Through-space Charge Transfer Research Articles

Tailoring Chain‐Length in Through‐Space Charge‐Transfer Donor‐σ‐Acceptor Multifunctional Emitters for Efficient Long‐Term Bioimaging

AbstractThis work presents a simple strategy to develop a new series of through‐space charge‐transfer (TSCT) donor–acceptor luminogens with varying alkyl chain lengths as spacer groups (D‐σ‐A), CznDPy [5‐(4‐(9H‐carbazol‐9‐yl) alkyl)‐5H‐pyrazino[2,3‐b] indole‐2,3‐dicarbonitrile] (n = 2, 3, 4, and 5) displaying rare multifunctional optical behaviors of aggregation‐induced emission (AIE), thermally activated delayed fluorescence (TADF), aggregation‐induced delayed fluorescence (AIDF), mechanoluminescence (ML), and mechanochromism (MCL) properties. Fine‐tuning the flexible chain lengths between donor and acceptor results in variable intermolecular interactions and charge transfer (CT) behavior, thereby modulating their respective optical properties in aggregated/solid states. The integrated emitters exhibit a maximum total quantum yield of 85% with a prolonged lifetime of 344 µs. Considering the challenges existing for developing AIDF molecules with longer lifetimes, enhanced fluorescence efficiency, and tunable emission characteristics, their utility is emphasized for efficient long‐term bioimaging of human breast cancer cells up to 7 days. These molecules constitute the first examples of multifunctional organic TSCT AIDF small molecules with such long lifetimes, tunable emission colors, and higher fluorescence efficiency used for the diagnostic imaging of cancer cells. This study also sheds light on the structure‐property relationships and offers valuable insights into the new class of tailored optical materials for various applications.

Through-Space Charge Transfer Dynamic Mechanism in V-Shaped Flexible Carbazole Aromatic Imides Dyads.

Cofacial electron donor-acceptor dyads exhibiting through-space charge-transfer (TSCT) characteristics are widely employed in the development of optoelectronic functional materials. The flexible molecular frameworks between the electron donor and acceptor components allow dynamic modulation of electronic coupling, influenced by excited-state structural relaxation or intermolecular interactions, thereby affecting the charge-transfer (CT) dynamics and the emission properties of TSCT states. In this work, we examine the TSCT dynamic processes of two electron donor-acceptor dyads, CzPhNI and CzPhPI formed by ortho-substitution of phenyl linkage with V-shaped flexible TSCT structures using carbazole as donor and naphthalimide or phthalimide as acceptor. A pseudo-cofacial TSCT conformation formed in the excited state effectively shortens the donor-acceptor distance and enhances CT coupling. Femtosecond spectroscopy reveals an ultrafast TSCT kinetics in the (200 fs)-1 timescale. Moreover, the intermolecular interaction-induced D-A stacking further strengthens the electronic coupling, accelerating the TSCT reaction rate from (2.07 ps)-1 to (174 fs)-1 as solution concentrations increases from 10-5 to 10-3 M. The results obtained in this work offers valuable physical insights into the TSCT dynamic mechanism, potentially explaining the widely observed emission enhancement in weakly-coupled, flexible TSCT emitters transitioning from solution to aggregation states.

Tunable Cluster Luminescence and High Quantum Yield in Amine-Modified Maleic Anhydride Polymers.

Cluster luminescent materials (CLgens) with nonconjugated structures have attracted considerable attention. However, their low quantum yield and limited emission wavelengths, which are confined to the blue-green spectrum, continue to restrict their applicability. In this study, maleic anhydride polymer chains were modified with N-tristyrylene-1,2-diamine (TPM-NH2), creating a secondary donor-acceptor structure through freely rotatable phenyl groups and amino-anhydride interactions. This modification facilitated the formation of charge transfer (CT) states and strengthened the through-space interaction (TSI), resulting in a remarkable red shift in emission wavelength from 400 to 640 nm. The flexible ethyl chain acted as a bridging unit within this framework, enhancing through-space charge transfer (TSCT) and elevating the quantum yield (QY) to 28.28%. This research offers a strategy for improving the QY of anhydride copolymers and demonstrates the potential for controllable emission wavelengths, thereby broadening their application domains, including in light-conversion agricultural films.

