Energy Gap Law Research Articles

De novo design of type-l photosensitizer agents based on structure-inherent low triplet energy for hypoxia photodynamic therapy.

Photodynamic therapy (PDT), owing to its low invasiveness, high efficiency, fewer side effects, spatiotemporal controllability and good selectivity, has attracted increasing attention for its tremendous potential in revolutionizing conventional strategies of tumor treatment. However, hypoxia is a common feature of most malignancies and has become the Achilles' heel of PDT. Currently, Type II photosensitizers (PSs) have inadequate efficacy for PDT due to the inherent oxygen consumption of the anoxic tumor microenvironment. Moreover, due to the absence of a general molecular design strategy and the limitations imposed by the energy gap law, Type-I PSs are less reported. Therefore, the development of Type-I PSs with hypoxia resistant capabilities is urgently required. Herein, in this study, we have obtained pure Type-I materials for the first time by employing a strategy that decreases the triplet energy levels of the π-conjunction bridge. A sufficient donor-acceptor interaction reduces the lowest triplet energy level and aids in the transfer of excitons from singlet to triplet levels. With this strategy, dibenzofulvene derivatives (FEs) displayed purely Type-I ROS generation. Among them, FE-TMI exhibits superior Type-I reactive oxygen species-generation performance, showcasing the great potential of PDT in treating tumor cells under hypoxic conditions and several types of solid tumors in mouse in vivo experiments. This work provides a practical solution for the future design of Type-I PDT materials and is aimed at enhancing PDT efficiency.

A hybridization-induced charge-transfer state energy arrangement reduces nonradiative energy loss in organic solar cells.

Here, we explain why the Energy Gap Law and the energy inversion related to the charge-transfer state have opposite effects on the trend of nonradiative energy loss of organic solar cells. The root is the existing condition of energy inversion. There is indeed a certain probability of energy inversion, but it will eventually be implicit or explicit as determined by the hybridization, which depends on the electron-withdrawing unit of the donor, giving rise to different stacking sites. The triplet-state hybridization leads to an explicit characteristic, while singlet-state hybridization leads to an implicit characteristic.

Single-molecule detection of a terrylenediimide-based near-infrared emitter.

Environment-sensitive fluorescent agents with near-infrared (NIR) emission are in great demand owing to their applications in biomedical and quantum technologies. We report a novel NIR absorbing (λ Abs max = 734 nm) and emitting (λ Fl max = 814 nm) terrylenediimide (TDI) based donor-acceptor chromophore (TDI-TPA4), exhibiting polarity-sensitive single-photon emission. By virtue of the charge transfer (CT) character, ensemble level measurements revealed solvatochromism and NIR emission (ϕ Fl = 26.2%), overcoming the energy gap law. The CT nature of the excited states is further validated by state-of-the-art fragment-based excited state theoretical analysis. To mimic the polarity conditions at the single-molecule level, TDI-TPA4 was immobilized in polystyrene (PS; low polar) and poly(vinyl alcohol) (PVA; high polar) matrices, which enables tuning of the energy levels of the locally excited state and charge-separated (CS) state. Minimal blinking and prolonged survival time of the TDI-TPA4 molecule in the PS matrix, in contrast to the PVA matrix, possibly confirms the implication of the energy gap law and polarity sensitivity of TDI-TPA4. The existence of the CT state in nonpolar and CS state in polar solvents was confirmed by transient absorption measurements in the femtosecond regime. The current work sheds light on the design principle for NIR single-photon emitting organic chromophores for deep tissue imaging and probing the nanoscale heterogeneity.

Ultrafast photophysics of an orange-red thermally activated delayed fluorescence emitter: the role of external structural restraint.

The application of thermally activated delay fluorescence (TADF) emitters in the orange-red regime usually suffers from the fast non-radiative decay of emissive singlet states (kSNR), leading to low emitting efficiency in corresponding organic light-emitting diode (OLED) devices. Although kSNR has been quantitatively described by energy gap law, how ultrafast molecular motions are associated with the kSNR of TADF emitters remains largely unknown, which limits the development of new strategies for improving the emitting efficiency of corresponding OLED devices. In this work, we employed two commercial TADF emitters (TDBA-Ac and PzTDBA) as a model system and attempted to clarify the relationship between ultrafast excited-state structural relaxation (ES-SR) and kSNR. Spectroscopic and theoretical investigations indicated that S1/S0 ES-SR is directly associated with promoting vibrational modes, which are considerably involved in electronic-vibrational coupling through the Huang-Rhys factor, while kSNR is largely affected by the reorganization energy of the promoting modes. By restraining S1/S0 ES-SR in doping films, the kSNR of TADF emitters can be greatly reduced, resulting in high emitting efficiency. Therefore, by establishing the connection among S1/S0 ES-SR, promoting modes and kSNR of TADF emitters, our work clarified the key role of external structural restraint for achieving high emitting efficiency in TADF-based OLED devices.

