Excited Singlet Research Articles

Optical Gaps of Ionic Materials from GW/BSE-in-DFT and CC2-in-DFT.

This work presents a density functional theory (DFT)-based embedding technique for the calculation of optical gaps in ionic solids. The approach partitions the supercell of the ionic solid and embeds a small molecule-like cluster in a periodic environment using a cluster-in-periodic embedding method. The environment is treated with DFT, and its influence on the cluster is captured by a DFT-based embedding potential. The optical gap is estimated as the lowest singlet excitation energy of the embedded cluster, obtained using a wave function theory method: second-order approximate coupled-cluster singles and doubles (CC2), and a many-body perturbation theory method: GW approximation combined with the Bethe-Salpeter equation (GW/BSE). The calculated excitation energies are benchmarked against the periodic GW/BSE values, equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) results, and experiments. Both CC2-in-DFT and GW/BSE-in-DFT deliver excitation energies that are in good agreement with experimental values for several ionic solids (MgO, CaO, LiF, NaF, KF, and LiCl) while incurring negligible computational costs. Notably, GW/BSE-in-DFT exhibits remarkable accuracy with a mean absolute error (MAE) of just 0.38 eV with respect to experiments, demonstrating the effectiveness of the embedding strategy. In addition, the versatility of the method is highlighted by investigating the optical gap of a 2D MgCl2 system and the excitation energy of an oxygen vacancy in MgO, with results in good agreement with reported values.

Influence of pseudo-Jahn-Teller activity on the singlet-triplet gap of azaphenalenes.

We analyze the possibility of symmetry-lowering induced by pseudo-Jahn-Teller interactions in six previously studied azaphenalenes that are known to have their first excited singlet state (S1) lower in energy than the triplet state (T1). The primary aim of this study is to explore whether Hund's rule violation is observed in these molecules when their structures are distorted from C2v or D3h point group symmetries by vibronic coupling. Along two interatomic distances connecting these point groups to their subgroups Cs or C3h, we relaxed the other internal degrees of freedom and calculated two-dimensional potential energy subsurfaces. The many-body perturbation theory (MP2) suggests that the high-symmetry structures are the energy minima for all six systems. However, single-point energy calculations using the coupled-cluster method (CCSD(T)) indicate symmetry lowering in four cases. The singlet-triplet energy gap plotted on the potential energy surface also shows variations when deviating from high-symmetry structures. A full geometry optimization at the CCSD(T) level with the cc-pVTZ basis set reveals that the D3h structure of cyclazine (1AP) is a saddle point, connecting two equivalent minima of C3h symmetry undergoing rapid automerization. The combined effects of symmetry lowering and high-level corrections result in a nearly zero singlet-triplet gap for the C3h structure of cyclazine. Azaphenalenes containing nitrogen atoms at electron-deficient sites - 2AP, 3AP, and 4AP - exhibit more pronounced in-plane structural distortion; the effect is captured by the long-range exchange-interaction corrected DFT method, ωB97XD. Excited state calculations of these systems indicate that in their low-symmetry energy minima, T1 is indeed lower in energy than S1, upholding the validity of Hund's rule. Jahn-Teller analysis predicts the symmetries of the in-plane distortion vibrational modes as or B2: C2v → Cs agreeing with the vibrational frequencies of the saddle-points.

Photoexcitation and One-Electron Reduction Processes of a CO2 Photoreduction Dyad Catalyst Having a Zinc(II) Porphyrin Photosensitizer.

