## 3 Results
### Charge Transfer Complex in Solution
#### 3.1.3 Spectroscopic Physical Parameters  
The oscillator strength (\(f\)) Equation (2) [7,17], and the transition dipole moment (\(\mu\), Debye) Equation (3) [7] of each complex were determined according to the equations:  
\[\mathbf{f}=\mathbf{4.32}\times\mathbf{10}^{-9}[ \epsilon_{max}\;\Delta\
u_{1/2}] \tag{2}\]  
and  
\[\mu=\mathbf{0.0958}\left[\frac{\epsilon_{max\Delta\
u_{1\over 2}}}{ \overline{v}_{max}}\right]^{1/2} \tag{3}\]  
where \(\Delta\
u_{1/2}\) is the bandwidth at half intensity, \(\epsilon_{max}\) is the molar extinction coefficient, and \(\overline{v}_{max}\) is the wavenumber at the absorbance maximum of the complex. The values of these parameters are shown in Table 2. The relatively high values of \(f\) (0.989 for Q-DDQ and 0.163 for Q-TCNQ) indicate a high interaction between Q and DDQ or TCNQ, which translates to the high stability of the two complexes. Furthermore, high values were observed for transition dipole moment, 10.09 for Q-DDQ and 5.41 for Q-TCNQ, indicating  
Figure 4: The 1:1 Benesi-Hildebrand Plot for Q-DDQ and Q-TCNQ CT complexes system. (Ca and Cd: initial concentration of acceptor, and donor, and A: absorbance). where \(v_{CT}\) is the wave number in cm\({}^{-1}\) related to the CT band formed due to the reaction between Q and the acceptors. The \(I_{P}\) values contributing to the CT complex formation are given in Table 2. The electron donation potential of Q is indicated by its \(I_{P}\). As the \(I_{P}\) decreases, the electron donation power of Q increases and, consequently, the stability of the CT complex increases. The ionization potentials were found to be 8.91 and 7.57 for Q-DDT and Q-TCNQ, respectively, and thus the stability follows the order: Q-DDQ >Q-TCNQ. **Energy of CT complex**: The energy (\(E_{CT}\)) of the CT complexes was estimated using the Equation (5) below [17]:  
\[E_{CT}=Iw_{CT}=1243.667/\lambda_{CT} \tag{5}\]  
where \(\lambda_{CT}\) is related to the wavelength of the complexation band. The obtained energy values were 2.56 ev and 1.47 ev for Q-DDQ and Q-TCNQ, respectively. **Resonance energy**: The resonance energy (\(R_{N}\)) of the CT complexes was assessed using the Briegleb and Czekalla Equation (6) [25]:  
\[\epsilon_{CT}=7.7\times 10^{-4}\;/\left[Iw_{CT}/R_{N}\right]-3.5 \tag{6}\]  
where \(\epsilon_{CT}\) corresponds to the molar absorptivity of the CT complexes. The values are indicated in Table 2. The stability of the CT complexes in the ground state, which contributes to the stability constant of the complex (a ground -state property). It was found that the resonance energies of Q-DDQ and Q-TCNQ are 0.112 ev and 0.194 ev, respectively. The stability of the complex in ground state was in the order Q-TCNQ > Q-DDQ. **Dissociation energy**: The dissociation energy (\(W\)) is used to express the nature of the CT complex in the excited state. It was calculated using the Equation (7):  
\[W=I_{P}-E^{A}-E_{CT} \tag{7}\]  
where \(E_{CT}\) is the energy of the CT complex, \(I_{P}\) is the ionization potential of the donor and \(E^{A}\) is the electron affinity of the acceptors. The values of \(W\) were found to be 4.45 ev and 3.3 ev for Q-DDQ and Q-TCNQ, respectively. Standard free energy: The nature of the CT interaction was indicated by the standard free-energy change values (\(\Delta G^{\circ}\)) (8) shown in Table 2. Negative values indicate that the reaction between Q and the acceptors is exothermic. As the values become more negative, the formation constant increases [17]. The standard free-energy change was calculated according to the equation below:  
\[\mu=\mathbf{0.0958}\left[\frac{\epsilon_{max\Delta\
u_{1\over 2}}}{ \overline{v}_{max}}\right]^{1/2} \tag{3}\]0  
where \(\Delta G^{\circ}\) is the free-energy change of the CT complex (kJ mol\({}^{-1}\)), \(R\) is the gas constant (1.987 cal mol\({}^{-1}\) K\({}^{-1}\)), \(T\) is the absolute temperature in Kelvins, and \(K_{CT}\) is the association constant of the CT complex at room temperature.