Donor/Acceptor Ligands Based on an o-Terphenyl Motif to Achieve Thermally Activated Delayed Fluorescence in Zn(II) Complexes.

The photophysical properties of six new luminescent tetrahedral Zn(II) complexes are presented that survey two electronic donor moieties (phenolate and carbazolate) and three electronic acceptors (pyridine, pyrimidine, and pyrazine). A unique ligand based on an o-terphenyl motif forms an eight-membered chelate, which enhances through-space charge-transfer (CT) interactions by limiting through-bond conjugation between the donor and acceptor. A single isomeric product was obtained in yields up to 90%. Single-crystal X-ray diffraction structures of Zn complexes incorporating either donor show complementary interligand π-π interactions. All of the Zn complexes display long-lived luminescence in the solid state consistent with emission involving the triplet state. The phenolate-based complexes show evidence of CT emission in the solid state only with the strongest (pyrazinyl) acceptor. In contrast, all carbazolate-based complexes show evidence of thermally activated delayed fluorescence (TADF) in the solid and solution state, with photoluminescent quantum yields of up to 39%. These ligands represent a new family of Zn coordination compounds demonstrating TADF/phosphorescent properties that expand upon and elucidate design principles in the pursuit of photoactive earth-abundant metal complexes.

Regulation of TADF by Internal and External Heavy Atom Effect in D-A MOF for Heterocrystal based Temperature-Compensated Photonic Device.

The application of temperature-compensated photonic device is hampered by poor accuracy and overly simplistic functions of propagation in photonic integrated circuits (PICs) field. Herein, we report a new library of donor-acceptor metal-organic framework (D-A MOF) with thermally activated delayed fluorescence (TADF) and the fabricating of temperature-compensated photonic device by virtue of the unique temperature response character of TADF emitters. Highly tunable through-space charge transfer (TSCT) of TADF was realized within the D-A MOFs through a novel strategy that synergistically combines the internal heavy atom effect (HAE) with an external HAE, induced by the incorporation of heavy atoms into different components, achieving the regulable photophysical indicators including adjustable PL wavelength (534 to 592 nm) and surging quantum yield (5.02%-47.39%). Further investigation of the impact of external HAE on TADF was conducted through crystal structures and Hirshfeld surface plots of four D-A regimes featuring substituent-based linkers. Notably, temperature-compensated photonic device based on heterocrystal was fabricated through integrating D-A MOFs with contrary temperature response. The emission signal output of the heterojunction remained nearly stable in 215 K to 295 K range, highlighting the promising potential application of TADF D-A MOF featuring sensitive temperature response in PICs field.

Enhancing Reverse Intersystem Crossing in TSCT-TADF Emitters: Heavy Atom Modulation of Multiresonance Acceptors.

With the rapid development of thermally activated delayed fluorescence (TADF) materials, achieving efficient reverse intersystem crossing (RISC) to mitigate triplet-triplet annihilation has emerged as a prominent research focus. This study investigates five derivative molecules, featuring varied bridging atoms/groups (O, S, Se, -CH2-), designed from the reported TADF molecule AC-BO with through-space charge transfer (TSCT) properties. Utilizing time-dependent density functional theory coupled with a PCM solution model, their excited state behaviors were simulated in a toluene environment. Interestingly, it was observed that RISC in AC-BO and one derivative, AC-BCO, occurs predominantly via the T2 state rather than the typical T1 state (3LEB, where B denotes the fluorene bridge), distinguishing it from conventional TSCT-TADF compounds, where RISC typically involves transitions between the 3CT and 1CT states. This distinctive mode is attributed to reduced spin-orbit coupling (SOC) between 1CT and 3LEB, with T2 representing a significant contributor to the RISC process through its 3CT character. Introduction of heavy atoms enhances the electron-withdrawing ability of the acceptor unit, leading to the T1 transitions exhibiting 3MRCT characteristics and increased SOC, thereby favoring RISC via 3MRCT to 1CT transitions. This study not only deepens our understanding of transition mechanisms in TSCT-TADF compounds but also provides crucial insights into the molecular design and regulation of excited triplet states.

Supramolecular method enabling effective through-space charge transfer in thermally activated delayed fluorescence materials with pure orange emission

A supramolecular strategy has been developed to enhance through-space charge transfer by precisely regulating the spatial arrangement of donor–acceptor pairs, resulting in thermally activated delayed fluorescence with pure orange emission.

