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Unraveling the intriguing aspects of the intramolecular charge transfer (ICT) phenomenon of multi‐modular donor‐acceptor‐based push–pull systems are of paramount importance considering their promising applications, particularly in solar energy harvesting and light‐emitting devices. Herein, a series of symmetrical and unsymmetrical donor‐acceptor chromophores1–6, are designed and synthesized by the Corey‐Fuchs reaction via Evano's condition followed by [2+2] cycloaddition retroelectrocyclic ring‐opening reaction with strong electron acceptors TCNE and TCNQ in good yields (~60–85 %). The photophysical, electrochemical, and computational studies are investigated to explore the effect of incorporation of strong electron acceptors 1,1,4,4‐tetracyanobuta‐1,3‐diene (TCBD) and dicyanoquinodimethane (DCNQ) with phenothiazine (PTZ) donor. An additional low‐lying broad absorption band extended towards the near‐infrared (NIR) region suggests charge polarization after the introduction of the electron acceptors in both symmetrical and asymmetrical systems, leading to such strong ICT bands. The electrochemical properties reveal that reduction potentials of3and6are lower than those of2and5, suggesting DCNQ imparts more on the electronic properties and hence largely contributes to the stabilization of LUMO energy levels than TCBD, in line with theoretical observations. Relative positions of the frontier orbitals on geometry‐optimized structures further support accessing donor‐acceptor sites responsible for the ICT transitions. Eventually, ultrafast carrier dynamics of the photoinduced species are investigated by femtosecond transient absorption studies to identify their spectral characteristics and target analysis further provides information about different excited states photophysical events including ICT and their associated time profiles. The key findings obtained here related to excited state dynamical processes of these newly synthesized systems are believed to be significant in advancing their prospect of utilization in solar energy conversion and related photonic applications.

Using the popular metal‐ligand axial coordination self‐assembly approach, donor‐acceptor conjugates have been constructed using zinc tetrapyrroles (porphyrin (ZnP), phthalocyanine (ZnPc), and naphthalocyanine (ZnNc)) as electron donors and imidazole functionalized tetracyanobutadiene (Im‐TCBD) and cyclohexa‐2,5‐diene‐1,4‐diylidene‐expanded‐tetracyanobutadiene (Im‐DCNQ) as electron acceptors. The newly formed donor‐acceptor conjugates were fully characterized by a suite of physicochemical methods, including absorption and emission, electrochemistry, and computational methods. The measured binding constants for the 1 : 1 complexes were in the order of 10⁴–10⁵ M⁻¹in o‐dichlorobenzene. Free‐energy calculations and the energy level diagrams revealed the high exergonicity for the excited state electron transfer reactions. However, in the case of the ZnNc:Im‐DCNQ complex, owing to the facile oxidation of ZnNc and facile reduction of Im‐DCNQ, slow electron transfer was witnessed in the dark without the aid of light. Systematic transient pump‐probe studies were performed to secure evidence of excited state charge separation and gather their kinetic parameters. The rate of charge separation was as high as 10¹¹ s⁻¹suggesting efficient processes. These findings show that the present self‐assembly approach could be utilized to build donor‐acceptor constructs with powerful electron acceptors, TCBD and DCNQ, to witness ground and excited state charge transfer, fundamental events required in energy harvesting, and building optoelectronic devices.

A far‐red absorbing sensitizer, BF₂‐chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push‐pull systems linked with different nitrogenous electron donors, viz.,N,N‐dimethylaniline (NND), triphenylamine (TPA), and phenothiazine (PTZ) via an acetylene linker. The structural integrity of the newly synthesized push‐pull systems was established by spectroscopic, electrochemical, spectroelectrochemical, and DFT computational methods. Cyclic and differential pulse voltammetry studies revealed different redox states and helped in the estimation of the energies of the charge‐separated states. Further, spectroelectrochemical studies performed in a thin‐layer optical cell revealed diagnostic peaks of azaBODIPY⋅⁻in the visible and near‐IR regions. Free‐energy calculations revealed the charge separation from one of the covalently linked donors to the¹azaBODIPY* to yield Donor⋅⁺‐azaBODIPY⋅⁻to be energetically favorable in a polar solvent, benzonitrile, and the frontier orbitals generated on the optimized structures helped in assessing such a conclusion. Consequently, the steady‐state emission studies revealed quenching of the azaBODIPY fluorescence in all of the investigated push‐pull systems in benzonitrile and to a lesser extent in mildly polar dichlorobenzene, and nonpolar toluene. The femtosecond pump‐probe studies revealed the occurrence of excited charge transfer (CT) in nonpolar toluene while a complete charge separation (CS) for all three push‐pull systems in polar benzonitrile. The CT/CS products populated the low‐lying³azaBODIPY* prior to returning to the ground state. Global target (GloTarAn) analysis of the transient data revealed the lifetime of the final charge‐separated states (CSS) to be 195 ps for NND‐derived, 50 ps for TPA‐derived, and 85 ps for PTZ‐derived push‐pull systems in benzonitrile.

Copper and silver tritolylcorroles (TTC) are symmetrically functionalized to carry two tetracyanobutadiene (TCBD) entities via [2+2] cycloaddition‐retroeletrocyclization reaction involving ethynyl functionalized corroles with an electron acceptor, tetracyanoethylene (TCNE) in excellent yields, as the first examples of corrole‐TCBD push‐pull systems. The strong push‐pull effect resulted in charge polarization in the ground state resulting in a considerable hypsochromic shift of the spectrum extending it into the near‐IR region. Electrochemical studies coupled with computational studies revealed considerable interactions between the two TCBD entities via the corrole π‐system and the degree of such interactions was found to depend on the metal ion present in the corrole cavity. Energy considerations suggested charge transfer (CT) from the S₂or vibrationally hot S₁state but not the relaxed S₁state in the case of CuTTC(TCBD)₂while CT to occur from all these states in the case of AgTTC(TCBD)₂. Additionally, the high‐energy CT states populate the low‐lying triplet states. Systematic femtosecond pump‐probe studies provided the ultimate proof for the occurrence of excited CT as a function of excitation wavelength followed by the efficient population of the triplet states. The present study brings out the significance of charge transfer in efficiently populating the triplet states in rather unusual copper and silver corroles carrying two TCBD entities.

Photoinduced charge transfer and separation events in a newly synthesized azobenzene‐bridged perylenediimide‐dimer (PDI‐dimer) are demonstrated. Trans‐to‐cis conversion (∼50 % efficiency) from the initial trans PDI‐dimer by 355 nm pulsed laser light, and its reversal, cis‐to‐trans, process by 435 nm laser light irradiation has been possible to accomplish. Efficient fluorescence quenching in the PDI‐dimer, more so for the cis isomer was witnessed, and such quenching increased with increasing solvent polarity. DFT‐calculated geometry and electronic structures helped in visualizing the charge transfer in the PDI‐dimer in both isomeric forms, and also revealed certain degree of participation of the azobenzene entity in the charge transfer events. Femtosecond transient absorption spectral studies confirmed occurrence of both charge transfer followed by charge separation in the studied PDI‐dimer in both trans and cis forms in polar solvents, and the evaluated time constants from Global target analysis revealed accelerated events in the cis PDI‐dimer due to proximity effects. The present study offers key insights on the role of the azobenzene bridge, and the dimer geometry in governing the excited state charge transfer and separation in symmetrically linked PDI dimer.