Efficient orange and red thermally activated delayed fluorescence materials based on 1,8-naphthalimide derivatives.

Thermally activated delayed fluorescence (TADF) molecules have emerged as a promising class of third-generation organic light-emitting diode (OLED) emitters that can achieve 100% internal quantum efficiency without the use of noble metals. However, the design of high-efficiency red TADF materials has been challenging due to limitations imposed by the energy-gap law. To overcome this challenge, two new TADF emitters, namely, 6-(4-(diphenylamino)phenyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (NI-TPA) and 6-(10H-phenothiazin-10-yl)-2-phenyl-1H-benzo[de]-isoquinoline-1,3(2H)-dione (NI-Pz), have been synthesized and characterized. These compounds exhibit strong TADF characteristics with a small energy gap (ΔEST) between the lowest excited singlet and triplet states, short delayed fluorescence lifetimes, high thermal stability, and high photoluminescence quantum yields. The OLED devices fabricated using NI-TPA and NI-Pz as emitters show orange and red electroluminescence with emission peaks at 593 nm and 665 nm, respectively, and maximum external quantum efficiencies (EQEs) of 11.3% and 7.6%, respectively. Furthermore, applying NI-TPA to cell imaging yielded excellent imaging results, indicating the potential of red TADF materials in the field of biological imaging.

Solvent-polarity dependence of ultrafast excited-state dynamics of trans-4-nitrostilbene.

Ultrafast excited-state dynamics of the simplest nitrostilbenes, namely trans-4-nitrostilbene (t-NSB), was studied in solvents of various polarities with ultrafast broadband time-resolved fluorescence and transient absorption spectroscopies, and by quantum-chemical computations. The results revealed that the initially excited S1(ππ*) state deactivation dynamics is strongly influenced by the solvent polarity. Specifically, the t-NSB S1-state lifetime decreases by three orders of magnitude from ∼60 ps in high-polarity solvents to ∼60 fs in nonpolar solvents. The strong solvent-polarity dependence arises from the differences in dipole moments among the S1 and relevant states, including the major intersystem crossing (ISC) receiver triplet states, and therefore, the solvent polarity can modulate their relative energies and ISC rates. In nonpolar solvents, the sub-100 fs lifetime is due to a combination of efficient ISC and internal conversion. In medium-polarity solvents, the S1-state population decays via a competing ISC relaxation mechanism in a biphasic manner, and the ISC rates are found to obey the inverse energy gap law of the strong coupling case. In high-polarity solvents, the S1 state is stabilized to a much lower energy such that ISC becomes energetically infeasible, and the S1 state decays via barrier crossing along the torsion angle of the central ethylenic bond to the nonfluorescent perpendicular configuration. Regardless of the initial S1-state deactivation pathways in various solvents, the excited-state population is ultimately trapped in the metastable T1-state perpendicular configuration, at which a slower ISC occurs to bring the system to the ground state and bifurcate into either trans or cis form of NSB.

Developing Bright Afterglow Materials via Manipulation of Higher Triplet Excited States and Relay Synthesis in Difluoroboron β‐Diketonate Systems

AbstractAfterglow brightness represents one of the most important characteristics in the application of afterglow materials. High molar absorption coefficient, high afterglow efficiency, and long afterglow lifetimes are required to achieve intense afterglow. However, current strategies cannot simultaneously fulfill these requirements due to specific intrinsic problems. Here, based on the understanding of difluoroboron β‐diketonate systems, the manipulation of higher triplet excited states is conceived to selectively enhance intersystem crossing with phosphorescence lifetimes remaining long. Aromatic substrates, which possess specific HOMO levels and T1 levels, are selected for relay synthesis to form difluoroboron β‐diketonate compounds with very close‐lying S1 and T2 levels; according to the energy gap law, such systems exhibit strong intersystem crossing. Upon doping into rigid matrices, the resultant difluoroboron β‐diketonate systems display the brightest ambient afterglow that has ever been observed.

