tribromides in solution Andrey S Mereshchenko 1 Kanykey E Karabaeva 1 Patrick Z ElKhoury 2 Suman K Pal 3 and Alexander N Tarnovsky 1 1 Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green Ohio 43403 ID: 1000079
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1. Ultrafast photoisomerization of carbon, boron and phosphorus tribromides in solutionAndrey S. Mereshchenko1, Kanykey E. Karabaeva1, Patrick Z. El-Khoury2, Suman K. Pal3 and Alexander N. Tarnovsky1, 1Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403;2Department of Chemistry, University of California Irvine, Irvine, CA 926973School of Basic Sciences IIT Mandi, Vallabh Degree College Campus, Mandi 175001, India.1
2. Previous Work1. CF2I2 iso-CF2-I-I Ultrafast time-resolved IR : iso-CF2-I-I observed at 400 fs after excitation 2. CH2Br2 iso-CH2-Br-Brh=350 nm h=255 nmIn cyclohexane: isomer stable In CH3CN: isomer formation in ~8.5 ps. Isomer decays (~100 ps) back to the parent.Couple cluster calculations: < 1 kcal mol-1 energy barrier for ground-state isomerizationPatrick El-Khoury et al. Chem. Phys. Lett. 2010, 493, 61CH2Br2Iso-CH2Br2TSPatrick El-Khoury et al. J. Chem. Phys. 2010, 132, 124501
3. ObjectsCHBr3, BBr3, and PBr3 in solution3MethodsUltrafast Time-Resolved Absorption SpectroscopyDFT and TDFT calculationsGoalsDo all this molecules form the isomer with Br-Br bond?Whether DFT methods are good enough to predict photochemistry mechanism?
4. Steady state absorption spectra4λexc = 255 nmnBrσ*X-Br4λexc = 310 nmλexc = 264 nm
5. Gas phase mechanisms5CHBr3CHBr2• + Br•CHBr + Br2hMcGivern, W.S.; Sorkhabi, O.; Suits, A.G.; Derecskei-Kovacs, A; North, S.W. J. Phys Chem. A 2000, 104, 10085. Zou, P.; Shu, J; Sears, T.J.; Hall, G.E.; North, S.W. J. Phys. Chem. A 2004, 108, 1482. Romazin,C.; Boye-Peronne, S.; Gauyacq, D..; Benilan, Y.; Gazeau, M.C; Douin, S. J. Chem. Phys. 2006, 125, 114312.Huang, H.-Y.; Chuang W.-T.; Sharma, R.C.; Hsu, C.-Y.; Lin, K.-C.; Hu, C.-H. J. Chem. Phys. 2004, 121, 5253.PBr3PBr2• + Br•PBr + Br2hBBr3BBr2• + Br•BBr + Br2hBriggs, A. G.; Simmons, R.E. Naturwissenschaften 1980, 67, 402.Moroz, A.; Sweany, L. Inorg. Chem 1992, 31, 5236-5242.Bowie, R.A.; Musgrave, O.C. J. Chem. Soc. 1966, C, 566-571.Ogata, Y.; Izawa, Y.; Tomioka, H.; Ukigai, T. Tetrahedron 1969, 25, 1817-1824.Kennedy, T.; Sinclair, R.S.; Sinclair, T.J. J. Inorg. Nucl. Chem 1971, 33, 2369-2376.Jan-Khan, M.; Samuel, R. Proc. Phys. Soc. 1936, 48 626-641.Bramwell, M. J.; Jaeger, S. E.; Whitehead, J. C. Chem. Phys. Lett. 1992, 196, 547.Bramwell, M. J.; Hughes, C.; Jaeger, S. E.; Whitehead, J. C. Chem. Phys. 1994, 183, 127-134.Latifzadeh, L.; Balasubramanian, K. Chem. Phys. Lett. 1996, 258, 393-399.Briggs, A.G. Spectrochimica Acta A, 1981, 37, 457-458.
