Synthesis, characterization and evaluation of the optical properties of novel meso-thienyl-4,4-diphenyl-BODIPY derivatives in solid state

Abstract

In this work, we report the synthesis of new meso-thienyl-BODIPY monomers with phenyl groups as substituents on the boron atom using a novel and strategic methodology to introduce directly the BPh₂ motif by coordination of the dipyrromethene with diphenylborinic acid. A new BODIPY dimer was then obtained from the monomeric unit via Glaser coupling as the most efficient method. These compounds were deposited on FTO-coated glass substrates via spin coating. A thorough characterization of the optical properties, both in solution and in the solid state, was carried out, revealing significant changes depending on the aggregation state of the material. The studied compounds showed no significant solvatochromic effect in absorption but exhibited varying emission intensities depending on the solvent. This is attributed to the interplay of intramolecular and intermolecular charge transfer, as shown by TDDFT calculations. A reaction mechanism for the coordination step involving borinic acid is also proposed, supported by computational data. Additionally, the thermal stability and air resistance were evaluated, showing remarkable stability of the dimer compared to the monomer, confirming it as a strong candidate for applications requiring temperature variations and prolonged exposure to air. Furthermore, a morphological analysis was conducted using AFM, revealing a dendritic surface in the dimer films, which contributed to higher surface roughness. Due to the high stability demonstrated by the new BODIPY dimer, it may be a suitable candidate for its use in optoelectronic devices and other fields of science and technology.