Photoinduced charge-transfer dynamics simulations in noncovalently bonded molecular aggregates

Abstract

The rational design of new materials as prototype systems for organic solar cells remains challenging. Perylene diimide has emerged as a promising material to replace fullerene derivatives because of its synthetic flexibility, leading to the manipulation of their optical properties. As a result of their fused aromatic core that favors π-π stacking interactions, the aggregation of these molecules can reach highly ordered nanostructures as one-dimensional nanofibers, with a fast photoinduced charge transfer mechanism. In this article, we present an atomistic description of the photoexcited exciton dynamics in noncovalently bonded perylene diimides by time integration of the electron density in the presence of external time varying electric fields. We show that our approach is able to capture and explain the physics that underlies the charge transport mechanism through perylene diimide aggregates.

A Real-Time Time-Dependent Density Functional Tight-Binding Implementation for Semiclassical Excited State Electron–Nuclear Dynamics and Pump–Probe Spectroscopy Simulations

“…The first term of the right-hand side of this equation is the electronic EOM known as the Liouville-von Neumann equation, 28 a generalized commutator in a non-orthogonal basis, and it has been implemented and extensively used for the calculation of optical properties of materials and time-dependent photo-induced phenomena keeping the nuclei "clamped". 12,13,[15][16][17]29,30 The second term gives rise to the non-adiabatic interactions, allowing energy exchange between electrons and nuclei at the Ehrenfest level.…”

“…Real-time time-dependent densityfunctional tight-binding (TD-DFTB) is a suitable formalism for these cases which has been widely used to calculate quantum-mechanically ground state static and dynamic properties of large atomistic systems. 12,13,[15][16][17] Here, we present the theoretical grounds and relevant computational details of a real-time Ehrenfest TD-DFTB implementation 1 in the DFTB+ code, 18 explained in section 2. The possibility to calculate the optical properties of periodic systems that this implemenetation allows is discussed in section 3.1 for graphene nanoribbons.…”

Photoinduced charge-transfer in chromophore-labeled gold nanoclusters: quantum evidence of the critical role of ligands and vibronic couplings

“…21 The latter can be used to access not only the absorption spectrum but the electron dynamics following excitation. 22 This method was succesfully used in the last decade to study the optoelectronic properties of a wide variety of organic and inorganic materials: the absorption spectra and photophysical properties of photosyntetic pigments 23,24 and DNA-protected silver emitters 25,26 , plasmonic properties of gold, 27-29 silver 28,29 and aluminium 30 metallic nanoparticles, optical properties of carbon-based materials like graphene nanoflakes 31 and graphene nanoribbons 32 and photoinduced charge transfer mechanisms elucidation in metal oxides [33][34][35][36][37] for dye-sensitized solar cells (DSSC) and molecular aggregates 38,39 for organic solar cells (OSC). These studies were performed within the electron-only quantum dynamics approach without considering nuclei movement, yet reaching a good agreement with experiments.…”

Density-functional tight-binding: basic concepts and applications to molecules and clusters

“…The TD-DFTB method was successfully used to study the charge migration in the caffeine molecule induced by an ionizing XUV pulse [361]. In addition to the simulation of exciton dynamics in molecular clusters [200,[362][363][364] reported in section 4.3, the FSSH scheme for non-adiabatic dynamics has been used to simulate excimer formation in the pyrene dimer [365] or relaxation of excited fluorene oligomers [200]. Relaxation dynamics enhanced by transition density analysis has been investigated by Stojanović et al for two cycloparaphenylene molecules (labelled [8]CPP and [10]CPP) in ref [201]).…”

“…The excitation energy transfer in molecular aggregates has been described through a Frenkel Hamiltonian whose parameters are computed from TD-DFTB [147,148,366,367]. The combination of non-adiabatic dynamics with long-range corrected DFTB [200] has been used to simulate the dynamical evolution of excitons in clusters of tetracene [362] and perylene diimides [363]. The dynamical coupling between local and charge transfer excitons in pentacene clusters was also investigated [364].…”