Franco Bertinelli

Monomers of 3-alkyl-substituted thiophene: synthetic routes for the functionalization with non-linear optical chromophores

Synthetic methods for the functionalization of alkylthiophenes with stilbenic and azobenzenic chromophores were successfully explored starting from 3-(ω-bromoalkyl)thiophenes as the main intermediates. The incorporation of the chromophores was achieved through ethereal and aminic linkages obtained by nucleophilic substitution under different experimental conditions. These methods permitted to synthesize a number of alkylthiophenic monomers functionalized at the end of the side chain with second-order non-linear optical chromophores. Some of the new monomers were chemically polymerized.

Optical characterization of alkyl-thiophenic monomers functionalized with second-order nonlinear chromophores

A series of thiophenic monomers functionalized with different chromophoric groups have been optically characterized in view of preparation of polymeric films for second-order nonlinear optics and electrooptics. In order to investigate the optical behaviour inside a solid host matrix, the molecules have been physically dispersed in poly(methylmethacrylate) (PMMA) films and poled through high-temperature corona-poling for characterization through in situ second harmonic generation and ex situ angle-resolved spectroscopy. The values of dipole moment μ and optical hyperpolarizability β have been estimated inside the host matrix and related to the molecular structure. For one of the chromophores the long-term reorientation dynamics has been monitored in order to investigate the stability and the interaction with the polymeric environment.

Anomalous solvatochromic effect. Comparison between decyl and ω-hydroxydecyl 3-substituted polythiophenes

The solvatochromic behavior of chloroform solutions of poly(3-decyl-2,5-thienylene), poly[3-(10-hydroxydecyl)-2,5-thienylene] and their copolymers was studied by the addition of the non-solvent methanol. A reversed chromic transformation was found associated with the content of the hydroxyalkyl substituent. This anomalous effect was investigated using a number of non-solvents, in particular aliphatic alcohols from methanol up to decanol. In the case of a chloroform/methanol mixture, which gives the maximum anomalous effect, the effect produced by temperature variation was also examined. An explanation based on a molecular approach was attempted.

Spectroscopic comparison between poly[3-(6-methoxyhexyl)thiophene]s with different steric hindrance

Abstract An alternating methoxyhexylthiophene–thiophene copolymer was synthesized from 3-(6-methoxyhexyl)-2,2′-bithiophene and studied chiefly by means of optical absorption and nuclear magnetic resonance spectroscopy. The results were compared with those of the previously obtained poly[3-(6-methoxyhexyl)-2,5-thienylene]. The differences in the UV-Vis spectra of the two polymers in pure solvents, solvent/non-solvent mixtures and in films are discussed on the basis of the microstructure and the steric hindrance along the backbone. NMR spectroscopy revealed copolymer configuration to be regiorandom with a slight prevalence of head-to-head and tail-to-tail junctions.

Analysis of UV-Vis spectral profiles of solvatochromic poly[3-(10-hydroxydecyl)-2,5-thienylene].

The paper discusses a systematic study of the UV-Vis spectral profiles of poly[3-(10-hydroxydecyl)-2,5-thienylene] during its solvatochromic transformation in different solvent/non-solvent mixtures. A simulation of the overlapped spectra of the two chromophores (A less and B more conjugated) of the polymer is made through the resolution of their pure forms by means of vibronic progressions of log normal curves. The increment of the absolute intensity observed in the transformation has been determined and related to the increment of the transition moment; its value strongly supports the hypothesis that the solvatochromic transition consists in a doubling of A chromophores. Estimation of the average length of B chromophores has made it possible to evaluate the oscillator strength in the different solvent mixtures, the Franck-Condon factor and the Huang-Rhys parameter in relation to the intensity distribution of the vibronic structure.

Solvent and temperature effects on the chromic behaviour of poly[3-(10-hydroxydecyl)-2,5-thienylene]

Abstract The chromic behaviour of a soluble ω-hydroxydecyl 3-substituted polythiophene has been investigated by UV–VIS spectroscopy in different solvent/non-solvent mixtures over a wide range of low temperatures. Some interesting new effects have been observed that is the first case of a reversal of the solvatochromic transformation in substituted polythiopenes and a concentration effect in dilute pure solvent solutions. A molecular approach based on solvent–polymer interactions has been adopted to study the conformational chromic transformation of the polymer.

Optical properties, conductivity and structure of the DTT-TCNQ CT complex

Abstract The crystal structure, the optical spectra and electrical conductivity of dithieno(3,2-b; 2′,3′-d)thiophene-tetracyanoquinodimethane (DTT-TCNQ) charge-transfer complex have been measured. DTT-TCNQ crystallizes in the monoclinic space group P21/c with a = 7.206(2), b = 7.574(2), c = 32.324(9), β - 92.18(4)°, Z - 4, and the donor and acceptor molecules are arranged in alternated stacks. The low conductivity (a = 10−2 S cm−1 for the single crystal, along the stacking axis a) is characteristic of a semiconductor with activation energy of .61-.76 eV, and is related to the alternate stack structure. Despite the poor condctivity of the DTT-TCNQ CT complex we estimated, from structure and IR data, a low degree of ionicity (p = .2–.3) which characterizes the DTT molecule as an interestign donor. The polarized IR spectra shows the effect of vibronic activation of some of the ag modes of TCNQ.

Chromic effects in poly(3‐(10‐hexanoyloxydecyl)‐2,5‐thienylene) as precursor of ω‐hydroxydecyl‐functionalized polythiophen

The preparation of a hexanoyloxydecyl 3-substituted polythiophene and its conversion to the corresponding hydroxydecyl polymer, soluble in common organic solvents, is described. Solvatochromic and thermochromic effects of the two polymers were investigated by UV–vis spectroscopy in pure solvent and in solvent/nonsolvent solutions. A very different response was found depending on the type of functional group. The carboxylate polymer requires the synergy of both nonsolvent and low temperature for a strong chromic effect comparable to that of the hydroxy polymer to be observed. A possible explanation of this behavior is discussed.

Electrical and Infrared Properties of a Polyheterocycle Structurally Related to Poly(p-Phenylene Sulfide)

Abstract A comparison between a thianthrenic polymer and the parent poly(p-phenylene sulfide) is presented on the basis of electrical and infrared properties. Evidence that the polyheterocycle has a higher conductivity after doping with different amounts of SbCl5 is reported. In this doped polymer significant spectral modifications are also observed, mostly around 1100 cm−1. On the contrary the spectral profile of poly(p-phenylene sulfide) remains nearly unchanged at all doping concentrations.