Direct observation of the luminescence from the 3δδ* excited state of Re2Cl2(p-OCH3form)4

There are only a few reports on the measurement of the energy of the low-lying (3)deltadelta* state of quadruply bonded bimetallic complexes, and the direct observation of the (1)delta*delta* excited electronic state was only recently reported. In the quadruply bonded bimetallic complexes reported to date, luminescence arises from their (1)deltadelta* excited state, and the (3)deltadelta* state is nonemissive. Here we report the luminescence of Re2Cl2(p-OCH(3)form)(4) [p-OCH(3)form = (p-CH3OC6H4)NCHN(p-CH3OC6H4)(-)] observed upon 400-460 nm excitation with maxima at 820 nm (CH2Cl2, tau = 1.4 mus) and 825 nm (CH3CN, tau = 1.3 mus) at 298 K. From the large Stokes shift, the vibronic progression at 77 K, the quenching by 02, the long lifetime, and the calculated energy of the (3)deltadelta* state, the luminescence of Re2Cl2(p-OCH(3)form)(4) and the corresponding transient absorption signal are assigned as arising from the (3)deltadelta* ((3)A(2u)) excited state of the complex.