Theoretical Design Study on Photophysical Properties of Light-emitting Pyrido[3,4-b]pyrazine-based Oligomers

Abstract

The electronic structures, charge injection and transport, and absorption and emission properties of four series of dimethylpyrido[3,4-b]pyrazine-based oligomers (5-(5,5-dimethyl-5H-dibenzo[b,d]silol-3-yl)-2,3-dimethylpyrido[3,4-b]pyrazine)n (SPP)n, (5-(dibenzo[b,d]thiophen-3-yl)-2,3-dimethylpyrido[3,4-b]pyrazine)n (TPP)n, (5-(9,9-dimethyl-9H-fluoren-2-yl)-2,3-dimethylpyrido[3,4-b]pyrazine)n (FPP)n, (2-(2,3-dimethylpyrido[3,4-b]pyrazin-5-yl)-9-methyl-9H-carbazole)n (PPC)n were investigated by the density functional theory approach. The ground-state geometries of (SPP)n, (TPP)n, (FPP)n and (PPC)n (n = 1–4) were optimized at the B3LYP/6–31G(d) level. The energies of the HOMO, LUMO and HOMO–LUMO energy gaps of (SPP)n, (TPP)n, (FPP)n and (PPC)n (n = 1–4) were obtained by a linear extrapolation method. Further, calculations of ionization potential, electronic affinity and reorganization energy were used to evaluate charge injection and transport abilities. For (SPP)n, (TPP)n, (FPP)n and (PPC)n (n = 1–4), the time-dependent density functional theory (TDDFT) calculation results revealed that the absorption peaks can be characterized as π–π* transitions and are coupled with the location of electron density distribution change in different repeat units. All the primary theoretical investigations are intended to establish structure–property relationships, which can provide guidance in designing and preparing novel efficient organic light-emitting materials with a high performance.