 the influence of 
 electronic symmetry on triplet state delocalization 
 in linear zinc porphyrin oligomers is explored by electron paramagnetic 
 resonance techniques . using a combination of transient continuous 
 wave and pulse electron nuclear double resonance spectroscopies , 
 it 
 is demonstrated experimentally that complete triplet state delocalization 
 requires the chemical equivalence of all porphyrin units . 
 these results 
 are supported by density functional theory calculations , showing uneven 
 delocalization in a porphyrin dimer in which a terminal ethynyl group 
 renders the two porphyrin units inequivalent . when the conjugation 
 length of the molecule is further increased upon addition of a second 
 terminal ethynyl group that restores the symmetry of the system , the 
 triplet state is again found to be completely delocalized . 
 the observations 
 suggest that electronic symmetry is of greater importance for triplet 
 state delocalization than other frequently invoked factors such as 
 conformational rigidity or fundamental length - scale limitations . 
Supplementary Material