Solvent effects on optically detected magnetic resonance in triplet spin labels

• We have calculated solvent effects on the zero-field splitting (ZFS) constants induced by electron spin-spin coupling (SSC) in the low-lying triplet states of azaaromatic molecules in solutions using multiconfiguration self-consistent-field wave functions and the polarizable continuum model. The second-order spin-orbit coupling (SOC) contribution to the splitting of the (3)pipi(*) states is found to be almost negligible, and the calculations therefore provide a good estimate of the ZFS parameters and their solvent dependence based only on the electron spin-spin coupling expectation values. The correlation between the shift in the ZFS and the phosphorescence frequency that has been observed in optically detected magnetic resonance experiments in low-temperature glasses is supported by our direct SSC calculations without taking SOC into account. This makes it possible to distinguish between the two theories that earlier were proposed to explain the inhomogeneous broadening of triplet state spectra, and discard the one that is exclusively based on the SOC-induced mixing of the singlet and triplet states.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

zero-field splitting

solvent effects

triplet spin label

optically detected magnetic resonance

electron spin-spin coupling

field splitting parameters

polarizable continuum model

g-tensor calculations

gaussian-basis sets

anisotropic dielectrics

ionic-solutions

dna complexes

state

phosphorescence

molecules

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