Achieving Long-Wavelength Electroluminescence Using Two-Coordinate Gold(I) Complexes: Overcoming the Energy Gap Law.

Two-coordinate coinage metal complexes have emerged as promising emitters for highly efficient organic light-emitting devices (OLEDs). However, achieving efficient long-wavelength electroluminescence emission from these complexes remains as a daunting challenge. To address this challenge, molecular design strategies aimed at bolstering the photoluminescence quantum yield (Φ) of Au(I) complex emitters in low-energy emission regions are investigated. By varying amido ligands, a series of two-coordinate Au(I) complexes is developed that exhibit photoluminescence peak wavelengths over a broad range of 533-750nm. These complexes, in particular, maintain Φ values up to 10% even in the near-infrared emission region, overcoming the constraints imposed by an energy gap. Quantum chemical calculations and photophysical analyses reveal the action of radiative control, which serves to overcome the energy gap law, becomes more pronounced as the overlap between hole and electron distributions (Sr (r)) in the excited state increases. It is further elucidated that Sr (r) increases with the distance between the hole-distribution centroid and the nitrogen atom in an amido ligand. Finally, multilayer OLEDs involving the Au(I) complex emitters exhibit performances beyond the borderline of the electroluminescence wavelength-external quantum efficiency space set by previous devices of coinage metal complexes.

Molecular design strategies for the highly efficient vacuum and solution-processable long wavelength thermally activated delayed fluorescence emitters

Simple device architecture-based solution-processed organic light-emitting diodes (OLEDs) are more advantageous over the multilayer vacuum-processed OLEDs for their commercial application. Highly efficient long wavelength thermally activated delayed fluorescent (TADF) emitters suitable for both vacuum and solution-processed OLEDs are rarely reported because of the stringent molecular design rules and the inherent limitation of the energy gap law. To resolve this issue, we designed and synthesized two TADF emitters namely, 5,8-bis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)-2,3-bis(4-(tert-butyl)phenyl)quinoxaline-6,7-dicarbonitrile (2tBuTPA-QxCN) and 2,3,5,8-tetrakis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)quinoxaline-6,7-dicarbonitrile (4tBuTPA-QxCN), for their use in both vacuum and solution-processed OLEDs. High external quantum efficiency (EQE) of 22 % and emission peak at 608 nm were demonstrated for the vacuum-deposited OLED fabricated with 4tBuTPA-QxCN TADF emitter as compared to the OLED fabricated with 2tBuTPA-QxCN TADF emitter exhibiting EQE value of 21.1 % and emission peak at 605 nm. In their solution-processed OLEDs, a high EQE of 15.6 % and pure-red emission peak at 630 nm was demonstrated for the 2tBuTPA-QxCN TADF emitter as compared to the EQE value of 11.6 % and emission peak at 628 nm for the 4tBuTPA-QxCN TADF emitter.

High-efficiency long-wavelength NIR iridium complexes constructed by extending rigid coordination and optimizing peripheral donor position to break cocoon into butterfly

Due to the non-radiative decay of excited states, it is extremely complicated for iridium (III) complexes to simultaneously harvest high-efficiency and long-wavelength emission in the near-infrared (NIR) region based on the energy-gap law. In order to address this issue, we designed and synthesized two butterfly-type iridium(III) complexes of (PyPz-TPA)2Ir(acac) and (PyQl-TPA)2Ir(acac), in which pyrene-pyrazine (PyPz) and pyrene-quinoxaline (PyQl) are respectively used as the rigid C^N bidentate coordinated cocoons, peripherally with two triphenylamine (TPA) units at 4, 5-positions. Their photophysical, electrochemical and electroluminescent properties are primarily investigated. It is found that the (PyQl-TPA)2Ir(acac) presents stronger spin-orbital coupling effect, a smaller ΔEST energy difference, and lower reorganization energy than (PyPz-TPA)2Ir(acac) by selecting rigid pyrene-quinoxaline coordination and optimizing peripheral TPA position. Furthermore, the (PyQl-TPA)2Ir(acac)-doped OLEDs exhibit a red-shifted NIR emission peaked at 784 nm with a record external quantum efficiency of 5.42% using CBP as host matrix by solution process, which is a rare representation to shrink the limitation of energy-gap law in NIR region for iridium(III) complexes. This study provides a feasible strategy to construct high-efficiency NIR-emitting iridium(III) complexes by an artfully motivated strategy of extending and breaking the C^N coordinate cocoon into butterfly.

