Heavy Atom Effect Research Articles

Real-time spectroscopic tracking of efficient intersystem crossing triggered by the heavy-atom effect in di-heteroatomic organic phosphorescent molecules

The development of efficient and long-lived halogen-free organic phosphorescent molecules remains a challenge. For the single-heteroatomic 9,10-dihydroacridine (AcH2), the evolution of singlet and triplet excited state absorption signals reveals an intersystem crossing (ISC) lifetime of 8.2 ns and a triplet state lifetime of 0.52 µs. In contrast, the ISC lifetimes of di-heteroatomic phenoxazine (PXZ) and phenothiazine (PTZ) are significantly accelerated to 1.7 ns and 1.1 ns, respectively, while the triplet state lifetimes are extended to 0.72 µs and 4 µs. These results confirm that the introduction of di-heteroatomic synergistic effects enhances ISC efficiency while simultaneously prolonging the triplet state lifetimes. Notably, these two critical factors are further improved in PTZ due to the heavy-atom effect of sulfur atom. The work emphasizes the di-heteroatomic synergistic effect, particularly the role of heteroatoms with large atomic numbers, which is crucial for the design of halogen-free organic phosphorescent materials.

Disulfide-Bridged Cationic Dinuclear Ir(III) Complex with Aggregation-Induced Emission and Glutathione-Consumption Properties for Elevating Photodynamic Therapy.

The ability of photosensitizers (PSs) to generate reactive oxygen species (ROS) is crucial for photodynamic therapy (PDT). However, many traditional PSs face the drawbacks that aggregation-caused quenching (ACQ) and highly expressed glutathione (GSH) in the tumor microenvironment seriously limit their ROS generation ability. Herein, we report two cationic dinuclear iridium complexes, Ir-C-C-Ir and Ir-S-S-Ir, which possess aggregation-induced emission (AIE). Ir-S-S-Ir was constructed for GSH consumption by introducing a disulfide linkage between the two auxiliary ligands with imine units. Quantum chemical calculations revealed that Ir-C-C-Ir and Ir-S-S-Ir possess many degenerate states, which provide more channels for singlet-to-triplet exciton transitions, and then the intersystem crossing rate is increased due to the heavy atom effect of the iridium and sulfur atoms. The ROS production experiments indicated that the singlet oxygen yield of Ir-S-S-Ir was 33 times more than that of the ACQ mononuclear iridium complex Ir-C. Most importantly, Ir-S-S-Ir consumed GSH through a thiol-disulfide exchange reaction, as demonstrated by mass spectrometry and high-performance liquid chromatography. Cell experiments testified that Ir-S-S-Ir consumes GSH in tumor cells, possesses good ROS production capacity, and exhibits an extraordinary PDT effect. This is the first report of an AIE dinuclear iridium complex with a GSH-consuming function.

Effective promotion of steric hindrance effect on singlet-triplet transition of para-linked carbazole-biphenyl by transient absorption spectroscopy

The para-linked carbazole-biphenyl (CBP) is commonly utilized in phosphorescent organic light-emitting diodes. This study investigates the steric hindrance and heavy-atom effects in CBP derivatives through transient absorption spectroscopy. In contrast to CBP, CBP derivatives shows new triplet–triplet absorption signals and isosbestic points, accompanied by the decay of excited state absorption signal, which indicates the occurrence of intersystem crossing (ISC). The experimental ISC lifetimes for mCBP, CDBP, and CPB-2Br are 8 ns, 7.4 ns, and 0.103 ns respectively, aligning with the increased theoretical spin–orbit coupling constants (ξ) of S1 → T1 (0.032 cm−1 < 0.034 cm−1 < 1.26 cm−1). Notably, compared to CDBP (0.75 cm−1, 0.3 μs), the lower ξ(T1, S0) of mCBP (0.014 cm−1) extending the experimental triplet-exciton lifetimes (τT) to 1.97 μs. The τT (1.92 μs) of CBP-2Br is prolonged due to the significantly reduced recombination energy (2073.52 cm−1). This study provides insights into prolonging the lifetime of halogen-free phosphorescent molecules.

