Synthesis and photophysical studies of through-space conjugated [2.2]paracyclophane-based naphthalene fluorophores

E. Benedetti (1) , M.-L. Delcourt (1) , B. Gatin-Fraudet (1) , S. Turcaud (1) , L. Micouin (1)

1 LCBPT - UMR 8601 - Laboratoire de Chimie et de Biochimie Pharmacologiques et Toxicologiques

In this work we report a straightforward method for the synthesis of a new class of small organic fluorophores bearing both [2.2]paracyclophane and naphthalene subunits using an intramolecular dehydrogenative Diels-Alder reaction as a key step. These compounds are characterized by a compact three-dimensional structure as well as through-space conjugated push-pull systems, and possess interesting spectroscopic characteristics that may be useful for the development of innovative chemical probes and optical sensors. Since the discovery of their parent compound in 1949, 1 mono-and polysubstituted [2.2]paracyclophane derivatives (pCp) have attracted increasing attention within the scientic community and have become the object of many studies in the last few decades. Initial investigations on the synthesis and derivatization of [2.2]paracyclophanes mainly aimed at disclosing the unusual reactivity of these molecules. 2 More recently, functionalized pCps have emerged as powerful ligands or auxiliaries in asym-metric catalysis and stereoselective synthesis. 3 Substituted paracyclophanes also found applications in material sciences as monomers for the synthesis of through-space conjugated polymers , 4 or for the production of functionalized surfaces using chemical vapor deposition (CVD) methods. 5 Due to their uncommon electronic structure, [2.2] paracyclophanes display intrinsic uorescence and can be employed to access new organic dyes. Accordingly, a wide range of pCp-based stilbene uorophores have been reported in the literature over the past few years. 6 These molecules typically present a "branched" p-extended three-dimensional structure functionalized with differently substituted para-phenylene vinylene subunits (Fig. 1a). The pCp-based stilbene uo-rophores, whose photophysical properties are generally tuned by introducing electron-donating or electron-withdrawing groups on their alkene moieties, revealed to be particularly useful in solid state application for the development of organic light-emitting diodes (OLEDs), 7 and non-linear optical materials. 8 A different approach to modulate the spectroscopic characteristics of the pCp-based uorophores consists in expanding the benzene rings of [2.2]paracyclophane to functionalized poly-condensed aromatic hydrocarbons. This should lead to more compact dyes potentially useful for the design of innovative chemical probes and biosensors. Surprisingly, this approach has only been scarcely investigated up to now. 9 In this context, our group recently became interested in the possibility to incorporate naphthalene p-conjugated frameworks (Fig. 1b) into one of the aromatic decks of pCp to tune their photophysical properties. 10 We therefore decided to focus our attention on the elaboration of pCp-based naphthalene frameworks (Fig. 1c) by an intramolecular dehydrogenative-Diels-Alder (DDA) reaction. This strategy was reported to be particularly versatile for the synthesis of tunable sol-vatochromic uorophores, 11 but has never been described on pCp. The DDA precursors 4a-h were prepared in three steps starting from differently substituted 4-formyl-[2.2] Fig. 1 (a) Structure of pCp-based stilbene fluorophores. (b) General structure of two-dimensional naphthalene systems. (c) Structure of pCp-based naphthalene fluorophores.

Domaines: Chimie; Chimie organique; Chimie analytique; Chimie théorique et/ou physique

E. Benedetti, M.-L. Delcourt, B. Gatin-Fraudet, S. Turcaud, L. Micouin. Synthesis and photophysical studies of through-space conjugated [2.2]paracyclophane-based naphthalene fluorophores. RSC Advances, 2017, 7 (80), pp.50472-50476. ⟨10.1039/C7RA10038H⟩. ⟨hal-02113405⟩