Non-photochemical spectral hole-burning mediated by water molecules in interligand pockets of [Cr(terpy)2]3+

Low temperature fluorescence line-narrowing (FLN) and spectral hole-burning experiments (SHB) were performed in the 2E←4A2 spin–flip transition of [Cr(2,2′:6′,2″-terpyridine)2]3+ in frozen ethylene glycol/water (2 ∶ 1) and DMSO/water (2 ∶ 1) glasses. In the FLN experiments an average 2E splitting of 23 cm−1 is observed. It is concluded that the interaction with water molecules in pockets provided by the ligands is most likely to be responsible for the relatively efficient non-photochemical hole-burning. Fast spectral diffusion and spontaneous hole-filling prevent the observation of holes above 20 K. The FLN and SHB experiments were performed by using a diode laser.