Search

The straightforward synthesis of three organotin clusters endowed with six triarylamine-based moieties is reported herein. The optoelectronic properties of the molecules, as well as their ability to form gels, were investigated. The association ability of the compounds was studied as well by means of variable temperature nuclear magnetic resonance (NMR) and ultraviolet–visible (UV–vis) spectroscopy. The optimization of the geometry of the compounds has been performed and compared to the X-ray diffraction of the crystals. The results obtained through this comparison are useful for the explanation of their different gelation behaviors. In fact, organostannoxane drum 1exhibits a strong ability to form organized supramolecular structures by means of a number of noncovalent short contacts that finally yield luminescent organogels in aromatic solvents.

A cobalt-catalyzed cyclotrimerization of bis(aryl)alkyne is used as an innovative tool to obtain hole-transport materials (HTMs). The novel HTM containing six units of oligotriarylamine (HAB1), characterized by UV–vis, cyclic voltammetry, DFT, and thermogravimetric analysis, confirms its suitability as an efficient HTM in PSCs. A PCE of 17.5% was obtained in HAB1-containing PSCs, a performance comparable to that obtained with spiro-OMeTAD and with slightly better thermal stability.

A series of novel polymers (P1–P6) derived from the combination of different units (including thiophene, triarylamine, and spirobifluorene) were successfully synthesized, completely characterized, and used as hole-transporting materials (HTMs) for perovskite solar cells (PSCs). Solar cells with some of these materials as HTMs showed very good performances of almost 13% (12.75% for P4and 12.38% for P6) even without additives, and devices based on these new HTMs show relatively improved stability against temperature compared to those based on PTAA. The presence of dopant additives has been linked to long-term degradation, which is the main barrier to the large-scale commercialization of this innovative type of solar cell. Obtaining efficient PSCs without using dopants could represent a further step toward improvement of long-term stability and thus their introduction into the market.

The absorption and emission properties of macrocyclic cis-indolenine squaraine dyes are studied experimentally and theoretically. As compared to the monomeric species, large Stokes shifts of the emission are observed for cyclic trimers and tetramers. The theoretical analysis predicts that these shifts are caused by deviations of the excited state geometries from the strictly symmetric configurations. Breaking the symmetry makes fluorescence from lower excited states possible which otherwise is forbidden. The line shapes of the spectra are dominated by vibronic structures which can be identified using a vibronic coupling model. From the results, the important fact emerges that macrocyclic squaraine aggregates can be effectively used as building blocks for near-infrared (NIR) emitters.

Low-band-gap polymers with broad spectral absorption are highly sought after for application in organic photovoltaic cells and other optoelectronic devices. Thus, a conjugated copolymer based on two different indolenine squaraine dyes SQA and SQB was synthesized by Suzuki coupling, and its steady-state and time-resolved optical properties were investigated in detail. In CHCl3the copolymer [SQA-SQB]nshows a strongly broadened and red-shifted absorption compared to that of its monomers, which was explained by exciton coupling of localized transition moments. The theoretical background of exciton coupling theory for copolymers was worked out in detail. In toluene, [SQA-SQB]ndisplays a spectral narrowing of the lowest excitation band which resembles the exchange narrowing effect found in cyanine J-aggregates. In this way [SQA-SQB]nbehaves like a one-dimensional covalently bound hetero-J-aggregate. The photoinduced dynamics of the copolymer was investigated by transient absorption pump–probe spectroscopy with femtosecond resolution. Because of the unusually high exciton diffusion constant, singlet–singlet annihilation is the rate-limiting step for deactivation of the copolymer in solution at high laser fluencies. This is unlike the situation for many conjugated polymers in the solid state, where diffusion-limited annihilation is usually found. Thus, the [SQA-SQB]ncopolymer is a unique model system which combines the excitonic features of J-aggregates with the chemical robustness of a polymer.

Various indolenine squarylium dyes with additional electron‐donating amine redox centres have been synthesised and their redox chemistry has been studied. A combination of cyclic voltammetry, spectro‐electrochemistry and DFT calculations has been used to characterise the electronic structure of the mono‐, di‐ and, in one case, trications. All monocations still retain the cyanine‐like, delocalised character due to the relatively low redox potential of the squaraine bridge and are therefore compounds of Robin–Day class III. Thus we extended previous studies on organic mixed‐valence systems by using the indolenine squaraine moiety as very electron‐rich bridge between two electron‐donating amine redox centres to provoke a strong coupling between the additional redox centres. We synthesised TA3, which has an N–N distance of 26 bonds between the triarylamine redox centres and is to our knowledge the longest bis(triarylamine) radical cation that is completely delocalised. We furthermore show that altering the symmetry of a squaraine dye by substitution of a squaric ring oxygen atom by a dicyanomethylene group has a direct impact on the optical properties of the monocations. In case of the dications, it turned out that the energetically most stable state of dianisylamine‐substituted squaraines is an anti‐ferromagnetically coupled open‐shell singlet state.

A polysquaraine lowbandgap polymer was synthesized by Yamamoto coupling of a monomeric dibromoindolenine squaraine dye. The resulting polymer has $\overline M _{\rm w} $  34 000 and PDI  1.7. The electronic properties of monomer and polymer were investigated by CV, absorption, and emission spectroscopy. Bulk heterojunction solar cells were prepared from blends of the polysquaraine with the fullerene derivative PCBM in different weight ratios 1:3 to 1:1. The power conversion efficiencies under simulated AM1.5 conditions yielded 0.45 for these nonoptimized systems. The EQE shows that the photoresponse spans the range from 300 to 850 nm, which illustrates the promising properties of this novel organic semiconductor as a low band gap donor material in organic photovoltaics.

No Abstract.