Construction of through-space charge transfer donor-acceptor coordination polymers through the combination of planar electron-deficient/rich ligands

Construction of through-space charge transfer donor-acceptor coordination polymers through the combination of planar electron-deficient/rich ligands

Enhanced Circularly Polarized Luminescence Modulation Using Dichroic Conjugated Polymer in Cholesteric Liquid Crystals

AbstractNegative dichroic dyes are crucial for enhancing the brightness of liquid crystal displays (LCDs) and modulating circularly polarized luminescence (CPL) in cholesteric liquid crystals (CLCs) through supramolecular co‐assembly. However, the majority of fluorescent molecules exhibit positive dichroism, and there is a limited understanding of designing negative dichroic molecules. In this paper, a novel design principle is proposed to construct the negative dichroic polymer by introducing through space charge transfer (TSCT) side chain structure to the polymer backbone. Specifically, two conjugated polymers (P1, P2) are synthesized using the Suzuki coupling reaction of two donor‐acceptor (D‐A) type monomers (V‐type M1 and I‐type M2) with fluorenyl monomer. P1 exhibits negative dichroism, and its orientational order parameter (SF) is up to SFP1 = –0.18. On the contrary, P2 is positive dichroism (SFP2 = + 0.27). This variation arises from the differing orientations of the rigidly functional side chains (SFM1 = + 0.07; SFM2 = + 0.31), which affect the alignment (parallel or perpendicular) of the polymer backbone toward CLCs molecules. This phenomenon facilitates controllable dichroism and precisely modulates the handedness of CPL signals, thereby facilitating the successful implementation of multidimensional information encryption systems in CLCs.

Enhancing reverse intersystem crossing process of thermally activated delayed fluorescence molecules with through-space charge transfer feature by acceptor engineering strategy

Developing efficient thermally activated delayed fluorescence (TADF) molecule with through-space charge transfer (TSCT) feature remains a great challenge, and theoretical investigation to reveal the inner luminescence mechanisms is highly desired. Herein, the photophysical properties of eight TSCT-type TADF molecules are studied by first-principle calculations. Results show that small S1–T1 energy gaps and large SOC constants are obtained for all molecules, and the transition properties can be adjusted by the acceptor engineering strategy. The ISC and RISC processes can be enhanced by adopting A–D–A configurations. Thus, previous experimental measurements are reasonably explained, and six new TSCT-type TADF molecules are proposed.

Non-noble Metal Single-Molecule Photocatalysts for the Overall Photosynthesis of Hydrogen Peroxide.

Despite the great progress in molecule photocatalytic solar energy conversion, it is particularly challenging to realize a photocatalytic overall reaction in a non-noble metal complex, which represents a new paradigm for photosynthesis. In this study, a class of novel non-noble metal complexes with head-to-tail geometry were designed and readily synthesized via the coordination of triphenylamine-modified 2,2': 6',2″-terpyridine ligands with Zn2+. As expected, these complexes exhibited the desired through-space charge-transfer transition, generating both long-lived excited states (on the order of microseconds) and separate redox centers under visible-light irradiation. These complexes have particularly low exciton binding energies, which make them excellent heterogeneous single molecular photocatalysts for the overall photosynthetic production of H2O2. Remarkably, a high H2O2 evolution rate (8862 μmol g-1 h-1) was achieved in pure H2O under an air atmosphere via precise molecular tailoring, revealing the unparalleled advantages of molecular photocatalysts in improving the catalytic rate of H2O2 production. This is the first time that single-molecule photocatalysts have been used to efficiently complete the photosynthesis of H2O2. This study presents a new paradigm for photocatalytic energy conversion and provides unique insights into the design of molecular photocatalysts.

Efficiency Boost in Through Space Charge Transfer Emitters: Insights from Spiro Lateral Rocking Confinement.

