Supramolecular organization of new chiral π-conjugated oligomers: synthesis and spectroscopic study

π-Conjugated polymers and oligomers are widely used as organic semiconductors in devices such as field-effect transistors (OFET), light-emitting diodes (OLED) and solar cells (OPV)1; in the last years, a very important role in this field has been played by olygothiophenes2. Their optoelectronic properties (structure of the absorption bands, fluorescence efficiency, charge and exciton transport) depend not only on the chemical nature and the conformation assumed, but also on their supramolecular organization in the solid state. In particular, the introduction of chiral groups can be used to drive their self-assembly. We shall summarize our recent results about the supramolecular aggregation of three new chiral π- conjugated oligomers, consisting of an aromatic central ring (1,4-hydroquinone, benzo[1,2-b:4,5-b′]dithiophene- 4,8-diol, 1,4-diketopyrrolo[3,4-c]pyrrole) functionalized with two (S)-3,7-dimethyl-1-octyl groups and connected to two 2,2'-bithienyl units. In particular, we shall discuss: a) the synthetic route developed for the preparation of these new molecules;b) the characterization of their supramolecular aggregates in solution and of their thin films through optical (UV-VIS, fluorescence) and chiroptical (electronic circular dichroism) spectroscopies, in connection with optical microscopy investigation

Sintesi e caratterizzazione spettroscopica di oligomeri pigreco-coniugati di benzoditiofeni

Polimeri ed oligomeri pigreco-coniugati sono materiali largamente impiegati come semiconduttori organici in dispositivi quali transistor e celle fotovoltaiche organiche; in questo ambito un ruolo di primissimo piano è rivestito dai sistemi oligotiofenici. Le proprietà optoelettroniche di questi materiali dipendono non soltanto dalla loro natura, ma anche dalla loro capacità di organizzarsi in aggregati supramolecolari. L'introduzione di raggruppamenti chirali sulla struttura del sistema rappresenta un valido strumento per guidare e modulare la costruzione di tali aggregati. Il presente lavoro di tesi prevede la messa a punto della preparazione di sistemi pigreco-coniugati, costituiti da un nucleo aromatico elettronricco a cui sono legate due unità bitiofeniche e funzionalizzato con uno spaziatore alchilico chirale. La struttura degli aggregati degli oligomeri ottenuti verrà studiata sia in soluzione che allo stato solido mediante tecniche spettroscopiche, quali Dicroismo circolare, fluorescenza e NMR

Silylcarbocyclisation-desilylation reactions of N-tosyl-2-ethynylaniline: a new protocol for the synthesis of 2-hydroxyindoline derivatives

2-Hydroxyindolines are useful building blocks for the preparation of pharmaceutical and biological-ly active compounds. (1) However, to the best of our knowledge only few synthetic procedures have been developed; most of them are based on the reduction of corresponding lactams or on cy-clisation processes of variously substituted anilines. (2) We found that β-lactams and β-lactones can be easily obtained from propargyl amides and propargyl alcohols by means of rhodium-catalysed silylcarbocyclisation reactions with dimethylarylsilanes; subsequent treatment with TBAF promotes a desilylation step, consisting in a 1,2-migration of aryl group from the silyl moiety to the adjacent carbon atom. (3) Very recently, we extended our silylcarbocyclisation-desilylation protocol to the preparation of various 4-(arylmethyl) isochroman-3-ones starting from 2-ethynylbenzyl alcohol and arylsilanes with different steric properties. (4) Here we report that silylcarbocyclisations of N-tosyl-2-ethynylaniline with dimethylarylsilanes, car-ried out with catalytic Rh+[(C7H8)(BPh4)]- (Rhsw, 0.3 mol%) under CO pressure (30 atm) at 100°C, generate (Z)-1-tosyl-3-((dimethylarylsilyl)methylene)indolin-2-ols with good yields (51-68%). These compounds can be submitted to a facile TBAF-promoted desilylation step with migration of the aryl group, affording the corresponding N-tosyl-3-(methylaryl)indolin-2-ols quantitatively and with very high diastereoselectivity (anti > 90%)

Synthesis of Functionalised Indoline and Isoquinoline Derivatives through a Silylcarbocyclisation/Desilylation Sequence

