Pentacene Dimers as a Critical Tool for the Investigation of Intramolecular Singlet Fission

Abstract

Singlet fission (SF) involves the spontaneous splitting of a photoexcited singlet state into a pair of triplets, and it holds great promise toward the realization of more efficient solar cells. Although the process of SF has been known since the 1960s, debate regarding the underlying mechanism continues to this day, especially for molecular materials. A number of different chromophores have been synthesized and studied in order to better understand the process of SF. These previous reports have established that pentacene and its derivatives are especially well-suited for the study of SF, since the energetic requirement E(S )≥2E(T ) is fulfilled rendering the process exothermic and unidirectional. Dimeric pentacene derivatives, in which individual pentacene chromophores are tethered by a "spacer", have emerged as the system of choice toward exploring the mechanism of intramolecular singlet fission (iSF). The dimeric structure, and in particular the spacer, allows for controlling and tuning the distance, geometric relationship, and electronic coupling between the two pentacene moieties. This Minireview describes recent advances using pentacene dimers for the investigation of iSF.

An Ethynylene‐Bridged Pentacene Dimer: Two‐Step Synthesis and Charge‐Transport Properties

“…Among these modifications, synthesizing pentacene dimers is good strategy to expand and utilize the large pentacene π‐system . Additionally, recent research indicates the importance of the synthetic variation of pentacene dimers to investigate singlet fission, since the electronic coupling could be systematically tuned in the system by synthesis . For example, 6,6′‐linked pentacene dimer ( Dip‐TIPS ) forms the desired two‐dimensional (2D) π‐stacking network due to the orthogonal orientation of the two pentacenes .…”

“…This can be attributed to the reactive nature and poor solubility of pentacene, though a number of ethynylpentacene derivatives and the diethynylene‐linked pentacene oligomers have been synthesized . Therefore, the development of a facile synthetic approach for ethynylene‐bridged pentacene has great potential to provide an effective synthetic access for attractive ethynylene‐bridged π‐conjugated systems …”

“…[4,7] Additionally,r ecentr esearch indicates the importance of the synthetic variation of pentacene dimers to investigate singlet fission,s ince the electronic cou-pling could be systematicallyt uned in the system by synthesis. [10][11][12][13] For example,6 ,6'-linked pentacene dimer (Dip-TIPS) formst he desired two-dimensional (2D) p-stacking network due to the orthogonal orientation of the two pentacenes. [4,7] This providesi sotropic charget ransport with FET hole mobilities of up to 0.11cm 2 V À1 s À1 .…”

“…[8,9,11] Therefore, the development of af acile synthetic approachf or ethynylene-bridged pentacene has great potential to provide an effectives ynthetic accessf or attractivee thynylene-bridged p-conjugated systems. [8][9][10][11][12][13][14] Herein, we report the first synthesis of PenD from pentacenequinonei nt wo steps, as ag ood candidate to investigate the p-elongation effect on packing motif and charge-transport properties (Scheme 1). Additionally,t he intrinsic charget ransport property of PenD single crystals was investigated by using as quare four-probe method, compared with the FET mobility of dip-coatedf ilms.…”

Feinabstimmung von intramolekularem resonantem Förster‐Energietransfer und Aktivierung intramolekularer Singulettspaltung

“…2 E(T 1 )e rfüllt sein, jedoch begrenzt eine solche thermodynamische Vorbedingung die Anzahl der Moleküle, die fürS Fi nfrage kommen;d azu gehçren Diphenylisobenzofurane, [5] Rylene [6] und Acene. [8] Zweitens wurden p-konjugierte,k reuzkonjugierte und nichtkonjugierte Linker verwendet, um die elektronische Kopplung zwischen den beiden Pentacenen durch die Bindungen zu untersuchen. [3,7] Im Vordergrund dieser Bemühungen stand der Einsatz eines Baukastens verschiedener molekularer Brücken, um die relative räumliche Orientierung zu modulieren sowie die elektronische Kopplung feinabzustimmen.…”