Internal conversion decay dynamics associated with the potential energy surfaces of three low-lying singlet excited electronic states, S-1 (pi pi (*), A '), S-2 (pi pi (*), A '), and S-3 (n pi (*), A ''), of tropolone are investigated theoretically. Energetic and spatial aspects of conical intersections of these electronic states are explored with the aid of the linear vibronic coupling approach. Symmetry selection rules suggest that non-totally symmetric modes would act as coupling modes between S-1 and S-3 as well as between S-2 and S-3. We found that the S-1-S-2 interstate coupling via totally symmetric modes is very weak. A diabatic vibronic Hamiltonian consisting of 32 vibrational degrees of freedom is constructed to simulate the photoinduced dynamics of S-0 -> S-1 and S-0 -> S-2 transitions. We observe a direct nonadiabatic population transfer from S-1 to S-3, bypassing S-2, during the initial wavepacket propagation on S-1. On the other hand, the initial wavepacket evolving on S-2 would pass through the S-2-S-3 and S-1-S-3 conical intersections before reaching S-1. The presence of multiple proton transfer channels on the S-1-S-2-S-3 coupled potential energy surfaces of tropolone is analyzed. Our findings necessitate the treatment of proton tunneling dynamics of tropolone beyond the adiabatic symmetric double well potentials.
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