We have explored the photophysical properties and one-electron reduction process in the dyad photocatalyst for CO2 photoreduction, ZnP-phen=Re, in which the catalyst of fac-[Re(1,10-phenanthoroline)(CO)3Br] is directly connected with the photosensitizer of zinc(II) porphyrin (ZnP), using time-resolved infrared spectroscopy, transient absorption spectroscopy, and quantum chemical calculations. We revealed the following photophysical properties: (1) the intersystem crossing occurs with a time constant of ∼20 ps, which is much faster than that of a ZnP single unit, and (2) the charge density in the excited singlet and triplet states is mainly localized on ZnP, which means that the excited state is assignable to the π-π* transition in ZnP. The one-electron reduction by 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole occurs via the triplet excited state with the time constant of ∼100 ns and directly from the ground state with the time constant of ∼3 μs. The charge in the one-electron reduction species spans ZnP and the phenanthroline ligand, and the dihedral angle between ZnP and the phenanthroline ligand is rotated by ∼24° with respect to that in the ground state, which presumably offers an advantage for proceeding to the next CO2 reduction process. These insights could guide the new design of dyad photocatalysts with porphyrin photosensitizers.

Diffusion‐Free Intramolecular Triplet–Triplet Annihilation Contributes to the Enhanced Exciton Utilization in OLEDs

AbstractTriplet–triplet annihilation (TTA), or triplet fusion, is a biexcitonic process in which two triplet‐excited molecules can combine their energy to promote one into an excited singlet state. To alleviate the dependence of the TTA rate and yield on triplet diffusion in both solid and solution environments, intramolecular TTA (intra‐TTA) has been recently proposed in conjugated molecular systems able to hold multiple triplet excitons simultaneously. Developing from the previous demonstration of TTA performance enhancement in sensitized upconversion solutions, here similar improvements in triplet harvesting in solid‐state films are reported under electrical excitation in organic light emitting diodes (OLEDs). At low dye concentration and low current densities, the intra‐TTA active OLED shows a +40% improved external quantum efficiency with respect to the reference device, and a TTA spin‐statistical factor f 4DPA of 0.4, close to that determined in fluid solution for the individual chromophore (0.45). These results therefore indicate the utility of this molecular design strategy across a wider range of TTA applications, and with particular utility in the further development of low‐power TTA‐enhanced OLEDs.

Reactive Oxygen Species Generated in Situ During Carbamazepine Photodegradation at 222 nm Far-UVC: Unexpected Role of H2O Molecules.

When 222 nm far-UVC is used to drive AOPs, photolysis emerges as a critical pathway for the degradation of numerous organic micropollutants (OMPs). However, the photodegradation mechanisms of the asymmetrically polarized OMPs at 222 nm remain unclear, potentially posing a knowledge barrier to the applications of far-UVC. This study selected carbamazepine (CBZ), a prevalent aquatic antiepileptic drug that degrades negligibly at 254 nm, to investigate its photodegradation mechanisms at 222 nm. Accelerated CBZ treatment by 222 nm far-UVC was mainly attributed to in situ ROS generation via self-sensitized photodegradation of CBZ. By quenching experiments and EPR tests, •OH radicals were identified as the major contributor to the CBZ photodegradation, whereas O2•- played a minor role. By deoxygenation and solvent exchange experiments, the H2O molecules were demonstrated to play a crucial role in deactivating the excited singlet state of CBZ (1CBZ*) at 222 nm: generating •OH radicals via electron transfer interactions with 1CBZ*. In addition, 1CBZ* could also undergo a photoionization process. The transformation products and pathways of CBZ at 222 nm were proposed, and the toxicities of CBZ's products were predicted. These findings provide valuable insights into OMPs' photolysis with 222 nm far-UVC, revealing more mechanistic details for far-UVC-driven systems.

Lowering of the singlet-triplet energy gap via intramolecular exciton-exciton coupling

Organic dyes typically have electronically excited states of both singlet and triplet multiplicity. Controlling the energy difference between these states is a key factor for making efficient organic light emitting diodes and triplet sensitizers, which fulfill essential functions in chemistry, physics, and medicine. Here, we propose a strategy to shift the singlet excited state of a known sensitizer to lower energies without shifting the energy of the triplet state, thus without compromising the ability of the sensitizer to do work. We covalently connect two to four sensitizers in such a way that their transition dipole moments are aligned in a head-to-tail fashion, but, through steric encumbrance, the delocalization is minimized between each moiety. Exciton coupling between the singlet excited states considerably lowers the first excited singlet state energy. However, the energy of the lowest triplet excited state is unperturbed because the exciton coupling strength depends on the magnitude of the transition dipole moments, which for triplets are very small. We expect that the presented strategy of designed intramolecular exciton coupling will be a useful concept in the design of both photosensitizers and emitters for organic light emitting diodes as both benefits from a small singlet-triplet energy gap.

