A combined theoretical and experimental study on the wavelength-dependent photophysics of (ν ⁶-benzene)Mo(CO) ₃

The photochemistry of (ν ⁶-benzene)Mo(CO)3 was investigated by picoseconds time-resolved infrared spectroscopy in n-heptane solution at room temperature. Two excitation wavelengths, 400 and 266 nm, were used. The photophysical processes of this system depend on the excitation wavelength. Excitation with 400 nm light populates predominantly a metal-to-arene charge-transfer excited state which relaxes to the ground state within 150 ps of excitation. In addition, (ν ⁶-benzene)Mo(CO) ₂(n- heptane) is produced in low yield within the rise time of these experiments (500 fs). Excitation with 266 nm radiation results in a depletion of (ν ⁶-benzene)Mo(CO) ₃ absorptions but no excited state or product v _CO absorptions are evident at short time scales (<10 ps). The CO-loss process proceeds over the subsequent 100 ps with concomitant formation of a metal-to-CO chargetransfer excited state and parent recovery. An excited-state model involving excited-state crossing is proposed to explain these observations.