CO-Bond Cleavage of Esters with a Naphthyl Group in the Higher Triplet Excited State during Two-Color Two-Laser Flash Photolysis

✍ Scribed by Xichen Cai; Masanori Sakamoto; Minoru Yamaji; Mamoru Fujitsuka; Tetsuro Majima

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 168 KB
• Volume: 13
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200600822

✦ Synopsis

Abstract

A CO‐bond cleavage of esters having a naphthyl group, NpCO‐OR and RCO‐ONp (Np=α‐ and β‐naphthyl (^α^Np and ^β^Np, respectively), R=Ph and Me), was found during the two‐color two‐laser flash photolysis in acetonitrile. The CO‐bond cleavage occurred when NpCO‐OR and RCO‐ONp were excited to the singlet excited states (S~1~). On the other hand, no reaction occurred from the lowest triplet excited states (T~1~). When NpCO‐OR(T~1~) and RCO‐ONp(T~1~) were excited to the higher triplet excited states (T~n~) using the second laser during the two‐color two‐laser flash photolysis, the CO‐bond cleavage occurred. The CO‐bond cleavage quantum yield (Φ) was estimated from the plots of the T~1~‐state esters disappeared within a laser flash versus the second laser intensities. The CO‐bond cleavage in ^β^NpCO‐OPh(T~n~) occurred more efficiently than in ^α^NpCO‐OPh(T~n~) and that in PhCO‐O^β^Np(T~n~) occurred more efficiently than in PhCO‐O^α^Np(T~n~). The Φ value for ester with Ph and β‐Np groups was larger than that for ester with Ph and α‐Np groups. The Φ value for MeCO‐O^α^Np(T~n~) was similar to those for PhCO‐ONp(T~n~), while that for MeCO‐O^β^Np(T~n~) was much smaller than those for PhCO‐ONp(T~n~) and MeCO‐O^α^Np(T~n~). On the other hand, no CO‐bond cleavage was observed in NpCO‐OMe(T~n~). The Φ value depended on the characters of the groups (Np, Ph, and Me) on the ester. Whether R is Ph or Me with or without π electron, respectively, is important for the CO‐bond cleavage. In other words, electronic delocalization of the T~n~ state including Np and ester groups is necessary for the occurrence of the CO‐bond cleavage in NpCO‐OR(T~n~) and RCO‐ONp(T~n~).