Theoretical and Experimental Studies on Raman Spectroscopy of Cyclic Fluorene-Based Strained Semiconductors

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