Intramolecular through-space charge-transfer (TSCT) excited states have emerged as promising candidates for thermally activated delayed fluorescence (TADF) emitters. This study addresses the challenges in tuning excited state dynamics through conformational engineering, which significantly impacts exciton utilization. An effective strategy is presented to enhance the performance of TSCT-TADF molecules by restricting the lateral rocking of the spiro unit via immobilizing groups, which indirectly adjusts the conformations of the donor and acceptor subunits. This approach is successfully illustrated with two TSCT-TADF emitters, 8PhDM-B and 8PyDM-B, featuring sterical aryl phenyl and pyridine substitutions at the C8 site of a rigid spiro-fluorene bridge. Organic light-emitting diodes (OLEDs) utilizing these emitters demonstrated impressive maximum external quantum efficiencies of 33.1% and 31.0%, respectively. The findings underscore the importance of the rocking confined strategy in refining excited state dynamics, thereby providing valuable insights for the design of highly efficient OLED emitters.

Unraveling the Configuration Modulation in Spiro-Based Through-Space Charge Transfer Materials.

Thermally activated delayed fluorescence (TADF) materials hold promise for optoelectronic applications. Among various design strategies, through-space charge transfer (TSCT) systems offer the potential for enhanced performance. However, the relationship between molecular configuration and TSCT properties remains unclear compared to traditional through-band charge transfer materials. In this study, we investigated the influence of spatial configuration on TSCT features and electronic properties of triplet excited states in these TSCT materials. By manipulating the spatial arrangement between donor and acceptor segments using different spiro skeletons, a series of TSCT materials (DMB2-DMB5) was synthesized. Together with the parent molecule, DM-B, these materials exhibited completely different TADF characteristics, demonstrating the impact of spatial arrangements on their optoelectronic properties. Thus, the external quantum efficiency of these materials ranged from as high as 28.0 % (DMB2) to as low as 3.6 % (DMB5) due to variations in their TADF characteristics. Our findings highlight the significance of spatial configuration, beyond distance alone, in influencing TSCT properties when donor and acceptor segments are sufficiently close. This insight provides valuable guidance for developing advanced TSCT materials and advancing TADF systems with improved performance and functionality.

Unraveling the Configuration Modulation in Spiro‐Based Through‐Space Charge Transfer Materials

AbstractThermally activated delayed fluorescence (TADF) materials hold promise for optoelectronic applications. Among various design strategies, through‐space charge transfer (TSCT) systems offer the potential for enhanced performance. However, the relationship between molecular configuration and TSCT properties remains unclear compared to traditional through‐band charge transfer materials. In this study, we investigated the influence of spatial configuration on TSCT features and electronic properties of triplet excited states in these TSCT materials. By manipulating the spatial arrangement between donor and acceptor segments using different spiro skeletons, a series of TSCT materials (DMB2‐DMB5) was synthesized. Together with the parent molecule, DM‐B, these materials exhibited completely different TADF characteristics, demonstrating the impact of spatial arrangements on their optoelectronic properties. Thus, the external quantum efficiency of these materials ranged from as high as 28.0 % (DMB2) to as low as 3.6 % (DMB5) due to variations in their TADF characteristics. Our findings highlight the significance of spatial configuration, beyond distance alone, in influencing TSCT properties when donor and acceptor segments are sufficiently close. This insight provides valuable guidance for developing advanced TSCT materials and advancing TADF systems with improved performance and functionality.

A Modular Approach to Tuning Emissive N-Quinolyl Through-Space Charge Transfer States Using sp3-Scaffolds.

We have shown that palladium-catalyzed cascade processes provide modular access to rigid quinoline-containing tetracyclic amines. This modular approach enables fine-tuning of the through-space charge transfer (TSCT) state formation between the lone pair localized on the nitrogen atom in the cage moiety and the quinoline moiety by variation of both the intramolecular N-aryl distance and quinoline substitution. Decreasing this N-aryl distance enhances the formation of the TSCT species, giving control over the emission color and photoluminescence quantum yield. Methoxylation of the quinoline unit decreases the propensity of TSCT formation. The development of this structure-activity relationship provides great insight for TSCT formation with an impact on further understanding dimeric, excimeric, and exciplex species. This understanding is crucial for the work underpinning their use in biosensor applications, and the conclusions are of relevance to the broader field of photoluminescence.

A Facile One-Step Self-Assembly Strategy for Novel Carbon Dots Supramolecular Crystals with Ultralong Phosphorescence Controlled by NH4.