Strong-Coupling Modification of Singlet-Fission Dynamical Pathways.

We investigate theoretically the influence of strong light-matter coupling on the initial steps of the phototriggered singlet-fission process. In particular we focus on intramolecular singlet fission in a TIPS-pentacene dimer derivative described by a vibronic Hamiltonian including the optically active singlet excited states, doubly excited and charge transfer states, as well as the final triplet-triplet pair state. Quantum dynamics simulations of up to four dimers in the cavity indicate that the modified resonance condition imposed by the cavity strongly quenches the passage through the intermediate charge transfer and double-excitation states, thus largely reducing the triplet-triplet yield in the bare system. Subsequently, we modify the system parameters and construct a model Hamiltonian where the optically active singlet excitation lies below the final triplet-triplet state such that the yield of the bare system becomes insignificant. In this case we find that using the upper polariton as the doorway state for photoexcitation can lead to a much enhanced yield. This pathway is operative provided that the system is sufficiently rigid to prevent vibronic losses from the upper polariton to the dark-states manifold.

Electron Spin Polarization in the Triplet State of Methoxy-substituted Phosphorus(V) Tetraphenyl Porphyrins

Photoexcited triplet states of porphyrins are of great relevance in various applications due to their high yield, long lifetime, and strong electron spin polarization. This study delves into properties and spin dynamics of the triplet state of a series of hypervalent phosphorus(V) porphyrins. Transient Electron Paramagnetic Resonance (TrEPR) measurements, supported by quantum chemical calculations as well as by optical absorption/luminescence experiments, reveal that, unlike singlet states, the lowest triplet state does not exhibit charge-transfer (CT) character upon photoexcitation. However, the presence of excited CT singlet states alters the intersystem crossing in phosphorus(V) porphyrins, leading to a sign change in the initial multiplet polarization of the photoexcited triplet state. TrEPR results further demonstrate that significant net polarization develops in the triplet states of the phosphorus(V) porphyrins due to the dynamic Jahn-Teller effect. Yet, this effect remains largely unaffected by differences in their molecular structures.

A Constraint-Based Orbital-Optimized Excited State Method (COOX).

In this work, we present a novel method to directly calculate targeted electronic excited states within a self-consistent field calculation based on constrained density functional theory (cDFT). The constraint is constructed from the static occupied-occupied and virtual-virtual parts of the excited state difference density from (simplified) linear-response time-dependent density functional theory calculations (LR-TDDFT). Our new method shows a stable convergence behavior, provides an accurate excited state density adhering to the Aufbau principle, and can be solved within a restricted SCF for singlet excitations to avoid spin contamination. This also allows the straightforward application of post-SCF electron-correlation methods like MP2 or direct RPA methods. We present the details of our constraint-based orbital-optimized excited state method (COOX) and compare it to similar schemes. The accuracy of excitation energies will be analyzed for a benchmark of systems, while the quality of the resulting excited state densities is investigated by evaluating excited state nuclear forces and excited state structure optimizations. We also investigate the performance of the proposed COOX method for long-range charge transfer excitations and conical intersections with the ground-state.

Singlet-Triplet Inversions in Through-Bond Charge-Transfer States.

Molecules where the lowest excited singlet state is lower in energy than the lowest triplet are highly promising for a number of organic materials applications as efficiency limitations stemming from spin statistics are overcome. All molecules known to possess such singlet-triplet inversions exhibit a pattern of spatially alternating but nonoverlapping HOMO and LUMO orbitals, meaning the lowest excited states are of a local character. Here, we demonstrate that derivatives of the bicyclic hydrocarbon calicene exhibit Hund's rule violations in charge-transfer (CT) states between its rings. These CT states can be tuned with substituents, so that the first excited singlet and triplet state are energetically inverted. This provides a conceptual connection between the emerging fields of inverted gap molecules and existing molecular design rules for state-of-the-art thermally activated delayed fluorescence materials.

