Charge-Transfer Luminescence in a Molecular Donor–Acceptor Complex: Computational Insights

Abstract

Donor–acceptor molecular complexes are a popular class of materials utilizing charge-transfer states for practical applications. A recent class of donor–acceptor dyads based on the fluorescent BODIPY functionalized with triphenylamine (TPA) shows the peculiar property of dual fluorescence. It is hypothesized that instead of the sensitized charge-transfer state being optically dark, it provides an additional bright radiative pathway. Here we use time-dependent density functional theory to characterize the energetic alignment of excitonic and charge-transfer states in a BODIPY-TPA molecular complex. We observe that using a long-range exchange corrected functional in combination with state-specific solvation scheme gives a qualitatively correct alignment of the exciton and charge-transfer states and an enhancement in oscillator strength for the equilibrium solvated charge-transfer state, in agreement with experiment. This work provides rationalization of charge-transfer state emission and provides a foundation to explore charge-transfer using ab initio excited-state nonadiabatic dynamics.

Acceleration of Nonradiative Charge Recombination Reactions at Larger Distances in Kinked Donor–Bridge–Acceptor Molecules

“…A long-range corrected functional (CAM-B3LYP and ωB97XD) incorrectly placed the RP state energetically higher than S1 BD*, while another hybrid functional PBEPBE correctly places the RP state lower than S1 BD*, but incorrectly places it lower than T1 BD* as well (Supporting Information, Table S3). The difficulty of modeling long-range charge-transfer excited states by TDDFT is well recognized, and very recently, Forde, Tretiak, and co-workers examined one of our D–B–A compounds, showing that state-specific schemes can more accurately describe solvation-induced stabilization of RP states. Their approach may prove useful in future studies.…”

Stabilization of Charge-Transfer Excited States in Biological Systems: A Computational Focus on the Special Pair in Photosystem II Reaction Centers

“…When including solvation in the conductive polarizable continuum medium (C-PCM), the solvent potential V s ( x ) is used to provide corrections to the linear-response excitation energies as normalΔ boldΩ bold-italicLR = bold-italicTr ( ξ k T V s false( bold-italicξ bold-italick false) ) It is well documented that linear-response does not provide even qualitative solvation corrections to CT excited states. , An alternative approach is to use state-specific solvation, where the solvent electrostatically interacts with the appropriate excited-state density. Here solvation corrections to the transition energies are computed as the differences in solvent potential energy between the specific excited-state charge density P k and the ground-state density P . boldΩ bold-italicSS = bold-italicTr ( P k V s false( bold-italicP bold-italick false) ) − bold-italicTr ( P V s false( bold-italicP false) ) In reality, approximate approaches are used for state-specific calculations which rely on an initial linear-response calculation with either perturbative corrections, such as corrected linear-response, or self-consistent methods, such as the vertical excitation method or external iteration, applied to obtain the transition energy Ω SS .…”

“…It is well documented that linear-response does not provide even qualitative solvation corrections to CT excited states. 30,42 An alternative approach is to use state-specific solvation, where the solvent electrostatically interacts with the appropriate excited-state density. Here solvation corrections to the transition energies are computed as the differences in solvent potential energy between the specific excited-state charge density P k and the ground-state density P.…”

Designing efficient materials for high-performance of non-fullerene organic solar cells through side-chain engineering on DBT-4F derivatives by non-fused-ring electron acceptors

“…Fullerene-free acceptors lowered voltage losses because of their high visible light absorbance, versatile synthetic techniques, and better light harvesting capabilities [14,15]. By introducing small-molecule acceptors (SMAs), particularly the Y6 acceptor along with its derivatives (with A-D-A-D-A structure), the power conversion efficiency of single-junction organic SCs has risen to 18%-19% [16,17]. However, the most reported SMAs having multi-fused-ring framework results in timeconsuming and poor yields.…”