Time-dependent density functional theory study of the excited-state dihydrogen bonding: clusters of 2-pyridone with diethylmethylsilane and triethylgermanium.

Density functional theory (DFT) was carried out to identify the existence of intermolecular dihydrogen bonds of the 2-pyridone (2PY)-diethylmethylsilane (DEMS) and 2PY-triethylgermanium (TEGH) clusters in the ground state. The H···H distances of both clusters are shorter than the sum of their van der Waals radii. Thus, intermolecular dihydrogen bonds N-H•••H-Si and N-H•••H-Ge exist in the 2PY-DEMS and 2PY-TEGH clusters, respectively. Based on the ground-state conformations, intermolecular dihydrogen bonds N-H•••H-Si and N-H•••H-Ge in the electronically excited state of the 2PY-DEMS and 2PY-TEGH clusters were also investigated using time-dependent density functional theory (TDDFT). Electronic transition of the 2PY-DEMS cluster resembles that of the 2PY-TEGH cluster. Their S(1) state is a locally excited (LE) state centered on 2PY moiety. The H•••H distances of the 2PY-DEMS and 2PY-TEGH clusters both stretch in the S(1) state compared to those in the ground state. Upon electronic excitation, intermolecular dihydrogen bonding N-H•••H-Si and N-H•••H-Ge can weaken with decreasing dihydrogen bonding energies.