Phosphorescent Modulation of Metallophilic Clusters and Recognition of Solvents through a Flexible Host-Guest Assembly: A Theoretical Investigation

MP2 (Second order approximation of Moller-Plesset perturbation theory) and DFT/TD-DFT (Density functional theory/Time-dependent density functional theory) investigations have been performed on metallophilic nanomaterials of host clusters [Au(NHC)(2) ](+)center dot center dot center dot[M(CN)(2)](-)center dot center dot center dot[Au(NHC)(2)](+) (NHC = N-heterocyclic carbene, M = Au, Ag) with high phosphorescence. The phosphorescence quantum yield order of clusters in the experiments was evidenced by their order of mu(S1)/Delta ES1-T1 values (mu(S1): S-0 -> S-1 transition dipole, Delta ES1-T1: splitting energy between the lowest-lying singlet Si and the triplet excited state T-1 states). The systematic variation of the guest solvents (S1: CH3OH, S2: CH3CH2OH, S3: H2O) are employed not only to illuminate their effect on the metallophilic interaction and phosphorescence but also as the probes to investigate the recognized capacity of the hosts. The simulations revealed that the metallophilic interactions are mainly electrostatic and the guests can subtly modulate the geometries, especially metallophilic Au center dot center dot center dot M distances of the hosts through mutual hydrogen bond interactions. The phosphorescence spectra of hosts are predicted to be blue-shifted under polar solvent and the excitation from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) was found to be responsible for the (MLCT)-M-3 (triplet metal-to-ligand charge transfer) characters in the hosts and host-guest complexes. The results of investigation can be introduced as the clues for the design of promising blue-emitting phosphorescent and functional materials.