Modulation of electronic structures of thienylene vinylene oligomers by substituents and solvents: ground and excited states

Abstract

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (S 0 ) states, the electronic structures of first singlet excited (S 1 ) states are rather delocalized. The electron-donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S 0 ! S 1 absorption energies and S 1 ! S 0 emission energies of 2TV derivatives. The NO 2and NH 2 -substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro-substituted 2TV exhibit noticeable red shifts as the medium polarity increases.ELECTRONIC STRUCTURES OF 2TV OLIGOMERS a The DFT and TD-DFT calculations were performed in TURBOMOLE package. b The shifts of transition energies for series 2-3 with respect to 2TV (1) are provided in parentheses. c Attempts to optimize the excited-state geometries of 2a and 2d using TD-DFT method at the B3LYP/TZVP level failed due to instabilities in their DFT reference wave functions. Figure 6. Solvent shifts of (a) S 0 ! S 1 absorption and (b) S 1 ! S 0 emission spectra of ring-substituted 2TV derivatives by NO 2 group, 3f, with increasing the solvent polarity. The data were obtained from TD-DFT/PCM calculations at the B3LYP/6-31þG * level

Tuning the Photophysical Properties of Pyrene-Based Systems: A Theoretical Study

“…The design of these new structures needs accurate knowledge of the effects induced by the substituents on the electronic properties of the pyrene moiety. Quantum chemical studies − can give a powerful test bench for an a priori correlation between the structural and electronic properties, thus helping to address the synthesis of new molecules for photovoltaic applications. In this field, the investigation of new hybrid systems based on organic dyes and noble metal (Ag, Au) or semiconductor (TiO 2 ) nanoparticles, seen in Scheme , can be of particular interest.…”