Soluble polydiacetylenes: molecular properties and solid state organization M. Alloisio a,* , I. Moggio a , D. Comoretto a,b , C. Cuniberti a , C. Dell'Erba a , G. Dellepiane a,b a INSTM Ð Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, I-16146 Genova, Italy b INFM Ð Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, I-16146 Genova, Italy Abstract The solution properties of a novel soluble polydiacetylene, poly[1,6-bis3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] polyDCHD-HS), have been investigated by use of spectroscopic UV±VIS absorption, ¯uorescence and FT-Raman) and light scattering techniques in benzene and toluene. The unique spectroscopic and molecular properties of these solutions are reported and discussed in relation to the particular interactions of the polymer substituents with aromatic solvents. The introduction of the long alkyl-substituents on the carbazolyl side groups not only improves the processability relative to the parent unsubstituted polymer but also suppresses the chromic effects observed in other soluble polydiacetylenes. The side groups are also responsible for the peculiar supramolecular organization observed in the powder phase of the red form. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Soluble polydiacetylenes; Light scattering; Spectroscopical properties 1. Introduction New soluble polyldiacetylenes PDA) CR±CBC±CR=) n have been recently prepared by topochemical polymeri- zation of alkylsubstituted diacetylenes homologous to DCHD 1,6-bisN-carbazolyl)-2,4-hexadiyne) [1]. The solubility of these PDA increases with the length of the alkyl groups inserted in the 3,6 positions of the carbazolyl ringssothatforoneofthesepolymers,thepoly[1,6-bis3,6- dihexadecyl-N-carbazolyl)-2,4-hexadiyne], hereafter named polyDCHD-HS, it was possible to prepare thin ®lms of good optical quality for waveguiding tests [2]. Moreover, the presence of the long aliphatic chains induces a peculiar organization of the polymeric chain in the powder red form [1] and it is responsible of the particular photoexcitation properties of polyDCHD-HS red ®lms [3]. On the basis of these results, a detailed characterization of the polymer in solution has been carried out [4]. Of particular interest is its behavior in aromatic solvents and especially in benzene solutions where both the electronic absorption and the ¯uorescence spectra at room temperature exhibit spectral features with a sharpness never observed before in PDA solutions. 2. Results and discussion Fig. 1 shows electronic absorption spectra of polyDCHD- HS in toluene and benzene at room temperature. Toluene purple±red solutions exhibit an evident excitonic peak at 538 nm followed by an unresolved vibronic feature at 500 nm. Similar spectra have been observed also in xylenes, cyclohexane and chlorobenzene. The same ®gure also shows the electronic absorption spectrum of the red± orange solution in benzene. This spectrum does not change withconcentrationnorwithtime.Whatismoreinterestingis the remarkable sharpness of the excitonic transition at 534 nm FWHM  532 cm 1 ) and the very large intensity of this peak relative to the well resolved vibronic replica at 494 and 479 nm, indicative of a small electron±phonon coupling. Spectra of this type have never been observed for PDA red solutions at room temperature. The vibronic bands, shifted of 1516 and 2150 cm 1 from the excitonic peak, correspond to the excited state carbon±carbon double and triple bond stretching modes, respectively. The corre- sponding frequencies in the ground state obtained by FT- Ramanscatteringinthesamesolventareveryclosetothose derived from the absorption spectra. The similarity of these frequenciesfurthercon®rmsthatthegeometryoftheexcited polymerisnotsubstantiallydifferentfromthatintheground state. The small broadening effect observed in benzene solution suggests that the intramolecular motions in the polydiacetylene chains are hindered by the interactions with Synthetic Metals 124 2001) 253±255 * Corresponding author. Tel.: 39-10-353-8725; fax: 39-10-353-6199. E-mail address: alma@chimica.unige.it M. Alloisio). 0379-6779/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0379-677901)00467-2