Substitution effects on the photoinduced excited state dynamics of perylenemonoimides in solution and thin films

Perylene monoimide (PMI) derivatives are attracting significant attention due to their strong absorption in the visible range, thermal stability, and synthetic accessibility. These properties make them promising for application in various areas such as optoelectronic devices, photosensitizers, etc. In this work, the photophysical properties and excited state dynamics of four different PMI derivatives (PMIB, BrPMITB, PMITB, and APITB) were studied in solution and thin films utilizing steady-state and time-resolved spectroscopic techniques. Among the four PMI derivatives, APITB is designed as a donor-acceptor dyad, with thianthrene as a donor and PMI as an acceptor. The activation of the triplet state through the spin-orbit charge transfer intersystem crossing (SOCT-ISC) process in THF was observed upon substitution with the thianthrene group at the peri position of the PMI moiety. The SOCT-ISC process facilitates triplet formation in the APITB dyad within 423 ps. Meanwhile, other PMI derivatives showed fluorescence within the femtosecond timescale in THF. The PMI derivatives in thin films displayed different photo physical properties to those in THF. This discrepancy arises due to the effective intermolecular coupling between the PMI derivatives in thin films.

Slip-Stacked J-Aggregate Materials for Organic Solar Cells and Photodetectors

Dye-dye interactions affect the optical and electronic properties in organic semiconductor films of light harvesting and detecting optoelectronic applications. This review elaborates how to tailor these properties of organic semiconductors for organic solar cells (OSCs) and organic photodiodes (OPDs). While these devices rely on similar materials, the demands for their optical properties are rather different, the former requiring a broad absorption spectrum spanning from the UV over visible up to the near-infrared region and the latter an ultra-narrow absorption spectrum at a specific, targeted wavelength. In order to design organic semiconductors satisfying these demands, fundamental insights on the relationship of optical properties are provided depending on molecular packing arrangement and the resultant electronic coupling thereof. Based on recent advancements in the theoretical understanding of intermolecular interactions between slip-stacked dyes, distinguishing classical J-aggregates with predominant long-range Coulomb coupling from charge transfer (CT)-mediated or -coupled J-aggregates, whose red-shifts are primarily governed by short-range orbital interactions, is suggested. Within this framework, the relationship between aggregate structure and functional properties of representative classes of dye aggregates is analyzed for the most advanced OSCs and wavelength-selective OPDs, providing important insights into the rational design of thin-film optoelectronic materials.

Conjugated donor–acceptor substituted systems involving the 1,3-indandione-derived electron accepting moieties

Conjugated donor–acceptor molecules are the focus of research owing to their unusual photo- and electro-physical properties. At the same time, several unusual features of these compounds are difficult to explain or predict. Here we present our results on the synthesis, X-ray structures and D-NMR spectra providing a deeper insight into the conjugation within the derivatives involving the 1,3-indandione-derived series of compounds with varying electron acceptor strength and conjugating bridge length. The X-ray structures show the presence of several intermolecular short contacts strongly affecting the molecular geometries. In solution, the coalescence temperatures corresponding to the rotation of the phenylamino moiety of all derivatives do not exceed 246 K indicating the unhindered rotation at room temperature. Using B3LYP/aug-cc-pVDZ, the calculated model chemistry barriers to rotation, dipole moments and first hyperpolarizabilities are within experimental error. We conclude that neglecting the electron donating properties of bridges themselves and internal rotation about the single bonds taking part in conjugation can result, for instance, in misinterpretation of their room temperature NMR spectra and overestimation of the computed molecular dipole moments by more than 5 D.

Determination of barriers to rotation using the D-NMR technique within a series of push–pull derivatives sheds light on the inability of stronger acceptors to considerably increase the dipole moments and nonlinear optical response.

