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Tictoid Expanded Pyridiniums: Assessing Structural, Electrochemical, Electronic and Photophysical Features.
MedLine Citation:
PMID:  22724580     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
As regards semirigid donor-spacer-acceptor (D-S-A) dyads devised for photoinduced charge separation and built from an unsaturated spacer, there exists a strategy of design referred to as "geometrical decoupling" that consists in introducing an inner-S twist angle approaching 90° to minimize adverse D/A mutual electronic influence. The present work aims at gaining further insights into the actual impact of the use of bulky substituents (R) of the alkyl type on the electronic structure of spacers (S) of the oligo-p-phenylene type, which can be critical in the functioning of derived dyads. To this end, a series of 12 novel expanded pyridiniums (EPs), regarded as model S-A assemblies, was synthesized, and its structural, electronic and photophysical properties were investigated at both experimental and theoretical levels. These EPs result from the combination of 4 types of pyridinium-based acceptor moieties with the 3 following types of S subunits connected at position 4 of the pyridinum core: xylyl (X), xylyl-phenyl (XP) and xylyl-tolyl (XT). From comparison of collected data with those already reported for 8 other EPs based on the same A components but linked to S fragments of 2 other types (i.e. phenyl, P, and biphenyl, PP), the following quantitative order as regards the pivotal S-centered HOMO energy perturbation was derived (sorted by increasing destabilization): P < X < PP ≈< XP ≈< XT. This indicates that spacers (S) are primarily distinguished on the basis of their mono- or bi-aryl composition and secondarily by their number of methyl substituents (R). The electron-donating inductive contribution of methyl substituents (HOMO destabilization) more than counterbalances the effect of conjugation disruption (HOMO stabilization). This "compensation effect" suggests that mildly electron-withdrawing hindering groups are better suited for "geometrical decoupling", given that high-energy S-centered occupied MOs can assist charge recombination with D-S-A dyads.
Authors:
Jérôme Fortage; Fabien Tuyèras; Cyril Peltier; Grégory Dupeyre; Adrian Calborean; Fethi Bedioui; Philippe Ochsenbein; Fausto Puntoriero; Sebastiano Campagna; Ilaria Ciofini; Philippe Pierre Lainé
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-6-22
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  -     ISSN:  1520-5215     ISO Abbreviation:  -     Publication Date:  2012 Jun 
Date Detail:
Created Date:  2012-6-25     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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