Theoretical Investigations on the Roles of Intramolecular Structure Distortion versus Irregular Intermolecular Packing in Optical Spectra of 6T Nanoparticles

Abstract

It is of vital importance to theoretically understand unique nanoparticle size-tunable and excitation wavelength-dependent multiple optical properties in organic nanoparticles. In this work, we proposed a theoretical protocol to calculate the optical spectrum of the organic nanoparticles, which combines molecular dynamics (MD) simulation, the quantum mechanics/molecular mechanics (QM/MM) approach, and vibronic-coupled Frenkel exciton spectrum theory. By using the protocol, we explored the relationship between intramolecular structure distortion, irregular intermolecular packing, and optical spectra in α-sexithiophene nanoparticles. Two representative clusters cutting from the simulated amorphous nanoparticle were investigated and found to exhibit a blue shift for absorption and emission spectra compared to the solution, which is totally different from the blue-shifted absorption and red-shifted emission in crystal. For the cluster with distorted monomer and disordered packing, the blue shift results from ...