Methoxy-groups, solvent shifts

In aromatic solutes PhR (R—Me, CH2OH, OCH3, COCH3) there is a marked tendency for the A c e values of the protons in R to become more negative when methoxy-groups are substituted in the 2-or the 2,6-positions, This is dramatically illustrated for the methylene protons of benzyl alcohol (37) and the methoxylated derivatives (38) and (39). The dependence of the solvent shifts of methoxy resonances on electronic, steric and conformational factors has been discussed. ... 

Solvent peaks can be observed at 2.5 ppm and 3.4 ppm (broad). A second broad, low peak due to the nitrate counter-ion proton is seen downfield at 14.33 ppm. The protons associated with the methoxy- and ethyl-carbons are deshielded by their adjacent groups (aromatic and heterocyclic rings and oxygen). Consequently they appear shifted downfield, between 4.3 and 5.2 ppm. 

Substituted PPVs are soluble in organic solvents, which is a very useful feature in the preparation of polymer LEDs. One of the first PPV soluble derivatives, prepared by the Santa Barbara group in California via the precursor route, was methoxy-ethylhexyloxy PPV (MEH-PPV), which emitted a red-orange color [107,108]. Subsequently another PPV derivative with the bulky cholestanoxy group was prepared, namely the poly [2,5-bis(3a-5b cholestanoxy)-1,4-pheny-lene vinylene] (BCHAPPV). A blue shift was observed in relation to MEH-PPV BCHA-PPV emitted in the yellow region [109,110]. 

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