Olesya A. Krumkacheva †, Vitaly R. Gorelik †, Elena G. Bagryanskaya †, Natalia V. Lebedeva ‡ and Malcolm D. E. Forbes ‡ Supramolecular Photochemistry in β-Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation † International Tomography Center, Institutskaya 3a, Novosibirsk , Russia ‡ Caudill Laboratories, Department of Chemistry, CB #3290, University of North Carolina, Chapel Hill, North Carolina

The Host-Guest systems as “nanocontainers” for the photochemical reaction It can be used for the directional synthesis hνhν The application the Chemical Induced Dynamic Nuclear Polarization (CIDNP) and TR EPR methods allows to obtain information about the mechanism of photochemical reaction inaccessible by other methods. Carrying out photochemical reaction in organized media can lead to the product structure changing  Alteration of the re-encounter statistics and average distance between partners in radical pair  Alter ation the nature of the excited states  Reactivity between host and guest

TR EPR method nonequilibrium population of spin level EPR signal Laser pulse Direct observation of the short-lived paramagnetic intermediates (triplet molecules, radicals) formed during photolysis M h R 1 (H)R 2 T S M *S M T R 1 (H) R2R2 absorption emission Investigation of the radical’s mobility

M h R 1 (H)R 2 T S In-cage products M *S M T R 1 (H) R2R2 Escape products CIDNP method emission enchanced absorption Advantages: 1)Investigation of the mechanisms of photochemical radical reactions 2)Possibility to detect product with low yield (10 -6 M/l) 3)Detection of intermediate product

Investigation of the influence of β-cyclodextrin presence on the mechanism of the ketones photolysis: dibenzyl ketone (DBK), deoxybenzoin (DOB) and benzophenone (BP) For the Complex formation : NMR and UV spectroscopy For the Mechanism of photochemical reaction: TR EPR and CIDNP methods Goal: Research Methods:

Ketone’s photolysis

Guest NMR spectrum PhCOPh CD CIDNP spectrum Observed TR EPR spectrum Ketyl radical CD radical Magnetic field, mT Photolysis of  -CD / benzophenone complex  hydrogen abstraction from CD cavity interior  Strong exchange interaction in radical pair  location of ketyl radical inside CD cavity  increasing of the Radical Pair lifetime

PhCH 2 COPh (PhCH 2 ) 2 Magnetic field, mT Ketyl radical Observed TR EPR spectrum NMR spectrum CIDNP spectrum Guest  α-cleavage and hydrogen abstraction Photolysis of  -CD / deoxybenzoin complex  Strong exchange interaction in radical pair  location of ketyl radical inside CD cavity  formation of rearrangement product  Increasing of radical pair lifetime  -CD radical CD

NO! TR EPR Signal  fast radicals recombination inside CD (  < 100 ns) (PhCH 2 ) 2 CO (PhCH 2 ) 2 NMR spectrum CIDNP spectrum Guest  α-cleavage Photolysis of  -CD / dibenzyl ketone complex (PhCH 2 ) 2 CO

 Photophysics and photochemistry of DOB, DBK, and BP in β- CD inclusion complexes had been examined in detail. The DOB triplet state undergoes both reactions whereas the DBK triplet shows exclusively  -cleavage and the BP triplet shows exclusively H-atom abstraction. Results  Observation of rearrangement product of the radicals from  - cleavage implies that there is substantial mobility of the radicals into the CD interior  It was found that there is a fast radicals recombination inside CD in the case of the  -cleavage reaction (t < 100 ns)  It was shown that there is a strong exchange interaction between the ketyl and CD radicals, due to location of ketyl radical inside CD. Langmuir, 2010, 26 (11), pp 8971–8980

Thank you for your kind attention ! Olesya A. Krumkacheva International Tomography Center SB RAS Supramolecular Photochemistry in β-Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation

Photochemistry in Octa Acid capsules Guest Radical, rotating in the capsule Radical, fixed into the capsule Varying the correlation between host and guest sizes we can manage the chemical reaction way NMR method CIDNP method CIDNP method

ХПЭ при фотолизе кетонов в водном растворе ЦД ДБК ДОБ Нет сигнала ХПЭ Быстрая рекомбинация радикалов в ЦД Кетильный радикал (a) + радикал от ЦД (c) БФ S-T - механизм формирования поляризации