Influence of Halogen Substituents on the Photophysical Properties of 7-Hydroxycoumarin: Insights from Experimental and Theoretical Studies.

Benzopyrone is a popular fluorescent scaffold, but how chemical modifications affect its properties is less understood. We investigated this using halogenated 7-hydroxycoumarin, unsubstituted 4-methylumbiliferone, and ortho-chloro and bromo substitutions on the phenolic ring. Experimental charge density data and computational methods revealed that halogenation at the ortho position significantly reduced quantum yield (QY). Specifically, 7-hydroxycoumarin (1) had a QY of 70%, while ortho-chloro (2) and ortho-bromo (3) had QYs of 61% and 30%, respectively. Experimental data showed that all probes excited similarly, but the electrostatic potential and dipole moments indicated that 2 and 3 dissipated excitation energy more easily due to charge separation. The heavy-atom effect of Cl and Br did not fully explain the QY reductions, suggesting other radiative decay processes were involved. By incorporating spin-orbit coupling (SOC) effects, we estimated intersystem crossing (ISC) and phosphorescence rates, providing theoretical QYs of 78% for 1, 59% for 2, and 15% for 3. The large deviation for 3 was attributed to its higher SOC potential. Our findings indicate that 3's reduced QY results from a mix of SOC-induced ISC and charge dissipation, while 2's reduction is primarily due to charge separation. Further studies are needed to validate this approach with other scaffolds.

The Photophysics of Naphthalimide-Phenoselenazine Electron Donor-Acceptor Dyads: Revisiting the Heavy-Atom Effect in Thermally Activated Delayed Fluorescence.

We prepared thermally activated delayed fluorescence (TADF) emitter dyads, NI-PTZ, NI-PTZ-2Br and NI-PSeZ, with naphthalimide (NI) as electron acceptor and 10H-phenothiazine (PTZ) or 10H-phenoselenazine (PSeZ) as electron donor to study the heavy-atom effect on the intersystem crossing (ISC) and reverse ISC (rISC) in the TADF emitters. The delayed fluorescence lifetimes of the dyads containing heavy atoms ( =5.9 μs for NI-PSeZ and =16.5 μs for NI-PTZ-2Br, respectively) are longer than the heavy atom-free counterpart NI-PTZ ( =2.0 μs). Nanosecond transient absorption (ns-TA) spectral study and the time-resolved electron paramagnetic resonance (TREPR) spectra show the presence of both 3LE and 3CS states. These findings represent solid experimental evidences for the spin-vibronic coupling mechanism of TADF. Moreover, the ns-TA spectra show that the heavy atoms don't have a significant effect since the lifetime of the triplet transient species (1.3 μs for NI-PTZ) is not shortened in their presence (4.5 μs for NI-PSeZ and 5.3 μs for NI-PTZ-2Br). These results show that the previously claimed heavy-atom effect on rISC and TADF is not a universal principle. The femtosecond transient absorption (fs-TA) spectra of the compounds indicate the occurrence of fast charge separation within 1-2 ps, and the charge recombination is slow (>4 ns).

Moderately Heavy Atom-Substituted BODIPY Photosensitizer with Mitochondrial Targeting Ability for Imaging-Guided Photodynamic Therapy.

