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Porphyrin‐[( E )‐1,2‐Diethynylethene] Scaffolding: Synthesis and Optical and Electrochemical Properties of Multinanometer‐Sized Porphyrin Arrays
Author(s) -
Wytko Jennifer,
Berl Volker,
McLaughlin Mark,
Tykwinski Rik R.,
Schreiber Martin,
Diederich François,
Boudon Corinne,
Gisselbrecht JeanPaul,
Gross Maurice
Publication year - 1998
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19981111)81:11<1964::aid-hlca1964>3.0.co;2-i
Subject(s) - bathochromic shift , chemistry , porphyrin , crystallography , electrochemistry , conjugated system , spectral line , photochemistry , stereochemistry , fluorescence , electrode , organic chemistry , physics , quantum mechanics , polymer , astronomy
Two series of linearly conjugated hybrid materials, consisting of ( E )‐1,2‐diethynylethene (DEE; hex‐3‐ene‐1,5‐diyne) and Zn II porphyrin components, were prepared by Pd 0 ‐catalyzed cross‐coupling reactions. In one series, one or two DEE substituents were introduced into the meso ‐positions of the Zn II porphyrins, leading from 5 ⋅ Zn , to 9 and 1 ( Scheme 1 ). The second series contains the linearly π ‐conjugated molecular rods 1 – 3 that span a length range from 23 Å ( 1 ) to 53 Å ( 3 ) ( Fig. 1) . The larger rods 2 and 3 consist of two or three porphyrin moieties, respectively, that are bridged at the meso ‐positions by trans ‐enediynediyl (hex‐3‐ene‐1,5‐diyne‐1,6‐diyl) linkers ( Scheme 2 ). The UV/VIS spectra in the series 5 ⋅ Zn , 9 , and 1 ( Fig. 2 ) showed a strong bathochromic shift of both Soret and Q bands of the Zn II porphyrin as a result of the addition of DEE substituents. Upon changing from 1 to 2 ( Fig. 3 ), the Q band was further bathochromically shifted, whereas the Soret band remained nearly at the same position but became broadened and displayed a shoulder on the lower‐wavelength edge as a result of excitonic coupling. The close resemblance between the UV/VIS spectra of 2 and 3 suggests that saturation of the optical properties in the oligomeric series already occurs at the stage of dimeric 2 . Stationary voltammetric investigations showed that the DEE substituents act as strong electron acceptors which induce large anodic shifts in the first reduction potential upon changing from 5 ⋅ Zn to 9 ( Δ E =190 mV) and to 1 ( Δ E =340 mV). Increasing the number of porphyrin moieties upon changing from 1 to 2 had no effect on the first reduction potential yet the first oxidation potential was substantially lowered ( Δ E =110 mV). Large differences in the potentials for one‐electron oxidation of the two porphyrin moieties in 2 ( Δ E =200 mV) confirmed the existence of substantial electronic communication between the two macrocycles across the trans ‐enediynediyl bridge.