Theoretical Investigation of the Excited States of Coumarin Dyes for Dye-Sensitized Solar Cells

Abstract

Using time-dependent density functional theory (TD-DFT), configuration interaction single (CIS) method, and approximate coupled cluster singles and doubles (CC2) method, we investigated the absorption spectra of coumarin derivative dyes (C343, NKX-2388, NKX-2311, NKX-2586, and NKX-2677), which have been synthesized for efficient dye-sensitized solar cells. The CC2 calculations are found in good agreement with the experimental results except for the smallest coumarin dye (C343). TD-DFT underestimates the vertical excitation energy of the larger coumarin dyes (NKX-2586 and -2677). Solvents (methanol) are found to induce a red shift of the vertical excitation energies, and their effects on the molecular geometry and the electronic structure are examined in detail. The deprotonated form of coumarin is also investigated, where a blue shift of the vertical excitation energies is observed.

Time‐dependent density functional theory study on the absorption spectrum of Coumarin 102 and its hydrogen‐bonded complexes

“…The solvent polarity effect on the C102 absorption wavelength could be divided into two contributions: a perturbation of the excitation transition energy and a modification of the groundstate geometry. 28,29 The perturbation of the excitation transition energy is evaluated by comparing the calculated absorption wavelengths in different solvents at the same geometry optimized in the cyclohexane solution. The absorption wavelengths are 359.54 nm in heptane, 360.69 nm in cyclohexane, 369.52 nm in THF, 374.65 nm in DMSO, 371.67 nm in acetone, 372.20 nm in acetonitrile, 372.02 nm in ethanol, 372.00 nm in methanol, 372.91 nm in water, respectively.…”

Novel Organic Sensitizers Containing 2,6-Difunctionalized Anthracene Unit for Dye Sensitized Solar Cells

“…The same functional was also applied for the calculation of excited states using time-dependent density functional theory (TD-DFT). There exist a number of previous works that employed TD-DFT to characterize excited states with charge-transfer character [37,38]. In some cases underestimation of the excitation energies was seen [36,39].…”

Heteroleptic Ruthenium Sensitizers That Contain an Ancillary Bipyridine Ligand Tethered with Hydrocarbon Chains for Efficient Dye‐Sensitized Solar Cells

“…TD-DFT calculations were previously employed to characterize excited states with chargetransfer character. [23] In some cases, underestimation of the excitation energies was observed. [23,24] Therefore, in the present work we characterize the electronic configuration and avoid drawing conclusions from the excitation energy.…”