Narrowband Pure Near-Infrared (NIR) Ir(III) Complexes for Solution-Processed Organic Light-Emitting Diode (OLED) with External Quantum Efficiency Over 16 .

Highly efficient near-infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light-emitting diode (OLED) fabricated by the solution-processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution-processed NIR-OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR-emitters.

Narrowband Pure Near‐Infrared (NIR) Ir(III) Complexes for Solution‐Processed Organic Light‐Emitting Diode (OLED) with External Quantum Efficiency Over 16 %

AbstractHighly efficient near‐infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light‐emitting diode (OLED) fabricated by the solution‐processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution‐processed NIR‐OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR‐emitters.

Minimizing non-radiative decay in molecular aggregates through control of excitonic coupling

The widely known “Energy Gap Law” (EGL) predicts a monotonically exponential increase in the non-radiative decay rate (knr) as the energy gap narrows, which hinders the development of near-infrared (NIR) emissive molecular materials. Recently, several experiments proposed that the exciton delocalization in molecular aggregates could counteract EGL to facilitate NIR emission. In this work, the nearly exact time-dependent density matrix renormalization group (TD-DMRG) method is developed to evaluate the non-radiative decay rate for exciton-phonon coupled molecular aggregates. Systematical numerical simulations show, by increasing the excitonic coupling, knr will first decrease, then reach a minimum, and finally start to increase to follow EGL, which is an overall result of two opposite effects of a smaller energy gap and a smaller effective electron-phonon coupling. This anomalous non-monotonic behavior is found robust in a number of models, including dimer, one-dimensional chain, and two-dimensional square lattice. The optimal excitonic coupling strength that gives the minimum knr is about half of the monomer reorganization energy and is also influenced by system size, dimensionality, and temperature.

Concerted Intramolecular and Intermolecular Charge Transfer for High‐Efficiency Near‐Infrared Thermally Activated Delayed Fluorescent Materials Approaching 900 nm

AbstractHindered by the energy gap law, the development of high‐efficiency near‐infrared (NIR) thermally activated delayed fluorescence (TADF) emitters with emission peaks over 800 nm remains challenging. The conventional strategy of enhancing intramolecular charge transfer for bathochromic shift commonly results in low radiative decay rates (kr) and emission efficiency. Herein, a superior strategy of concerted intramolecular CT (intra‐CT) and intermolecular CT (inter‐CT) for high‐efficiency NIR‐TADF materials is demonstrated. As a proof‐of‐concept, two novel emitters DTPZ and DtBuTPZ are developed based on a new acceptor phenazine‐2,3‐dicarbonitrile (PZ). High kr is achieved by large oscillator strength from appropriate intra‐CT property in monomers and effective electronic couplings between inter‐CT and intra‐CT states in aggregates. Suppressed nonradiative decay processes are realized through strong inter‐CT properties, abundant intermolecular attractive interactions, and negligible π∙∙∙π stacking. Consequently, organic light‐emitting diodes based on those emitters showed record‐high maximum external quantum efficiencies and radiances of 2.28%, 24.18 W Sr−1 m−2 at 817 nm, 0.57%, 14.38 W Sr−1 m−2 at 877 nm for DTPZ, and 2.34%, 23.55 W Sr−1 m−2 at 807 nm for DtBuTPZ, respectively.

Short-Wavelength Infrared Organic Light-Emitting Diodes from A-D-A'-D-A Type Small Molecules with Emission beyond 1100nm.

