Predicting Structures of Ru-Centered Dyes: A Computational Screening Tool

Abstract

Dye-sensitized solar cells (DSCs) represent a means for harvesting solar energy to produce electrical power. Though a number of light harvesting dyes are in use, the search continues for more efficient and effective compounds to make commercially viable DSCs a reality. Computational methods have been increasingly applied to understand the dyes currently in use and to aid in the search for improved light harvesting compounds. Semiempirical quantum chemistry methods have a well-deserved reputation for giving good quality results in a very short amount of computer time. The most recent semiempirical models such as PM6 and PM7 are parameterized for a wide variety of molecule types, including organometallic complexes similar to DSC chromophores. In this article, the performance of PM6 is tested against a set of 20 molecules whose geometries were optimized using a density functional theory (DFT) method. It is found that PM6 gives geometries that are in good agreement with the optimized DFT structures. In order to reduce the differences between geometries optimized using PM6 and geometries optimized using DFT, the PM6 basis set parameters have been optimized for a subset of the molecules. It is found that it is sufficient to optimize the basis set for Ru alone to improve the agreement between the PM6 results and the DFT results. When this optimized Ru basis set is used, the mean unsigned error in Ru-ligand bond lengths is reduced from 0.043 Å to 0.017 Å in the set of 20 test molecules. Though the magnitude of these differences is small, the effect on the calculated UV/Vis spectra is significant. These results clearly demonstrate the value of using PM6 to screen DSC chromophores as well as the value of optimizing PM6 basis set parameters for a specific set of molecules.

Semiempirical configuration interaction calculations for ru‐centered dyes*

“…To realize a complete screening methodology for transition metal dyes, it is necessary to be able to optimize candidate molecular structures and compute their UV/vis spectrum quickly, cheaply, and accurately. In a previous publication, we showed that geometries calculated using Ru basis set parameters optimized for the semiempirical PM6 Hamiltonian for Ru‐centered dye‐sensitized solar cell molecules were in good agreement with optimized DFT geometries. As mentioned in that article, the speed and accuracy of the PM6 method, particularly with optimized basis set parameters, makes it an excellent candidate for computational screening of the geometries of thousands of candidate dyes.…”

“…To optimize the Ru basis set for Ru‐DSC geometries, a testing set of 20 molecules that contains the 13 molecules listed above and identical to the set used in our previous paper, was used. From this set, a training set of 5 molecules (Ru(DQPl) 2 (DQPl = 1,3‐ bis (8‐quinolinyl)‐pyrrole), Ru(DQPNH 2 ) 2 , Ru(DQP) 2 , Ru(DQPzP) 2 , Ru(TPy) 2 ) was taken.…”

“…From this set, a training set of 5 molecules (Ru(DQPl) 2 (DQPl = 1,3‐ bis (8‐quinolinyl)‐pyrrole), Ru(DQPNH 2 ) 2 , Ru(DQP) 2 , Ru(DQPzP) 2 , Ru(TPy) 2 ) was taken. This training set differs from the one used in our previous paper . (Optimized geometries of all 20 molecules are given in the Supporting Information.)…”

“…(Optimized geometries of all 20 molecules are given in the Supporting Information.) Using the methodology described in our previous article, we have optimized a Ru basis set for PM6 as implemented in MOPAC (Tables and ). Differences in the training set and parameters exposed in the MOPAC implementation of PM6 led to the need for a new optimization of the basis set.…”

rPM6 Parameters for Manganese and Application to Transition State Search for Oxidation Reactions of Cyclohexene by Manganese(IV)-Oxo Species

“…6 Semiempirical quantum mechanical (SQM) calculations 7,8 are considered as a likely alternative, and reparameterization and/or modifications make it possible to apply SQM methods to energy minimizations for metalcontaining complexes. 9,10 We proposed a reparameterization of PM6 11 (called rPM6) targeting for open-shell molecules including 3d transition metal complexes, and the rPM6 parameters for several basic elements (i.e., H, C, N, O, P, and S) are now available. 1214 The applications of UrPM6 to various organic (di)radicals demonstrated its superior performance in both the electronic and geometric structures.…”