[60]Fullerene-based liquid crystals acting as acid-sensitive fluorescent probes

Abstract

a Functionalization of [60]fullerene with liquid-crystalline dendrimers and a dibutylaniline-based phenylenevinylene moiety leads to supramolecular materials, the fluorescence of which responds to acid-base stimuli.The design of organic materials which can be used for reversible optical data storage and for the construction of photochemical switches requires the synthesis and assembly of components, the physical properties of which can be modulated by light.1 Photonic processes display properties superior to those of electron processes 2 for the following main reasons: (1) in the wavelength domain, multiple processing is achievable, (2) they present a high signal to noise ratio, and, more importantly, (3) since energy and electron transfer processes can occur on a subpicosecond timescale, it is possible to produce devices that respond with equal rapidity.On the other hand, liquid crystals (LCs) are soft materials with great potential for sophisticated applications in advanced technologies.3 LCs exhibit unique properties such as self-organizing behavior within a precise temperature range or a change in refractive index by changing their alignment. Furthermore, LCs are of interest as supramolecular platforms in, e.g., solar cell technology (e.g. fullerene associated with oligophenylenevinylene derivatives) 4 and for the development of photoactive switches (e.g., fullerene associated with ferrocene). 5We report, herein, on the synthesis, liquid-crystalline properties, electrochemical and photophysical behavior of compounds 1a and 1b (Scheme 1) which contain three subunits, i.e.(1) a donor unit formed by two dibutylanilines located at the periphery of a phenylenevinylene-based dendron, (2) [60]fullerene (C 60 ) as an electron acceptor unit, and (3) a secondor third-generation poly(arylester) dendron carrying four or eight cyanobiphenyl mesogenic units, respectively, as a liquid-crystalline promoter. As we will see below, it is possible to control the fluorescence of both the donor and acceptor units by protonation.The synthesis of 1a and 1b (Scheme 1) required the reaction of second- (4a) 6 or third-generation (4b) 7 dendron carrying a carboxylic acid function ( Fig. 1) with thionyl chloride in CH 2 Cl 2 to prepare the corresponding acid chlorides followed by their in situ condensation with fulleropyrrolidine 2 in CH 2 Cl 2 .Fulleropyrrolidine 2 was prepared in 28% yield by [3+2] dipolar cycloaddition of C 60 with the azomethine ylide 8 generated in situ from aldehyde 3 and glycine in chlorobenzene. Aldehyde 3 was prepared in 91% yield using the Scheme 1 Reagents and conditions: (i) t BuOK, THF, r.t., 2 h, then 1 M HCl, 91%; (ii) C 60 , glycine, chlorobenzene, reflux, 6 h, 28%; (iii) 4a or 4b, thionyl chloride, CH 2 Cl 2 , reflux, 7 h, then 2, CH 2 Cl 2 , pyridine, r.t., 30 min, quantitative yields.

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

“…All compounds selforganized into S phases with a reversible acid-triggered switching in fluorescence emission from 498 to 710 nm. 1293 S B phases were also reported by Ohta in a series of fullerodendrons periphery functionalized with cyanobiphenyl mesogens (Scheme 99). 1294 In order to investigate the effect of fullerene on columnar lattice formation, a series of mono, twin, and Janus fullerodendrimers substituted with Percec-type dendrons that exhibit Φ h and Φ r self-organization were prepared through the Bingel reaction (Figure 450).…”

“…The Percec-type dendron was replaced with a phenylene vinylene dendron with dibutyl aniline periphery groups (Scheme ). All compounds self-organized into S phases with a reversible acid-triggered switching in fluorescence emission from 498 to 710 nm . S B phases were also reported by Ohta in a series of fullerodendrons periphery functionalized with cyanobiphenyl mesogens (Scheme ) …”

Fullerenes

“…Electrochemical and photophysical properties of the supramolecular materials have been reported. 64 A series of soluble, high-content C 60 methacrylate polymers have been obtained via controlled addition of an amine-tagged C 60 derivative. The resulting polymers were characterised by UV-Vis, FT-IR and GPC.…”

Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

“…The B1-type AMYs can be generated from the decarboxylative condensation of aldehydes with α-and N-dialkylglycines or from cyclic amino acids (such as proline) [31][32][33], while AMYs of type B2 are accessible through the decarboxylative condensation of N-dialkylglycines [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. The N-H-type semi-stabilized AMYs B3 are generated through decarboxylative condensation of arylaldehydes with α-alkylglycines, while B4-type AMYs are derived from the reaction of glycine [52][53][54][55][56][57][58]. The [3 + 2] cycloadditions of AMYs B1-B4 with alkenes lead to the formation of cycloaddition products 3a-d with attenuated regioand stereoselectivity, since the Ar group is not strong enough to fully localize the negative charge on the carbon connecting to Ar in the 1,3-dipoles.…”