Spatial Control of 3D Energy Transfer in Supramolecular Nanostructured Host−Guest Architectures (original) (raw)
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The Journal of Physical Chemistry C, 2013
We report on the dependence of time-resolved photoluminescence (PL) and photocurrent in small-molecule bulk heterojunctions on the donor− acceptor (D/A) LUMO offset, D/A separation, and acceptor domain structure. We chose a high-performance functionalized fluorinated anthradithiophene (ADT) derivative, ADT-TES-F, as the donor and two other fluorinated ADT derivatives, ADT-R-F (where R is a variable side group), as well as two functionalized fluorinated pentacene (Pn) derivatives, Pn-R-F8, as acceptors. The choice of ADT and Pn acceptors enabled us to separate the effects of the D/A LUMO offset, which was approximately zero in the case of ADT acceptors and ∼0.55 eV in the case of Pn acceptors, from those of molecular packing on the optoelectronic properties. The acceptor side groups R were chosen based on (i) packing motifs in the solid state and (ii) size, to achieve different D/A separations at the D/A interface. Addition of an ADT-R-F acceptor to the ADT-TES-F donor introduced disorder, which resulted in increased PL emission, depending on the acceptor's packing motif, and in reduced photocurrents. In ADT-TES-F/Pn-R-F8 films, charge transfer from ADT-TES-F to Pn-R-F8 was observed with an acceptor packing-dependent formation of an exciplex, which dissociated under applied electric field, contributing to charge carrier photogeneration. However, this contribution was not sufficient to compensate for a photocurrent reduction due to an increased disorder at Pn-R-F8 concentrations of 7 wt % and above, regardless of the acceptor's R-groups and packing motifs.
Pure and Applied Chemistry, 2003
Encapsulation of chromophores within Cram-type hemicarcerands allowed the investigation of fundamental photophysical phenomena, such as long-range triplet energy transfer, electron transfer, and the remote heavy atom effect. Furthermore, novel water-soluble hemicarcerands are being used to develop unique hybrid materials composed of semiconductor nanoparticles and host–guest assemblies. Photoinduced charge injection from the “incarcerated” guest into the conduction band of the semiconductor has been demonstrated.
A Multidimensional View of Charge Transfer Excitons at Organic Donor–Acceptor Interfaces
Journal of the American Chemical Society, 2017
How tightly-bound charge transfer (CT) excitons dissociate at organic donor-acceptor interfaces has been a long-standing question in the organic photovoltaics community. Recently, it has been proposed that exciton delocalization reduces the exciton binding energy and promotes exciton dissociation. In order to understand this mechanism, it is critical to resolve the evolution of the exciton's binding energy and coherent size with femtosecond (fs) time resolution. However, because the coherent size is just a few nanometers (nm), it presents a major experimental challenge to capture the CT process simultaneously in the energy, spatial and temporal domains. In this work, the challenge is overcome by using time-resolved photoemission spectroscopy. The spatial size and electronic energy of a manifold of CT states are resolved at the zincphthalocyanine (ZnPc)-fullerene (C 60) donor-acceptor interface. It is found that CT at the interface first populates delocalized CT excitons with a coherent size of 4 nm. Then, this delocalized CT exciton relaxes in energy to produce CT states with delocalization sizes in the range of 1-3 nm. While the CT process from ZnPc to C 60 occurs in about 150 fs after photoexcitation, the localization and energy relaxation occur in 2 ps. The multi-dimensional view on how CT excitons evolve in time, space and energy provides key information to understand the exciton dissociation mechanism and to design nanostructures for effective charge separation.
New stable donor–acceptor dyads for molecular electronics
Journal of Materials Chemistry, 2011
A series of new donor-bridge-acceptor dyads with high chemical, electrochemical, thermal and conformational stability were synthesized by Stille coupling of oligo(3,4-ethylenedioxy)thiophenes (nEDOTs) and 1,4,5,8-naphthalenetetracarboxydiimide (NDI) building blocks. The molecular design provides for complete separation of HOMO and LUMO orbitals. A thiol functionality allows for selective anchoring of the dyads to metal electrodes, through either the donor or acceptor sides of the molecule. The optoelectronic properties of the dyads, both in solution and in self-assembled monolayers on gold, were characterized by electrochemistry, spectroelectrochemistry and UV-Vis absorption/emission spectroscopy and the results were further supported by DFT calculations.
The presence of energetically low-lying triplet states is a hallmark of organic semiconductors. Even though they present a wealth of interesting photophysical properties, these optically dark states significantly limit optoelectronic device performance. Recent advances in emissive charge-transfer molecules have pioneered routes to reduce the energy gap between triplets and " bright " singlets, allowing thermal population exchange between them and eliminating a significant loss channel in devices. In conjugated polymers, this gap has proved resistant to modification. Here, we introduce a general approach to reduce the singlet−triplet energy gap in fully conjugated polymers, using a donor−orthogonal acceptor motif to spatially separate electron and hole wave functions. This new generation of conjugated polymers allows for a greatly reduced exchange energy, enhancing triplet formation and enabling thermally activated delayed fluorescence. We find that the mechanisms of both processes are driven by excited-state mixing between π−π*and charge-transfer states, affording new insight into reverse intersystem crossing.
