 'A' is the absorbance of the formed CT complexes at λ max; 'E' is the molar absorptivity of the complexes; and 'Kc' is the association constant of the complexes (L mol<sup>−</sup>1).
