Rainbow Perylene Monoimides: Easy Control of Optical Properties

Perylene Diimide-Based Dimeric Electron Acceptors with Molecular Conformations for Perovskite Solar Cells

This paper reports five novel PDI dimer type electron transport materials (ETMs) employing o-indoloquinoxaline (o-Iq), m-indoloquinoxaline (m-Iq), and cibalackrot (Ci) groups as the core building blocks and presents the twisted structures of PDI dimers coded as PDI-NHR-o-Iq, PDI-o-Iq, PDI-NHR-m-Iq, PDI-m-Iq and PDI-NHR-Ci dyes (see Scheme 1 and 2). We have systematically compared their photophysical, electrochemical, and optoelectronic properties with respect to the reference dye (2PDI-NHR), which is directly connected of two PDI planes. Their calculated HOMO-LUMO energy levels are sufficient for charge transfer to the perovskite material so that structure-photovoltaic performance relationship of synthesized ETM dyes can be evaluated. When the binding position of indoloquinoxaline group between PDI rings are changed from o- to m- positions, most of the photophysical and electrochemical properties of PDI dimer are dramatically changed, finally improving the photovoltaic performances.

Recent Advances in Applications of Fluorescent Perylenediimide and Perylenemonoimide Dyes in Bioimaging, Photothermal and Photodynamic Therapy

The emblematic perylenediimide (PDI) motif which was initially used as a simple dye has undergone incredible development in recent decades. The increasing power of synthetic organic chemistry has allowed it to decorate PDIs to achieve highly functional dyes. As these PDI derivatives combine thermal, chemical and photostability, with an additional high absorption coefficient and near-unity fluorescence quantum yield, they have been widely studied for applications in materials science, particularly in photovoltaics. Although PDIs have always been in the spotlight, their asymmetric counterparts, perylenemonoimide (PMI) analogues, are now experiencing a resurgence of interest with new efforts to create architectures with equally exciting properties. Namely, their exceptional fluorescence properties have recently been used to develop novel systems for applications in bioimaging, biosensing and photodynamic therapy. This review covers the state of the art in the synthesis, photophysical characterizations and recently reported applications demonstrating the versatility of these two sister PDI and PMI compounds. The objective is to show that after well-known applications in materials science, the emerging trends in the use of PDI- and PMI-based derivatives concern very specific biomedicinal applications including drug delivery, diagnostics and theranostics.

Fast Charge Separation in Distant Donor-Acceptor Dyads Driven by Relaxation of a Hot Excited State

A series of three perylenemonoimide-p-oligophenylene-dimethylaniline molecular dyads undergo photoinduced charge separation (CS) with anomalous distance dependence as a function of increasing donor-acceptor (DA) distances. A comprehensive experimental and computational investigation of the photodynamics in the donor-bridge-acceptor (DBA) chromophores reveals a clear demarcation concerning the nature of the CS accessed at shorter (bridgeless) and longer DA distances. At the shortest distance, a strong DA interaction and ground-state charge delocalization populate a hot excited state (ES) with prominent charge transfer (CT) character, via Franck-Condon vertical excitation. The presence of such a CT-polarized hot ES enables a subpicosecond CS in the bridgeless dyad. The incorporation of the p-oligophenylene bridge effectively decouples the donor and the acceptor units in the ground state and consequentially suppresses the CT polarization in the hot ES. Theoretically, this should render a slower CS at longer distances. However, the transient absorption measurement reveals a fast CS process at the longer distance, contrary to the anticipated exponential distance dependence of the CS rates. A closer look into the excited-state dynamics suggests that the hot ES undergoes ultrafast geometry relaxation (τ < 1 ps) to create a relaxed ES. As compared to a decoupled, twisted geometry in the hot ES, the geometry of the relaxed ES exhibits a more planar conformation of the p-oligophenylene bridges. Planarization of the bridge endorses an increased charge delocalization and a prominent CT character in the relaxed ES and forms the origin for the evident fast CS at the longest distance. Thus, the relaxation of the hot ES and the concomitantly enhanced charge delocalization adds a new caveat to the classic nature of distance-dependent CS in artificial DBA chromophores and recommends a cautious treatment of the attenuation factor (β) while discussing anomalous CS trends.