Advanced photodynamic therapy requires photosensitizers with targeting, diagnostic, and therapeutic properties. To fulfill this multifunctionality, we report the synthesis of two triphenylphosphonium (TPP)-functionalized boron-dipyrromethene (BODIPY) dyes, TPPB-H and TPPB-Br, which incorporate a hydrogen atom and dibrominated vinyl moiety at the 6-position of the BODIPY core, respectively. The heavy-atom effect of the moderately heavy bromine atoms allowed TPPB-Br to achieve a proper balance between the toxic singlet oxygen (1O2) production and fluorescence efficiencies. In this dye, the bromine atom-induced stimulation of the singlet-to-triplet intersystem crossing dynamics resulted in an approximately 45-fold increase in the 1O2 quantum yield with respect to that of the nonbrominated counterpart (0.0059 and 0.28 for TPPB-H and TPPB-Br, respectively). This increase was accompanied only a 2-fold reduction in the fluorescence quantum yield (0.54 and 0.22 for TPPB-H and TPPB-Br, respectively). During multicolor confocal laser scanning microscopy observations conducted using two carcinomas, MCF-7 and HeLa, both BODIPY dyes exhibited high targeting specificity toward cancer cell mitochondria owing to the TPP cation functionalization. The two dyes also showed the feasibility of fluorescence cell imaging; however, only the dibrominated BODIPY TPPB-Br manifested pronounced photocytotoxicity with half-maximal inhibitory concentrations of 0.12 and 0.77 μM obtained for MCF-7 and HeLa cells, respectively. These findings demonstrate the potential applicability of TPPB-Br as an imaging-guided photodynamic therapy agent with mitochondrial specificity.

Unravelling the intricacies of fluorescence enhancement in heptamethine cyanine dyes induced by heavy halogen atoms

The classic heavy-atom effect refers to the photophysical phenomenon observed in fluorophores, where the interaction with heavy atoms quenches fluorescence emission. Many fluorophores containing heavy halogen atoms, such as xanthenes, BODIPYs, porphyrins, and anthracenes, adhere to this effect, while the photophysical behavior of others, e.g. halogenated heptamethine cyanine dyes, is poorly studied having contradicting results. In this study, we explored for the first time unexpected fluorescence enhancement induced by heavy halogen atoms in heptamethine dyes, contrasting the classic heavy-atom effect. To this end, a series of novel heptamethine cyanine dyes were synthesized and their photophysical properties were experimentally and theoretically investigated. Heavy halogen atoms were found to significantly affect the fluorescence behaviour of heptamethine dyes depending on the number and position of the attached halogens. Thus, the introduction of bromine and iodine atoms at the non-conjugated positions to the chromophore moieties led to an increase in the fluorescence quantum yields, which contradicts the classic principle and could be explained by heavy halogen-induced vibration restrictions. The value of halogen atom-promoted singlet oxygen generation quantum yield ΦΔ is also not straightforward and depends on the number, position and weight of the halogen atom. The breaking of the classic heavy-atom effect in halogenated heptamethine dyes provides an effective strategy to substantially increase the fluorescence intensity of long-wavelength cyanine dyes, providing new functional advantages for fluorescence imaging, diagnostics, and photodynamic therapy, among other applications.

Heavy Atom at Bay of Perylene Significantly Improves Intersystem Crossing.

We studied the photophysical properties of substituted perylenes using time-dependent density functional theory (TDDFT) with Tamm-Dancoff Approximation (TDA). The TDA-TDDFT method allowed us to examine how luminescence activity alters by substituting halogens at different positions (bay, ortho, and peri) of perylenes. Substituting larger halogens like chlorine and bromine at the bay position significantly affects the planarity of the π-system in perylenes. Interestingly, bay-bromoperylene (P-bBr) showed pronounced spin-orbit coupling (SOC) between singlet and triplet excited states. The heavy atom effect (HAE) functioned efficiently with a distorted π-system and substantially enhanced the SOC in P-bBr. Therefore, a rapid intersystem crossing (ISC) is responsible for turning off the fluorescence of P-bBr. In contrast, bromine substitution other than the bay position (i.e., ortho- and peri-bromoperylenes (P-oBr and P-pBr), which maintained planarity), or substituting lighter elements like a methyl group (similar in size to Br) at the bay position of perylene did not substantially improve the SOC. Thus, the ISC is insufficient to quench the fluorescence in these systems. Additionally, substituting multiple bromines in perylene with at least one in the bay position (i.e., P-boBr2, P-bpBr2, and P-bopBr3) further improved the SOC, leading to much faster ISC (1011 s-1) in P-bopBr3. While multiple bromine substitutions other than the bay position (i.e., P-opBr2) exhibited low ISC due to the planar π-system. So, the heavy bromine at the bay position of perylene causes significant enhancement of the ISC.

