Near-Infrared Fluorescence of Silicon Phthalocyanine Carboxylate Esters

Seven silicon(IV) phthalocyanine carboxylate esters (SiPcs, 1-7) with non-, partially- and per-fluorinated aliphatic (linear or branched at the alpha-carbon) and aromatic ester groups have been synthesized, their solid-state structures determined and their optoelectronic properties characterized. The SiPcs exhibit quasi-reversible oxidation waves (vs. Fc⁺/Fc) at 0.58-0.75 V and reduction waves at -0.97 to -1.16 V centered on the phthalocyanine ring with a narrow redox gap range of 1.70-1.75 V. Strong absorbance in the near-infrared (NIR) region is observed for 1-7 with the lowest-energy absorption maximum (Q band) varying little as a function of ester between 682 and 691 nm. SiPcs 1-7 fluorescence in the near-infrared with emission maxima at 691-700 nm. The photoluminescence quantum yields range from 40 to 52%. As a function of esterification, the SiPcs 1-7 exhibit moderate-to-good solubility in chlorinated solvents, such as 1,2-dichlorobenzene and chloroform.