Fluorene Analogues of Prodan with Superior Fluorescence Brightness and Solvatochromism

Abstract

In a search for environmentally sensitive (solvatochromic) dyes with superior properties, we extended the electronic conjugation of one of the best solvatochromic dyes, Prodan, by substituting its naphthalene core with fluorene. The newly synthesized fluorene derivatives bearing strong electron-donor (dialkylamino) and -acceptor (carbonyl) groups at the 2 and 7 positions showed red-shifted absorption (close to 400 nm), twice as large of a absorption coefficient (43 000 M -1 cm -1 ), and a manifold larger two-photon absorption cross section (∼400 GM) compared to Prodan. Studies in solvents revealed much stronger fluorescence solvatochromism of the new dyes, which is connected with their twice as large transition dipole moment (14.0 D). Similarly to Prodan, they exhibit high fluorescence quantum yields, while their photostability is largely improved. Thus, substitution of the naphthalene core in Prodan with fluorene resulted in new fluorophores with superior spectroscopic and solvatochromic properties. We expect them to find a variety of applications as environmentally sensitive probes and labels in biology.

A Study of the Kinetics and Mechanism of Oxidation of Fluorene by Alkaline Hexacyanoferrate(III)

“…Fluorene and its derivatives have a large list of significant applications [3][4][5][6][7][8][9][10] as dye-sensitized solar cells, polymer light-emitting diodes and electroemitting materials. Moreover, fluorene is considered as effective and pronounced precursor for synthesis of photochromic di and tetrahydroindolizines [11][12][13][14].…”

Synthesis and Structure of Benzotriazolyl Fluorenes

“…The synthesis and characterization of fluorene derivatives have attracted much attention in recent years because of their interesting properties and potential applications in various fields, such as two-photon absorption dyes, [1][2][3][4][5][6][7][8][9] fluorescent probes, [10][11][12][13][14][15][16][17] and light-emitting materials. [18][19][20][21] It has also been shown that fluorene derivatives exhibit high binding affinity to human serum albumin, 13 β2-integrins, 22 and β-amyloid.…”

“…Alkylation at the 9-position of the fluorene ring can be easily carried out utilizing the acidity of the hydrogens at the 9-position, 5,6,9,[13][14][15][16]21 and introduction of substituents at 2-or 7-position was also effectively accomplished by electrophillic substitution of the fluorene ring. 5,9,[12][13][14][15]21 Further manipulation at 2-or 7-position has been carried out by standard procedures starting from the appropriate fluorene compounds having diversely transformable substituents such as nitro and/or halogen group.…”

“…Alkylation at the 9-position of the fluorene ring can be easily carried out utilizing the acidity of the hydrogens at the 9-position, 5,6,9,[13][14][15][16]21 and introduction of substituents at 2-or 7-position was also effectively accomplished by electrophillic substitution of the fluorene ring. 5,9,[12][13][14][15]21 Further manipulation at 2-or 7-position has been carried out by standard procedures starting from the appropriate fluorene compounds having diversely transformable substituents such as nitro and/or halogen group. In particular, various metal-catalyzed coupling reactions of bromo-or iodo-fluorenes with stannyl compounds (Stille reaction), 1,9 alkenes (Heck reaction), [1][2][3]5,6,15,16 arylboronic acid (Suzuki reaction), 10,18,21 terminal alkynes (Sonogashira reaction), 10 or amines (Buchwald-Hartwig or Ullmann reaction) 5,9,16 provided a variety of alkenyl-, aryl-, alkynyl-, or amino-substituted fluorene derivatives.…”

A Comparative Kinetic Study on the Efficacious Permanganate Oxidation of Fluorenes in Perchloric and Sulfuric Acid Media

“…pronounced high fluorescent quantum yield, countless optical nonlinear properties, photo-stability, and outstanding hole-transporting possessions [7] [8]. For these inserting and multi-addressable properties, fluorenes have been used extensively as focused constituents for organic light-emitting diodes, dye-sensitized solar cells, photosensitizers, emission microscopy [9] [10].…”