Photosynthetic Antenna‐Reaction Center Mimicry with a Covalently Linked Monostyryl Boron‐Dipyrromethene–Aza‐Boron‐Dipyrromethene–C₆₀ Triad

Abstract

An efficient functional mimic of the photosynthetic antenna-reaction center has been designed and synthesized. The model contains a near-infrared-absorbing aza-boron-dipyrromethene (ADP) that is connected to a monostyryl boron-dipyrromethene (BDP) by a click reaction and to a fullerene (C60 ) using the Prato reaction. The intramolecular photoinduced energy and electron-transfer processes of this triad as well as the corresponding dyads BDP-ADP and ADP-C60 have been studied with steady-state and time-resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge-separated states. Such calculations show that electron transfer from the singlet excited ADP ((1) ADP*) to C60 yielding ADP(.+) -C60 (.-) is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from (1) BDP* to ADP in the dyad BDP-ADP and electron transfer from (1) ADP* to C60 in the dyad ADP-C60 . Sequential energy and electron transfer have also been clearly observed in the triad BDP-ADP-C60 . By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10(11) s(-1) ). The dynamics of electron transfer through (1) ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge-separation process from (1) ADP* to C60 has been detected, which gives the relatively long-lived BDP-ADP(.+) C60 (.-) with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge-separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP-ADP and ADP-C60 , and the triad BDP-ADP-C60 are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems.

Directly Connected AzaBODIPY–BODIPY Dyad: Synthesis, Crystal Structure, and Ground- and Excited-State Interactions

“…This is anticipated due to closeness of the donor and acceptor entities unlike previous studies on BODIPYazaBODIPY dyads where the donor and acceptor entities were separated by spacers. 35,42,[45][46][47][48][49][50] As discussed earlier, formation of BODIPY •+ -azaBODIPY •-charge separated state from 1 azaBODIPY*, formed either by energy transfer or by direct excitation, is an exergonic process.…”

“…35,42,[45][46][47][48][49][50] Herein, we report the synthesis of such a covalently linked, strongly coupled, BODIPY-azaBODIPY dyad, 1 (Figure 1 for structure) using 2-formyl azaBODIPY, 2 as a key reactant that was obtained in high yield under simple reaction conditions. The X-ray structure of the newly synthesized BODIPY-azaBODIPY dyad 1 reveals the spatial orientation of the two macrocycles with respect to one another.…”

“…[31][32][33] Compared to BODIPYs, the azaBODIPYs exhibited red shifted absorption and emission spectra with high molar absorption coefficients and fluorescence quantum yields which captured the attention of researchers to construct azaBODIPY based photosynthetic model compounds. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] The strongly coupled dual chromophoric systems such as covalently linked BODIPYazaBODIPY are desired to achieve fast photoinduced intercomponent electron and energy transfer events, leading to valuable functions such as energy migration and/or charge separation.…”

Photosynthetic Antenna–Reaction Center Mimicry by Using Boron Dipyrromethene Sensitizers

“…[119] The model contains the near-IR-absorbing azaBODIPY, which is connected to a monostyryl-BODIPY through a click reaction and to a fullerene (C 60 ) by using the Prato reaction ( Figure 16). [119] The model contains the near-IR-absorbing azaBODIPY, which is connected to a monostyryl-BODIPY through a click reaction and to a fullerene (C 60 ) by using the Prato reaction ( Figure 16).…”

Excitation Dynamics in Hetero‐bichromophoric Calixarene Systems

“…Many of these simplified "artificiala ntennas" were based on naturallyo ccurring chromophores, such as chlorophylls, porphyrins, and carotenoids, but different dyes and metal-containing molecules have also been used. [1,2,7,[19][20][21][22][23][24][25][26][27][28] Herein, we present the synthesis and characterization of af amily of covalent bichromophorics ystemsa ble to efficiently perform intramolecular energy transfer from the donort ot he acceptorchromophore.The chosen central scaffold is acalix [4]arene macrocycle, which is particularly suited for our purposes, as it could be functionalized with severalm oieties positioned at aw ell-definedd istance and orientation.C alixarenes have been previously used as convenient scaffolds for chromophores acting as fluorescent probes, and af ew examples are reported for which energy transfer between two or more linked chromophores was investigated. [29][30][31][32][33] In our case, two well-known dyes, 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) and am odified Nile Red (NR), were selected as energy-donor and energy-acceptor units,r espectively,a nd linked at the 1,3-distal positions of the upper rim of acone and apartial cone calix [4]arene derivative to obtain af amily of three hetero-bichromophoric systems (Scheme 1).…”