RESUMO
Communication between chromophores is vital for both natural and non-natural photophysical processes. Spatial confinements offer unique conditions to scrutinize such interactions. Polynorbornene- and polycyclobutene-based ladderphanes are ideal model compounds in which all tetraarylethylene (TAE) linkers are aligned coherently. The spans for each of the monomeric units in these ladderphanes are 4.5-5.5â Å. Monomers do not exhibit emission, because bond rotation in TAE can quench the excited-state energy. However, polymers emit at 493â nm (Φ=0.015) with large Stokes shift under ambient conditions and exhibit dual emission at 450 and 493â nm at 150â K. When the temperature is lowered, the emission intensity at 450â nm increases, whereas that at 493â nm decreases. At 100â K, both monomers and polymers emit only at 450â nm. This shorter-wavelength emission arises from the intrinsic emission of TAE chromophore, and the emission at 493â nm could be attributed to the excimer emission in the confined space of ladderphanes. The fast kinetics suggest diffusion-controlled formation of the excimer.
Assuntos
Ciclobutanos/química , Etilenos/química , Plásticos/química , Difusão , Cinética , PolimerizaçãoRESUMO
The racemic total synthesis of elegansidiol, farnesiferol B, and farnesiferol D has been obtained following a Diels-Alder approach. Gillman addition, cross metathesis reaction are the other key steps involved in the target synthesis.