Decoupling Optical and Potentiometric Band Gaps in π-Conjugated Materials

Syntheses, optical spectroscopy, potentiometric studies, and electronic structural calculations are reported for two classes of conjugated (porphinato)metal oligomers that feature a meso-to-meso ethyne-bridged linkage topology. One set of these systems, bis(5,5'-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]ethyne (DD), 5,15-bis[5'-10',20'-bis[3,5-di(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]ethynyl]-10,20-bis3,5-di(9-methoxy-1,4,7-trioxanonyl)phenylporphinato)zinc(II) (DDD), and 5,15-bis[15' '-(5'-10',20'-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]-(5' '-10' ',20' '-bis[3,5-di(9-methoxy-1,4,7-trioxanonyl)phenylporphinato)zinc(II)]ethyne]ethynyl]-10,20-bis3,5-di(9-methoxy-1,4,7-trioxanonyl)phenylporphinato)zinc(II) (DDDDD), constitute highly soluble analogues of previously studied examples of this structural motif having simple 10,20-diaryl substituents, while a corresponding set of conjugated oligomers, (5-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]-(5'-15'-ethynyl-10',20'-bis[10,20-bis(heptafluoropropyl)porphinato)zinc(II)ethyne (DA), 5,15-bis[5'-10',20'-bis[3,5-di(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]ethynyl]-10,20-bis(heptafluoropropyl)porphinato]zinc(II) (DAD), and 5,15-bis[15' '-(5'-10',20'-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenylporphinato)zinc(II)]-(5' '-(10' ',20' '-bis(heptafluoropropyl)porphinato)zinc(II)ethyne]ethynyl]-10,20-bis3,5-di(9-methoxy-1,4,7-trioxanonyl)phenylporphinato)zinc(II) (DADAD), features alternating electron-rich and electron-poor (porphinato)zinc(II) units. Electrooptic and computational data for these species demonstrate that it is possible to engineer conjugated oligomeric structures that possess highly delocalized singlet (S1) excited states yet manifest apparent one-electron oxidation and reduction potentials (E1/20/+ and E1/2-/0 values) that are essentially invariant with respect to those elucidated for their constituent monomeric precursors.