Chemistry of Materials
In this work, we demonstrate several organic amorphous donor−acceptor systems that exhibit sub-bandgap features over a more than 2 eV spectral range. An in-depth study of one of these systems, NPB:HAT-CN (NPB is N,N′di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine and HAT-CN is 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile), reveals that the broad sub-bandgap features are attributed to multiple electronic charge transfer (CT) state transitions, broadened by energetic disorder sourcing from the fluctuations of intramolecular conformations and by the disordered intermolecular environment. These unique CT features originate from an unconventional donor and acceptor selection that reveals new insight about photocurrent generation and nonradiative recombination. Unlike materials employed in high performing organic solar cells, the materials studied here feature large optical energy gaps with very large frontier orbital energy level offsets, creating high bandgap devices with low open-circuit voltage. In addition to multiple electronic CT levels, we reveal that the internal quantum efficiency of these multiple CT transitions is not constant but photon energy dependent and with photoluminescence that originates primarily from the second lowest electronic CT state implying slow (relative to radiative and nonradiative rates) internal conversion within the CT manifold. Overall, this class of donor−acceptor pairs provides an opportunity to probe CT states in unique ways to potentially unravel their role in carrier generation−recombination and energy loss mechanisms.
Origin of efficient light emission from a phosphorescent polymer/organometallic guest-host system
Physical Review B, 2003
Time-resolved photoinduced absorption measurements were performed at 77 K and room temperature on thin films of tris͓9,9-dihexyl-2-͑phenyl-4Ј-͑-pyridin-2Љ-yl͒fluorene͔iridium͑III͒ ͓Ir(DPPF) 3 ͔ doped into a blend of poly(N-vinylcarbazole͒ ͑PVK͒ with 2-͑4-biphenylyl͒-5-͑4-tert-butylphenyl͒-1,3,4-oxadiazole ͑PBD͒. We observe that in the PVK-PBD host blend, charge trapping ͑CT͒ plays an important role in the excited-state dynamics, in addition to exciplex formation and intensity-dependent decay of primary excitations. We develop a physical model which includes all interactions and which is in excellent agreement with the data. We find that 35% of the initial photoexcitation channels into CT states and that exciplexes are formed at a rate of 1/10 ps Ϫ1. For the Ir(DPPF) 3 doped host composite, we write the rate equations for all population densities ͑which include the above excited-state species͒ and include energy-transfer rates from the host to the guest molecules. In both 0.2% and 2% Ir(DPPF) 3 :(PVK-PBD) blends, Förster energy-transfer rates drop to half their lowtemperature values at room temperature. We attribute this difference to a limited availability of guest molecules ready for energy transfer following charge trapping and insufficient spectral overlap due to shifts in the highest occupied and lowest unoccupied molecular orbital levels of the guest upon hole trapping. We conclude that the overall host-guest energy transfer is almost complete at room temperature in the 2% phosphorescent blend, with a large contribution ͑35%͒ from CT states which exhibit emission at all probe wavelengths.
Chromophores in nanochannels for energy transfer and conversion
Synthetic Metals, 2003
Host-guest organic systems obtained by the inclusion of thiophene and phenylene based molecules in perhydrotriphenylene (PHTP) display efficient resonant energy transfers (RET) from short wavelength to longer wavelength emitters. The quantum efficiency of the longer wavelength emitter is lowered of about 20% when donor-acceptor transfer steps are required. A co-inclusion compound (IC) obtained with three molecules shows an efficient conversion of the near ultra violet (250-400 nm) energy into visible (400-600 nm) light with a high photoluminescence (PL) quantum yield (QY) of 45-60%. A proper design of host-guest materials exploiting energy transfer processes can provide interesting artificial nanostructures for optoelectronic applications.
2022
In this study, the computational studies of the PO3H2, CONHOH and SO2H (A1-A3) molecules were investigated for optoelectronic applications on the basis of tetrahydroquinoline (C1-1) dye. Besides, a detailed calculation of the molecular structures, energy levels, driving force of injection, regeneration, Non-linear optical (NLO) property, chemical hardness, excitation binding energy, light-harvesting efficiency (LHE), absorption spectra and photovoltaic (PV) parameters were all discussed in details using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The optoelectronic properties of C1-1 based A1-A3 molecules are originated to be tuned by changing the position of the acceptor. To get a maximum absorption spectrum of C1-1, Becke’s three-parameter and Lee-Yang-Parr (B3LYP), coulomb-attenuating method-B3LYP (CAM-B3LYP) and Head-Gordon model (ωB97XD) were used for the TD-DFT method. Results reveal that the TD-ɷB97XD and 6-31G(d) combined functionals were provide...