Exciton coupling effects and conformational change of perhexyloligosilanes with optically active methyl(1-naphthyl)phenylsilyl terminals

• Published in: Chirality (New York, N.Y.) N.Y.), 2003, Vol.15 (7), p.646-653
• Main Authors: Oh, Hyun-Shik, Park, Lee-Soon, Kawakami, Yusuke
• Format: Article
• Language: English
• Subjects: CD exciton chirality; conformation control; exciton coupling effect; oligosilane; optically active; silicon stereochemistry
• ISSN: 0899-0042; 1520-636X
• DOI: 10.1002/chir.10276

Perhexyloligosilanes (R,R)‐(+)‐MeNpPhSi*(Hex2Si)nSi*PhNpMe (n = 2; (R,R)‐(+)‐4a, n = 4; (R,R)‐(+)‐6a, n = 6; (R,R)‐(+)‐8a) with chiral methyl(1‐naphthyl)phenylsilyl terminals were synthesized and characterized. The absorption wavelengths λmax by 1La,Ph transition of phenyl chromophore conjugated with oligosilane units in (R,R)‐(+)‐4a – (R,R)‐(+)‐8a show bathochromic shift of about 3–4 nm compared with those of the α,ω‐phenyl substituted perhexyloligosilanes Ph(Hex2Si)mPh (m = 4; 4b, m = 6; 6b, m = 8; 8b) having the same silicon chain length. Longer chain length induces the separated λmax of 1La,Ph from 1Bb,Np of naphthyl chromophore with positive exciton chiralities. In (R,R)‐(+)‐8a, although the extremum wavelengths λext of exciton coupling between 1Bb,Np and 1La,Ph are separated by about 80 nm, the compound retains the positive exciton chirality, which provides definite information on the absolute configuration of terminal chiral silicon atoms. Bulky terminal substituents and lowering the temperature affect the conformation of the main chain, inducing extended silicon backbone structure. Chirality 15:646–653, 2003. © 2003 Wiley‐Liss, Inc.