ASSIGNMENTS OF GROUND-STATE AND EXCITED-STATE SPECTRA FROM TIME-RESOLVED ABSORPTION AND CIRCULAR-DICHROISM MEASUREMENTS OF THE E-2 STATE OF (DELTA)-CR(BPY)3(3+)

Time-resolved absorption and circular dichroism (CD) spectra of the 2E excited state of (Δ)-Cr(bpy)33+ are obtained, and assignments of both spectra are made. Excited-state absorption bands at 445 (є ≃ 3800) and 385 nm (є ≃ 8000) are assigned as due to the sum of intensity from both ligand-to-metal charge-transfer (LMCT) and metal-to-ligand charge-transfer (MLCT) transitions. Excited-state CD bands at 430 nm (Δє ≃ −8) and 334 nm (Δє ≃ −11) are also attributed to a sum of CD intensity from LMCT and MLCT transitions, while an excited-state CD band at 268 nm (Δє ≃ −26) is assigned as due solely to an LMCT transition. The magnitudes of the CDs in the ligand long-axis ππ* transitions are similar for the 2E excited state and the 4A2 ground state. The excited-state absorption and CD spectra are consistent with a purely metal-centered description of the excited state. Reassignments of the ground-state absorption and CD spectra are made. Both ground-(4A2) and excited-state (2E) CD spectra reveal transitions not seen in the unpolarized absorption spectra. © 1990, American Chemical Society. All rights reserved.