Inverse Design of Singlet Fission Materials with Uncertainty-Controlled Genetic Optimization.

Singlet fission has shown potential for boosting the power conversion efficiency of solar cells, but the scarcity of suitable molecular materials hinders its implementation. We introduce an uncertainty-controlled genetic algorithm (ucGA) based on ensemble machine learning predictions from different molecular representations that concurrently optimizes excited state energies, synthesizability, and singlet exciton size for the discovery of singlet fission materials. The ucGA allows us to efficiently explore the chemical space spanned by the reFORMED fragment database, which consists of 45,000 cores and 5,000 substituents derived from crystallographic structures assembled in the FORMED repository. Running the ucGA in an exploitative setup performs local optimization on variations of known singlet fission scaffolds, such as acenes. In an explorative mode, hitherto unknown candidates displaying excellent excited state properties for singlet fission are generated. We suggest a class of heteroatom-rich mesoionic compounds as acceptors for charge-transfer mediated singlet fission. When included in larger conjugated donor-acceptor systems, these units exhibit strong localization of the triplet state, favorable diradicaloid character and suitable triplet energies for exciton injection into semiconductor solar cells. As the proposed candidates are composed of fragments from synthesized molecules, they are likely synthetically accessible.

Inverse Design of Singlet Fission Materials with Uncertainty‐Controlled Genetic Optimization

Singlet fission has shown potential for boosting the power conversion efficiency of solar cells, but the scarcity of suitable molecular materials hinders its implementation. We introduce an uncertainty‐controlled genetic algorithm (ucGA) based on ensemble machine learning predictions from different molecular representations that concurrently optimizes excited state energies, synthesizability, and singlet exciton size for the discovery of singlet fission materials. The ucGA allows us to efficiently explore the chemical space spanned by the reFORMED fragment database, which consists of 45,000 cores and 5,000 substituents derived from crystallographic structures assembled in the FORMED repository. Running the ucGA in an exploitative setup performs local optimization on variations of known singlet fission scaffolds, such as acenes. In an explorative mode, hitherto unknown candidates displaying excellent excited state properties for singlet fission are generated. We suggest a class of heteroatom‐rich mesoionic compounds as acceptors for charge‐transfer mediated singlet fission. When included in larger conjugated donor‐acceptor systems, these units exhibit strong localization of the triplet state, favorable diradicaloid character and suitable triplet energies for exciton injection into semiconductor solar cells. As the proposed candidates are composed of fragments from synthesized molecules, they are likely synthetically accessible.

Effect of Electron-Donating Substituents and an Electric Field on the ΔEST of Selected Imidazopyridine Derivatives: A DFT Study.

A series of thermally activated delayed fluorescent (TADF) molecules having an imidazopyridine acceptor, a benzene linker, and a 9,9-dimethyl-9,10-dihydroacridine donor are designed and examined using a quantum chemical approach. The above framework spatially separates the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), minimizing their overlap, ultimately resulting in a reduced energy gap between the excited singlet and triplet states (ΔEST). The impact of electron-donating substituents (-Me, -Et, -t-Bu, -OMe, and -NMe2) on the donor moiety of the parent molecule 2-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)imidazo[1,2-a]pyridine-3,6-dicarbonitrile (Ac-CNImPy) is investigated. The calculated results revealed that for a given substituent, the para-substituted derivatives exhibit relatively less ΔEST, compared to that of the respective ortho- and meta derivatives. The value of ΔEST decreased with an increase in the electron-donating capacity of the substituent. Additionally, the ΔEST of the disubstituted derivatives is found to be less than that for the monosubstituted derivatives. The charge transport studies revealed that molecules with strong electron-donating substituents act as electron transporters. The effect of an external electric field (EEF) on ΔEST of the parent molecule Ac-CNIMPY and its derivative is also examined and revealed that the ΔEST can be further reduced by applying an electric field of appropriate strength in a direction perpendicular to the dipole moment of the molecule and in the plane of the acceptor moiety.

