Synthesis, characterization, physicochemical, and photophysical studies of redox switchable NIR dye derived from a ruthenium−dioxolene−porphyrin system

Newly synthesized semi-quinone derivatives of the ruthenium polypyridyl, covalently linked to a porphyrin core, show very high e values (59000-83500 M<SUP>-1</SUP>cm<SUP>-1</SUP>) for the absorption band in the near infrared (NIR) region of the spectrum. Further, complexes 1-4 show an interesting reversible electrochromic behavior as a function of the redox state of the coordinated dioxolene functionality, and a switching phenomenon between bleaching and the restoration of the NIR peak could be achieved electrochemically. Thus, complexes 1-4 could be ideal candidate materials for NIR-active electrochromic devices. Ultrafast studies on 1 and its mononuclear components, 5-(3,4-dihydroxyphenyl)-10,15,20-triphenyl-21H,23H-porphyrin (H<SUB>2</SUB>L<SUB>1</SUB>) and Ru(bpy)<SUB>2</SUB>(bsq)<SUP>+</SUP>, reveal that there is no electron or energy transfer from the porphyrin to the Ru(bpy)<SUB>2</SUB>sq<SUP>+</SUP> (bpy is 2,2'-bipyridine and sq is the deprotonated species of a substituted semi-quinone fragment) fragment or vice versa in 1. The observed decrease in the luminescence quantum yield for 1 compared to that of H<SUB>2</SUB>L<SUB>1</SUB> can be ascribed to the increased nonradiative pathway due to higher vibronic coupling because of the direct linkage of the metal center to the porphyrin moiety