TY - JOUR
T1 - Zwitterionic ladder stilbenes with phosphonium and borate bridges
T2 - Intramolecular cascade cyclization and structure-photophysical properties relationship
AU - Fukazawa, Aiko
AU - Yamaguchi, Eriko
AU - Ito, Emi
AU - Yamada, Hiroshi
AU - Wang, Jian
AU - Irle, Stephan
AU - Yamaguchi, Shigehiro
PY - 2011/7/25
Y1 - 2011/7/25
N2 - The synthesis and properties of the phosphonium- and borate-bridged stilbenes are reported. The zwitterionic ladder stilbenes were synthesized by the intramolecular cascade cyclization from the phosphanyl- and boryl-substituted diphenylacetylenes 1. The study of the substituent effects of the phosphanyl and boryl groups revealed the significant dependence of the reactivity on both the nucleophilicity of the phosphanyl group and the electrophilicity of the boryl group. Theoretical calculations indicated that this reaction is initiated by the nucleophilic attack of the phosphanyl group, irrespective of the degree of the electrophilicity of the boryl group, in contrast to the analogous intermolecular reaction promoted by the frustrated Lewis pairs of R3P and B(C6F5)3. Moreover, even in the case of compound 1c, which does not undergo cascade cyclization under thermal conditions, photoexcitation promoted the cyclization to produce the corresponding zwitterionic stilbene 2c, indicative of the potential use as a photoresponsive material. The photophysical properties of a series of zwitterionic stilbenes, 2a-e, also display dependence on the substituents. The fluorescence quantum yields (φF) of the stilbenes 2d and 2e, with electron-withdrawing diarylboryl groups, were an order of magnitude higher than those of 2a-c, with a dimesitylboryl group. Time-resolved fluorescence spectroscopy as well as the measurement of φF in the polymer matrices revealed that the electron-withdrawing diarylboryl groups significantly retarded the nonradiative decay process from the singlet excited state, resulting in a higher φF.
AB - The synthesis and properties of the phosphonium- and borate-bridged stilbenes are reported. The zwitterionic ladder stilbenes were synthesized by the intramolecular cascade cyclization from the phosphanyl- and boryl-substituted diphenylacetylenes 1. The study of the substituent effects of the phosphanyl and boryl groups revealed the significant dependence of the reactivity on both the nucleophilicity of the phosphanyl group and the electrophilicity of the boryl group. Theoretical calculations indicated that this reaction is initiated by the nucleophilic attack of the phosphanyl group, irrespective of the degree of the electrophilicity of the boryl group, in contrast to the analogous intermolecular reaction promoted by the frustrated Lewis pairs of R3P and B(C6F5)3. Moreover, even in the case of compound 1c, which does not undergo cascade cyclization under thermal conditions, photoexcitation promoted the cyclization to produce the corresponding zwitterionic stilbene 2c, indicative of the potential use as a photoresponsive material. The photophysical properties of a series of zwitterionic stilbenes, 2a-e, also display dependence on the substituents. The fluorescence quantum yields (φF) of the stilbenes 2d and 2e, with electron-withdrawing diarylboryl groups, were an order of magnitude higher than those of 2a-c, with a dimesitylboryl group. Time-resolved fluorescence spectroscopy as well as the measurement of φF in the polymer matrices revealed that the electron-withdrawing diarylboryl groups significantly retarded the nonradiative decay process from the singlet excited state, resulting in a higher φF.
UR - http://www.scopus.com/inward/record.url?scp=79960512532&partnerID=8YFLogxK
U2 - 10.1021/om200453w
DO - 10.1021/om200453w
M3 - Article
AN - SCOPUS:79960512532
SN - 0276-7333
VL - 30
SP - 3870
EP - 3879
JO - Organometallics
JF - Organometallics
IS - 14
ER -