1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis, Characterization, Photophysical Studies, and Hydrogen Evolution Catalysis

In this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3 S13 ]2- clusters in aqueous solution for stable visible light driven hydrogen evolution over three days.

Directing charge transfer in perylene based light-harvesting antenna molecules

Directing energy and charge transfer processes in light-harvesting antenna systems is quintessential for optimizing the efficiency of molecular devices for artificial photosynthesis. In this work, we report a novel synthetic method to construct two regioisomeric antenna molecules (1-D2A2 and 7-D2A2), in which the 4-(n-butylamino)naphthalene monoimide energy and electron donor is attached to the perylene monoimide diester (PMIDE) acceptor at the 1- and 7-bay positions, respectively. The non-symmetric structure of PMIDE renders a polarized distribution of the frontier molecular orbitals along the long axis of this acceptor moiety, which differentiates the electron coupling between the donor, attached at either the 1- or the 7-position, and the acceptor. We demonstrate that directional control of the photo-driven charge transfer process has been obtained by engineering the molecular structure of the light-harvesting antenna molecules.

Fuller-Rylenes: Paving the Way for Promising Acceptors

The hybridization of different acceptors remains a fertile ground awaiting exploration, to fully promote the properties of both components. The concept of this work is to exploit a new form of fuller-rylene hybrids as promising acceptors by integrating planar rylene dye and spherical fullerene for boosting the power conversion efficiency. The synthesis of the fuller-rylenes via a straightforward synthetic strategy by one-pot Pd-catalyzed cyclization can be scaled-up. Specifically, our strategy allows the supplements and enhancement of absorption in the visible region, much wider structural and electronic variations by installing R₁ groups as well as decorating R₂ on the perylene core at will, and good processability without compromising the superior characteristics of fullerene. Thus, bay-decorated fuller-rylene S-Fuller-PMI revealed a ground-breaking efficiency as high as 8.01%, even outperforming [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) as a parallel comparison (7.09%). Our exploration paves a new way for the design of high-efficiency acceptors, which are promising alternatives to PC₆₁BM in photovoltaic devices.

Charge separation, recombination and intersystem crossing of directly connected perylenemonoimide-carbazole electron donor/acceptor dyads

Perylenemonoimide (PMI)-carbazole (Cz) compact electron donor/acceptor dyads were prepared to study the relationship between the mutual orientation of the electron donor/acceptor in the dyads and the spin-orbit charge transfer intersystem crossing (SOCT-ISC) efficiency. The PMI and the Cz units are connected via either a C-C or C-N bond, or with an intervening phenyl moiety. The photophysical properties of the dyads were studied with steady state and time-resolved optical spectroscopies. The fluorescence of the PMI unit in the dyads was generally quenched, due to photo-induced electron transfer, especially in polar solvents (the fluorescence has a biexponential decay in acetonitrile, τ_F = 1.4 ns/population ratio: 98.9%, and 9.6 ns/population ratio: 1.1%). The triplet state (lifetime τ_T = 14.7 μs) formation of the dyads is dependent on the solvent polarity, which is characteristic for SOCT-ISC. Femtosecond transient absorption spectra show that the charge separation takes 0.28 ps and the charge recombination takes 1.21 ns. Reversible photo-reduction of the PMI-Cz dyads and generation of the near IR-absorbing (centered at 604 nm and 774 nm) PMI radical anion (PMI^-˙) were observed in the presence of a sacrificial electron donor (triethylamine). These results are useful for study of the fundamental photochemistry of compact electron donor/acceptor dyads and for design of new heavy atom-free triplet photosensitizers.

