Structure and Properties of 9-(Cycloheptatrienylidene)fluorene and Its Derivatives

Abstract

One sesquifulvalene, 9-(cycloheptatrienylidene)fluorene, was found to be composed of a flat fluorenylidene part and a non-planar cycloheptatrienylidene moiety. 1-Substituted 9-(cycloheptatrienylidene)fluorene was not obtained because of a steric repulsion between the 1-substituent and the 7′-hydrogen of the seven-membered ring. Upon consideration of their 13C NMR spectra, the electronic properties of the seven-membered ring are slightly influenced by introducing a substituent (halogen, methoxy group, etc.) on the fluorenylidene part. The dissolution of 9-(cycloheptatrienylidene)fluorene in trifluoroacetic acid–chloroform afforded the (9-fluorenyl)tropylium cation. The substituent attached to the fluorene part also slightly influences the tropylium moiety.

Fluorescent chemosensors based on 9-cycloheptatrienylidene fluorenes (9-CHFs)

“…In 2001, Minabe et al reported that 9-CHF was composed of a flat fluorenylidene part and a non-planar cycloheptatrienylidene moiety (Scheme 2). 17 The bond length at C9-C1 0 was 1.360 Å with A mostly double bond character, while the dihedral angle between C9-C1 0 -C2 0 -C3 0 was found to be 1371. This result indicated that a stronger interaction existed in the molecule and the aromaticity was repelled.…”

“…A variation in the chemical shifts was observed by 1 H NMR spectra. 17 In fact, the acidification process of 9-CHF could be tracked and measured by an UV-vis spectrophotometer. 36 As a result of the gradual addition of concentrated sulfuric acid or concentrated hydrochloric acid, two new bands at 267 nm and 230 nm were observed with the appearance of three clear isosbestic points at 316 nm, 258 nm, 235 nm (Scheme 4).…”

“…Sesquifulvalene has been actively studied since the 1960s, [1][2][3][4][5][6][7][8] and 9-cycloheptatrienylidene fluorene (9-CHF) is one of the most attractive sesquifulvalenes. [9][10][11][12][13] However, most researchers have focused their attention on its structure [14][15][16][17] and reactivities, 13,18,19 and only a few of them have paid attention to its applications, 17 e.g., as a fluorescent chemosensor. Because 9-CHF itself is non-emissive, caused by the non-planar configuration, 17 modification of 9-CHF to make its derivative compounds fluorescent is the key to breaking through the limitation of its fluorescent applications.…”

“…[9][10][11][12][13] However, most researchers have focused their attention on its structure [14][15][16][17] and reactivities, 13,18,19 and only a few of them have paid attention to its applications, 17 e.g., as a fluorescent chemosensor. Because 9-CHF itself is non-emissive, caused by the non-planar configuration, 17 modification of 9-CHF to make its derivative compounds fluorescent is the key to breaking through the limitation of its fluorescent applications. This is quite different from the versatile BODIPYs, [20][21][22][23][24][25][26] which emit light inherently and are frequently used as fluorescent chemosensors with high emission efficiencies.…”

Electron Transfer and Aggregate Formation Coinduced Emission Enhancement of 9-Cycloheptatrienylidene Fluorenes in the Presence of Cupric Chloride

“…2,7-Dibromo-9-(cycloheptatrienylidene)fluorene, 2,7-dibromo-9-(2,4,6-cycloheptatrienyl)fluorene, 3 , 5 , 6 , and 8 were prepared and characterized as described previously. , …”