The photophysical and two-photon absorption (2PA) properties of two tri-podal molecules and of their quadrupolar and dipolar counterparts are reported for a series of solvents with varying polarity. The molecules possess a tri-phenylamine electron donating group and mono-cyano acceptors while olefinic and acetylenic p-linkers have been used. Branching led to an increase of the molar extinction coefficient and to a slight bathochromic shift of the absorption spectra while the fluorescence quantum yields decrease but they are maintained to relatively high values. Solvatochromic measurements in the tripodal molecules revealed an emitting state with a polar nature. The 2PA cross sections in general increase upon branching but the observed behaviour strongly depends on the type of solvent. The highest 2PA cross sections are obtained in solvents of medium polarity and values as high as 1420 GM are reported.

The coordination-driven synthesis of a rhomboid cavitand composed of two different Bodipys and its inclusion complex with 1,3,6,8-tetrasulfopyrene via ionic self-assembly was established by X-ray crystallography. Highly efficient and unidirectional intra-host and guest-to-host energy transfer was demonstrated by femtosecond fluorescence spectroscopy.

Atomic layer deposition of HfO2 significantly increases the efficiency and prolongs the lifetime of organic solar cells.

Effective interface engineering has been shown to play a vital role in facilitating efficient charge-carrier transport, thus boosting the performance of organic photovoltaic devices. Herein, we employ water-soluble lacunary polyoxometalates (POMs) as multifunctional interlayers between the titanium dioxide (TiO) electron extraction/transport layer and the organic photoactive film to simultaneously enhance the efficiency, lifetime, and photostability of polymer solar cells (PSCs). A significant reduction in the work function (W) of TiO upon POM utilization was observed, with the magnitude being controlled by the negative charge of the anion and the selection of the addenda atom (W or Mo). By inserting a POM interlayer with ∼10 nm thickness into the device structure, a significant improvement in the power conversion efficiency was obtained; the optimized POM-modified poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2- 33 ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]:[6,6]-phenyl-C butyric acid methyl ester (PTB7:PCBM)-based PSCs exhibited an efficiency of 8.07%, which represents a 21% efficiency enhancement compared to the reference TiO cell. Similar results were obtained in POM-modified devices based on poly(3-hexylthiophene) (P3HT) with electron acceptors of different energy levels, such as PCBM or indene-C bisadduct (ICBA), which enhanced their efficiency up to 4.34 and 6.21%, respectively, when using POM interlayers; this represents a 25-33% improvement as compared to the reference cells. Moreover, increased lifetime under ambient air and improved photostability under constant illumination were observed in POM-modified devices. Detailed analysis shows that the improvements in efficiency and stability synergistically stem from the reduced work function of TiO upon POM coverage, the improved nanomorphology of the photoactive blend, the reduced interfacial recombination losses, the superior electron transfer, and the more effective exciton dissociation at the photoactive layer/POM/TiO interfaces.

The photophysical properties of two octupolar (T) molecules and of their linear (L) and quadrupolar (Q) analogues are studied by means of steady state and femtosecond to nanosecond spectroscopy. The compounds bear a triphenylamine donor, cyano acceptors and acetylenic (series 1) or olefin (series 2) π-bridges. In the octupolar compound of series 2 (2T), fluorescence is emitted from an excited state localized on a single branch, while in that of series 1 (1T), the emitting state is delocalized among branches pointing to a reduced excited state polarity. Excited state dynamics in series 1 has shown an increase of lifetime with solvent polarity. In the branched compounds of series 2, multiexponential dynamics in polar solvents is exhibited indicating a distribution of emitting geometries. Femtosecond anisotropy in 1T indicates incoherent excitation transfer on the timescale of a few ps, in agreement with the hopping time predicted by the Förster model. However, no hopping mechanism is observed in 2T possibly because of an increased intramolecular charge transfer leading to a low energy relaxed excited state localized on a single branch.