Synthesis and photochemistry of free base and zinc tetraaryl porphyrins mono-substituted with tungsten pentacarbonyl via a pyridine linker

A series of free base and zinc porphyrins, mono meso-substituted with a pyridyl group via an amide link, have been prepared by stepwise functionalisation of free base tetraphenylporphyrin, H(2)tpp. Four [W(CO)(5)L] (L = pyridylporphyrin) complexes have been synthesised; [M{tpp-NHCO-py-W(CO)(5)}], where M = 2H or Zn, one phenyl group is substituted at the 4-position and the pyridine is substituted at the 3- or 4-position. The spectroscopic data of the [W( CO) 5 L] complexes have been compared with those of the porphyrin ligands alone and with those of the model compounds, [W(CO)(5)(3-H2NCO-py)] and [W(CO)(5) (4-H2NCO-py)]. The UV-Vis spectra of the model compounds show that the MLCT and LF absorption bands overlap and no emission is observed at room temperature in solution. The UV-Vis absorption and emission spectra of the porphyrins with peripheral W( CO) 5 are dominated by porphyrin bands. Time-resolved emission was observed from the porphyrin moiety in the [W(CO)(5)L] complexes and fitted to mono-exponential kinetics to give lifetimes of less than or equal to10 ns for the zinc porphyrins and of ca. 22 ns for the free base porphyrins. Transients characteristic of the porphyrin (3)(pi-pi*) excited state have been observed by time-resolved absorption and their decay kinetics have been fitted to an appropriate rate law. Long wavelength photolysis of [W(CO)(5)(3-H2NCO-py)] and [W(CO)(5)(4-H2NCO-py)] in THF resulted in conversion to [W(CO)(5)(THF)]. The [W(CO)(5)L] complexes behaved similarly with photolysis at lambda > 395 nm but were photostable with lambda > 495 nm.