Synthesis, computational and optical studies of tetraphenylethene-linked Pd(ii)dipyrrinato complexes

Abstract

This work is focused on the design and synthesis of homoleptic and heteroleptic dipyrrinato complexes with palladium at the centre. The C-5 position of the dipyrrin ligand was substituted with pentaflourophenyl/naphthalene/tetraphenylethylene moieties. Scanning electron microscopy (SEM) measurement revealed the formation of aggregates in binary solvents for the homoleptic Pd(II) complexes. These complexes showed enhanced emission with noticeable red shifts (20–30 nm) in the aggregated state, suggesting the formation of J-aggregates in a THF/water mixture. All of the Pd(II)dipyrrinato complexes exhibited strong absorption in the range of 440–560 nm; the DFT optimized geometries also showed absorption transitions similar to the experimentally observed values. The Pd3 complex with pentafluorophenyl groups was able to generate efficient singlet oxygen in polar solvents. Also, Pd3 was used to catalyse the photo-oxidation of aromatic aldehydes in good yields (51–93%) in the presence of a white LED.