Exploring the Versatile Uses of Triplet States: Working Principles, Limitations, and Recent Progress in Phosphorescence, TADF, and TTA.

Triplet excited states in organic semiconductors are usually optically dark and long-lived as they have a spin-forbidden transition to the singlet ground state and therefore hinder processes in light-harvesting applications. Also, triplets often cause damage to the system as they can sensitize the formation of reactive singlet oxygen. Despite these unfavorable characteristics, there exist mechanisms through which we can utilize triplet states, and that constitutes the scope of this review.

Multilayer films for photon upconversion-driven photoswitching.

Photoswitchable materials are of significant interest for diverse applications from energy and data storage to additive manufacturing and soft robotics. However, the absorption profile is often a limiting factor for practical applications. This can be overcome using indirect excitation complementary photophysical pathways, such as triplet sensitisation or photon upconversion.

Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule.

Optical pump-probe techniques allow for an in-depth study of dark excited states. Here, we utilize them to map and gain insights into the excited states involved in the thermally activated delayed fluorescence (TADF) mechanism of a benchmark TADF emitter . The results identify different electronic excited states involved in the key TADF transitions and their nature by combining pump-probe and photoluminescence measurements.

Unusual Excimer/Dimer Behavior of a Highly Soluble C,N Platinum(II) Complex with a Spiro-Fluorene Motif.

In this work, we introduce a spiro-fluorene unit into a phenylpyridine (CN)-type ligand as a simple way to deplanarize the structure and increase the solubility of the final platinum(II)···complex. Using a spiro-fluorene unit, orthogonal to the main coordination plane of the complex, reduces intermolecular interactions, leading to increased solubility but without significantly affecting the ability of the complex to form Pt···Pt dimers and excimers. This approach is highly important in the design of platinum(II) complexes, which often suffer from low solubility due to their mainly planar structure, and offers an alternative to the use of bulky alkyl groups.

Donor, Acceptor, and Molecular Charge Transfer Emission All in One Molecule.

The molecular photophysics in the thermally activated delayed fluorescence (TADF) spiro-acridine-anthracenone compound, ACRSA, is dominated by the rigid orthogonal spirocarbon bridging bond between the donor and acceptor. This critically decouples the donor and acceptor units, yielding photophysics, which includes (dual) phosphorescence and the molecular charge transfer (CT) states giving rise to TADF, that are dependent upon the excitation wavelength. The molecular singlet CT state can be directly excited, and we propose that supposed "spiro-conjugation" between acridine and anthracenone is more accurately an example of intramolecular through-space charge transfer.

Room Temperature Phosphorescence in Solution from Thiophene-Bridged Triply Donor-Substituted Tristriazolotriazines.

Most organic room-temperature phosphorescence (RTP) emitters do not show their RTP in solution. Here, we incorporated sulfur-containing thiophene bridges between the donor and acceptor moieties in D A-type tristriazolotriazines (TTTs). The thiophene inclusion increased the spin-orbit coupling associated with the radiative T →S pathway, allowing RTP to be observed in solution for all compounds, likely assisted by protection of the emissive TTT-thiophene core from the environment by the bulky peripheral donors.

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases.

We present a detailed and comprehensive picture of the photophysics of thermally activated delayed fluorescence (TADF). The approach relies on a few-state model, parametrized on a prototypical TADF dye, that explicitly accounts for the nonadiabatic coupling between electrons and vibrational and conformational motion, crucial to properly address (reverse) intersystem crossing rates. The Onsager model is exploited to account for the medium polarity and polarizability, with careful consideration of the different time scales of relevant degrees of freedom.

Delayed Fluorescence by Triplet-Triplet Annihilation from Columnar Liquid Crystal Films.

Delayed fluorescence (DF) by triplet-triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO-LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF.

Laplace Transform Fitting as a Tool To Uncover Distributions of Reverse Intersystem Crossing Rates in TADF Systems.

Donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) molecules are exquisitely sensitive to D-A dihedral angle. Although commonly simplified to an average value, these D-A angles nonetheless exist as distributions across the individual molecules embedded in films. The presence of these angle distributions translates to distributions in the rates of reverse intersystem crossing (), observed as time dependent spectral shifts and multiexponential components in the emission decay, which are difficult to directly quantify.

ConA-Coated Liposomes as a System to Delivery β-Lapachone to Breast Cancer Cells.

Background: Target treatment using site-specific nanosystems is a hot topic for treating several diseases, especially cancer.

Objective: The study was set out to develop site-specific liposomes using ConcanavalinA (ConA) to target β- lapachone(β-lap) to human breast cancer cells.

Methods: Liposomes were prepared and characterized according to diameter size, zeta potential, ConA conjugation(%) and β-lap encapsulation efficiency (%).

Investigation of Intramolecular Through-Space Charge-Transfer States in Donor-Acceptor Charge-Transfer Systems.

Commonly, thermally activated delayed fluorescence (TADF) emitters present a twisted donor-acceptor structure. Here, electronic communication is mediated through-bond via π-conjugation between donor and acceptor groups. A second class of TADF emitters are those where electronic communication between donor and acceptor moieties is mediated through-space.

The Critical Role of nπ* States in the Photophysics and Thermally Activated Delayed Fluorescence of Spiro Acridine-Anthracenone.

The molecular photophysics and thermally activated delayed fluorescence (TADF) in spiro compounds are distinct because of the rigid orthogonal C-C bridging bond between donor and acceptor. The photophysics is found to be highly complex, with unprecedented multiple anti-Kasha emissions from three different singlet states, two of which are one-photon forbidden. The TADF mechanism is critically controlled by local acceptor nπ* states; the singlet nπ* state undergoes rapid intersystem crossing populating an energetically close acceptor ππ* triplet state.

Photophysics of TADF Guest-Host Systems: Introducing the Idea of Hosting Potential.

The thermally activated delayed fluorescence (TADF) donor-acceptor (D-A) molecule, DMAC-TRZ, is used as a TADF emitter "probe" to distinguish the environmental effects of a range of solid-state host materials in guest-host systems. Using the guest's photophysical behavior in solution as a benchmark, a comprehensive study using a variety of typical TADF organic light-emitting diode hosts with different characteristics provides a clearer understanding of guest-host interactions and what affects emitter performance in solid state. We investigate which are the key host characteristics that directly affect charge-transfer (CT) state energy and singlet triplet energy gaps.

Marrow hypoplasia: a rare complication of untreated Grave's disease.

Atypical presentation forms of hyperthyroidism are always a challenge to the clinician. We present a female patient with the typical symptoms of thyrotoxicosis, without any thionamides treatment before, associated with pancytopenia, which recovered after euthyroidism state was achieved. Although the major cases of pancytopenia in Grave's disease are seen as a complication of antithyroid drugs (thioamides), in this case report the alteration in blood tests was associated with untreated hyperthyroidism.

A meta-analysis of patients with chronic hepatitis C treated with interferon-alpha to determine the risk of autoimmune thyroiditis.

Objective: In order to analyze the effect on autoimmune thyroiditis (AT) of current anti-hepatitis C virus (HCV) treatment in HCV-infected patients, we performed a systematic review with meta-analysis of the available literature. The present meta-analysis was conducted to evaluate the strength and the consistency of the association between treatments with interferon-alpha (IFN-alpha) for HCV infection and AT.

Material And Methods: A search in Medline, PubMed, and EMBASE was conducted with a systematic review of clinical studies in English and other languages.