Modulating Room‐Temperature Phosphorescence of Phenothiazine Dioxide via External Heavy Atoms

Developing pure organic materials with ultralong lifetimes and balanced quantum efficiency is attractive but challenging. In this study, we propose a novel strategy to investigate external heavy atoms by linking molecular emitters with halogen through a flexible alkyl chain. X‐ray crystal analysis clearly reveal the halogen C‐X‐π interactions, which can be tuned by halogen donors, as well as the distance and geometry between them. Impressively, DOPTZ‐C3Cl featuring a chloride atom as donor, exhibits a balanced long phosphorescence lifetime of 1351 ms and a phosphorescence quantum yield of 10.1%. We also first demonstrate that Cl can induce more positive effect than heavier halogens (Br and I) on prolonging the lifetime. We envisage that the present study will expedite new molecular design to manipulate the room temperature phosphorescence via external heavy atom effect, and highlight a special C‐Cl··π interaction for the development of ultralong phosphorescent materials.

Modulating Room-Temperature Phosphorescence of Phenothiazine Dioxide via External Heavy Atoms.

Developing pure organic materials with ultralong lifetimes and balanced quantum efficiency is attractive but challenging. In this study, we propose a novel strategy to investigate external heavy atoms by linking molecular emitters with halogen through a flexible alkyl chain. X-ray crystal analysis clearly reveal the halogen C-X-π interactions, which can be tuned by halogen donors, as well as the distance and geometry between them. Impressively, DOPTZ-C3Cl featuring a chloride atom as donor, exhibits a balanced long phosphorescence lifetime of 1351 ms and a phosphorescence quantum yield of 10.1 %. We also first demonstrate that Cl can induce more positive effect than heavier halogens (Br and I) on prolonging the lifetime. We envisage that the present study will expedite new molecular design to manipulate the room temperature phosphorescence via external heavy atom effect, and highlight a special C-Cl⋅⋅⋅π interaction for the development of ultralong phosphorescent materials.

Simultaneous visualization of lipid droplets and tracking of the endogenous hypochlorous acid in psoriatic mice models with a novel fluorescent probe in a wash-free fashion

Psoriasis is an autoimmune inflammation-related disease accompanied by a variety of complications. Reactive oxygen species (ROS) are modulators of inflammation, and their excessive production caused by oxidative/anti-oxidative imbalance has been observed in psoriatic patients. Hypochlorous acid (HOCl) is a ROS produced by myeloperoxidase (MPO) from chloride ions (Cl-) and hydrogen peroxide (H2O2). Endogenous HOCl has recently been studied as a potential biomarker of psoriasis underlying the necessity for the development of efficient analytical tools for its detection and real time monitoring. Herein, we designed a novel highly sensitive and selective coumarin-based fluorescent probe for HOCl detection, named CN2-CF3-S. The probe itself featured negligible fluorescence because of the heavy atom effect of the thiocarbonyl group. However, upon responding to HOCl a conversion to sulfur-free derivative CN2-CF3-O occurs, resulting in a dramatical fluorescent enhancement setting the detection limit for HOCl of 3.2 nM. The HOCl-recognition mechanism could be ascribed to the HOCl-triggered oxidative desulfurization process that agrees with liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) computations. The probe’s design incorporated a synergistic combination of two structural features for efficient lipid droplets (LDs)-targeting imaging. An efficient push–pull system reinforced by the presence of two strongly electron-donating dimethylamino groups equipped CN2-CF3-O with pronounced solvatochromism realized through the enhanced blue-shifted emission in non-polar media. Meanwhile, the presence of trifluormethylphenyl moiety at the acceptor side led to an increased lipophilicity. The CN2-CF3-S probe has been successfully utilized to track the endogenous HOCl in cells and on skin of the psoriatic mice in a wash-free manner. As a result, we have demonstrated that the concentration of HOCl in skin might correlate positively with the degree of inflammation in psoriasis. Thus, CN2-CF3-S constitutes the first example of LDs-imaging fluorescent probe for detecting the psoriasis-linked HOCl, offering a convenient tool for further in-depth investigation of psoriasis pathophysiology.

