Remarkable Dependence of Exciplex Decay Rate on Through-Space Separation Distance between Porphyrin and Chemically Converted Graphene

Abstract

A series of chemically converted graphenes (CCGs) covalently functionalized with multiple zincporphyrins (ZnPs) through tuned lengths of linear oligo-p-phenylene bridges (ZnP-ph n -CCG, n = 1−5) were prepared to address the bridge length effect on their photodynamics. Irrespective of the bridge length, photoexcitation of ZnP-ph n -CCG led to exclusive formation of an exciplex state, which rapidly decayed to the ground state without yielding the completely charge-separated state. The notable dependence of the exciplex lifetime as a function of separation distance between the porphyrin and CCG has been observed for the first time, supporting the hypothesis that the decay to the ground state is dominated by the through-space interaction rather than the through-bond one. The basic information on the interaction between ZnP and CCG in the excited state will provide us with deeper insight on the intrinsic nature of the exciplex state as a function of donor− acceptor interaction.

Graphene and Carbon‐Nanotube Nanohybrids Covalently Functionalized by Porphyrins and Phthalocyanines for Optoelectronic Properties

“…e) Dependence of the exciplex decay rate constant ( k ) on the edge‐to‐edge separation distance ( R ee ) in semilogarithmic representation. Reproduced with permission . Copyright 2016, American Chemical Society.…”

“…Another internal electronic interaction is seen between photoexcited Por and graphene/CNT when a covalent bridge of one or several p ‐phenylene units is employed, namely a CT interaction that leads to the formation of an exciplex . This exciplex decays rapidly to the ground state rather than to the CS state, resulting in no contribution to photocurrent generation.…”

“…TA studies revealed a rather broad and structureless band due to the partial positive and negative charges localized on the ZnPor and nanocarbon moieties, respectively. ZnPor–graphene nanoconjugates with systematically varied oligo‐ p ‐phenylene bridges (ZnPor–(1,4‐C 6 H 4 ) n –graphene, n = 1–5) were employed to investigate the effect of the D–A interaction between the ZnPor and the graphene units on the photodynamics . Upon photoexcitation, all samples, irrespective of the bridge length, evolved to an exciplex state which then experienced a rapid decay to the ground state.…”

Exciplex emissions derived from exceptionally long-distance donor and acceptor molecules

“…For exciplex formation, the distance between electron-donor and electron-acceptor molecules has to be very small, on the order of a few nanometers at most. [11][12][13] However, Nakanotani et al observed exciplex emissions derived from long-distance coupled donor and acceptor molecules with a 10 nm thick spacer layer, 14 and then, Chapran et al, Li et al, and Sych et al also observed similar exciplex emissions with a several nanometer spacer layer, using different types of donor and acceptor molecules. [15][16][17] Colella et al reported that donor and acceptor molecules diluted in a host matrix (i.e.…”

Exclusive occurrence of photoinduced energy transfer and switching of its direction by rectangular π-extension of nanographenes

“…To achieve synergistic effects of the combinations of porphyrins and 2D nanocarbons on their performances in the applications, the occurrence of efficient photoinduced energy transfer (EnT) or electron transfer (ET) from the attached porphyrins to the 2D nanocarbons or vice versa is of extreme importance. Systematic investigations on porphyrin–2D nanocarbon covalently linked systems revealed that their photodynamics is profoundly affected by the spacer structures that govern separation distances and mutual orientations between porphyrins and 2D nanocarbons 22–24. However, 2D nanocarbons in the porphyrin-linked systems reported so far consist of complicated mixtures with a range of sizes, shapes, and defects of the sp 2 carbon network.…”