Theoretical Investigation On Optical Properties Of Nitro-stilbene Derivatives Via Different Bridged Bond

Conjugated compounds have been widely applied in many fields as optical devices, electroluminescent devices, dye-sensitized solar cells, two-photon materials, nonlinear optical materials due to the machinability, flexibility, easily filming, readily adjusted energy band tuned by chemical method. In 1997, Marder and coworkers reported that derivatives with donor-Ï€- acceptor, donor-Ï€-donor, and donor - acceptor - donor structural motifs exhibit exceptionally high-quality optical properties. In addition, the derivatives with the structure of the donor and acceptor display exceptional photophysical properties and chemical stability. The absorption wavelength of dyes can extend the entire visible region by the variation of their chemical structure. It is significant to investigate the spectral properties of dye molecules, which is the fundamental requirement for application. In this paper, the comprehensive researches were carried out about nitro-stilbene derivatives with different bridged bond by Ab initio method and DFT method. Results showed that the spectral properties of dyes and intramolecular charge transfer exhibited an interrelationship. Intramolecular charge transfer could be regulated by the variation of of substituents to tune the spectral properties of dye at the molecular level. The geometry, Mulliken charge, frontier orbital energy levels, dipole moment, molecular spectroscopy, and so on in the ground state and the excited state were calculated, which provided the theoretical basis for the development of new luminescent materials. Meanwhile, the results are helpful for exploring the high quality and efficient luminescent materials.Nitro-stilbene derivative with benzophenones via ester bridged bond and the"parent moiety"nitro-stilbene derivative with hydroxyl were studied and compared, which revealed a greater difference on the structural characteristics. The electron density in diphenylethylene part in nitro-stilbene containing benzophenone units via ester bridged bond is lower than that of diphenylethylene part in"parent moiety". As a consequence, the ultraviolet/visible absorption of nitro-stilbene derivatives with benzophenones is blue shifted remarkbly. Nitro-stilbene derivatives via ether or ester bridged bond were studied and compared.The results showed that molecular frontier orbital and geometry in excited state have a close dependence. Ester as substituent leads the negative charge transfer to electron-Withdrawing group,the effective conjugation length and dipole moment difference becomes small. Energy gap is enlarged, and thus the absorption spectral nature exhibits blue-shift significantly. Furthermore, comparing with the absorption obtained by TDDFT/HF, the absorption calculated by TDDFT/DFT and are red-shifted for all derivatives. The emission spectrum by TDDFT/CIS is red-shifted with respected to that obtained by TDDFT/HF.