Regulating Optoelectronic and Thermoelectric Properties of Organic Semiconductors by Heavy Atom Effects.

Heavy atom effects can be used to enhance intermolecular interaction, regulate quinoidal resonance properties, increase bandwidths, and tune diradical characters, which have significant impacts on organic optoelectronic devices, such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), etc. Meanwhile, the introduction of heavy atoms is shown to promote charge transfer, enhance air stability, and improve device performances in the field of organic thermoelectrics (OTEs). Thus, heavy atom effects are receiving more and more attention. However, regulating heavy atoms in organic semiconductors is still meeting great challenges. For example, heavy atoms will lead to solubility and stability issues (tellurium substitution) and lack of versatile design strategy and effective synthetic methods to be incorporated into organic semiconductors, which limit their application in electronic devices. Therefore, this work timely summarizes the unique functionalities of heavy atom effects, and up-to-date progress in organic electronics including OFETs, OPVs, OLEDs, and OTEs, while the structure-performance relationships between molecular designs and electronic devices are clearly elucidated. Furthermore, this review systematically analyzes the remaining challenges in regulating heavy atoms within organic semiconductors, and design strategies toward efficient and stable organic semiconductors by the introduction of novel heavy atoms regulation are proposed.

Liposomal Formulations of Novel BODIPY Dimers as Promising Photosensitizers for Antibacterial and Anticancer Treatment.

Synthesis, photochemical properties, liposomal encapsulation, and in vitro photodynamic activity studies of novel BODIPY dimer connected at meso-meso positions and its brominated and iodinated analogs were described. UV-Vis measurements indicated that the dimeric structure of obtained BODIPYs did not significantly influence the positions of the absorption maxima. Emission properties and singlet oxygen generation studies revealed a strong heavy atom effect of brominated and iodinated BODIPY dimers, manifested by fluorescence intensity reduction and increased singlet oxygen generation ability compared to analog without halogen atoms. For the in vitro photodynamic activity studies, dimers were incorporated into two different types of liposomes: positively charged DOTAP:POPC and negatively charged POPG:POPC. The photoinactivation studies revealed high activity of brominated and iodinated dimers incorporated into DOTAP:POPC liposomes on both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Anticancer studies on human breast adenocarcinoma MDA-MB-231 and human ovarian carcinoma A2780 cells revealed that DOTAP:POPC liposomes containing brominated and iodinated dimers were active even at low nanomolar concentrations. In addition, they were more active against MDA-MB-231 cells than A2780 cells, which is particularly important since the MDA-MB-231 cell line represents triple-negative breast cancer, which has limited therapeutic options.

Molecular Engineering for High-Performance X-ray Scintillators.

X-ray scintillators, materials that convert high-energy radiation into detectable light in the ultraviolet to visible spectrum, are widely used in industrial and medical applications. Organic and organic-inorganic hybrid systems have emerged as promising alternatives for X-ray detection and imaging due to their mechanical flexibility, lightweight, tunable excited states, and solution processability for large-scale fabrication. However, these systems often suffer from weak X-ray absorption and insufficient exciton utilization, which seriously affects their scintillation performance, limiting their potential for broader application and commercialization. This review highlights recent advances in molecular engineering for developing high-performance X-ray scintillators. Itfocuses on molecular design principles, such as the heavy atom effect, donor-acceptor/host-guest strategies, hydrogen/halogen bonding, molecular sensitization, and crystal packing, for enhancing scintillation performance. By leveraging these approaches, researchers have made significant strides in improving X-ray scintillation efficiency and advancing the potential of these materials for commercial applications.

Halogen Impact on the Supramolecular Organization of Chiral Phthalimide Emitters Displaying Room Temperature Phosphorescence.

