Tuning the Quinoid versus Biradicaloid Character of Thiophene-Based Heteroquaterphenoquinones by Means of Functional Groups

A series of quinoidal bithiophenes (QBTs) with controlled variations in steric hindrance and electron activity of the substituents has been synthesized. Evidence of their quinoidal versus biradicaloid ground-state electronic character has been experimentally detected and coherently identified as fingerprints by spectroscopic methods such as NMR, UV–vis, multiwavelength Raman. From this analysis, alkoxy groups have been shown to strongly affect the electronic structure and the ground-state energy and stability of QBTs. Quantum-chemical calculations correctly predict the experimental spectroscopic response, even while changing the alkyl on phenone from a tertiary carbon atom to secondary to primary toward an unsubstituted phenone, further confirming the validity of the approach proposed. A control of the electronic structure accompanied by negligible variations of the optical gap of the molecules has thus been demonstrated, extending the potential use of quinoidal species in fields ranging from photon harvesting to magnetic applications

Solution Processed, Versatile Multilayered Structures for the Generation of Metal-Enhanced Fluorescence

We present an all-solution processed multilayered structure completely obtained via spin-coating, which can be used to study and optimize the phenomenon of metal-enhanced fluorescence. Indeed, the electromagnetic interactions occurring between fluorescent probes and localized surface plasmons typical of metal nanoparticles (NPs), which influence the fluorescence quantum yield, are strongly dependent on the nanoparticle/molecule distance. The platform proposed here offers unique advantages in terms of processability, allowing a fine-tuning of such a distance in a single deposition step. Fluorescence versus fluorophore/AuNP spacing curves are shown for two organic systems, namely, a perylene-based dye dispersed in a polymer matrix and a polyconjugated polymer (poly­(3-hexyl­thio­phene)), interacting with a nanostructured gold thin film. In both cases, optimal distances and enhancement factors have been measured

Photochromic Electret: A New Tool for Light Energy Harvesting

In this paper, a photochromic electret for light energy harvesting is proposed and discussed. Such electret directly converts the photon energy into electric energy thanks to a polarization modulation caused by the photochromic reaction, which leads to a change in dipole moment. Theoretical concepts on which the photochromic electret is based are considered with an estimation of the effectiveness as a function of material properties. Finally, an electret based on a photochromic diarylethene is shown with the photoelectric characterization as a proof of concept device

New Insight into the Fatigue Resistance of Photochromic 1,2-Diarylethenes

Photochromic diarylethenes represent one of the most important classes of molecular switches, and their fatigue resistance is reported in several papers. Previous studies have demonstrated that the presence of perfluorocyclopentene and methyl in the 4-positions of dithienylethenes improve the switching resistance. However, general guidelines to correlate chemical structure to fatigue resistance have not been found yet. In this work, we provide a different thought in the description of the fatigue resistance of diarylethenes, which is related to the light absorbed by the two isomeric states during photoconversion. For two series of 1,2-diarylethenes, which differ from the aromatic rings without bearing any electroactive substituent, it turns out that the fatigue resistance depends on the dose of light absorbed by the colored form rather than on the specific molecular structure, namely, the presence of specific molecular building blocks

Structure–Photoluminescence Correlation for Two Crystalline Polymorphs of a Thiophene–Phenylene Co-Oligomer with Bulky Terminal Substituents

Two crystal polymorphs of a thiophene–phenylene hexamer with bulky terminal substituents are characterized by different molecular conformations and parallel versus herringbone packing. Irrespective of their similar emissive spectra and common H-aggregate features, evidenced by crystal structure analysis and confirmed by solid-phase and excited-state first-principles calculations, their luminescence is relatively high and, for one form, nearly double than that for the other. Interaromatic packing energy contributions are established by quantum chemical calculations and can be compared quantitatively as the same species in different crystal environments is examined. The different luminescence efficiency of the two phases highlights the crucial role of the interaromatic packing for the luminescence properties of polyaromatic oligomers