Effect of an external heavy atom on the EPR spectrum of the fluorescein semiquinone radical

High-Resolution Ultraviolet Spectroscopy of Neutral and Ionic Clusters: Hydrogen Bonding and the External Heavy Atom Effect

“…118 Its origin is an enhanced spin-orbit coupling strength induced by the heavy atom in the surrounding solvent. Since then, many manifestations of the EHA have been obtained in liquid and rigid solutions, [119][120][121] doped molecular crystals, [122][123][124] and rare-gas matrices. 125,126 Most investigations have focused on the fluorescence quenching of triplet state decay or on the enhancement of T 1 r S 0 absorption in neutral molecules.…”

“…Its origin is an enhanced spin−orbit coupling strength induced by the heavy atom in the surrounding solvent. Since then, many manifestations of the EHA have been obtained in liquid and rigid solutions, − doped molecular crystals, − and rare-gas matrices. , Most investigations have focused on the fluorescence quenching of triplet state decay or on the enhancement of T 1 ← S 0 absorption in neutral molecules. Gas-phase measurements of the influence of the EHA on the triplet lifetime in neutral van der Waals clusters were published for tetracene·Kr and tetracene·Xe, octatetraene·rare-gas clusters, 9-methoxyanthracene·rare-gas clusters, and benzene·Ar and benzene·Kr, whereas a lack of an EHA was reported for 9-cyanoanthracene·rare-gas clusters .…”

Effect of heavy atoms on photochemically induced dynamic nuclear polarization in liquids

“…This result is somewhat surprising because it is known that the EHA effect influences both photophysical and magnetic characteristics of the colliding molecule (in this case the photo-CIDNP dye), including magnetic properties such as the g tensor of the dye. For instance, ESR studies of the fluorescein radical anion dissolved in heavy-atom-containing media like Cs + showed ESR resonance line-broadening in viscous solution [45]. In addition, investigations on magnetic-field effects (MFE) [46, 47] involving quantification of the changes in radical concentration in the absence and presence of magnetic fields showed a reduction in the MFE experienced by p-cresol and fluorescein in the presence of external heavy atoms in fairly viscous solution of >3.5 cp/K, corresponding to, for instance, >1,032 cp at 295 K. Negligible effects were observed media below 1cp/K.…”

“…It is known that the EHA effect is significant only when the collision frequency of the heavy-atom-containing molecule is greater than the rotational frequency of the dye radical [45, 47, 48].…”