A new methodological design is proposed for carbon dots (CDs)-based crystallization-induced phosphorescence (CIP) materials via one-step self-assembled packaging controlled by NH4 +. O-phenylenediamine (o-PD) as a nitrogen/carbon source and the ammonium salts as oxidants are used to obtain CDs supramolecular crystals with a well-defined staircase-like morphology, pink fluorescence and ultralong green room-temperature phosphorescence (RTP) (733.56ms) that is the first highest value for CDs-based CIP materials using pure nitrogen/carbon source by one-step packaging. Wherein, NH4 + and o-PD-derived oxidative polymers are prerequisites for self-assembled crystallization so as to receive the ultralong RTP. Density functional theory calculation indicates that NH4 + tends to anchor to the dimer on the surface state of CDs and guides CDs to cross-arrange in an X-type stacking mode, leading to the spatially separated frontier orbitals and the through-space charge transfer (TSCT) excited state in turn. Such a self-assembled mode contributes to both the small singlet-triplet energy gap (ΔEST) and the fast inter-system crossing (ISC) process that is directly related to ultralong RTP. This work not only proposes a new strategy to prepare CDs-based CIP materials in one step but also reveals the potential for the self-assembled behavior controlled by NH4 +.

Anomalous Pressure-Induced Blue-Shifted Emission of Ionic Copper-Iodine Clusters: The Competitive Effect between Cuprophilic Interactions and Through-Space Interactions.

Developing ionic copper-iodine clusters with multiple emitting is crucial for enriching lighting and display materials with various colors. However, the luminescent properties of traditional ionic copper-iodine clusters are often closely associated with low-energy cluster-centered triplet emission, which will redshift further as the Cu⋅⋅⋅Cu bond length decreases. This article utilizes a pressure-treated strategy to achieve an anomalous pressure-induced blue-shifted luminescence phenomenon in ionic Cu4I6(4-dimethylamino-1-ethylpyridinium)2 crystals for the first time, which is based on dominant through-space charge-transfer (TSCT). Herein, we reveal that the more advantageous through-space interactions in the competition between cuprophilic interactions and through-space interactions can lead to a blue-shifted luminescence. High-pressure angle-dispersive X-ray diffraction and high-pressure infrared experiments show that the enhanced through-space interactions mainly originate from forming new intermolecular C-H⋅⋅⋅I hydrogen bonds and the enhancement of van der Waals interactions between organic cations and anionic clusters. Theoretical calculations and experimental studies of excited-state dynamics confirm that the blue-shifted emission is due to the increased energy gap between the excited triplet and ground states caused by the electron delocalization under stronger through-space interactions. This work deepens previous understanding and provides a new avenue to design and synthetic ionic copper-iodine clusters with high-energy TSCT emission.

Anomalous Pressure‐Induced Blue‐Shifted Emission of Ionic Copper‐Iodine Clusters: The Competitive Effect between Cuprophilic Interactions and Through‐Space Interactions

AbstractDeveloping ionic copper‐iodine clusters with multiple emitting is crucial for enriching lighting and display materials with various colors. However, the luminescent properties of traditional ionic copper‐iodine clusters are often closely associated with low‐energy cluster‐centered triplet emission, which will redshift further as the Cu⋅⋅⋅Cu bond length decreases. This article utilizes a pressure‐treated strategy to achieve an anomalous pressure‐induced blue‐shifted luminescence phenomenon in ionic Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 crystals for the first time, which is based on dominant through‐space charge‐transfer (TSCT). Herein, we reveal that the more advantageous through‐space interactions in the competition between cuprophilic interactions and through‐space interactions can lead to a blue‐shifted luminescence. High‐pressure angle‐dispersive X‐ray diffraction and high‐pressure infrared experiments show that the enhanced through‐space interactions mainly originate from forming new intermolecular C−H⋅⋅⋅I hydrogen bonds and the enhancement of van der Waals interactions between organic cations and anionic clusters. Theoretical calculations and experimental studies of excited‐state dynamics confirm that the blue‐shifted emission is due to the increased energy gap between the excited triplet and ground states caused by the electron delocalization under stronger through‐space interactions. This work deepens previous understanding and provides a new avenue to design and synthetic ionic copper‐iodine clusters with high‐energy TSCT emission.

Exploring Through-Space Charge Transfer-Mediated Optoelectrochemical Properties of Dual-State Luminescent Aliphatic Polymers and Optoelectronic Responses toward Metal Ions.

