Time-Resolved Studies of Aryl Carbenes

Picosecond transient absorption spectroscopy (using a Nd:YAG laser with 355 nm excitation and 440 nm to 640 nm probe) was used to study three aryl carbenes generated by photolysis of their parent diazo compounds in fluid solution. Irradiation of 9-diazofluorene generates a transient with an absorption maximum at 470 nm which is believed to be triplet fluorenylidene. The rate constant for formation of this intermediate was found to be 2.4 (+OR-) 0.7 x 10('9) s('-1) in acetonitrile, 2.0 (+OR-) 0.5 x 10('9) s('-1) in hexafluorobenzene, and > 7 (+OR-) 1 x 10('9) s('-1) in cyclohexane. An additional transient absorbing at 470 nm and 500 nm which is attributed to the 9-fluorenyl radical appears with a rate constant of 7.2 (+OR-) 1.9 x 10('8) s('-1) in cyclohexane and 3.0 (+OR-) 1.8 x 10('8) s('-1) in cyclohexane-d(,12). A broad weak absorption (450 nm to 550 nm) can be detected in under 100 ps after irradiation of 10-diazo-9-mesityl-9,10-dihydro-9-bora-anthracene in cyclohexane. This absorption is most likely due to triplet boraanthrylidene. Transients are rapidly formed (under 100 ps) following irradiation of 11-diazobenzo{b}fluorene in acetonitrile, benzene, and cyclohexane. The transient absorption maximum is at roughly 460 nm in acetonitrile or benzene but is apparently 5 nm to 10 nm less in cyclohexane. These absorptions can be attributed to a carbene(s). A similarly absorbing transient was studied by nanosecond flash photolysis in several solvents and in the presence of a variety of quenchers. EPR studies indicate that irradiation of 11-diazobenzo{b}fluorene in methylcyclohexane (T (LESSTHEQ) 55) generates a triplet ground state carbene (Curie law followed within error).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Brauer, Beth-Ellen

• Chemistry, Physical

Identifier

(UMI)AAI8502081

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70267