环状芴基张力半导体拉曼光谱理论与实验研究

Cyclic fluorene-based strained semiconductors which achieve both merits of hoop-shaped cycloparaphenylenes and fluorene-based emitters with high-efficiency feature have attracted increasing attention from synthetic chemists and theoreticians due to their aesthetic molecular structure, radial p orbitals and nanosized cavities. Compared with linear fluorene-based semiconductors, Cyclic fluorene-based strained semiconductors exhibit unique photoelectrical properties. For example, contrary to the deep blue emission of linear fluorene-based molecules, the controlled cyclic fluorene-based strained molecules show stronger green emission. However, the properties of molecular vibrations of cyclic fluorene-based strained materials have not been reported so far. In this article, [4]Cyclo-9,9-dipropyl-2,7-fluorene (CF) and linear quaterfluorenes (LF) were synthesized as modeling compounds to explore the differences of Raman spectra on structures by theoretical and experimental studies. Raman spectroscopy measurements have been presented on polymer poly(9,9-dioctylfluorene) (PFO) and LF, and compare them with CF. In addition, we have calculated the theoretical Raman spectra of CF and LF based on time-dependent density functional theory (TDDFT), which are then compared to the experimental results for the assignment of different modes. All calculations were performed at 6-31G (d) basis set along with the range corrected B3LYP density functional. The results demonstrate that the Raman peak positions of CF which are analogous to those of carbon nanotubes such as G band are shifted. Compared to the Raman spectra of LF, G₁ and G₂ peaks of CF shifted to lower frequency region, however G₃ peaks shifted to higher frequency region. The relative intensity of Raman peaks in CF especially in low frequency region has increased. These properties of Raman in CF can be assigned to the changed structure of conjugated backbone and electrical structure due to strain and every fluorene unit of CF has involved in vibration and the delocalization of π electrons gets higher. These results provide powerful basis for correlating structure and properties on strain organic semiconductors by Raman spectra.