Decelerating Charge Recombination Using Fluorinated Porphyrins in N,N-Bis(3,4,5-trimethoxyphenyl)aniline—Aluminum(III) Porphyrin—Fullerene Reaction Center Models

Abstract

In supramolecular reaction center models, the lifetime of the charge-separated state depends on many factors. However, little attention has been paid to the redox potential of the species that lie between the donor and acceptor in the final charge separated state. Here, we report on a series of self-assembled aluminum porphyrin-based triads that provide a unique opportunity to study the influence of the porphyrin redox potential independently of other factors. The triads, BTMPA-Im→AlPorF n -Ph-C 60 (n = 0, 3, 5), were constructed by linking the fullerene (C 60 ) and bis(3,4,5-trimethoxyphenyl)aniline (BTMPA) to the aluminum(III) porphyrin. The porphyrin (AlPor, AlPorF 3 , or AlPorF 5 ) redox potentials are tuned by the substitution of phenyl (Ph), 3,4,5-trifluorophenyl (PhF 3 ), or 2,3,4,5,6-pentafluorophenyl (PhF 5 ) groups in its meso positions. The C 60 and BTMPA units are bound axially to opposite faces of the porphyrin plane via covalent and coordination bonds, respectively. Excitation of all of the triads results in sequential electron transfer that generates the identical final charge separated state, BTMPA •+ -Im→AlPorF n -Ph-C 60•− , which lies energetically 1.50 eV above the ground state. Despite the fact that the radical pair is identical in all of the triads, remarkably, the lifetime of the BTMPA •+ -Im→AlPorF n -Ph-C 60 •− radical pair was found to be very different in each of them, that is, 1240, 740, and 56 ns for BTMPA-Im→AlPorF 5 -Ph-C 60 , BTMPA-Im→AlPorF 3 -Ph-C 60 , and BTMPA-Im→AlPor-Ph-C 60 , respectively. These results clearly suggest that the charge recombination is an activated process that depends on the midpoint potential of the central aluminum(III) porphyrin (AlPorF n ).

Formation of Highly Efficient, Long‐Lived Charge Separated States in Star‐Shaped Ferrocene‐Diketopyrrolopyrrole‐Triphenylamine Donor–Acceptor–Donor Conjugates

“…It is likely that the recombination path does not rigorously follow the predicted path of direct charge recombination to the ground state but might involve different degrees of electronic coupling in these star‐shaped supramolecular systems ultimately prolonging the lifetime of charge‐separated states. The current results nicely demonstrate how redox modulation in multi‐modular donor–acceptor conjugates direct the kinetics of excited state electron transfer events [24] …”

“…The current resultsn icely demonstrate how redox modulation in multi-modular donoracceptorc onjugatesd irect the kinetics of excited state electron transfer events. [24] In summary,t he newly synthesized star-shaped, multi-modular donor-acceptor-donor type conjugates revealed several Figure 5. Fs-TAs pectra at the indicated delay timeso f( a) DPP-control, (b) 1,and (c) 3 in DCB.…”

Charge stabilization via electron exchange: excited charge separation in symmetric, central triphenylamine derived, dimethylaminophenyl–tetracyanobutadiene donor–acceptor conjugates

“…Excited state charge transfer in donor-acceptor conjugates is one of the widely investigated topics in recent years due to their usage in building energy harvesting photonic devices. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Understanding the principles governing the kinetics of charge transfer and separation, securing high charge separation quantum yields, avoiding large energy losses, and prolonging the lifetime of the radical ion pairs by molecular engineering of the conjugates have been the main focus of these studies. [1][2][3][4][5][6][7][8][9][10][11][12] In simple donoracceptor conjugates, charge separation from the excited singlet state of the donor or acceptor can store the greatest amount of energy; however, since the process originates from the singlet excited state, the charge separated states are generally short-lived.…”

Charge‐Transfer in Panchromatic Porphyrin‐Tetracyanobuta‐1,3‐Diene‐Donor Conjugates: Switching the Role of Porphyrin in the Charge Separation Process

“…Photoinduced electron transfer (PET) is the main step in the conversion of solar light into chemical energy in plant and bacterial systems, [1][2] and a process with countless relevance in research fields including artificial photosynthesis, photocatalysis, photoconductivity, or molecular photovoltaics. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] In a simplistic scheme, PET consists of two main steps, namely, light absorption by a chromophore resulting in the formation of an excited state species, followed by a charge transfer between an electron donor (D) and an electron acceptor (A) leading to a charge separated D + -A À species. [16] The optimization of these processes and comprehending their mutual interplay to ultimately achieving charge separated species is of paramount importance for the development of efficient systems in solar light conversion schemes.…”