Iridium(III) Carbene Complexes Featuring either Metal-to-Ligand Charge Transfer (MLCT) or Through-Space Charge Transfer (TSCT) Blue Luminescence.

Through-space charge transfer (TSCT) rather than the commonly postulated metal-to-ligand charge transfer (MLCT) process was proposed in getting the lowest lying excited state of newly designed Ir(III) blue phosphors. Accordingly, two benzo[d]imidazolylidene pro-chelates L12H2+ and L13H2+, one with two cyano groups at the peri-benzo and N-aryl pendent and the other with its peri-cyano group being replaced with methyl substituent, were employed in syntheses of Ir(III) complexes f-ct12b,c and f-ct13b,c. Notably, complexes f-ct12b,c exhibited the traditional MLCT process, while f-ct13b,c were dominated by the TSCT transition, resulting in a smaller S1-T1 energy gap ΔEST.

Multiple Enol-Keto Isomerization and Excited-State Unidirectional Intramolecular Proton Transfer Generate Intense, Narrowband Red OLEDs.

A novel series of excited-state intramolecular proton transfer (ESIPT) emitters, namely, , , and , endowed with dual intramolecular hydrogen bonds, were designed and synthesized. In the condensed phase, exhibit unmatched absorption and emission spectral features, where the minor 0-0 absorption peak becomes a major one in the emission. Detailed spectroscopic and dynamic approaches conclude fast ground-state equilibrium among enol-enol (EE), enol-keto (EK), and keto-keto (KK) isomers.

Repairing Interfacial Defects in Self-Assembled Monolayers for High-Efficiency Perovskite Solar Cells and Organic Photovoltaics through the SAM@Pseudo-Planar Monolayer Strategy.

Lately, carbazole-based self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). Nevertheless, these SAMs tend to aggregate in solvents due to their amphiphilic nature, hindering the formation of a monolayer on the ITO substrate and impeding effective passivation of deep defects in the perovskites. In this study, a series of new SAMs including DPA-B-PY, CBZ-B-PY, POZ-B-PY, POZ-PY, POZ-T-PY, and POZ-BT-PY are synthesized, which are employed as interfacial repairers and coated atop CNph SAM to form a robust CNph SAM@pseudo-planar monolayer as HSL in efficient inverted PSCs.

Hydrogen-Bonded Thiol Undergoes Unconventional Excited-State Intramolecular Proton-Transfer Reactions.

The chapter on the thiol-related hydrogen bond (H-bond) and its excited-state intramolecular proton-transfer (ESIPT) reaction was recently opened where compound 4'-diethylamino-3-mercaptoflavone () undergoes ESIPT in both cyclohexane solution and solid, giving a 710 nm tautomer emission with an anomalously large Stokes shift of 12,230 cm. Considering the thiol H-bond to be unconventional compared to the conventional Pauling-type -OH or -NH H-bond, it is thus essential and timely to probe its fundamental difference between their ESIPT. However, thiol-associated ESIPT tends to be nonemissive due to the dominant π* character of the tautomeric lowest excited state.

Entropy-driven charge-transfer complexation yields thermally activated delayed fluorescence and highly efficient OLEDs.

Exciplex-forming systems that display thermally activated delayed fluorescence are widely used for fabricating organic light-emitting diodes. However, their further development can be hindered through a lack of structural and thermodynamic characterization. Here we report the generation of inclusion complexes between a cage-like, macrocyclic, electron-accepting host (A) and various N-methyl-indolocarbazole-based electron-donating guests (D), which exhibit exciplex-like thermally activated delayed fluorescence via a through-space electron-transfer process.

Self-Assembled Monolayers of Bi-Functionalized Porphyrins: A Novel Class of Hole-Layer-Coordinating Perovskites and Indium Tin Oxide in Inverted Solar Cells.

Self-assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid-functionalized porphyrin derivatives, namely AC-1, AC-3, and AC-5, and present, for the first time, a strategy to exploit the large π-moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron-rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects.

Photoinduced Aryl Transfer from Imidazolyl-Quinoline π-Conjugated Systems.

Aryl transfer between heteroatoms was photochemically available through radical initiation followed by a bimolecular reaction. However, such an excited-state reaction has rarely been reported through a photoinduced intramolecular pathway in the π-conjugated systems. Herein, we found, for the first time, a clean photoinduced intramolecular aryl shift for imidazolyl-quinoline derivatives (imidazophenanthrene) and (imidazophenanthroline), of which the photoproducts are thermally reversible.

Engineering of Cyano Functionalized Benzo[]imidazol-2-ylidene Ir(III) Phosphors for Blue Organic Light-Emitting Diodes.

