Picosecond anisotropy of the transient absorption of the photochromic mercury dithizone complex in solution

A picosecond Kerr ellipsometry study of the transient anisotropy of the met al dithizonate Hg(HDz)(2) in solution with different organic solvents is pr esented. The Hg(HDz)(2) photochromic complex is one of the first organic dy es shown to exhibit photochromic proprieties. The complex exhibits reversib le photochromism, changing from the normal form A (of orange-yellow colour) to the active form B (of blue colour) after excitation with 532 nm laser l ight. The Kerr ellipsometry signal is observed to decrease with a single ex ponential decay of about 100 ps, that is shown to be independent of the sol vent. This indicates that the signal is dominated by the excited state life time of the molecule. The absence of any spectral signatures relevant to th e excited states of the normal form indicates that formation of the photois omer is a fast process with respect to the lifetime of the exited state. (C ) 2000 Elsevier Science B.V. All rights reserved.