Synthesis and photovoltaic application of NIR-emitting perylene-monoimide dyes with large Stokes-shift

An efficient Sonogashira coupling protocol is developed for tetra-alkynylation at the bay and peri-positions of the perylene-monoimide (PMI) dye in its PMI(Br)4 form. The absorption band for these PMI dyes covered from the visible to Near-infrared (NIR) region and PMI(NMe2)4 is found to exhibit a record-breaking Stokes-shifted NIR emission with good photovoltaic properties.

Electrooxidative para-selective C-H/N-H cross-coupling with hydrogen evolution to synthesize triarylamine derivatives

Oxidative C–H/N–H cross-coupling is one of the most atom-economical methods for the construction of C–N bonds. However, traditional oxidative C–H/N–H cross-coupling either required the use of strong oxidants or high reaction temperature, which makes it difficult to tolerate redox active functional groups. Herein we describe an external chemical oxidant-free electrooxidative C–H/N–H cross-coupling between electron-rich arenes and diarylamine derivatives. Under undivided electrolytic conditions, a series of triarylamine derivatives are produced from electron-rich arenes and diarylamine derivatives with high functional group tolerance. Both of the coupling partners are redox active in oxidative C–H/N–H cross-coupling, which enables high regioselectivity in C–N bond formation. Exclusive para-selectivity is observed for the coupling with anilines.

Oxidative C–H/N–H cross-coupling is a convenient method to construct C–N bonds, however this is rarely achieved in a sustainable manner. Here, the authors show an oxidant-free electrochemical C–H/N–H cross-coupling between electron-rich arenes and diarylamines to afford triarylamines with exclusive para-selectivity.

Perylene bisbenzimidazole nonlinear dielectric material for energy storage

A novel perylene bisbenzimidazole comprising both donor and acceptor functional groups was designed, synthesized, and characterized. This structure exhibits potentially useful physical properties, including a nonlinear dielectric response to an increasing electric field. This material can be used in energy storage devices as the dielectric part of a capacitor. Energy storage devices based on film capacitors are targeting applications in a wide range of industrial, residential and transportation systems.

We synthesized and characterized an organic molecule which can serve as a unit for high-density energy storage.

Insights into the effect of donor ability on photophysical properties of dihydroindeno[2,1-c]fluorene-based imide derivatives

The photophysical properties of dihydroindeno[2,1-c]fluorene-based imide (DHIFI) derivatives were investigated by steady-state and time-resolved spectroscopy as well as quantum chemical calculations.

Bandgap Engineering in π-Extended Pyrroles. A Modular Approach to Electron-Deficient Chromophores with Multi-Redox Activity

A family of bandgap-tunable pyrroles structurally related to rylene dyes was computationally designed and prepared using robust, easily scalable chemistry. These pyrroles show highly variable fluorescence properties and can be used as building blocks for the synthesis of electron-deficient oligopyrroles. The latter application is demonstrated through the development of π-extended porphyrins containing naphthalenediamide or naphthalenediimide units. These new macrocycles exhibit simultaneously tunable visible and near-IR absorptions, an ability to accept up to 8 electrons via electrochemical reduction, and high internal molecular free volumes. When chemically reduced under inert conditions, the most electron-deficient of these macrocycles revealed reversible formation of eight charged states, characterized by remarkably red-shifted optical absorptions, extending beyond 2200 nm. Such features make these oligopyrroles of interest as functional chromophores, charge-storage materials, and tectons for crystal engineering.

N,N′-Diaryl-perylene-3,9-diamine derivatives: synthesis, characterization and electroluminescence properties

In this work, N,N′-diaryl-perylene-3,9-diamine (PDA) derivatives featuring different alkoxyl substituents at para position of the N-aryl rings were synthesized and employed as emitters in solution processed organic light emitting diodes.

Supramolecular aggregates as sensory ensembles

Recent research progress in sensing based on induced supramolecular aggregation or disaggregation.

