Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe
The photophysics and photochemistry of (l-biphenyl-4-yl-l-methyl-ethyl)- tert-butyl diazene were thoroughly studied by laser flash photolysis from the picosecond to the microsecond time domain. The compound has favorable features as a radical photoinitiator and as a probe for cage effect studies in...
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2009
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v113_n19_p5531_Hoijemberg http://hdl.handle.net/20.500.12110/paper_10895639_v113_n19_p5531_Hoijemberg |
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paper:paper_10895639_v113_n19_p5531_Hoijemberg2025-07-30T18:42:14Z Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe Hoijemberg, Pablo Ariel Aramendía, Pedro Francisco Biphenyl moiety C-O stretching Cage effect Compressed gas Diazene Disproportionation Electronic energies Ethyl radicals Fluorescence lifetimes IR measurements Laser flash photolysis N-Hexane NO dissociation Photo-initiator Photophysics Picosecond Reference compounds Room temperature Second-order rate constants Time domain Time range Effluent treatment Hexane Ketones Photodissociation Photolysis Probes Sulfur compounds Supercritical fluids Rate constants The photophysics and photochemistry of (l-biphenyl-4-yl-l-methyl-ethyl)- tert-butyl diazene were thoroughly studied by laser flash photolysis from the picosecond to the microsecond time domain. The compound has favorable features as a radical photoinitiator and as a probe for cage effect studies in liquids, supercritical fluids, and compressed gases. The biphenyl moiety acts as an antenna efficiently transferring electronic energy to the dissociative 1n,π* state centered on the azo moiety. By picosecond experiments irradiating at the biphenyl-and at the azo-centered transitions, we were able to demonstrate this fact as well as determine a lifetime of 0.7 ps for the buildup of 1-biphenyl-4-y1-1-methyl-ethyl radicals (BME ·). The sum of in-cage reaction rate constants of BME· radicals by combination and disproportionation is 5 × 1010 s-1. The free radical quantum yield in solution is 0.21 (ØBME·) in n-hexane at room temperature, whereas the dissociation quantum yield approaches 50%. The symmetric ketone, 2,4-bis-bipheny1-4-y1-2,4-dimethyl-pentan-2-one, was used as a reference compound for the production and reaction of BME· radicals. Transient IR measurements show CO stretching bands of the excited 3π, π* and 1n,π* states but no dissociation up to 0.5 ns. A fluorescence lifetime of 1 ns for this ketone is consistent with this observation. By transient actinometry and kinetic decays in the microsecond time range, we measured εBME· = (2.3 ± 0.2) × 104 M-1 cm-1 at 325 nm and a second-order rate constant of 5.8 × 109 M -1s-1 for the consumption of BME· radicals. © 2009 American Chemical Society. Fil:Hoijemberg, P.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Aramendía, P.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2009 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v113_n19_p5531_Hoijemberg http://hdl.handle.net/20.500.12110/paper_10895639_v113_n19_p5531_Hoijemberg |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Biphenyl moiety C-O stretching Cage effect Compressed gas Diazene Disproportionation Electronic energies Ethyl radicals Fluorescence lifetimes IR measurements Laser flash photolysis N-Hexane NO dissociation Photo-initiator Photophysics Picosecond Reference compounds Room temperature Second-order rate constants Time domain Time range Effluent treatment Hexane Ketones Photodissociation Photolysis Probes Sulfur compounds Supercritical fluids Rate constants |
| spellingShingle |
Biphenyl moiety C-O stretching Cage effect Compressed gas Diazene Disproportionation Electronic energies Ethyl radicals Fluorescence lifetimes IR measurements Laser flash photolysis N-Hexane NO dissociation Photo-initiator Photophysics Picosecond Reference compounds Room temperature Second-order rate constants Time domain Time range Effluent treatment Hexane Ketones Photodissociation Photolysis Probes Sulfur compounds Supercritical fluids Rate constants Hoijemberg, Pablo Ariel Aramendía, Pedro Francisco Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| topic_facet |
Biphenyl moiety C-O stretching Cage effect Compressed gas Diazene Disproportionation Electronic energies Ethyl radicals Fluorescence lifetimes IR measurements Laser flash photolysis N-Hexane NO dissociation Photo-initiator Photophysics Picosecond Reference compounds Room temperature Second-order rate constants Time domain Time range Effluent treatment Hexane Ketones Photodissociation Photolysis Probes Sulfur compounds Supercritical fluids Rate constants |
| description |
The photophysics and photochemistry of (l-biphenyl-4-yl-l-methyl-ethyl)- tert-butyl diazene were thoroughly studied by laser flash photolysis from the picosecond to the microsecond time domain. The compound has favorable features as a radical photoinitiator and as a probe for cage effect studies in liquids, supercritical fluids, and compressed gases. The biphenyl moiety acts as an antenna efficiently transferring electronic energy to the dissociative 1n,π* state centered on the azo moiety. By picosecond experiments irradiating at the biphenyl-and at the azo-centered transitions, we were able to demonstrate this fact as well as determine a lifetime of 0.7 ps for the buildup of 1-biphenyl-4-y1-1-methyl-ethyl radicals (BME ·). The sum of in-cage reaction rate constants of BME· radicals by combination and disproportionation is 5 × 1010 s-1. The free radical quantum yield in solution is 0.21 (ØBME·) in n-hexane at room temperature, whereas the dissociation quantum yield approaches 50%. The symmetric ketone, 2,4-bis-bipheny1-4-y1-2,4-dimethyl-pentan-2-one, was used as a reference compound for the production and reaction of BME· radicals. Transient IR measurements show CO stretching bands of the excited 3π, π* and 1n,π* states but no dissociation up to 0.5 ns. A fluorescence lifetime of 1 ns for this ketone is consistent with this observation. By transient actinometry and kinetic decays in the microsecond time range, we measured εBME· = (2.3 ± 0.2) × 104 M-1 cm-1 at 325 nm and a second-order rate constant of 5.8 × 109 M -1s-1 for the consumption of BME· radicals. © 2009 American Chemical Society. |
| author |
Hoijemberg, Pablo Ariel Aramendía, Pedro Francisco |
| author_facet |
Hoijemberg, Pablo Ariel Aramendía, Pedro Francisco |
| author_sort |
Hoijemberg, Pablo Ariel |
| title |
Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| title_short |
Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| title_full |
Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| title_fullStr |
Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| title_full_unstemmed |
Photophysics and photochemistry of an asymmetrically substituted diazene: A suitable cage effect probe |
| title_sort |
photophysics and photochemistry of an asymmetrically substituted diazene: a suitable cage effect probe |
| publishDate |
2009 |
| url |
https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v113_n19_p5531_Hoijemberg http://hdl.handle.net/20.500.12110/paper_10895639_v113_n19_p5531_Hoijemberg |
| work_keys_str_mv |
AT hoijembergpabloariel photophysicsandphotochemistryofanasymmetricallysubstituteddiazeneasuitablecageeffectprobe AT aramendiapedrofrancisco photophysicsandphotochemistryofanasymmetricallysubstituteddiazeneasuitablecageeffectprobe |
| _version_ |
1840323229692985344 |