Ultrasonic synthesis and spectral characterization of a new blue fluorescent dendrimer as highly selective chemosensor for Fe3+ cations

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Abstract

A poly(propyleneamine) dendrimer, comprising four 4-(N,N-dimethylaminoethyloxy)-1,8-naphthalimide units in the dendrimer periphery has been synthesized for the first time. The new blue fluorescent dendrimer has been obtained by nucleophilic substitution of the nitro groups at C-4 position of 1,8-naphthalimide units by N,N-dimethylaminoethyloxy moiety under ultrasonic conditions. Its photophysical characteristics have been investigated in organic solvents of different polarity. The influence of different metal cations on the dendrimer fluorescence has been also investigated viewing its sensor potential.

Highlights

► New blue fluorescent poly(propyleneamine) dendrimer has been synthesized under ultrasonic conditions. ► Photophysical properties have been investigated in organic solvents with different polarity. ► The new dendrimer is selective for Fe3+ ions.

Introduction

In the recent years dendrimers as a new class of polymer compounds have been intensively studied [1]. The modification of the macromolecule comprising fluorophore fragments yields dendrimers possessing new properties that broaden their sphere of applications. Dendrimers are used for versatile purposes in biology, medicine, pharmacy, and electronics; hence the great scientific and practical interest in those compounds [2], [3], [4], [5], [6], [7].

Dendrimers emitting yellow-greenish fluorescence can be obtained by modifying the periphery of poly(amidoamine) (РАМАМ) [8] or poly(propyleneamine) (РРА) [9] dendrimers with 1,8-naphthalimide chromophoric units. Some of those dendrimers have been investigated with regard to their eligibility as fluorescent sensors based on photoinduced electron transfer designed to detect transition metal cations and protons.

In general 4-alkoxy derivatives of 1,8-naphthalimide can be obtained by different synthetic routes. Most of those synthetic methods are based on the nucleophilic substitution of halogen atoms (bromo or chloro) by alkoxylating agents in aprotic organic solvents [10] or alcoholates in the respective alcohols, or solvents [11] at reflux at atmospheric or higher pressure. A hydroxyl group at C-4 position of the 1,8-naphthalimides also can be used for the synthesis of alkoxy derivatives [12]. Interphase catalysis [13] and ultrasound [14] are new modern methods used recently for the synthesis of alkoxy derivatives of 1,8-naphthalimides. The ultrasound as an energy source in the organic synthesis offers many advantages as it reduces reaction time, energy consummation, improves products quality and purity.

In this study we present our firs results about the possibility to utilize ultrasound for the synthesis of a blue fluorescent poly(propyleneamine) dendrimer whose periphery is modified with a 4-(N,N-dimethylaminoethyloxy)-1,8-naphthalimide. The photophysical properties of the new dendrimer in organic solvents of different polarity have been studied. Its sensor potential also has been investigated in the presence of metal cations.

Section snippets

Materials

The synthesis of 4-nitro-1,8-naphthalimide-labelled PPA dendrimer as a precursor for the synthesis was described previously [9b].

Organic solvents (methanol, ethanol, n-propanol, acetonitrile, N,N-dimethylformamide (DMF), acetone, dichloromethane, chloroform, tetrahydrofuran and dimethylsulfoxide) used in this study were of spectroscopic grade, and were used as obtained. Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, PbNO3, Co(NO3)2·6H2O, Zn(NO3)2·4H2O, and Fe(NO3)3·9H2O salts were the metal cation sources and

Synthesis of dendrimer

First we tried to synthesize a blue fluorescent dendrimer with sensor properties using a conventional synthetic route, namely nucleophilic substitution of the bromo atom from 4-bromo-1,8-naphthalimide units with alkoxy groups in boiling N,N-dimethylaminoethanolamine in the presence of sodium hydroxide for 6 h. The product thus obtained was oil-like, dark in color, emitting low fluorescence intensity. Most probably in this case thermal oxidative–destructive processes take place and as a result

Conclusion

For the first time the nucleophilic substitution of a nitro group in a 4-nitro-1,8-naphthalimide bonded to poly(propyleneamine) dendrimer by a N,N-dimethylaminoethyloxy has been carried out under the conditions of ultrasonic synthesis. The reaction yielded a new blue fluorescent dendrimer whit high purity. Its photophysical properties have been investigated in organic solvents of different polarity. The influence of various metal cations (Pb2+, Zn2+, Co2+, Ni2+, Cu2+ and Fe3+) on the

Acknowledgement

PB acknowledge financial support from Spanish Ministry of Science and Innovation, project MAT2009-09671.

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