A two steps sequence of silylcarbocyclisation-TBAF promoted desilylation/aryl migration has been applied to the synthesis of indolines and tetrahydroisoquinolines derivatives starting from suitable tosylamides and aryldimethylsilanes. In both cases silylcarbocyclisation reactions determined the formation of the heterocyclic ring together with the insertion of a CO functionality. Under the experimental conditions the carbonyl moiety is reduced to OH quantitatively. Subsequent treatment of silylated indolinols with TBAF generates stereoselectively the corresponding arylmethyl-tosylindolinols. In the case of tetrahydroisoquinolinols, during the desilylation step, migration of the aryl moiety is followed by spontaneous loss of water thus affording 3,4-dihydroisoquinolines exclusively

Chiroptical response inversion upon sample flipping in thin films of a chiral benzo[1,2-b:4,5-b′]dithiophene-based oligothiophene

A new chiral benzo[1,2-b:4,5-b']dithiophene-based oligothiophene has been synthesized and spectroscopically characterized in solution and in the solid state. The electronic circular dichroism (ECD) spectra of the thin films revealed the occurrence of an uncommon phenomenon, consisting of the inversion of the circular dichroism sign by sample flipping. To the best of our knowledge, this is unprecedented in samples where no preferential orientation of the chromophores has been induced, and must be due to spontaneous local anisotropies. It reveals peculiar features upon the usual solvent annealing procedure, but finally results in stable and very strong signals, which are perfectly reproduced in sign, and relative and even absolute magnitude. Although the recorded signal cannot be considered as a true ECD spectrum, it corresponds to a very large discrimination of light circular polarization, which is well explained by means of the Mueller matrix analysis and does not depend on instrumental defects. It is a genuine property of this material, which correlates with polarized optical microscopy (POM) images and only depends on the self-assembling properties of this molecule. This phenomenon may have relevant implications, on account of its strength and of the interest of oligothiophenes in current optoelectronic devices

Chiral oligothiophenes for optoelectronic applications: synthesis and spectroscopic study of supramolecular aggregation

Nowadays, conjugated polymers and oligomers are widely used as organic semicon-ductors in optoelectronic devices such as field-effect transistors (OFET), light-emitting diodes (OLED) and solar cells (OPV) [1]; in particular, a very important role in this field has been played by thiophene-based systems. Their optical and electrical properties (structure of absorption bands, fluorescence efficiency, charge and exciton transport, etc.) depend not only on the chemical nature and the conformation assumed, but also on their supramolecular organization in the solid state [2]. The introduction of chiral groups in the chemical structure of conjugated systems represents a valid tool to drive their self-assembly. We shall summarize our recent studies about the supramolecular aggregation for a set of new chiral conjugated oligomers, ad hoc designed and synthesized, consisting of an aromatic central ring (1,4-hydroquinone, 9H-carbazole, 1,4-diketopyrrolo[3,4-c] pyrrole and benzo[1,2-b:4,5-b′]dithiophene-4,8-diol) functionalized with (S)-3,7-dimethyl-1-octyl groups and connected to two 2,2'-bithienyl units (Figure 1)

Lymphatic and blood vasculature in primary cutaneous melanomas of the scalp and neck

Background Scalp/neck melanomas have a poor prognosis, possibly because of a rich vascular supply that prompts tumor cells' dissemination. Methods We compared the accuracy of immunohistochemical (IHC) staining with morphology for the identification of lymphovascular invasion in 156 scalp/neck melanomas. We then analyzed the association of vessel invasion and density with pathological features and survival. Results IHC-detected lymphatic vessel invasion (LVI) and blood vessel invasion (BVI) were identified in 34.6% and 13.5% of cases, respectively. IHC increased the LVI/BVI detection compared to morphology (40.4% vs 16.6%; p &lt;.001). The degree of peritumoral and intratumoral blood vessel density (BVD) was greater than lymphatic vessel density (LVD). Ulceration was the only factor independently associated with intratumoral (p = .029) and peritumoral (p = .047) BVD. Tumor thickness was the only independent predictor of survival (p = .002). Conclusion IHC allows accurate assessment of lymphovascular invasion in scalp/neck melanomas. In these tumors, we observed a high incidence of BVI, which deserves further investigations.</br