Synthesis and spectroscopic studies of axially bound tetra(phenothiazinyl)/tetra(bis(4′-tert-butylbiphenyl-4-yl)aniline)-zinc(II)porphyrin-fullero[C60 & C70]pyrrolidine donor–acceptor triads

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.

Light-induced energy transfer followed by electron transfer in axially co-ordinated benzothiazole tethered zinc porphyrin-fullero[C60/C70]pyrrolidine triads

Benzothiazole (BTZ)-zinc porphyrin (ZnP) dyads, Dyad-1 and Dyad-2 connected together with two different spacers, ester and ethoxy esters, were synthesized and light induced energy and electron transfer events were investigated. Within these dyads, due to the spectral overlap of the BTZ emission with the ZnP absorption, a selective photoexcitation of BTZ at 325 nm resulted in the photo-induced energy transfer (PEnT) from 1BTZ* to ZnP displaying the quenching of the BTZ emission followed by the concurrent appearance of the ZnP emission at 600 and 650 nm suggesting the formation of the 1ZnP* [Formula: see text]. 1BTZ*-ZnP [Formula: see text] BTZ-1ZnP*. When the dyads are titrated with imidazole appended fullero[C[Formula: see text]/C[Formula: see text]]pyrrolidines, four supramolecular triads, involving the axial co-ordination of the imidazole to the zinc center of the ZnP, were formed and the assembly formation was systematically monitored by the optical absorption technique. Cyclic voltammetry and the density functional theory calculations have revealed that, in these triads, the zinc porphyrin acts as an electron donor and fullerene moiety as the electron acceptor. Steady state fluorescence studies revealed that, upon selective excitation of the ZnP moiety at 550 nm, the emission of ZnP at 600 and 650 nm was quenched revealing the occurrence of photo-induced electron transfer (PET) from 1ZnP* to fullerene moiety leading to the formation of charge separated state [Formula: see text]. BTZ-1ZnP* : (ImC[Formula: see text] BTZ-ZnP[Formula: see text]:(ImC[Formula: see text]. More importantly, when the supramolecular triads were excited at 325 nm, the wavelength at which the BTZ absorbs predominantly, the emission of the BTZ moiety which was quenched due to PEnT from 1BTZ* to ZnP followed by the PET from 1ZnP* to fullerene indicates the probability of occurrence of 1BTZ*-ZnP:(ImC[Formula: see text] [Formula: see text] BTZ-1ZnP*[Formula: see text]: (ImC[Formula: see text] BTZ-ZnP[Formula: see text]:(ImC[Formula: see text].

Porphyrin bearing phenothiazine pincers as hosts for fullerene binding via concave–convex complementarity: synthesis and complexation study

Free base porphyrin hosts, m-(PTZ)4-H2P and p-(PTZ)4-H2P, tethered with four phenothiazine moieties at the meso-position via a flexible ethoxy phenyl linker were synthesized and used for the selective complexation of fullerenes, C60 and C70.

One-Photon Excitation Followed by a Three-Step Sequential Energy-Energy-Electron Transfer Leading to a Charge-Separated State in a Supramolecular Tetrad Featuring Benzothiazole-Boron-Dipyrromethene-Zinc Porphyrin-C60

A panchromatic triad, consisting of benzothiazole (BTZ) and BF₂ -chelated boron-dipyrromethene (BODIPY) moieties covalently linked to a zinc porphyrin (ZnP) core, has been synthesized and systematically characterized by using ¹ H NMR spectroscopy, ESI-MS, UV-visible, steady-state fluorescence, electrochemical, and femtosecond transient absorption techniques. The absorption band of the triad, BTZ-BODIPY-ZnP, and dyads, BTZ-BODIPY and BODIPY-ZnP, along with the reference compounds BTZ-OMe, BODIPY-OMe, and ZnP-OMe exhibited characteristic bands corresponding to individual chromophores. Electrochemical measurements on BTZ-BODIPY-ZnP exhibited redox behavior similar to that of the reference compounds. Upon selective excitation of BTZ (≈290 nm) in the BTZ-BODIPY-ZnP triad, the fluorescence of the BTZ moiety is quenched, due to photoinduced energy transfer (PEnT) from ¹ BTZ^* to the BODIPY moiety, followed by quenching of the BODIPY emission due to sequential PEnT from the ¹ BODIPY* moiety to ZnP, resulting in the appearance of the ZnP emission, indicating the occurrence of a two-step singlet-singlet energy transfer. Further, a supramolecular tetrad, BTZ-BODIPY-ZnP:ImC₆₀ , was formed by axially coordinating the triad with imidazole-appended fulleropyrrolidine (ImC₆₀ ), and parallel steady-state measurements displayed the diminished emission of ZnP, which clearly indicated the occurrence of photoinduced electron transfer (PET) from ¹ ZnP* to ImC₆₀ . Finally, femtosecond transient absorption spectral studies provided evidence for the sequential occurrence of PEnT and PET events, namely, ¹ BTZ^* -BODIPY-ZnP:ImC₆₀ →BTZ-¹ BODIPY^* -ZnP:ImC₆₀ →BTZ-BODIPY-¹ ZnP^* :ImC₆₀ →BTZ-BODIPY-ZnP^.+ :ImC₆₀ ^.- in the supramolecular tetrad. The evaluated rate of energy transfer, k_EnT , was found to be 3-5×10¹⁰  s^-1 , which was slightly faster than that observed in the case of BODIPY-ZnP and BTZ-BODIPY-ZnP, lacking the coordinated ImC₆₀ . The rate constants for charge separation and recombination, k_CS and k_CR , respectively, calculated by monitoring the rise and decay of C₆₀ ^.- were found to be 5.5×10¹⁰ and 4.4×10⁸  s^-1 , respectively, for the BODIPY-ZnP:ImC₆₀ triad, and 3.1×10¹⁰ and 4.9×10⁸  s^-1 , respectively, for the BTZ-BODIPY-ZnP:ImC₆₀ tetrad. Initial excitation of the tetrad, promoting two-step energy transfer and a final electron-transfer event, has been successfully demonstrated in the present study.