Phenothiazine Functionalized Multifunctional A-π-D-π-D-π-A-Type Hole-Transporting Materials via Sequential C-H Arylation Approach for Efficient and Stable Perovskite Solar Cells

Three phenothiazine-based A-π-D-π-D-π-A-type small molecules containing various terminal acceptor units, which act as Lewis base blocks, have been synthesized via an efficient and step-economical, direct C-H arylation strategy in the aim toward the development of hole-transporting materials (HTMs) with multifunctional features (such as efficient hole extraction layer, trap passivation layer, and hydrophobic protective layer) for perovskite solar cells (PrSCs). Optical-electrochemical correlation and density functional theory studies reveal that dicyanovinylene acceptor in SGT-421 downshifted the highest occupied molecular orbital (HOMO) level (-5.41 eV), which is more proximal to the valence band (-5.43 eV) of the perovskite, whereas N-methyl rhodanine in SGT-420 and 1,3-indanedione (IND) in SGT-422 destabilized the HOMO, leading to an increased interfacial energy-level offset. SGT-421 exhibits superior properties in terms of a sufficiently low-lying HOMO level and favorable energy-level alignment, intrinsic hole mobility, interfacial hole transfer, hydrophobicity, and trap passivation ability over spiro-OMeTAD as a benchmark small-molecule HTM. As envisaged in the design concept, SGT-421-based PrSC not only yields a comparable efficiency of 17.3% to the state-of-art of spiro-OMeTAD (18%), but also demonstrates the enhanced long-term stability compared to the spiro-OMeTAD because of its multifunctional features. More importantly, the synthetic cost of SGT-421 is estimated to be 2.15 times lower than that of spiro-OMeTAD. The proposed design strategy and the study of acceptor-property relationship of HTMs would provide valuable insights into and guidelines for the development of new low-cost and efficient multifunctional HTMs toward the realization of efficient and long-term stable PrSCs.

Triisopropylsilylethynyl-substituted indenofluorenes: carbonyl versus dicyanovinylene functionalization in one-dimensional molecular crystals and solution-processed n-channel OFETs

Carbonyl vs. dicyanovinylene functionalization in indenofluorenes leads to substantial differences in solid-state packings and results in significant variations (×1000) in electron mobilities.

Spin–orbit charge transfer intersystem crossing in perylenemonoimide–phenothiazine compact electron donor–acceptor dyads

Efficient triplet excited state production (57%) was observed for perylenemonoimide–phenothiazine compact electron donor–acceptor dyads based on spin–orbit charge transfer ISC.

A new fluorophore displaying remarkable solvatofluorochromism and solid-state light emission, and serving as a turn-on fluorescent sensor for cyanide ions

A new fluorophore displays remarkable solvatofluorochromism, a CIEE effect, and an intense blue-green fluorescence in the presence of cyanide ions.

Synthesis of largely π-extended naphthalenediimides via C–H activation towards highly soluble and narrow band-gap organic optoelectronic materials

Largely π-extended naphthalenediimides were synthesized by using efficient palladium catalyzed C–H/C–H homocouplings, with the yields of up to 94%.

The influence of the central acceptor unit on the optoelectronic properties and photovoltaic performance of A–D–A–D–A-type co-oligomers

A series of A–D–A–D–A co-oligomers was developed and implemented as donor materials in solution-processable organic solar cells showing the dependence of molecular structures on the power conversion efficiency upon solvent vapor annealing.

Facile synthesis of annulated heterocyclic benzo[kl]acridine derivatives via one-pot N–H/C–H coupling

A facile and efficient synthesis of benzo[kl]acridines was developed based on a domino reaction via a combinatorial catalyst approach.

Synthesis, photophysical, electrochemical, and DSSC application of novel donor–acceptor triazole bridged dendrimers with a triphenylamine core and benzoheterazole as a surface unit

Triazole bridged novel donor–acceptor dendrimers were synthesized via click chemistry. Lower generation dendrimers when used as additives exhibit better current-generating capacity and power conversion efficiency in DSSCs.