Conjugated polymers with strongly twisted backbones, such as MEHPPV with fluorinated vinylene units (F-MEHPPV), demand a redefinition of the all-important 'effective conjugation length' ECL, which we extract here by a facile graphical method. In MEHPPV (being essentially planar), the ECL coincides with the 'maximum conducive chainlength'MCC and extends over about n  9 repetition units (RU). In F-MEHPPV, the MCC is similarly long with n  8, while ECL localizes on just one RU. The strong twist in F-MEHPPV persists in the excited state, broadening the emission spectrum and quenching the fluorescence by reduced radiative and enhanced non-radiative rates.The strong twist in F-MEHPPV persists in the excited state, broadening the emission spectrum, reducing the radiative rate, and enhancing the non-radiative deactivation, so that the fluorescence quantum yield of 30% in MEHPPV drops to 4% in F-MEHPPV. This example strikingly demonstrates how already small geometrical distortions (substitution of H by F) can lead to strong sterical effects, generating dramatic changes in the optical absorption and emission process.

New poly‐phenylenevinylenes PPVs containing 1,3,4‐thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time‐dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH2–P(=O)(OCH3)2, and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy Evert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n‐type semiconductors.

Since the early nineties, countless publications have been devoted to the study of possible uses of [60] fullerene (C60) and its derivatives in the fields of materials and nano-biomedical sciences. However, in spite of the importance of conformers notably from the pharmacological point of view, the cis/trans isomerization of C60 mono-adducts has been rarely seldom investigated. Here we present the results of DFT calculations of the structural, vibrational and NMR properties of both cis and trans isomers of fulleropyrrolidine mono-adduct obtained by photo-addition of glycine methyl ester to C60. Taken together, our results have shown that the cis isomer is more stable than the trans one. For the cis conformation, the simulated vibrational spectrum shows a more intense peak at 1298 cm-1. While 13C spectra revealed no significant differences between the two isomers as compared to experimental results, the calculated 1H chemical shifts show a significant difference between the two conformers in both the gas phase and in solution. The trans isomer presents a proton at 5.86 ppm, which is more deshielded than the proton of the cis conformer (5.24 ppm).

A new series of 3N-substituted triazolo-[1,5-c]pyrimidine 7, 8 and 9 have been synthesized in good yields (78-91%) trough a facile method using substituted 2-amino-3-cyano-pyrans 1, 2-amino-3-cyano-4-methylfuran 2, 1-Phenyl-3-thiomethyl-5-aminopyrazole-4-carbonitrile 3 as building block and cyanoacetic acid hydrazide as reagent in one framework. The structure of the synthesized compounds was established on the basis of their mass, spectral data and DFT at B3LYP. Graphic AbstractN N N N CN R N CN NH 2 OEt R CN H 2 N H N O CN RC(OEt) 3

A detailed theoretical investigation of bis-adduct fulleropyrrolidines was developed in our work. All the possible isomers of our molecule were determined. Corresponding structures were optimized, their energies were calculated and their stability was discussed using the density functional theory method. The theoretical calculation carried out in our work shows that the trans and equatorial structures of the bis adduct are the most stable structures among the eight different possible isomers. The LUMO energy calculated for the bis adduct shows that it is higher than the LUMO of C60 and the LUMO of the mono adduct calculated at the same level. This suggests that this compound can be used efficiently as electron acceptor in photovoltaic cell application.