Room temperature phosphorescence from organic materials has attracted an increasing attention in the recent years due to their potential application in various advancing technologies, notably in bioimaging and displays. In this context, heavy atoms such as halogen ones revealed useful tools to enhance the spin-orbit coupling (SOC) of molecular organic phosphors. However, the effect of halogen at the supramolecular level remains less understood, especially in the field of molecular crystals where additional factors can impact the phosphorescence emission. Here, we investigate external effect of halogens on the phosphorescence of chiral phthalimides molecular crystals. The results show that changing the nature of the halogen atom onto the phthalimide core leads to an evolution of the photophysical properties of the materials which does not necessarily follow the classical trend imposed by the expected internal heavy atom effect. Beyond this aspect, we showed that the halogen atom has a profound impact on the packing between the chromophores at the supramolecular level which is of paramount importance towards the optical properties (PLQY and lifetimes) of the different phosphors examined.

Regulating the Twisted Intramolecular Charge Transfer and Anti-heavy Atom Effect at Supramolecular Level for Favorable Photosensitizing Activity in Water.

Photosensitizing assemblies based on twisted intramolecular charge transfer (TICT) active donor-acceptor-donor (D-A-D) system BrTPA-Qx having bromine atoms at the periphery have been developed. Through strategic incorporation of bromine atoms at the para-position to the nitrogen-carbon bonds of phenyl rings at the periphery, halogen-halogen interactions are induced in BrTPA-Qx nanoassemblies in H2O:DMSO (99:1) solution. Hence, the anti-heavy atom effect is induced, and the limitations of TICT (dark excited state) and heavy atom effect (triplet deactivation via radiative decay) could be overcome. Because of TICT and anti-heavy atom effect, supramolecular BrTPA-Qx nanoassemblies demonstrate high efficiency in promoting activation of aerial oxygen via electron and energy transfer pathways in aqueous media. The significant influence of the stabilized TICT state and anti-heavy-atom effect in controlling the ROS generation was validated through in-depth solvent-dependent photophysical studies and investigations of the structure-activity relationship in several model compounds. The notable photosensitizing activity of BrTPA-Qx nanoassemblies is manifested in their ability to efficiently catalyze the oxidative coupling of benzylamine (via type I and type II mechanisms), Knoevenagel condensation of aromatic aldehydes (type II), and oxidative hydroxylation of arylboronic acids (type I) under mild conditions.

BODIPY photosensitizers functionalized with mannose for fluorescence cell-imaging and photodynamic therapy

The synthesis of four water-soluble mannose-tethering BODIPY-based photosensitizers (PSs) with varying substituents (H, OMe, NO2 and I) in the para-phenyl moiety attached to the meso-position of the BODIPY core, offering tumor-targeting and photodynamic therapeutic (PDT) potentials, is reported. The PDT capability of the synthesized PSs was investigated using the cervical cancer cell line HeLa. Owing to the heavy atom effect, BODIPY I, enhanced the intersystem crossing (ISC) to produce singlet oxygen (1O2) and maintained a high fluorescence quantum yield (ΦF) of 0.71. In contrast, the electron-donating methoxy substituent (BODIPY OMe) caused a notable perturbation in the occupied frontier molecular orbitals, subsequently achieving a higher 1O2 generation capability with a high ΦF of 0.85. Conversely, substitution with the electron-withdrawing nitro group (BODIPY NO2) resulted in a perturbation of unoccupied frontier molecular orbitals and generated a forbidden dark S1 state, negatively affecting both fluorescence and 1O2 generation efficiencies. The cytotoxicity of the synthesized water-soluble BODIPY PSs in the dark and under LED irradiation against the HeLa cell line was also assessed, with BODIPY I, OMe and H showing favorable PDT activity. Collectively, the performance of the mannose-conjugated BODIPY PSs in this study contributed promising results for the development of photodynamic therapeutic agents for cancer treatment.

Ultralong Room-Temperature Phosphorescence in Ca(II) Metal-Organic Frameworks Based on Nicotinic Acid Ligands.

