title: Effect of the C(3)-Substituent in Verdazyl Radicals on their Profluorescent Behavior.
abstract: 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.
authors.affiliation: Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Eusterwiemann
authors.affiliation: Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Matuschek
authors.affiliation: Center for Nanotechnology, Institute of Physics, Westfälische Wilhelms-Universität Münster, Heisen-bergstrasse 11, 48149 Münster, Germany.
authors.forename: Linda
authors.initials: L
authors.lastname: Stegemann
authors.affiliation: Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany.
authors.forename: Sina
authors.initials: S
authors.lastname: Klabunde
authors.affiliation: Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany.
authors.forename: Carsten C
authors.initials: CC
authors.lastname: Doerenkamp
authors.affiliation: Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: Constantin G
authors.initials: CG
authors.lastname: Daniliuc
authors.affiliation: Institut für Festkörpertheorie and Center for Multi- scale Theory & Computation, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, 48149 Münster, Germany. nikos.doltsinis@uni-muenster.de.
authors.forename: Nikos L
authors.initials: NL
authors.lastname: Doltsinis
authors.affiliation: Center for Nanotechnology, Institute of Physics, Westfälische Wilhelms-Universität Münster, Heisen-bergstrasse 11, 48149 Münster, Germany. ca.s@uni-muenster.de.
authors.forename: Cristian A
authors.initials: CA
authors.lastname: Strassert
authors.affiliation: 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. eckerth@uni-muenster.de.
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert
authors.affiliation: Institute of Organic Chemistry, Department of Chemistry and Pharmacy, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany. studer@uni-muenster.de.
authors.forename: Armido
authors.initials: A
authors.lastname: Studer