Photochemical Dimerization of Indones: A DFT Study

In this study, DFT calculations were performed in order to identify the reaction products of the photochemical dimerization of indones. Calculations allowed us to assume that all tested reactions occurred in the first excited singlet state. The irradiation of 2-phenyl-5-nitroindone gave the main product, the <i>anti-cis</i> head-to-tail dimer, while the other two compounds found in the experiments were the <i>syn-cis</i> head-to-head dimer and the <i>anti-cis</i> head-to-tail dimer. The irradiation of 2-phenylindone gave the main product, <i>syn-cis</i>-head-to-tail dimer, while the minor products were <i>anti-cis</i>-head-to-tail and <i>anti-cis</i>-head-to-head dimer. The photochemical dimerization of 2-methyl-3-phenylindone gave the main product, <i>anti-cis</i>-head-to-tail dimer, while the minor component of the mixture was <i>syn-cis</i>-head- to-head dimer.

Oxygen-doped Carbon Nitrides with Visible Room-temperature Phosphorescence and Invisible Thermal-Stimuli-Responsive Ultraviolet Delayed Fluorescence for Security Applications.

Multi-mode emissive materials with stimuli-responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen-doped carbon nitrides (O-CNs) are prepared via microwave-assisted heating of urea, which exhibit ultraviolet (UV) solid-state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal-stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O-CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal-stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet-triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra-narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O-CNs, security protection strategies with superior concealment by virtue of the thermal-stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

Oxygen‐doped Carbon Nitrides with Visible Room‐temperature Phosphorescence and Invisible Thermal‐Stimuli‐Responsive Ultraviolet Delayed Fluorescence for Security Applications

Multi‐mode emissive materials with stimuli‐responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen‐doped carbon nitrides (O‐CNs) are prepared via microwave‐assisted heating of urea, which exhibit ultraviolet (UV) solid‐state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal‐stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O‐CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal‐stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet‐triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra‐narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O‐CNs, security protection strategies with superior concealment by virtue of the thermal‐stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

One-Pot In Situ Construction of a Highly Stable Acylhydrazone-Derived Dy9 Cluster with Photodynamic Sterilization Property.

The extremely low stability of lanthanide clusters with precise structures and nanometer dimensions in aqueous solutions limits their application in the field of photodynamic sterilization. In this study, an hourglass-shaped nine-nucleated Dy9 cluster (1) with excellent light-driven reactive oxygen species (ROS) generation ability and photodynamic sterilization property was constructed using acylhydrazone multidentate chelating ligands obtained via an in situ reaction. The eight chelating ligands were distributed outside cluster 1, tightly wrapping the cluster core, thus preventing solvent molecules from attacking the cluster nucleus and ensuring the stability of cluster 1 in solution, which was demonstrated via X-ray diffraction and high-resolution electrospray ionization mass spectrometry (HRESI-MS). Time-dependent HRESI-MS monitoring of the self-assembly process of cluster 1 allowed two possible self-assembly mechanisms. The heavy atom effect of multiple Dy(III) ions in the Dy9 cluster enhanced the ISC pathway through spin-orbit coupling, promoting energy transfer from the excited singlet state (S1) to the triplet state (T1), which was stabilized, inducing the generation of more ROS. Cluster 1 showed a remarkable sterilization effect due to the generation of abundant ROS under light irradiation conditions. To our knowledge, this is a rare instance of lanthanide clusters with photodynamic sterilization, providing new horizons for the construction of fast and efficient sterilizers.