Short-wavelength infrared (SWIR) organic light-emitting diodes (OLEDs) have attracted great interest due to their potential applications in biological imaging, infrared lighting, optical communication, environmental monitoring, and surveillance. Due to an intrinsic limitation posed by the energy-gap law, achieving high-brightness in SWIR OLEDs remains a challenge. Herein, the study reports the use of novel A-D-A'-D-A type small molecules NTQ and BTQ for high-performance SWIR OLEDs. Benefiting from multiple D-A effect in conjugated skeleton, the small molecules NTQ and BTQ exhibit narrow optical gaps of 1.23 and 1.13eV, respectively. SWIR electroluminescence (EL) emission from OLEDs based on NTQ and BTQ is achieved, with emission peaks at 1140 and 1175nm, respectively. Not only owing to a negligible efficiency roll-off across the full range of applied current density but also the ability to afford a high operation current density of 5200mA cm-2 , the resultant SWIR OLEDs based on NTQ exhibit a maximal radiant exitance of =1.12mW cm-2 . Furthermore, the NTQ-based OLEDs also possess sub-gap turn-on voltage of 0.85V, which is close to the physical limits derived from the generalized Kirchhoff and Planck equation. This work demonstrates that A-D-A'-D-A type small molecules offer significant promise for NIR/SWIR emitting material innovations.

Simple A–D–A pure blue fluorescent emitters based on hybridized local and charge-transfer excited state for non-doped OLEDs with narrow full width at half-maximum of 0.20 eV and CIEy< 0.06

Narrowband emitters possess great potential in organic light emitting diodes (OLEDs) to achieve high color purity. However, developing highly efficient pure blue emitters with a simultaneously narrow full width at half-maximum (FWHM) value is a major challenge due to the energy-gap law and molecular stacking effect. Few efforts have focused on this challenging pursuit. Herein, an ingenious synthetic method was devised to achieve pure blue emitters incorporating bulky rigid planes as donors and highly twisted steric units as acceptors. Four emitters with aggregation-induced emission (AIE) characteristics, namely BCzPPM, BC-zPSP, IDCz-DBPM, and IDCz-BPSP, have been developed and used to fabricate non-doped devices. IDCz-BPSP achieves narrowed photoluminescence (PL) and electroluminescence (EL) with the benefit of suppressing vibronic coupling. Non-doped OLEDs based on IDCz-BPSP have achieved maximum external quantum efficiency (EQEmax) of 4.61% with a FWHM of 25 nm/0.20 eV. The Commission Internationale de L'Eclairage (CIE) coordinates was (0.154, 0.059), with CIEy being superior to the standard of European Broadcasting Union (EBU) 0.06. The hybridized local and charge-transfer (HLCT) states of IDCz-BPSP have simultaneously boosted the PL efficiency and exciton utilization. The EL process has even achieved exciton utilization at exceeding the theoretical limit of 25%. These results indicate that the strategy of combining bulky rigid plane donor units and steric hindrance effect is a favorable strategy for constructing emitters with narrow FWHM.

Rational design of dibenzo[a,c]phenazine-derived isomeric thermally activated delayed fluorescence luminophores for efficient orange-red organic light-emitting diodes

It is an immense challenge to develop efficient long-wavelength (orange-to-red) thermally activated delayed fluorescence (TADF) materials due to the increasing nonradiative decay rates following the energy-gap law. Herein, two pairs of asymmetric isomers; DPyPzTPA and TPAPzDPy, and PyPzDTPA and DTPAPzPy based on electron-deficient moieties dibenzo[a,c]phenazine (Pz) and pyridine (Py) combined with electron-donor units of triphenylamine (TPA) were designed and synthesized. Their photophysical properties could be finely modulated by changing the position and number of Py groups as well as TPA fragments onto Pz cores. DPyPzTPA and DTPAPzPy possess much more rigidity and thus less geometry relaxation and non-radiative decay between ground states and excited states than those of PyPzDTPA and TPAPzDPy. Intriguingly, DPyPzTPA exhibits the highest relative photoluminescence quantum yield (ΦPL) and the fastest reverse intersystem crossing (rISC) rate among them owing to relatively stronger rigidity and spin-orbit coupling (SOC) interactions between the lowest singlet (S1) and energetically close-lying excited triplet state and therefore, the device showed the highest maximum external quantum efficiency (EQEmax) of 16.6% (60.9 lm/W, 53.3 cd/A) with Commission Internationale de I'Eclairage (CIE) coordinates of (0.43, 0.55), peak wavelength 556 nm. In stark contrast, due to its lower rigidity and extremely weak delayed fluorescence (DF) characteristic and thus the much lower ΦPL, TPAPzDPy-based devices are only half as efficient (30.8 lm/W, 27.5 cd/A, 8.3% EQE) despite the isomers possessing equal singlet-triplet energy gaps (ΔEST) of 0.43 eV. On the other hand, the device based on DTPAPzPy also demonstrated a strongly enhanced performance (59.1 lm/W, 52.7 cd/A, 16.1% EQE) than its isomer PyPzDTPA-based device (39.5 lm/W, 35.2 cd/A, 10.3% EQE). This work explicitly implicates that the asymmetric and isomeric molecular design is a potential strategy for promoting the development of highly efficient long-wavelength TADF materials.

