TD-DFT calculations of one- and two-photon absorption in Coumarin C153 and Prodan: attuning theory to experiment

Abstract

We use TD-DFT to calculate the one-photon absorption (1PA) and two-photon absorption (2PA) properties of C153 and Prodan in toluene and DMSO, and benchmark different methods relative to accurate experimental data available from the literature on these particular systems. As the first step, we modify the range-separated TD-DFT to provide the best prediction for the peak 1PA wavelength, and then apply the optimized functionals to achieve quantitative predictions of the corresponding two-photon absorption cross section, σ, with an accuracy ∼10-20% in C153 and ∼20-30% in Prodan. To elucidate the origin of residual discrepancies between the theory and experimental observations, we invoked the two essential states model for σ, which allows us to verify not only the transition wavelength and the σ value, but also to quantitatively benchmark the calculation of key molecular parameters such as the transition dipole moment and the change of the permanent dipole moment. Such comprehensive cross-checking indicates that a larger discrepancy in Prodan is most likely caused by a noted failure of DFT to predict the relative intensity and relative ordering of closely lying excited states with different degrees of intramolecular charge transfer, which we further support by analyzing the predictions obtained by high-level coupled-cluster calculations in the gas phase. Our results highlight the utility of benchmarking the calculations not only relative to other theoretical methods, but also in comparison to the experimental measurements, wherever such data are available.

Solute-solvent electronic interaction is responsible for initial charge separation in ruthenium complexes [Ru(bpy)3]2+ and [Ru(phen)3]2+

“…It has been shown previously that appropriately tuned range-separated hybrid functional CAM-B3LYP 44 with mild coulombic attenuation provides reasonable transition energies in both linear response (LR) and quadratic response (QR) applications, matching and in many cases exceeding the performance of B3LYP functional 45 . Therefore, the modified CAM-B3LYP was used for all TD-DFT 46 calculations.…”

Ultrafast Formation of the Charge Transfer State of Prodan Reveals Unique Aspects of the Chromophore Environment

“…The GW-BSE approach for excited state prediction is inherently better suited to CT states than TD-DFT approaches that have been previously applied to the same compounds. [11][12][13][14][15][16][17][18] Together, these two components yield a very high accuracy, quantitative method with the potential to reveal the mechanism of other more recently developed, less well understood chromophores.…”

“…1) and related dyes have used time-dependent density functional theory (TD-DFT) with a continuum treatment of the environment. [11][12][13][14][15][16][17][18] Although these methods give results in qualitative agreement with polarity-dependent spectroscopies, they fall short in two important respects. First, conventional DFT functionals are not well-suited to CT states due to the lack of proper long-range interactions, 19 unless special system-tuned corrections are taken into account.…”

Multiphoton spectroscopy: An optical window into molecular electrostatics

“…Where applicable, our experiments show good correspondence with reports by other groups using conventional dipole moment measurement methods such as Stark effect and electrochromism. We will also compare our experimental findings with quantumchemical theoretical calculations and discuss how to optimize the calculated 2PA spectra and dipole moment values by choosing appropriate methods [11]. In summary, our results indicate that our 2-photon absorption based approach may be a viable alternative to more traditional methods of determining the electric dipole change based, while offering higher versatility associated with all-optical access.…”