6. Transient Absorption Spectra: CHBr3 in MeCH The DA signal < 0.2 ps is due to solventAt 0.2-0.3 ps, the band maxima: ~260, 355, and 395 nmThe 355 nm band decays with the build up of the 395 nm bandThe 395 nm band narrows and red-shifts to 415 nmFinal 255 and 415 nm bandsPump: 255-nm, <1.5 mJ pulse-1
7. Absorption of CHBr2·+ iso-CHBr3Absorption of iso-CHBr3Br·MCH CT absorption
8. Transient Absorption Spectra: CHBr3 in Acetonitrile Early times: 255 nm bandThe 500 nm band emerges after 2 ps,8 ps rise time255-nm Pump: <1.5 mJ pulse-1Long times:the 255 nm band slowly decaysThe 500 nm band:decays completely,270 ps lifetime
9. CHBr2+Iso-CHBr3Iso-CHBr3Br-ACN CT complexCHBr2Isomer decays completely
10. Bromoform: Proposed Scheme
11. BBr3 in Methylcyclohexane11Early times: The 360 nm band rises within our time resolution and decays fast.The 430 band rises and sharpens, 9 ps rise time264-nm Pump: 4 mJ pulse-1Long times:The 430 nm band decays,210 ps lifetime
12. Absorption of iso-BBr3Br-MCH CT absorptionIso-BBr3/MCHExperimental430 nmM062x/PCM402 nmB3LYP/PCM429 nm CAM-B3LYP/PCM440 nmPBE1PBE/PCM400 nm
13. PBr3 in Methylcyclohexane13Early times: The broad 370-400 nm feature rises ≤ 0.3 ps. This follows by narrowing /decay.The 560 nm band rises and blue-shifts, 11 ps rise time310-nm Pump: 4 mJ pulse-1Long times:The 380 nm band decays concurrently with thedecay of the 560 nm band,420 ps lifetime
14. Absorption of iso-PBr3Br-MCH CT complexand PBr2•Iso-PBr3/MCHPBr2•/MCHExperimental560, 390 nm390 nm B3LYP/PCM550, 374 nm391, 325 nmPBE1PBE/PCM487, 348 nm377, 302 nmAbsorption of iso-PBr3
15. Proposed Photochemistry of CHBr3, BBr3, and PBr3Molecule/SolventdecayCHBr3/MCH>>1 nsCHBr3/ACN270 psBBr3/MCH220 psPBr3/MCH440 psX=CH, B, P
16. 16Activation energy vs Reaction rateMolecule/SolventdecayETS -Eiso-XBr3,Kcal/molCHBr3/MCH>>1 ns9.0CHBr3/ACN270 ps5.7BBr3/MCH220 ps5.5PBr3/MCH440 ps6.1X=CH, B, P
17. ConclusionsBromoform, tribromides of boron and phosphorus all afford isomers with Br-Br bond. Possible photochemical mechanism: through the geminate combination of radical fragmentsAb-initio DFT/TDFT calculations accurately predict the UV/vis spectra of intermediates (better than 0.3 eV) as well as decay rates of isomers.17
18. Funding:Ohio Supercomputer CenterBGSU NSF (CAREER, MRI) Tarnovsky group:Veniamin BorinMax PanovButaeva Evgeniia Acknowledgements former members of Tarnovsky group:Dr. Patrick El-Khoury (U. California, Irvine)Dr. Suman Pal (Maldi, India)Igor Zheldakov (University of Kansas, Lawrence)Nathan Crozier (Ohio State University, Columbus)
19. Bromoform in MeCH
20. MeCHACN
21. Isomer lifetime: iso-CH2I2, iso-CHI3 ~5 msPrevious assignment of the 415 nm band to CHBr3-Br CT iserroneousDiffusion-controlled reaction times:10 mM ~ 10-8 sec90 mM ~ 10-9 secNo major bimolecular chemistry !No Major Bimolecular Chemistry