Noncovalent Interaction And Its Influence On Spectrum:A Theoretical Study On The Two Kinds Of Aggregates

In this paper, we calculated the electronic structures, the vibrational frequencies and spectral properties of the TPP-DCN mixed coaggregates and PTCDI aggregates using the DFT and TDDFT methods (B3LYP, PBEO, Bhandh, M062X, ωB97XD). Then we analyzed the π-π stacking interactions and electrostatic interactions using the results of the coB97XD method. Furthermore, in order to explore the influence of the π-π stacking interactions on the first excited state, we calculated the structures and vibrational frequencies of the first exited state of the TPP-DCN. The fluorescence spectrum and Huang-Rhys were also calculated. The present results agree well with the experimental observation.1. Noncovalent Interaction and Its Influence on Excited-state Behavior:A Theoretical Study on the Mixed Coaggregates of Dicyanonaphthalene and PyrazolineIn the present work, we investigated the noncovalent interactions of the mixed coaggregates (TPP-DCN) between1,3,5-triphenyl-2-pyrazoline (TPP) and1,4-dicyanonap-hthalene (DCN), and the influence of noncovalent interactions on the excited-state properties of the TPP-DCN was also studied. We calculated the electronic structures, vibrational frequencies, spectral properties,π-π stacking interactions and electrostatic interactions of the TPP-DCN. The effect of the π-π interactions on the excited-state properties of the TPP-DCN was also fully investigated. The calculated results show that the absorption spectrum is equal to the superposition of the monomers’ absorption spectra, whereas the emission spectrum has a new absorption peak. These indicated that the TPP and DCN do not form an intermolecular charge-transfer complex in the ground state, whereas they form an exciplex in the excited state. These feature stand clearly in the spectrum. The theoretical results show that the π-π stacking interactions play an important role in the noncovalent interactions of the TPP-DCN coaggregates, which is the possible reason to result in the new band in the fluorescence spectrum of the TPP-DCN.2. Noncovalent Interaction and Its Influence on absorption spectrum:A Theoretical Study on the PTCDI aggregatesThe equilibrium geometries and vibrational frequencies of the ground states of the3,4,9,10-perylenetetra-carboxylic diimide (PTCDI) monomers and the aggregates are first optimized at the B3LYP, M062X, Bhandh, ωB97XD levels with the6-311++G**and6-31g*basis sets. Based on these results, we calculated the absorption spectra of the monomers and the aggregates using the TD-B3LYP, TD-M062X, TD-Bhandh, TD-coB97XD methods. We select the results of the coB97XD method to analyze the π-π stacking interactions and electrostatic interactions. Our theoretical results indicated that the M062X and ωB97XD methods are much more accurate than the B3LYP method. The Bhandh method has an excellent performance on the calculations of the absorption spectra. The results expose that the π-π interactions are the driving force of noncovalent interactions in the PTCDI aggregates. Comparing the results in the vacuum with that in the solvent, we found that the solvent have a positive influence on the π-π stacking interactions.