Effect of dynamic disorder on charge carrier dynamics in Ph4DP and Ph4DTP molecules

Abstract

Electronic structure calculations were used to study the charge transport and optical properties of 2,2′,6,6′-tetraphenyldipyranylidene (Ph4DP) and its sulfur analogue 2,2′,6,6′-tetraphenyldithiopyranylidene (Ph4DTP) based molecules. The dynamic disorder effect is included while calculating the charge transfer kinetic parameters such as rate coefficient, disorder drift time, hopping conductivity and mobility of charge carriers through the kinetic Monte Carlo simulations. The existence of degeneracy levels promotes the delocalization of charge carrier and charge transfer. Theoretical results show that if the orbital splitting rate is larger than the static charge transfer rate (O_R > k_static), the charge transfer is kinetically favored. If O_R < k_static, the charge carrier is potentially trapped in the localized site. In the case of O_R ∼ k_static, the charge carrier motion is not affected by the dynamic disorder. The calculated hole mobility in Ph4DP and Ph4DTP molecules is 0.04 and 0.03 cm² V⁻¹ s⁻¹ and is in agreement with the experimental results. It has been found that fluorine and chlorine substituted Ph4DP molecules have good ambipolar transporting character. The absorption and emission spectra were calculated using the time dependent density functional theory (TDDFT) method at the CAM-B3LYP/6-31G(d,p) and M062X/6-31G(d,p) levels of theory. The calculated absorption spectra are in agreement with the experimental results.