Theoretical Investigation On The Vibrationally Resolved Electronic Spectra Of Phenanthrene And Its Derivatives

In the present work, the equilibrium geometries, oscillator strengths, symmetr y together with the vibrational frequencies were calculated based on the density functio na l theory and its time-dependent extension(B3LYP, PBE0, BHandHLYP, M06 L, M062 X and CAM-B3LYP) with different basis sets. For comparison, these parameters of the ground state are also calculated by the second-order perturbation theory(MP2 method) using the same basis sets in this work. In addition, based on the calculated equilibr i um geometries and vibrational frequencies, the vibrational resolved electronic absorption and emission spectra were simulated using Franck-Condon approximation includ ing Herzberg-Teller and Duschinsky effects. By comparing the wel-resolved electronic spectra calculated in this work with the available experimental data and other previous theoretical results, we tentatively assigned most of the vibrational normal modes that appeared in the experimental spectra of phenanthrene and its derivatives. Results indicated that most of vibrational transitions were reproduced correctly. Moreover, in the spectral simulation of phenanthrene, the first-order anharmonic correction was also taken into account. Furthermore, the big difference between the simulated FH(considering the Franck-Condon, Herzberg-Teller and Duschinsky mode mixing effects) spectrum and the FC one(only the Franck-Condon approximation is included) indicated that the contributions of Herzberg-Teller effect and the Duschinsky mode mixing were important and cannot be ignored for the simulation of the weak or forbidden transitions like the S1?S0 band of phenanthrene and its derivatives.1. Improving the simulation of vibrationally resolved electronic spectra of phenanthrene: A computational InvestigationBased on the density functional theory and its time-dependent extension, the equilibrium geometry, oscillator strengths, symmetry and the vibrational frequencies of the ground(S0) and first excited(S1) states of phenanthrene were calculated. In this paper, the information of the S0 and S1 states was obtained at the TDDFT/cc-pVDZ level. The agreement between theoretical calculations and experimental observations was very satisfactory, which served as a basis to discuss the absorption and emission spectra. Besides, the vertical excitation energies were compared with the available experimenta l findings, and a good agreement between the simulated and experimental values could be found. The S1 state was identified as 1Lb. Besides, in approximations of harmonic and anharmonic oscillators, the wel-resolved absorption and emission spectra of phenanthrene were simulated using the Franck-Condon approximation combined with Herzberg-Teller and Duschinsky effects. Moreover, the comparison of the excitation and emission spectra showed that the most notable difference in the spectral profiles was the enormous changes in intensity of the corresponding vibrational bands in the ground and excited states. This indicated that there was a remarkable asymmetry between the excitation and fluorescence and the mirror symmetry was broken down. Exploring these factors is crucial for understanding the photophysical properties of phenanthrene. In our present work, the calculated results indicated that the mirror symmetry breakdown(MSB) is originated mainly from the remarkable Duschinsky mode mixing, Herzberg-Teller effect and the frequency discrepancies between the ground and excited states. Furthermore, most of the vibrational modes were tentatively assigned and compared with the available experimental values.2. Theoretical investigation on the molecular structure and vivrationally resolved electronic spectra of 7, 8-benzoquinolineThe density functional theory and its time-dependent extension together with the second-order perturbation theory(MP2 method) were used for the equilibrium geometry, IR and Raman spectra calculation of 7, 8-benzoquinoline, the calculated results are in good agreement with the experimental data. It can be found that the electronic transitio n to the first excited state of 7, 8-benzoquinoline is not confined to the neighborhood of nitrogen atom, but is delocalized over entire aromatic tings system, much alike that in the molecule of phenantherne. With the optimized geometry of the ground and excited states of 7, 8-benzoquinoline, the transition energies, oscillator strength and frequencies of the vibrational fundamental modes were calculated. Besides, by analyzing the results of molecular orbital of 7, 8-benzoquinoline, it can be found that the electron is inspired from the π orbital and its absorption process should belong to the π-π transition. Moreover, the vibrationally resolved electronic spectrum of phenanthrene in the low-frequency region is simulated in the harmonic approximation considering the contributions of FranckCondon, Herzberg-Teller and Duschinsky effects. The present simulation reproduced correctly most of vibrational transitions in the experimental observations which indicated that the contributions of Herzberg-Teller effect and the Duschinsky mode mixing is indispensable for the simulation of the weak or forbidden transitions like the S1?S0 band of phenanthrene and 7, 8-benzoquinoline. Further more, we attempted to assign a few bands which were not unambiguously assigned in the experimental spectrum of 7, 8-benzoquinoline molecule. Especially, by comparing the vibrationally resolved electronic spectra of 7, 8-benzoquinoline molecule with the spectra of phenanthrene simulated and analyzed in our previous study, it can be found that the spectra of 7, 8-benzoquino l ine contain much more vibrational features, and this increased vibronic activity is related to the symmetry break caused by the introduction of N-heteroatom into the aromatic ring system of phenanthrene.3. Equilibrium geometry and vibrationally resolved electronic spectra of two phenanthridine biguanides: A theoretical studyIn the present work, the equilibrium geometry and vibrational frequencies of two phenanthridine biguanides in the ground and first excited states were computed using the density functional theory(B3LYP and M062X) and its time-dependent extension together with the second-order perturbation theory(MP2 method). Six different basis sets(6-31g*, 6-311+g*, 6-311++g**, TZVP, QZVP and cc-pVDZ) were considered. The infrared and Raman spectra were also calculated and compared with the experimental results, and a good agreement between the simulated and experimental spectra could be found. It indicated that the present calculated equilibrium geometry is consistent with the experimental result. Based on the accurately calculated equilibrium geometry, we simulated the vibrationally resolved electronic absorption and emission spectra in harmonic approximation including the contributions of Franck-Condon, Herzberg-Teller and Duschinsky effects. Moreover, we tentatively assigned the main vibrational modes and compared the theoretical results with the experimental ones. As far as we know, the absorption or emission spectra of the phenanthridine biguanides have not been reported yet. Thus, we expect that the spectral simulations presented in this paper could be helpful to have a better understanding of the photophysical properties of phenanthrid ine biguanides.