Effect of the C(3)-Substituent in Verdazyl Radicals on their Profluorescent Behavior
Steffen Eusterwiemann,
Hellmut Eckert,
Cristian A. Strassert,
Nikos L. Doltsinis,
Constantin G. Daniliuc,
Carsten C Doerenkamp,
Sina Klabunde,
Linda Stegemann,
David Matuschek,
Armido Studer
Affiliations
Steffen Eusterwiemann
Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
Hellmut Eckert
Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany; Instituto da Física em Sao Carlos, Universidade de Sao Paulo, Avenida Trabalhador Saocarlense 400, Sao Carlos, SP 13560, Brazil. [email protected]
Cristian A. Strassert
Center for Nanotechnology, Institute of Physics, Westfälische Wilhelms-Universität Münster, Heisen-bergstrasse 11, 48149 Münster, Germany. [email protected]
Nikos L. Doltsinis
Institut für Festkörpertheorie and Center for Multi- scale Theory & Computation, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, 48149 Münster, Germany. [email protected]
Constantin G. Daniliuc
Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
Center for Nanotechnology, Institute of Physics, Westfälische Wilhelms-Universität Münster, Heisen-bergstrasse 11, 48149 Münster, Germany
David Matuschek
Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
Armido Studer
Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany. [email protected]
Methods for the detection of reactive intermediates such as transient radicals are important in organic chemistry, polymer chemistry, biology or medicine. Along these lines we recently reported that 1,5-diphenyl-6-oxo verdazyl radicals can be used as fluorescent spin sensors. In situ generated C-centered radicals are efficiently trapped by the verdazyls, which in turn undergo transformation from a paramagnetic non-fluorescent state to a diamagnetic fluorescent state. Whereas the N-phenyl substituent in the spin probes is of high importance for obtaining profluorescent behavior, the effect of the C(3)-substituent has not been investigated to date. We herein present the synthesis and characterization of various 1,5-diphenyl-6-oxo-verdazyl radicals bearing differently hybridized C-substituents at the C(3) position. Steady-state and time-resolved fluorescence spectroscopy in solution and in the solid state along with time-dependent density functional theory (TDDFT) calculations reveal that a C(3)-aryl substituent is crucial for obtaining fluorescence after spin trapping. In addition, it is shown that the emission wavelength of the C(3)-aryl substituted verdazyl derivatives can be tuned by selective destabilization of the HOMO and the LUMO.
