Computational note on the calculation of the molecular structure and properties of 3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide derivatives for organic photovoltaics

Abstract

While the performance of organic photovoltaics has been improving steadily, this technology still faces fundamental limitations in efficiency and stability that need to be overcome for it to be competitive with other solar cells. This makes mandatory to develop new molecular materials and nanostructures using organic heterocycles. The objective of this computational note is to report the results of the calculation of the molecular structure and properties of 3-(2-pyrrolyl)-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide and 2-benzoyl-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide [1] using a recently developed density functional [2]. By considering a model-chemistry specially designed to study heterocyclic compounds called CHIH-DFT (Density Functional Theory for Heterocyclic Systems), the 3-(2-pyrrolyl)-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide and 2-benzoyl-3,4-diphenyl 1,2,5thiadiazoline 1,1-dioxide molecules have been characterized using the Gaussian 03W program [3]. The PBEg functional was considered, which is analog to the PBE0 functional [4]. The difference resides in the g factor which is a measure of the amount of Hartree–Fock exchange incorporated in the hybrid functional, and whose value is dependent on the structure of the heterocycle being studied. For the 3-(2-pyrrolyl)-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide and 2-benzoyl-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide molecules it is equal to 0.5. The 3-21G* and the CBSB2** basis sets were used and all this together is called CHIH-DFT(small) theory. The calculation of the absorption spectra (UV–vis) of 3-(2-pyrrolyl)-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide and 2-benzoyl3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide have been performed by solving the time dependent Kohn–Sham equations according to the method implemented in Gaussian 03W [5]. The equations have been solved for 10 excited states. The geometry of the first excited state in each case has been optimized by resorting to a HFCIS/3-21G* calculation. The emission spectra were thus obtained by solving again the TD-DFT equations at the same level of theory as for the absorption spectra. The values of the dipole moment, polarizability and static first hyperpolarizability for the 3-(2-pyrrolyl)-3,4-diphenyl 1,2,5-thiadiazoline 1,1-dioxide and 2-benzoyl-3,4-diphenyl 1,2,5-thiadiaz-