Synthesis, photophysical, electrochemical and electrochemiluminescence properties of A 2 B 2 zinc porphyrins: the effect of π-extended conjugation

The synthesis of two A 2 B 2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc( ii ) ( 4 ) and {5,15-bis-(carbazol-3-yl-ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc( ii ) ( 9 ), is reported. Their photophysical properties were studied by steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a large bathochromic shift of all the absorption bands, a notable increase in the absorption coefficient of the Q(0,0) band, and higher fluorescence quantum yield compared to porphyrin 4 , with two unsubstituted meso positions. Cyclic voltammetry and digital simulation show that electrogenerated radical ions of 9 are more stable than those of 4 . The lack of substituents at the meso positions of 4 leads to dimerization reactions of the radical cation. Despite this, the annihilation reaction of 4 and 9 produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical experiments demonstrate that the electroreduction of 9 leads to a strong absorption band that might quench the ECL.