Energy flow dynamics within cofacial and slip-stacked perylene-3,4-dicarboximide dimer models of π-aggregates

Robust perylene-3,4-dicarboximide (PMI) π-aggregates provide important light-harvesting and electron-hole pair generation advantages in organic photovoltaics and related applications, but relatively few studies have focused on the electronic interactions between PMI chromophores. In contrast, structure-function relationships based on π-π stacking in the related perylene-3,4:9,10-bis(dicarboximides) (PDIs) have been widely investigated. The performance of both PMI and PDI derivatives in organic devices may be limited by the formation of low-energy excimer trap states in morphologies where interchromophore coupling is strong. Here, five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states. Femtosecond near-infrared transient absorption spectroscopy was used to observe the growth of a low-energy transition at ~1450-1520 nm characteristic of the excimer state in these covalent dimers. The excimer-state absorption appears in ~1 ps, followed by conformational relaxation over 8-17 ps. The excimer state then decays in 6.9-12.8 ns, as measured by time-resolved fluorescence spectroscopy. The excimer lifetimes reach a maximum for a slip-stacked geometry in which the two PMI molecules are displaced along their long axes by one phenyl group (~4.3 Å). Additional displacement of the PMIs by a biphenyl spacer along the long axis prevents excimer formation. Symmetry-breaking charge transfer is not observed in any of the PMI dimers, and only a small triplet yield (<5%) is observed for the cofacial PMI dimers. These data provide structural insights for minimizing excimer trap states in organic devices based on PMI derivatives.

Self-Assembly of Supramolecular Light-Harvesting Arrays from Symmetric Perylene-3,4-dicarboximide Trefoils

Unlike the widely studied perylene-3,4:9,10-bis(dicarboximide) (PDI) dyes, self-assembly of the corresponding perylene-3,4-dicarboximide (PMI) dyes into large arrays and studies of their excited state properties have received far less attention. Two symmetric PMI trefoils were synthesized by connecting the 9-position of the perylene core either directly (1) or through a phenylene linker (2) to the 1,3,5-positions of a central benzene ring. Synchrotron-based small- and wide-angle X-ray scattering measurements in methylcyclohexane show that trefoil 1 self-assembles into cofacial trimers (13) on average, while trefoil 2 forms much larger assemblies that are tridecamers (213) on average. Their photophysics were characterized using steady-state as well as transient absorption and emission spectroscopy. Time-resolved spectroscopy reveals that both 13 and 213 initially form excitonically coupled excited states that subsequently relax to excimer states having 20 and 8.4 ns lifetimes, respectively, which decay to ground-state primarily nonradiatively. The data are consistent with stronger electronic coupling between the PMI molecules in 213 relative to 13.

A surface-bound molecule that undergoes optically biased Brownian rotation

Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate.

Understanding the electronic structures and absorption properties of porphyrin sensitizers YD2 and YD2-o-C8 for dye-sensitized solar cells

The electronic structures and excitation properties of dye sensitizers determine the photon-to-current conversion efficiency of dye sensitized solar cells (DSSCs). In order to understand the different performance of porphyrin dye sensitizers YD2 and YD2-o-C8 in DSSC, their geometries and electronic structures have been studied using density functional theory (DFT), and the electronic absorption properties have been investigated via time-dependent DFT (TDDFT) with polarizable continuum model for solvent effects. The geometrical parameters indicate that YD2 and YD2-o-C8 have similar conjugate length and charge transfer (CT) distance. According to the experimental spectra, the HSE06 functional in TDDFT is the most suitable functional for describing the Q and B absorption bands of porphyrins. The transition configurations and molecular orbital analysis suggest that the diarylamino groups are major chromophores for effective CT excitations (ECTE), and therefore act as electron donor in photon-induced electron injection in DSSCs. The analysis of excited states properties and the free energy changes for electron injection support that the better performance of YD2-o-C8 in DSSCs result from the more excited states with ECTE character and the larger absolute value of free energy change for electron injection.

