Core substituted perylene diimides (PDIs) are promising candidates as non-fullerene acceptor materials for organic solar cells. The functionalization of PDIs in the bay positions using chemical groups with different electron donating abilities and with steric hindrance is a versatile tool to modify both the optoelectronic properties and the morphology in the solid state.

Herein we present two new PDI based molecules having bulky aromatic substituents linked into the bay positions: PDI-SF with spirobifluorene group and PDI-BSF with bithienyl-spirobifluorene moieties. The high steric hindrance of spirobifluorene reduce the tendency to form aggregates that has been identified as a limiting factor for the photovoltaic performances in PDI based solar cells.

The PDI molecules were tested as electron acceptors in bulk heterojunction solar cells with P3HT as electron donor. Power conversion efficiencies (PCE) of 1.58% and 1.18% were obtained for PDI-SF and PDI-BSF devices.

Chiral polyalkylthiophenes are noncentrosymmetric organic materials which can be used both in second harmonic-generation devices and in polarized light emitting diodes. In this work we present the synthesis and the characterization of a polyalkylthiophene with a chiral center very close to the conjugated backbone: poly(3-[(S)-2-methylbutyl]thiophene) (PMBT). Circular dichroism (CD) measurements have been carried out to ascertain the chirality of these materials. The CD spectra show intense signals both in mixed solvents and in the solid state. The strong Cotton effect can be associated to a highly ordered aggregated phase whose nature is still under investigation. We also present the photo and electroluminescence characterization of single layer light emitting diode (LED) with the following configuration: ITO (Tin Indium Oxide)/PMBT/Al.

Poly(dithieno[3,4-b:3',4'-d]thiophene) (pDTT1), poly(dithieno[3,4-b:3',2'-d]thiophene (pDTT2) and poly(dithieno[3,4-b:2',3'-d]thiophene) (pDTT3) are low band-gap polymers that undergo both p- (oxidation) and n- (reduction) type electrochemical reversible doping in organic electrolytes. In this work we report on the in-situ IR spectroscopic characterization of both doping types using attenuated total reflection (ATR) FTIR spectroelectrochemistry. Thin polymer films were prepared on Ge reflection elements by electrosynthesis. During electrochemical potential cycling experiments in a spectroelectrochemical cell, the evolution of infrared active vibrational (IRAV) modes, correlated with the generation of charge within the polymer chain, was studied. In addition to electrochemical doping, the polymers exhibit also charged excitations by photodoping. FTIR spectra recorded by illumination/dark cycles show photoinduced IRAV bands which are similar to those found for the electrochemically p-doped materials. The infrared spectroscopic results are compared with Raman spectra of the neutral polymers. The relationship between vibrational properties and structure of the polymers is discussed in terms of different contribution of the φ-electrons within the repeating units to the electronic structure of the conjugated backbone.

Conjugated polymers with narrow band gap are promising candidates for symmetric electrochemical devices, such as electrochromics and redox supercapacitors, which involve the pand n-doped state of the polymer. Polydithienothiophene materials which are prepared from isomer monomers show this characteristic. The copolymerisation of two dithienothiophene isomers leads to materials whose electronic properties depend on the monomer ratio. Optical and electrochemical characterizations of different copolymers are reported and discussed.

We report on a spectroscopical study of a novel class of push-pull molecules containing a Chromium or Tungsten atom connected to an oligothiophene through a carbenic bond. The electronic coupling between the π electrons of the conjugated system and the π electrons of the transition metal has been monitored through absorption and Raman spectra.

This interaction between d and π electrons leads to a red shift of the thienylene π-π* absorption band and to the appearance of a new strong metal to ligand charge transfer band at lower energies. In this latter transition the electrical dipole reverses its direction upon photoexcitation from the ground to the first excited state, thus accounting for the enhanced non linear optical response of these molecules. Solvatochromic effect has been used to estimate the second order molecular hyperpolarizability.

The photoluminescence properties of thiophene-based polymers obtained by the random copolymerization of 3,4-dibutylthiophene and 3-butylthiophene are reported. Optical absorption spectra, cw photolumninescence (PL) spectra, PL quantum efficiencies and PL decays have been measured in dilute solutions. By varying the copolymer chemical composition it is possible to tune the intensity and the color of the luminescence spectra in the whole visible range. We evidence the role of disorder, controlled by interring rotations, as the tuning factor for the disexcitation pathway of the photoexcitations in these materials.

We report a study of the optical and photoexcitation properties of a new polyalkylthiophene:poly[(3-pentyl-5-oxoazobenzene)thiophene]. UV-Vis absorption and emission, IR absorption, Raman scattering, indicate that the steric hindrance of the side chain induces some rotational disorder of the backbone but the π electron delocalization is not substantially differing from other polyalkylthiophenes. Long lived photoexcitations have been characterized by photoinduced absorption. The spectral features are intrinsic to the polyconjugated thiophene chain, even when the backbone and the azo chromophore are both photoexcited by UV light.

The copolymerization of 3-alkylthiophene and 3,4-dialkylthiophene units in well defined ratios leads to materials in which it is possible to modulate continuously the electronic properties such as the conjugation length and the energy-gap. The soluble materials have optical properties depending on the chemical composition of the chain. A macromolecular and optical characterisation has been performed on two copolymer series.

Photoinduced absorption spectra of different polycarbazolyldiacetylenes in the visible and infrared regions are reported. Long-lived bipolaronic defects, photogenerated by excitation above the band-gap (2.54 eV), are found responsible for the observed signals. Associated with these defects, photogenerated infrared active vibrations (IRAV) are observed as absorption bands or apparent bleachings arising from Fano-type interference. This different behaviour originates from the different degree of overlap of the IRAV Modes with the associated low-energy bipolaronic absorption.

We report a study of the near infrared photoinduced absorption of a series of poly -3-decylthiophene with different supermolecular organization as solution cast films, good solvent and aggregated bad solvent solutions.

Photoinduced subgap electronic states are detected both in the solid and in solutions independently from the presence of polymer aggregates. The study of the photoinduced activity Δ/T on the laser intensity I indicate a I0.6 dependence for the films and a I0.95 dependence for the solutions. This is the evidence that the photoinduced states are generated in the solid via an inter-chain mechanism while in the solution via an intra-chain mechanism.

A possible role of the solvent into the photoexcitation pathway is discussed.

We report Raman scattering measurements on poly-3-heptylthiophene and poly-3-undecylthiophenes both on resonance and preresonance conditions. We have studied different samples as solutions ,solution cast films and electrosynthetized as grown films. Our results indicate that the vibrational frequency of the mode which is strongly coupled to the π - π* electronic transition is sensible to “small” torsions between thiophenes rings , which do not necessarly interrupt completely the conjugation path.