Knowledge Bank

We have extended the study of field effects on triplet-triplet $annihilation1,2$ to a system in which triplet encounters can result in excimer ($\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}D\ast$) formation (1) as well as in energy transfer (2).\begin{eqnarray}\[-12pt]{^3{M}^{}+^3{M}^{}}^{\nearrow\raise5pt\hbox{$1D\ast$}}_{\searrow\lower5pt\hbox{$1M\ast +1M$}}\end{eqnarray} The field effect on the intensities of monomer and excimer delayed fluorescence (df) was found to be identical under all conditions. This result suggests a common spin-selective step in the processes giving rise to df and is discussed in the light of previously proposed mechanisms. The field dependence of the df was found to be strongly solvent dependent. This is attributed to photochemical doublet radical formation ($\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Q). $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Q affects the field dependence through spin selectivity in the triplet quenching reaction (3).\begin{equation}^2{Q}+^3{M}^{*}\longrightarrow^2{Q}+^1{M}\end{equation}