In this study, we designed and synthesized three series of blue emitting homoleptic iridium(III) phosphors bearing 4-cyano-3-methyl-1-phenyl-6-(trifluoromethyl)-benzo[]imidazol-2-ylidene (mfcp), 5-cyano-1-methyl-3-phenyl-6-(trifluoromethyl)-benzo[]imidazol-2-ylidene (ofcp), and 1-(3-(-butyl)phenyl)-6-cyano-3-methyl-4-(trifluoromethyl)-benzo[]imidazol-2-ylidene (5-mfcp) cyclometalates, respectively. These iridium complexes exhibit intense phosphorescence in the high energy region of 435-513 nm in the solution state at RT, to which the relatively large T → S transition dipole moment is beneficial for serving as a pure emitter and an energy donor to the multiresonance thermally activated delayed fluorescence (MR-TADF) terminal emitters via Förster resonance energy transfer (FRET). The resulting OLEDs achieved true blue, narrow bandwidth EL with a max EQE of 16-19% and great suppression of efficiency roll-off with ν-DABNA and -DABNA.

Quest for singlet fission of organic sulfur-containing systems in the higher lying singlet excited state: application prospects of anti-Kasha's rule.

In this study, we explore the possibilities of the deactivating pathways of organic thione containing systems through first-principles calculations. We particularly pay attention to the second lying singlet excited state, S, due to its large energy difference from the lowest lying S state in the sulfur-containing systems. Several theoretical models including the previously synthesized thiones and the strategically designed molecules are investigated to search for the basic conjugation unit that exhibits the prospect of S fission.

Rational Design of Asymmetric Polymethines to Attain NIR(II) Bioimaging at >1100 nm.

Organic molecules having emission in the NIR(II) region are emergent and receiving enormous attention. Unfortunately, attaining accountable organic emission intensity around the NIR(II) region is hampered by the dominant internal conversion operated by the energy gap law, where the emission energy gap and the associated internal reorganization energy λ play key roles. Up to the current stage, the majority of the reported organic NIR(II) emitters belong to those polymethines terminated by two symmetric chromophores.

Comprehensive Thione-Derived Perylene Diimides and Their Bio-Conjugation for Simultaneous Imaging, Tracking, and Targeted Photodynamic Therapy.

In this study, the chromophore 3,4,9,10-perylenetetracarboxylic diimide (PDI) is anchored with phenyl substituents at the imide N site, followed by thionation, yielding a series of thione products , , , , and , respectively, with = 1, 2, 3, and 4 thione. The photophysical properties are dependent on the number of anchored thiones, where the observed prominent lower-lying absorption is assigned to the S → S(ππ*) transition and is red-shifted upon increasing the number of thiones; the lowest-lying excited state is ascribed to a transition-forbidden S(π*) configuration. All s are non-emissive in solution but reveal an excellent two-photon absorption cross-section of >800 GM.

Tuning intramolecular charge transfer and spin-orbit coupling of AIE-active type-I photosensitizers for photodynamic therapy.

Development of photosensitizers (PSs) featuring type-I reactive oxygen species (ROS) with aggregation-induced emission (AIE) properties is a judicious approach to overcome the deficit of conventional photodynamic therapy (PDT). However, it remains a challenge to design AIE-active type-I ROS PSs using a simple theranostic scaffold paired with a delicate balance between intramolecular charge transfer (ICT) and large spin-orbit coupling (SOC) features to facilitate intersystem crossing (ISC) and hence to intensify triplet excitons for type-I ROS generation as well as to improve optical properties for the desired biomedical applications. In this work, a rationally designed series of PSs based on C-6-substituted tetraphenylethylene-fused benzothiazole-coumarin scaffolds, named TPE-nCUMs, were synthesized a fused-ring-electron-acceptor (FREA) strategy, endowed with AIE properties in aqueous solution and thus self-monitoring type-I ROS generation under white-light irradiation to study the effects of diverse ICT and SOC potentials on their photochemical and optical properties.

Reducing the internal reorganization energy symmetry controlled π-electron delocalization.

The magnitude of the reorganization energy is closely related to the nonradiative relaxation rate, which affects the photoemission quantum efficiency, particularly for the emission with a lower energy gap toward the near IR (NIR) region. In this study, we explore the relationship between the reorganization energy and the molecular geometry, and hence the transition density by computational methods using two popular models of NIR luminescent materials: (1) linearly conjugated cyanine dyes and (2) electron donor-acceptor (D-A) composites with various degrees of charge transfer (CT) character. We find that in some cases, reorganization energies can be significantly reduced to 50% despite slight structural modifications.

Modulation of Perovskite Grain Boundaries by Electron Donor-Acceptor Zwitterions ,-Diphenylamino-phenyl-pyridinium-(CH) -sulfonates: All-Round Improvement on the Solar Cell Performance.

Inverted perovskite solar cells (PSCs) have attracted intense attention because of their insignificant hysteresis and low-temperature fabrication process. However, the efficiencies of inverted PSCs are still inferior to those of commercialized silicon solar cells. Also, the poor stability of PSCs is one of the major impedances to commercialization.

[2,2](5,8)Picenophanedienes: Syntheses, Structural Analyses, Molecular Dynamics, and Reversible Intramolecular Structure Conversion.

This study presents an important and efficient synthetic approach to 5,8-dibromo-2,11-dibutylpicene (), with multigram scale, which was then converted to a new series of picenophanes (-). The tub-shaped [2,2](5,8)picenophanediene with two -ethylene linkers was explored using X-ray crystallography. The tub-to-tub inversion proceed through the successive bending of the linkers and the barrier for isopropyl-substituted derivative was experimentally estimated to be 18.