Photoinduced Electron Transfer in Bisporphyrin–Diimide Complexes

Abstract

The bisporphyrin host ZnH was synthesized, and its complexation with two aromatic diimide guest molecules, bis(pyridyl)naphthalenediimide NIN and bis(pyridyl)phenyldiimide PIN, was investigated by 1H NMR and UV/Vis spectroscopy. The diimide guests were complexed simultaneously with both metalloporphyrins of the host, with association constants on the order of 108 M−1. The processes occurring in the complex after excitation of the porphyrinic host were studied by steady‐state and time‐resolved emission and transient absorption spectroscopy. Complexation alters the photophysical properties of the host ZnH; the luminescence bands shift to the red by 30 nm in the complexed forms, while the emission quantum yield and the lifetime decrease. Comparison of a complex between ZnH and a model guest unable to undergo photoinduced processes allowed us to establish that, in the diimide complexes, quenching of the porphyrinic luminescence occurs with a rate of 1.1×1010 s−1. The process is identified as an electron transfer from the excited singlet of the porphyrinic host to the imide guest, which yields charge‐separated states with a lifetime of 710 ps for ZnH+‐NIN− and 260 ps for ZnH+‐PIN−.

A practical approach to the study of photoactive self-assembled porphyrin systems

“…facilities and experimental procedures have been described in detail in previous publications [35][36][37][38][39], where references to synthetic procedures can also be found. The solvents used were spectroscopic grade toluene and spectroscopic grade acetonitrile.…”

“…Photoinduced electron transfer in a host-guest complex, K a ≥ 10 7 M -1 , non-absorbing and nonemitting guest (case a) [35,36] The system consists of a zinc bis-porphyrinic clamp, ZnH, able to complex by axial coordination a guest of a proper size, NIN, containing two pyridyl residues, Fig. 1.…”

“…An introductory section will present the type of approach and will focus on the conditions for a correct experimental approach; subsequent sections will present examples and applications of the methods with emphasis on the determination of association parameters and their relevance to the photophysical study. For a detailed discussion of the photoinduced phenomena, their interpretation in the frame of the current theories and comparison with the related systems reported in the literature, the readers should refer to the original publications mentioned in the text [35][36][37][38][39] .…”

Femtosecond Time-Resolved Photophysics of 1,4,5,8-Naphthalene Diimides

“…Derivatives of 1,4,5,8-naphthalene diimides (NDIs) are known for such air-stable conductivity. 13 Due to this, NDIs have been used in the study of electron-transfer processes, [14][15][16][17][18] as liquid crystalline and photorefractive materials, [19][20][21] as photosynthetic model compounds, 22 and for opto-electronic applications. 23 Electrochemical and photophysical properties of NDI have been explored previously by several groups.…”

Supramolecular assemblies for electron transfer

“…Simultaneous with the shifts, the emission quantum yields and the lifetimes both decrease. The process is identified as an electron transfer from the singlet excited of the ZnP host to the NIN / PIN guests, which yields charge-separated states with a lifetime of 710 ps for NIN and 260 ps for PIN [11].…”