In recent years, metal-organic framework (MOF) materials with long persistent luminescence (LPL) have inspired extensive attention and presented various applications in security systems, information anticounterfeiting, and biological imaging fields. However, obtaining LPL materials with ultralong lifetime remains challenging. Halogen atoms, as nonmetallic elements existing in the frameworks, can not only induce the heavy-atom effect, effectively enhancing spin-orbit coupling and promoting intersystem crossing (ISC) processes, but also suppress non-radiative transition of the triplet states through the intra- and intermolecular interactions. Specifically, fluorine atoms with the strongest electronegativity may form intermolecular aggregate interlockings through halogen-bonding interactions that restrict molecular motions and vibrations, thereby improving phosphorescent lifetime. With the aforementioned considerations, two distinct types of MOFs with/without fluorine atoms (namely, Ca-MOF and 5FCa-MOF) were synthesized. Notably, by introducing fluorine atoms into MOFs, fluorine-induced intermolecular aggregate interlockings effectively enhanced the phosphorescent lifetime of 5FCa-MOF exceeding 264 ms compared to that of Ca-MOF (103.94 ms). Remarkably, both MOFs displayed bright LPL to the naked eye after removal of the irradiation source, especially 5FCa-MOF which can last for about 2 s. By introducing fluorine atoms, 5FCa-MOF exhibits greatly enhanced ISC with a rate constant up to 4.1 × 106 s-1 and suppressed non-radiative decay down to 3.73 s-1, thereby extending the LPL time. The thus obtained LPL provides potential in information encryption, security systems, optical anticounterfeiting, and so on.

Highly Efficient Red/Near‐Infrared Phosphorescence from Doped Crystals

AbstractOrganic red/near‐infrared (NIR) room temperature phosphorescence (RTP) materials with low toxicity and facile synthesis are highly sought after, particularly for applications in biotechnology and encryption. However, achieving efficient red/NIR RTP emitters has been challenging due to the weak spin‐orbit coupling of organics and the rapid nonradiative decay imposed by the energy gap law. Here we demonstrate highly efficient red/NIR RTP with boosted quantum yields (Φps) of up to 32.96 % through doping the thionated derivatives of phthalimide (PAI) (MTPAI and DTPAI) into PAI crystals. The red‐shifted photoluminescence (PL) stems from a combination of the external heavy atom effect and the formation of emissive clusters centered around electron‐rich sulfur atoms. Furthermore, the dopants enhance exciton generation efficiency and facilitate energy transfer from smaller PAI units to larger aggregates, leading to dramatically increased Φp. This strategy proves universal, opening possibilities for acquiring long‐wavelength RTP with tunable photophysical properties. The doped crystals exhibit promising applications in optical waveguides and encryption paper/ink. This research provides a practical approach to obtaining long‐wavelength RTP materials and offers valuable insights into the mechanisms governing host‐guest systems.

Highly Efficient Red/Near-Infrared Phosphorescence from Doped Crystals.

Organic red/near-infrared (NIR) room temperature phosphorescence (RTP) materials with low toxicity and facile synthesis are highly sought after, particularly for applications in biotechnology and encryption. However, achieving efficient red/NIR RTP emitters has been challenging due to the weak spin-orbit coupling of organics and the rapid nonradiative decay imposed by the energy gap law. Here we demonstrate highly efficient red/NIR RTP with boosted quantum yields (Φps) of up to 32.96 % through doping the thionated derivatives of phthalimide (PAI) (MTPAI and DTPAI) into PAI crystals. The red-shifted photoluminescence (PL) stems from a combination of the external heavy atom effect and the formation of emissive clusters centered around electron-rich sulfur atoms. Furthermore, the dopants enhance exciton generation efficiency and facilitate energy transfer from smaller PAI units to larger aggregates, leading to dramatically increased Φp. This strategy proves universal, opening possibilities for acquiring long-wavelength RTP with tunable photophysical properties. The doped crystals exhibit promising applications in optical waveguides and encryption paper/ink. This research provides a practical approach to obtaining long-wavelength RTP materials and offers valuable insights into the mechanisms governing host-guest systems.