Theoretical investigation of steric effects on the S1 potential energy surface of o-carborane-anthracene derivatives.

TDDFT scan calculations were performed for s-carborane-anthracene derivatives ( o- CB - X -Ant where X=-H, -CH 3 , -C 2 H 5 and tert -butyl or - t Bu) in order to understand the interplay between the steric effects, S 1 potential energy surface (PES) and photophysical properties. The results show that all systems exhibit three local minima on the S 1 PES, which correspond to the emissive LE and TICT state, along with the nonemissive CT state respectively. In the case of the unsubstituted system ( o- CB - H -Ant ), and - CH 3 and - C 2 H 5 substituted cases, S 1 PES is predicted to be quite flat for certain conformations indicating that it is possible for these systems to reach the nonemissive CT state without a large energy penalty. In comparison, conformational pathways for the nonemissive CT state are predicted to be energetically unfavorable for o- CB -t Bu -Ant as a result of both steric and electronic effects. These results provide a mechanism for the enhanced emission of σ-CB-fluorophore molecules with bulky ligands.