Tris(rhenium fac-tricarbonyl) Polypyridine Functionalized Cyclotriguaiacylene Ligands with Rich and Varied Emission

Trinuclear rhenium fac-tricarbonyl bromide complexes have been synthesized coordinated to the host ligands tris(4-[4-methyl-2,2′-bipyridyl]methyl)cyclotriguaiacylene (L1), tris(4-[4-methyl-2,2′-bipyridoyl])cyclotriguaiacylene (L2), and tris(4-[2,2′,6′,2″-terpyridyl]benzyl)cyclotriguaiacylene (L3). The structure of L1 and complexes [{Re(CO)3Br}3(L1)] (1) and [{Re(CO)3Br}3(L3)] (3) have been elucidated through X-ray single-crystal diffraction, with complex 3 crystallizing as a conglomerate. The steady-state luminescent properties and time-resolved fluorescence studies of the complexes have been conducted and revealed an unusual dual-emission phenomenon for complex 2. Complexes 1 and 2 show red-shifted emission wavelengths in comparison with those typical of monometallic Re(CO)3-bipy-Br complexes, while complex 3 showed an unusual excitation-dependent variation of emission wavelength.