Luminescent one-dimensional nanostructures of perylene bisimides

Perylene bisimides form a unique class of organic semiconductors, in this investigation two symmetrical perylene bisimides caped with 1-butyl (B-PTCDI) and 4,4-diethoxybutyl (DB-PTCDI) have been synthesized and characterized. The compounds self-assembled as a network of nanobelts and nanorods in the solution based self-assembly process. Morphologies of these self-assembled structures were characterized by optical, fluorescence, scanning and transmission electronic microscopic techniques. One-dimensional self-assemblies of B-PTCDI and DB-PTCDI molecules are due to the strong π-π stacking ability of perylene core and assistance given by the side chains and solvent. Observed molecular self-assembly and electronic properties of the molecules. The observed self-assembly was supported by molecular modeling studies using density functional theory.

The role of the conjugate bridge in electronic structures and related properties of tetrahydroquinoline for dye sensitized solar cells

To understand the role of the conjugate bridge in modifying the properties of organic dye sensitizers in solar cells, the computations of the geometries and electronic structures for 10 kinds of tetrahydroquinoline dyes were performed using density functional theory (DFT), and the electronic absorption and fluorescence properties were investigated via time dependent DFT. The population analysis, molecular orbital energies, radiative lifetimes, exciton binding energies (EBE), and light harvesting efficiencies (LHE), as well as the free energy changes of electron injection (ΔG^inject ) and dye regeneration ( ΔGdyeregen ) were also addressed. The correlation of charge populations and experimental open-circuit voltage (V_oc) indicates that more charges populated in acceptor groups correspond to larger V_oc. The elongating of conjugate bridge by thiophene units generates the larger oscillator strength, higher LHE, larger absolute value of ΔG^inject, and longer relative radiative lifetime, but it induces the decreasing of EBE and ΔGdyeregen. So the extending of conjugate bridge with thiopene units in organic dye is an effective way to increase the harvest of solar light, and it is also favorable for electron injection due to their larger ΔG^inject. While the inversely correlated relationship between EBE and LHE implies that the dyes with lower EBE produce more efficient light harvesting.

Perylene imides for organic photovoltaics: yesterday, today, and tomorrow

Perylene imides have been an object of research for 100 years and their derivatives are key n-type semiconductors in the field of organic electronics. While perylene diimides have been applied in many electronic and photonic devices, their use can be traced back to the first efficient organic solar cell. By functionalizing different positions of the in total 12 positions (four peri, four bay, and four ortho-positions) on the perylene core, perylene imides with significantly different optical, electronic and morphological properties may be prepared. Perylene imides and their derivatives have been used in several types of organic photovoltaics, including flat-, and bulk-heterojunction devices as well as dye-sensitized solar cells. Additionally perylene imides-based copolymers or oligomers play an important role in single junction devices. In this review, the relationship between the photovoltaic performance and the structure of perylene imides is discussed.

Organic polyaromatic hydrocarbons as sensitizing model dyes for semiconductor nanoparticles

The study of interfacial charge-transfer processes (sensitization) of a dye bound to large-bandgap nanostructured metal oxide semiconductors, including TiO(2), ZnO, and SnO(2), is continuing to attract interest in various areas of renewable energy, especially for the development of dye-sensitized solar cells (DSSCs). The scope of this Review is to describe how selected model sensitizers prepared from organic polyaromatic hydrocarbons have been used over the past 15 years to elucidate, through a variety of techniques, fundamental aspects of heterogeneous charge transfer at the surface of a semiconductor. This Review does not focus on the most recent or efficient dyes, but rather on how model dyes prepared from aromatic hydrocarbons have been used, over time, in key fundamental studies of heterogeneous charge transfer. In particular, we describe model chromophores prepared from anthracene, pyrene, perylene, and azulene. As the level of complexity of the model dye-bridge-anchor group compounds has increased, the understanding of some aspects of very complex charge transfer events has improved. The knowledge acquired from the study of the described model dyes is of importance not only for DSSC development but also to other fields of science for which electronic processes at the molecule/semiconductor interface are relevant.