Photofunctional Scope of Fluorescent Dithienylethene Conjugates with Aza-Heteroaromatic Cations.

A series of dithienylethene (DTE) photoswitches with aza-heteroaromatic cationic moieties is synthesized. The switches are characterized regarding their photochemical and photophysical properties in acetonitrile and in water. The efficiency of the switching and the photostationary state composition depend on the degree of π-conjugation of the heteroaromatic systems. Thus, DTEs with acridinium-derived moieties have very low quantum yields for the ring-closing process, which is in contrast to switches with pyridinium and quinolinium moieties. All switches emit fluorescence in their open forms. The involved electronic transitions are traced back to an integrative picture including the DTE core and the cationic arms. The emission can be fine-tuned by the π-conjugation of the heteroaromatic cations, reaching the red spectral region for DTEs with acridinium moieties. On ring-closing of the DTEs the fluorescence is not observable anymore. Theoretical calculations point to rather low-lying energy levels of the highly conjugated ring-closed DTEs, which would originate near-infrared emission (> 1200nm). The latter is predicted to be very weak due to the concurrent non-radiative deactivation, according to the energy-gap law. In essence, an ON-OFF fluorescence switching as the result of the electrocyclic ring-closing reaction is observed.

Design of Near-Infrared-Triggered Metallo-Photosensitizers via a Self-Assembly-Induced Vibronic Decoupling Strategy.

Development of highly efficient near-infrared (NIR)-excited photosensitizers is hampered by the fast nonradiative vibrational relaxation process regulated by the energy gap law. Here, from the fundamental perspective we propose that the intermolecular coupling of well-designed photosensitizers has the potential to facilitate exciton delocalization and hence reduce the exciton-vibration coupling, thereby boosting their phototherapeutic efficacy via inhibition of the vibrational relaxation pathway. Such conceived NIR-excited metallo-photosensitizers (IrHA1 and IrHA2) were prepared and studied for experimental validation. The resulting iridium complexes exhibited a little singlet oxygen (1O2) production in the monomeric state, but produced substantially enhanced 1O2 generation efficiency via benefiting from the exciton-vibration decoupling in the self-assembly state. Particularly, IrHA2 exhibits an unprecedented high 1O2 quantum yield of 54.9% (FDA-approved NIR dye indocyanine green: ΦΔ = 0.2%) under 808 nm laser irradiation with negligible heat generation, probably attributed to the suppression of vibronic couplings from the stretching mode of the acceptor ligand. In phototherapy, IrHA2-NPs with high biocompatibility and low dark toxicity can induce substantial tumor regression with 92.9% tumor volume reduction in vivo. This self-assembly-induced vibronic decoupling strategy would offer an effective approach to the design of high-performance NIR-excited photosensitizers.

Enhanced Deep-Red Phosphorescence in Cyclometalated Iridium Complexes with Quinoline-Based Ancillary Ligands.

Compounds with good photoluminescence quantum yields (ΦPL) in the deep-red to near-infrared parts of the spectrum are desired for a variety of applications in optoelectronics, imaging, and sensing. However, in this region of the spectrum, quantum yields are usually modest, which is explained by the energy gap law and the inherently slower radiative decay rates for low-energy emitters according to the second-order perturbation theory. In this work, we outline a new direction in deep-red luminescence, introducing a new suite of bis-cyclometalated iridium complexes with efficient luminescence beyond 650 nm. Seven new complexes are prepared using two different cyclometalating (C^N) ligands with four quinoline-derived ancillary ligands (L^X). The chosen cyclometalating ligands are well-established to produce deep-red phosphorescence and include a metalated phenyl ring appended to a conjugated heterocycle. The ancillary ligands combine a rigid quinoline or benzoquinoline "L" donor with a variable anionic "X" donor comprised of an O-donor aryloxy or carboxylate or an N-donor amidate. These complexes phosphoresce in the deep-red region with wavelengths between 650 and 700 nm and solution quantum yields between 0.018 and 0.42.