Investigating the role of corrole as an excitation energy relay in light-induced processes in closely connected N,N'-bis(biphenyl-4-yl)aniline functionalized corrole donor-acceptor dyad.

A photosynthetic antenna-reaction center model, BBA-PFCor comprised of N,N'-bis(biphenyl-4-yl)aniline (BBA) covalently functionalized to bis(pentafluoro)corrole moiety has been prepared and the contribution of the BBA as the photoinduced energy transfer antenna was investigated. UV-visible studies have shown that integrating the electron-rich BBA chromophore into the corrole core has broadened the soret band of the corrole moiety with the absorption spanning from 300 to 700 nm. Electrochemical studies, in corroboration with the computational calculations, revealed that, BBA moiety can act as an electron reservoir and, in the excited state, it would transfer the excited energy to the corrole moiety in the dyad. Steady-state fluorescence studies have demonstrated that, upon photoexcitation of the BBA moiety of BBA-PFCor at 310 nm in solvents of varied polarity, the BBA emission centered at 400 nm was observed to be quenched, with the concomitant appearance of the corrole emission from 500 to 700 nm, indicating the happening of photoinduced energy transfer (PEnT) from 1BBA* to corrole moiety. Parallel control experiments involving the excitation of the corrole moiety at 410 nm did not result in the diminishing of the corrole emission, suggesting that the quenching of the BBA emission in BBA-PFCor is majorly due to intramolecular PEnT from 1BBA* to corrole moiety leading to the formation of singlet excited corrole, that is, 1BBA*-PFCor ➔ BBA-1PFCor*. The free energy changes of PEnT, ΔGEnT, were found to be thermodynamically feasible in all the solvents used for the study. Parallel time-resolved fluorescence studies were congruent with the steady-state fluorescence results and provided further evidence for the occurrence of ultrafast PEnT from 1BBA*➔corrole in the dyad with the rates of energy transfer (kEnT) of ~108 s-1.

Synthesis, structure and photophysical properties of ferrocenyl or mixed sandwich cobaltocenyl ester linked meso-tetratolylporphyrin dyads.

We report here the design and synthesis of porphyrin-metallocene dyads consisting of a metallocene [either ferrocene or mixed sandwich η(5)-[C5H4(COOH)]Co(η(4)-C4Ph4) connected via an ester linkage at meso phenyl position of either free-base or zinc porphyrin. All these dyad systems were characterized by various spectroscopic and electrochemical methods. A dimeric form of this molecule was observed in the X-ray crystal structure of Zn-TTPCo. The absorption spectra of all four dyads indicated the absence of electronic interactions between porphyrin macrocycle and metallocene in the ground state. However, interestingly, in all four dyads, fluorescence emission of the porphyrin was quenched (19-55%) as compared to their monomeric units. The quenching was more pronounced in ferrocene derivatives rather than cobaltocenyl derivatives. The emission quenching can be attributed to the excited-state intramolecular photoinduced electron transfer from metallocene to singlet excited state of porphyrin and the electron-transfer rates (k(ET)) were established in the range 1.51 × 10(8) to 1.11 × 10(9) s(-1). They were found to be solvent dependent.