Direct Observation of the Luminescence from the 3(delta)(delta)* Excited State of Re2Cl2(p-OCH3form)4

There are only a few reports on the measurement of the energy of the low-lying 3(delta)(delta)* 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(delta)(delta)* excited state, and the 3(delta)(delta)* state is nonemissive. Here we report the luminescence of Re2Cl2(p-OCH3form)4 [p-OCH3form = (p-CH3OC6H4)NCHN(p-CH3OC6H4)-] observed upon 400-460 nm excitation with maxima at 820 nm (CH2Cl2, (tau)= 1.4 (mu)s) and 825 nm (CH3CN, (tau)= 1.3 (mu)s) at 298 K. From the large Stokes shift, the vibronic progression at 77 K, the quenching by O2, the long lifetime, and the calculated energy of the 3(delta)(delta)* state, the luminescence of Re2Cl2(p-OCH3form)4 and the corresponding transient absorption signal are assigned as arising from the 3(delta)(delta)* (3A2u) excited state of the complex.