Evaluation of Excitonic Coupling and Charge Transport Integrals in P3HT Nanocrystal

An attempt has been made to predict the crystallographic packing parameters of poly(3-hexylthiophene) (P3HT) nanocrystal with the help of both X-ray diffraction and computational methods. Excitonic coupling integrals were calculated using various methods such as point-dipole approximation (PDA), line-dipole approximation (LDA), ZINDO method, and transition density cube (TDC) method in crystallographic directions. ZINDO method leads to reasonably accurate integrals when compared to TDC results. PDA and LDA approaches fail badly in predicting the excitonic coupling integrals, though latter yields improved results. The calculations one more time show that PDA should be avoided in cases where interchromophoric distance is comparable to chromophore size. In general, the magnitude of both excitonic and charge transfer integrals are larger in stacking direction of chains than those in other crystallographic directions, suggesting preferential diffusion of both excitons and charge carriers between the chains. The hole transfer integrals were also found to be larger than those for electrons, confirming P3HT as p-type semiconducting material.