OS100: A Benchmark Set of 100 Digitized UV–Visible Spectra and Derived Experimental Oscillator Strengths

Abstract

The scientific method involves validating computational theories and methods against experimental results. However, the comparison between theory and experiments is not always straightforward; in UV-visible spectroscopy, experiments provide a plot of wavelength-dependent molar extinction/attenuation coefficients (ε) while computations typically provide single-valued excitation energies and oscillator strengths (ƒ) for each band. ε and ƒ are related, but this relation is complicated by various broadening and solvation effects. We describe a protocol to fit and integrate experimental UV-visible spectra to obtain ƒ exp values for absorption bands and to estimate the uncertainty in the fitting. We apply this protocol to derive 164 ƒ exp values from 100 organic molecules ranging in size from 6-34 atoms. The corresponding computed oscillator strengths (ƒ comp ) are obtained with time-dependent density functional theory and a polarizable continuum solvent model. By expressing experimental and computed absorption strengths using a common quantity, we directly compare ƒ comp and ƒ exp . While ƒ comp and ƒ exp are well correlated (linear regression R 2 =0. 914), ƒ comp in most cases significantly overestimates ƒ exp (regression slope=1.31).The agreement between absolute ƒ comp and ƒ exp values is substantially improved by accounting for a solvent refractive index factor, as suggested in some derivations in the literature. The 100 digitized UV-visible spectra are included as plain text files in the supporting information to aid in benchmarking computational or machine-learning approaches that aim to simulate realistic UVvisible absorption spectra.

Theoretical investigation on the functional group modulation of UV-Vis absorption profiles of triphenylamine derivatives

“…S14–S17 (ESI†), only the UV-Vis spectra simulated in toluene are presented), which may be allocated to the lower accuracy of the oscillator strength than the excitation energy from TDDFT calculations. 38–40 Taking both accuracy and cost into account, we conclude that a combined B3LYP//MN15 scheme, namely the sequential calculations of the ground state geometry optimization and (TD-)single point, which was adopted in extensive studies, 67,68 is a preferred choice for molecules with relatively planar framework and abundant delocalized electrons. B3LYP was vastly used for the geometry optimization and provided comparatively reasonable structural information without consuming too many computational resources.…”

“…37 Sometimes, benchmark studies using experiments or high-level theoretical methods are entailed to shortlist a proper functional. In the practice of TDDFT calculations, although considerable efforts have been spared to accurately predict the absorption or emission wavelength, benchmark studies on the oscillator strength are still scarce, [38][39][40] which hinders the deep understanding of the photoelectric properties of OSMs.…”

How does theory compare to experiment for oscillator strengths in electronic spectra? Proposing range-separated hybrids with reliable accountability

“…So, finding a coherent benchmark set for oscillator strengths is even more difficult. 14,[25][26][27][28][29][30][31][32] Indeed, how to theoretically predict the reliable data of oscillator strengths as a measure of the probability of absorption or emission, which in turn allows us to screen out potential candidates for practical purposes, is still an unaccomplished task. In particular, choosing an appropriate and affordable level of theory that is able to provide a reliable description of the oscillator strengths of the bands in the electronic spectra is an important issue.…”

“…In this respect, high-correlated single-and multi-reference approaches have revealed some successes, as in recent computational investigations on the case studies of the oscillator strengths the variants of these methods were employed. [25][26][27][28][29][30][31][32] Concerning the computational cost of the high-level electron correlation approaches due to their large scaling and slow convergence, density functional theory (DFT) [33][34][35][36] in the timedependent (TD) domain (TD-DFT) [37][38][39] can be considered as an alternative, mainly due to its high-throughput computational feasibility with an effective ratio of accuracy to cost. In some of the earlier efforts comparing the performances of different TD-DFT approximations for predicting the oscillator strengths, the superiority of range-separated hybrid functionals was also pointed out.…”

Effect of Organic Molecular Volume on Organic Photodiodes

“…Furthermore, it does not provide information on molecular volume or packing density and its accuracy is limited. [9][10][11][12] Thus, for a given molecule, a higher oscillator strength does not guarantee a high absorption coefficient of the thin film.…”