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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 chromophores 1–6, 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 of 3 and 6 are lower than those of 2 and 5, 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. [ABSTRACT FROM AUTHOR]

Two novel p-functionalized push-pull zinc porphyrins with amine or phenyl push-groups and cyclic imide or carboxylic esters pull-groups have been newly synthesized for light energy harvesting applications. The ethynylphenyl spacers extended the conjugation of the porphyrin [pi]-systems, as reflected by their red-shifted absorbance and fluorescence spectra. Computational studies performed at the B3LYP/6-31G* level indicated no steric hindrance between the porphyrin w-system and the substituents. The calculated HOMO and LUMO orbitals displayed significant delocalization in 1, where the electron density in the HOMO was localized over the push groups, whereas the LUMO was extended over the porphyrin [pi]- and pull-groups. On the other hand, 2 did not display significant orbital segregation, which is attributed to its weaker push-pull character. Electrochemical studies revealed smaller HOMO-LUMO gaps for the push-pull zinc porphyrins. As a consequence of the push-pull effects, reduction in fluorescence intensity and lifetime was observed. Femtosecond transient absorption spectral studies revealed successful formation of singlet excited state in both of the push-pull porphyrins. Donor-acceptor conjugates were subsequently built and characterized by coordinating an electron acceptor, [C.sub.60]Im, via metal-ligand axial coordination. Efficient photo-induced charge separation in both donor-acceptor conjugates was witnessed wherein the charge-separated states persisted tens of nanoseconds prior returning to the ground state. Key words: push-pull zinc porphyrin, fullerene, metal-ligand axial coordination, photoinduced electron transfer. Nous avons realise la premiere synthese de deux nouvelles porphyrines-zinc de type<< push-pull>>fonctionnalisees en positions p, dans lesquelles les groupes electrodonneurs sont des amines ou des groupes phenyl et les groupes electroattracteurs, un imide cyclique ou des esters carboxyliques, en vue d'applications de recuperation d'energie lumineuse. Les groupes ethynylphenyl tenaient lieu d'espaceurs servant a etendre les systemes de conjugaison [pi]des porphyrines, comme en temoigne le deplacement vers le rouge des spectres d'absorbance et de fluorescence de ces composes. Des etudes de modelisation realisees au niveau B3LYP/6-31G (*) n'ont pas revele d'encombrement sterique entre le systeme w des porphyrines et leur substituants. La modelisation des orbitales HOMO et LUMO du compose 1 a revele une delocalisation importante, la densite electronique de la HOMO etant localisee sur les groupes electrodonneurs, tandis que la LUMO s'etendait sur le systeme w de la porphyrine et les groupes electroattracteurs. Par contre, le compose 2 n'a pas presente de segregation orbitalaire marquee, ce qui s'explique par son caractere << push-pull >> plus faible. Des etudes electrochimiques menees sur les porphyrines-zinc de type << push-pull >> ont revele que leurs bandes interdites HOMO-LUMO etaient plus etroites. Les effets de type << push-pull >> se sont traduits par une reduction de l'intensite et de la duree de vie de la fluorescence. L'analyse des spectres d'absorption des especes transitoires a l'echelle de la femtoseconde a revele que les deux porphyrines de type<>donnaient lieu a la formation d'un etat excite singulet. Nous avons par la suite forme les conjugues donneur-accepteur par coordination axiale metal-ligand d'un accepteur d'electron, le [C.sub.60]Im, et nous les avons caracterises. Nous avons observe qu'une separation de charge photo-induite se produisait efficacement dans les deux conjugues donneur-accepteur, et que ces etats de separation de charge ont persiste des dizaines de nanosecondes avant de revenir a l'etat fondamental. [Traduit par la Redaction] Mots-cles: porphyrine zinc de type <>, fullerene, coordination axiale metal-ligand, transfert electronique photo-induit., Introduction Push-pull porphyrins have been of intense research interest in recent years owning to their exceptional performance in dyesensitized solar cells. (1-5) The important roles of the push (electrondonating) and [...]