Bis(4′-tert-butylbiphenyl-4-yl)aniline (BBA)-substituted A3B zinc porphyrin as light harvesting material for conversion of light energy to electricity

Limited synthetic steps via low-cost starting materials are needed to develop large-scale light-active materials for efficient solar cells. Here, novel bis(4[Formula: see text]-tert-butylbiphenyl-4-yl)aniline (BBA) based A3B zinc porphyrin (GB) is synthesized and applied as a light harvesting/electron injection material in dye-sensitized solar cells. The GB sensitizer was characterized by various spectroscopic techniques and the optimized device shows [Formula: see text] of 10.98 ± 0.37 mA/cm2 and power conversion efficiency (PCE) of 3.34 ± 0.26%. In addition, performance is enhanced up to ∼3.9% by the addition of co-adsorbent 3a,7a-dihydroxy-5b-cholic acid (chenodeoxycholic acid, CDCA) to minimize [Formula: see text]-[Formula: see text] staking of the planar porphyrin macrocycles. These results demonstrate that novel broad-absorbing light-active material (GB) could be used for indoor solar panels.

A Convenient Synthesis of Pentaporphyrins and Supramolecular Complexes with a Fulleropyrrolidine

A simple and straightforward synthesis of diporphyrins and pentaporphyrins is reported here. The supramolecular interactions of the new porphyrin derivatives with C60 and PyC60 (a pyridyl [60]fulleropyrrolidine) were evaluated by absorption and fluorescence titrations in toluene. While no measurable modifications of the absorption and fluorescence spectra were observed upon addition of C60 to the porphyrin derivatives, the addition of PyC60 to the corresponding mono-Zn(II) porphyrins resulted in the formation of Zn(porphyrin)-PyC60 coordination complexes and the binding constants were calculated. Results show that the four free-base porphyrin units in pentaporphyrin 6 have a significant contribution in the stabilization of the 6-PyC60 complex. The crystal and molecular features of the pentaporphyrin Zn5 were unveiled using single-crystal X-ray diffraction studies.

Intramolecular electron transfer in porphyrin-anthraquinone donor–acceptor systems with varying molecular bridges

Photoinduced electron transfer has been investigated in porphyrin anthraquinone (ZnTTP-AQ) donor–acceptor dyads having either ester (ZnTTP-AQ1) or ether (ZnTTP-AQ2) linkages. Both dyads were characterized by spectroscopic and electrochemical methods. Absorption spectra show absence of any ground state interaction between the porphyrin and anthraquinone moieties. The quenched fluoresence and lifetime indicate electron transfer from the porphyrin to the anthraquinone moiety. The quenching is more pronounced in ZnTTP-AQ1 with ester linkage, suggesting efficient electronic coupling compared to the ether linkage in ZnTTP-AQ2. Computational analysis and frontier molecular orbitals confirmed the formation of charged separated state por[Formula: see text]AQ[Formula: see text]. The electron transfer rates ([Formula: see text] of these triads are found in the range 0.43 × 108 to 10.52 × 109 s[Formula: see text] and are found to be solvent polarity dependent.

Photoinduced energy transfer in carbazole–BODIPY dyads

A series of carbazole (CBZ)–boron dipyrromethene (BODIPY) based donor–acceptor dyads, CB1, CB2, and CB3, with CBZ as an energy donor, tethered together with spacers of varied sizes i.e., phenyl bridge, biphenyl bridge and diphenylethyne bridge, respectively, are reported.