1831 Research Article Received: 24 November 2008 Accepted: 28 March 2009 Published online in Wiley Interscience: 5 August 2009 (www.interscience.wiley.com) DOI 10.1002/jrs.2327 Photopolymerization in water of diacetylenes chemisorbed onto noble metal nanoparticles: a spectroscopic study Corinna Raimondo, a Marina Alloisio, a Anna Demartini, a Carla Cuniberti, a Giovanna Dellepiane, a* Sushilkumar A. Jadhav, a Giovanni Petrillo, a Emilia Giorgetti, b Cristina Gellini c and Maurizio Muniz-Miranda d Gold and silver nanoparticles of different size, decorated by a diacetylenic monomer having a COOH anchor group, were prepared in aqueous dispersions. Topochemical polymerization of the colloidal suspensions was obtained by UV irradiation and studied by means of spectroscopic techniques (UV – visible absorption, IR and Raman spectroscopies). A variety of polymer phases were found in the case of silver nanohybrids. The main contribution for this investigation was supplied by the Raman spectra, which provide detailed information on the polymer forms and on the preferred conformation of the alkylic side chains. Copyright c  2009 John Wiley & Sons, Ltd. Keywords: nanohybrids; polydiacetylenes; UV – vis spectroscopy; Raman spectroscopy Introduction The preparation of properly functionalized nanostructures is one of the nowadays challenges in materials chemistry. Colloidal nanohybrids composed of a noble metal core coated by a protective shell of organic molecules are considered the first step towards the fabrication of devices to be applied in several areas, [1–8] due to the large electromagnetic field generated in the vicinity of the metal surfaces when excited near the plasmon wavenumber. Recently, we have been involved in the study of these nanoassemblies decorated with an intriguing class of conjugated polymers, the polydiacetylenes (PDAs). It is well known that the incorporation of photopolymerizable diacetylene groups within the monolayer of alkyl chains on metal surfaces provides stable and robust polymeric architectures that could be applied in chemical sensing, as well as in optical and electronic devices. [9 – 12] In a recent work in this field, we have reported about the direct synthesis in toluene solution of gold nanoparticles coated with the diacetylene DS9 (henicosa-10,12-diyn-1-yl disulfide) and their photopolymerization. [13] The formation of the intra- particle polydiacetylene chains, whose colour was found to be strictly correlated to the size of the nanoparticle (NP) core, was demonstrated. In particular, the highly conjugated blue-coloured polymer requires the more extended surfaces provided by NPs with sufficiently large core diameters, whereas on small clusters only the less conjugated red phase was observed. The blue form, known to be highly sensitive to a variety of external stimuli, was shown to undergo a transition to the red phase at long irradiation times. In this paper, the time-dependence photopolymerization of another diacetylene, PCDA (10,12-pentacosadiynoic acid, CH 3 –(CH 2 ) 11 –C C–C C–(CH 2 ) 8 –COOH), chemisorbed onto noble metal cores in aqueous suspensions, is reported. The pres- ence of a carboxylic end-group in this monomer favours the anchoring of the molecule particularly on the AgNPs, thus allow- ing more stable nanohybrids to be formed. That water is the best solvent for reliable data when using photoirradiation is widely recognized as the metal clusters size may be sensibly affected in organic solvents. [14] These nanosystems, herein referred to as PCDA–AuNPs and PCDA – AgNPs and prepared as described in section Experimental, were morphologically characterized with the TEM technique. Their photopolymerization was carried out directly in water and monitored step by step by UV–vis absorption, IR and Raman spectroscopies. Actually, Raman scattering represents one of the most useful techniques for the investigation on different materials. Here, the problems of scarce sensitivity related to the low Raman scattering cross-section were overcome by the strong enhancement supplied by the surface-enhanced Raman scattering (SERS) [15 – 17] effect, due to the presence of gold or silver nanoparticles. ∗ Correspondence to: Giovanna Dellepiane, Dipartimento di Chimica e Chimica Industriale, Universit` a di Genova, Via Dodecaneso 31, 16146 Genova, Italy. E-mail: gide@chimica.unige.it a INSTM and Dipartimento di Chimica e Chimica Industriale, Universit` a di Genova, Via Dodecaneso 31, 16146 Genova, Italy b INSTM and Istituto dei Sistemi Complessi – CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy c Dipartimento di Chimica, Universit` a di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy d INSTM and Dipartimento di Chimica, Universit` a di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy J. Raman Spectrosc. 2009, 40, 1831–1837 Copyright c  2009 John Wiley & Sons, Ltd.