Insight into the photodegradation of methylisothiazolinone and benzoisothiazolinone in aquatic environments

Methylisothiazolinone (MIT) and Benzisothiazolinone (BIT) are two widely used non-oxidizing biocides of isothiazolinones. Their production and usage volume have sharply increased since the pandemic of COVID-19, inevitably leading to more release into water environment. However, their photochemical behaviors in water environment are still unclear. Therefore, this study investigated photodegradation properties of MIT and BIT in natural water under simulated sunlight. The results demonstrated that direct photolysis was mainly responsible for their photodegradation which occurred through their excited singlet states rather than triplet states. The quantum yields of MIT and BIT photodegradation were 11 - 13.6 × 10−4 and 2.43 - 5.79 × 10−4, respectively. pH had almost no effect on the photodegradation of MIT, while the photodegradation of BIT was significantly promoted under alkaline condition due to abundance of BIT in its deprotonated form (BIT-N−). Cl−, NO3− and dissolved organic matter (DOM) in natural water inhibited the photodegradation of both MIT and BIT, with the light screening effect of DOM being the most significantly inhibitory factor. The addition of other isothiazolinones, which possibly coexisted with MIT and BIT in actual condition, slightly inhibited the photodegradation of MIT and BIT. The estimated half-life under natural sunlight at a 30°N latitude was estimated to be approximately 1.1 days. The photodegradation pathways of MIT and BIT are similar, primarily initiated from the ring-opening at the N-S bond, with Frontier electron densities (FED) calculations suggesting the likelihood of oxidation and ·OH addition reactions at the O, N, and S sites. While the photodegradation products exhibited significantly reduced acute toxicity compared to their parent compounds, they nonetheless posed substantial chronic toxicity. These insights are vital for assessing the ecological impacts of MIT and BIT in aquatic environments.

Photolysis of dinotefuran and nitenpyram in water and ice phase: Influence mechanism of temperature over photolysis

Neonicotinoids are widely used pesticides around the world, but the photolysis of neonicotinoids in cold agricultural region are still in blank. This paper aimed to study the influence of cold temperature over photolysis of neonicotinoids. To this end, the photolysis rates and photoproducts of dinotefuran and nitenpyram in water, ice and freeze-thawing condition were determined. Coupled with quantum chemistry calculation, the influence mechanisms of temperature and medium were investigated. The results showed the photolysis rates of neonicotinoids in water condition slightly declined with the lowered temperature due to the photolysis reactions were endothermic reactions. However, the photolysis rates increased by 89.8 %, 59.2 %, 49.4 % and 9.5 % for dinotefuran and nitenpyram in ice and thawing condition, respectively. This phenomenon was posed by the concentration-enhancing effect and change of photo-chemical properties of neonicotinoids in ice condition, which included lowered bond cleavage energy, lowered first excited singlet state energy and expanded light absorption range. The photolysis pathways of the two neonicotinoids did not change in different medium, but the concentration of carboxyl products was relatively higher than that of water condition due to the more amounts of reactive oxygen species in ice medium, which might increase the secondary pollution risk after ice-off in spring due to the higher ecotoxicity to nontarget organism of these photoproducts. The influence of cold temperature and medium change should be considered for the environmental fate and risk assessment of neonicotinoids in cold agricultural region.

Ultrafast Processes in Upper Excited Singlet States of Free and Caged 7-Diethylaminothiocoumarin.

The photochemistry and photophysics of thiocarbonyl compounds, analogues of carbonyl compounds with sulfur, have long been overshadowed by their counterparts. However, recent interest in visible light reactions has reignited attention toward these compounds due to their unique excited-state properties. This study delves into the ultrafast dynamics of 7-diethylaminothiocoumarin (TC1), a close analogue of the well-known probe molecule coumarin 1 (C1), to estimate intersystem crossing rates, understand the mechanisms of fluorescence and phosphorescence, and evaluate TC1's potential as a solvation dynamics probe. Enclosing TC1 within an organic capsule indicates its potential applications, even in aqueous environments. Ultrafast studies reveal a dominant subpicosecond intersystem crossing process, indicating the importance of upper excited singlet and triplet states in the molecule's photochemistry. The distinct fluorescence and phosphorescence origins, along with the presence of closely spaced singlet excited states, support the observed efficient intersystem crossing. The sulfur atom alters the excited-state behavior, shedding light on reactive triplet states and paving the way for further investigations.