Pentacene Appended to a TEMPO Stable Free Radical: The Effect of Magnetic Exchange Coupling on Photoexcited Pentacene

Understanding the fundamental spin
dynamics of photoexcited pentacene
derivatives is important in order to maximize their potential for
optoelectronic applications. Herein, we report on the synthesis of
two pentacene derivatives that are functionalized with the [(2,2,6,6-tetra­methyl­piperidin-1-yl)­oxy]
(TEMPO) stable free radical. The presence of TEMPO does not quench
the pentacene singlet excited state, but does quench the photoexcited
triplet excited state as a function of TEMPO-to-pentacene distance.
Time-resolved electron paramagnetic resonance experiments confirm
that triplet quenching is accompanied by electron spin polarization
transfer from the pentacene excited state to the TEMPO doublet state
in the weak coupling regime.