Herein, natural-synthetic hybrid dual-state luminescent conducting polymers (DLCPs/DLCP1-DLCP8) possessing significant optoelectrochemical properties are strategically developed by the polymerization of prop-2-enamide, cis-butenedioic acid, 2-acrylamido-2-methylpropane-1-sulfonic acid, and in situ-generated 2-(3-acrylamidopropanamido)-2-methylpropane-1-sulfonic acid alongside the grafting of gum tragacanth. The spectroscopic data of aliphatic DLCPs affirm DLCP7 as the most stable supramolecular assembly endowing optoelectronic properties. Computational calculations identified -C(═O)NH-, -C(═O)OH, -OH, and -SO3H as subluminophores. The absorption spectra, excitation wavelength-/solvent-polarity-/concentration-dependent luminescence, solid state luminescence, aggregation-induced enhanced luminescence, and time-correlated single photon count (TCSPC) studies confirm the occurrence of aggregation-mediated intramolecular through-space charge transfer (ITSCT) in the excited state of DLCP7. Mulliken charge, natural bond orbital, dipole moments, and electronic potential surface analyses confirm the charge donor-acceptor system in DLCP7. Furthermore, the selective optoelectronic response of DLCP7 toward Ca2+/Cu(II) at 438/574 nm is explored using ultraviolet-visible spectra, TCSPC analyses, a dynamic light scattering study, and computational investigations. The chelation-enhanced luminescence and ITSCT inhibition are responsible for turn-on and turn-off detections of Ca2+ and Cu(II), respectively. Cu(II) → Cu(I) reduction in a DLCP7 solution is inferred from electrochemical and spectroscopic analyses. The conductivities of 9.65 × 10-5 S cm-1 (solid state) and 44.35 × 10-5 S cm-1 (solution) in DLCP7 are validated by current-voltage and electrochemical impedance measurements. Again, strong electronic conductivities of 43.89 × 10-5 S cm-1 (solid state)/53.34 × 10-5 S cm-1 (solution) and 45.42 × 10-5 S cm-1 (solid state)/64.81 × 10-5 S cm-1 (solution) are observed in Ca2+-DLCP7 and Cu(II)-DLCP7, respectively.

Storehouse of Peculiar Supramolecular Architecture: Probing the Charge-Transfer Phenomenon and Effect of Altering the pH in a Meta-Oriented Single Donor-Double Acceptor Fluorophore.

The investigation of excited-state intramolecular charge transfer (ESICT) has been a fascinating area of research. Although the ESICT events have been studied mostly for para-disubstituted donor-acceptor type molecules, the meta-oriented donor-acceptor type molecules have also shown tremendous potential as ESICT active molecules. In the current work, a small fluorescent probe diethyl 5-amino isophthalate (DE-5A-IPA) was investigated as a potential model to investigate ESICT events in the solution as well as solid phase. DE-5A-IPA was synthesized easily starting from commercially available 5-amino isophthalic acid in excellent yield. In the solid state, differing extents of CH···π-type binding led to formation of fully planar and puckered "cyclobutane" mimic supramolecular architecture, as evidenced from the crystal structure analysis. In addition, the single crystal structure of DE-5A-IPA shows that the donor (-NH2) and acceptor (-CO2Et) are situated in the same plane, thereby assuring the prerequisites of a through-space charge transfer. DE-5A-IPA undergoes noticeable Stokes shift (in cm-1) when the polarity of the medium was changed (4820 cm-1 in hexane; 9375 cm-1 in water). The excited-state dipole moment (μe) was calculated to be 4.0 units higher than the ground-state dipole moment (μg). DE-5A-IPA had an appreciable quantum yield (0.10 ± 0.03 to 0.27 ± 0.04). The ESICT phenomenon was also investigated by ground- and excited-state structural calculations using Gaussian 16 software. The excited-state lifetime measured by the time correlated single photon counting technique was found to vary with the polarity of the solvent, thereby providing further support to the ESICT phenomenon being operative in DE-5A-IPA. Taking advantage of the -NH2 group (which is susceptible to protonation) in DE-5A-IPA, steady state and time-resolved photodynamics were investigated in solutions of varying pH values. Interestingly, the emission quantum yields as well as the emission lifetime increase with an increase in pH value, thereby establishing DE-5A-IPA as a pH-sensitive probe. The current findings shall boost the understanding of meta-oriented ESICT enabled compounds in terms of their excited-state photophysics.