skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, October 10 until 2:00 AM ET on Friday, October 11 due to maintenance. We apologize for the inconvenience.


Title: A Carbon Nanotube Binding BODIPY‐C 60 Nano Tweezer: Charge Stabilization through Sequential Electron Transfer
Abstract

Electron donor–acceptor (DA) hybrids comprised of single‐wall carbon nanotubes (SWCNTs) are promising functional materials for light energy conversion. However, the DA hybrids built on SWCNTs have failed to reveal the much‐sought long‐lived charge separation (CS) due to the close proximity of the DA entities facilitating charge recombination. Here, we address this issue and report an elegant strategy to build multi‐modular DA hybrids capable of producing long‐lived CS states. For this, a nano tweezer featuring V‐shape configured BODIPY was synthesized to host SWCNTs of different diameters via π‐stacking. Supported by spectral, electrochemical, and computational studies, the established energy scheme revealed the possibility of sequential electron transfer. Systematic pump‐probe studies covering wide spatial and temporal scales provided evidence of CS from the initial1BODIPY* ultimately resulting in C60‐BODIPY‐SWCNT⋅+CS states of lifetimes in the 20‐microsecond range.

 
more » « less
NSF-PAR ID:
10379854
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Angewandte Chemie
Volume:
134
Issue:
49
ISSN:
0044-8249
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Electron donor–acceptor (DA) hybrids comprised of single‐wall carbon nanotubes (SWCNTs) are promising functional materials for light energy conversion. However, the DA hybrids built on SWCNTs have failed to reveal the much‐sought long‐lived charge separation (CS) due to the close proximity of the DA entities facilitating charge recombination. Here, we address this issue and report an elegant strategy to build multi‐modular DA hybrids capable of producing long‐lived CS states. For this, a nano tweezer featuring V‐shape configured BODIPY was synthesized to host SWCNTs of different diameters via π‐stacking. Supported by spectral, electrochemical, and computational studies, the established energy scheme revealed the possibility of sequential electron transfer. Systematic pump‐probe studies covering wide spatial and temporal scales provided evidence of CS from the initial1BODIPY* ultimately resulting in C60‐BODIPY‐SWCNT⋅+CS states of lifetimes in the 20‐microsecond range.

     
    more » « less
  2. Abstract

    BF2‐chelated dipyrromethene, BODIPY, was functionalized to carry two styryl crown ether tails and a secondary electron donor at themesoposition. By using a “two‐point” self‐assembly strategy, a bis‐alkylammonium‐functionalized fullerene (C60) was allowed to self‐assemble the crown ether voids of BODIPY to obtain multimodular donor–acceptor conjugates. As a consequence of the two‐point binding, the 1:1 stoichiometric complexes formed yielded complexes of higher stability in which fluorescence of BODIPY was found to be quenched; this suggested the occurrence of excited‐state processes. The geometry and electronic structure of the self‐assembled complexes were derived from B3LYP/3‐21G(*) methods in which no steric constraints between the entities was observed. An energy‐level diagram was established by using spectral, electrochemical, and computational results to help understand the mechanistic details of excited‐state processes originating from1bis‐styryl‐BODIPY*. Femtosecond transient absorbance studies were indicative of the formation of an exciplex state prior to the charge‐separation process to yield a bis‐styryl‐BODIPY.+–C60.radical ion pair. The time constants for charge separation were generally lower than charge‐recombination processes. The present studies bring out the importance of multimode binding strategies to obtain stable self‐assembled donor–acceptor conjugates capable of undergoing photoinduced charge separation needed in artificial photosynthetic applications.

     
    more » « less
  3. Abstract

    The effect of donor‐acceptor distance in controlling the rate of electron transfer in axially linked silicon phthalocyanine‐C60dyads has been investigated. For this, two C60‐SiPc‐C60dyads,1and2, varying in their donor‐acceptor distance, have been newly synthesized and characterized. In the case of C60‐SiPc‐C601where the SiPc and C60are separated by a phenyl spacer, faster electron transfer was observed withkcsequal to 2.7×109 s−1in benzonitrile. However, in the case of C60‐SiPc‐C602, where SiPc and C60are separated by a biphenyl spacer, a slower electron transfer rate constant,kcs=9.1×108 s−1, was recorded. The addition of an extra phenyl spacer in2increased the donor‐acceptor distance by ∼4.3 Å, and consequently, slowed down the electron transfer rate constant by a factor of ∼3.7. The charge separated state lasted over 3 ns, monitoring time window of our femtosecond transient spectrometer. Complimentary nanosecond transient absorption studies revealed formation of3SiPc* as the end product and suggested the final lifetime of the charge separated state to be in the 3–20 ns range. Energy level diagrams established to comprehend these mechanistic details indicated that the comparatively high‐energy SiPc.+‐C60.−charge separated states (1.57 eV) populated the low‐lying3SiPc* (1.26 eV) prior returning to the ground state.

     
    more » « less
  4. Abstract

    Two wide‐band‐capturing donor‐acceptor conjugates featuring bis‐styrylBODIPY and perylenediimide (PDI) have been newly synthesized, and the occurrence of ultrafast excitation transfer from the1PDI* to BODIPY, and a subsequent electron transfer from the1BODIPY* to PDI have been demonstrated. Optical absorption studies revealed panchromatic light capture but offered no evidence of ground‐state interactions between the donor and acceptor entities. Steady‐state fluorescence and excitation spectral recordings provided evidence of singlet‐singlet energy transfer in these dyads, and quenched fluorescence of bis‐styrylBODIPY emission in the dyads suggested additional photo‐events. The facile oxidation of bis‐styrylBODIPY and facile reduction of PDI, establishing their relative roles of electron donor and acceptor, were borne out by electrochemical studies. The electrostatic potential surfaces of the S1and S2states, derived from time‐dependent DFT calculations, supported excited charge transfer in these dyads. Spectro‐electrochemical studies on one‐electron‐oxidized and one‐electron‐reduced dyads and the monomeric precursor compounds were also performed in a thin‐layer optical cell under corresponding applied potentials. From this study, both bis‐styrylBODIPY⋅+and PDI⋅could be spectrally characterizes and were subsequently used in characterizing the electron‐transfer products. Finally, pump–probe spectral studies were performed in dichlorobenzene under selective PDI and bis‐styrylBODIPY excitation to secure energy and electron‐transfer evidence. The measured rate constants for energy transfer,kENT, were in the range of 1011 s−1, while the electron transfer rate constants,kET, were in the range of 1010 s−1, thus highlighting their potential use in solar energy harvesting and optoelectronic applications.

     
    more » « less
  5. Abstract

    A panchromatic triad, consisting of benzothiazole (BTZ) and BF2‐chelated boron‐dipyrromethene (BODIPY) moieties covalently linked to a zinc porphyrin (ZnP) core, has been synthesized and systematically characterized by using1H NMR spectroscopy, ESI‐MS, UV‐visible, steady‐state fluorescence, electrochemical, and femtosecond transient absorption techniques. The absorption band of the triad, BTZ‐BODIPY‐ZnP, and dyads, BTZ‐BODIPY and BODIPY‐ZnP, along with the reference compounds BTZ‐OMe, BODIPY‐OMe, and ZnP‐OMe exhibited characteristic bands corresponding to individual chromophores. Electrochemical measurements on BTZ‐BODIPY‐ZnP exhibited redox behavior similar to that of the reference compounds. Upon selective excitation of BTZ (≈290 nm) in the BTZ‐BODIPY‐ZnP triad, the fluorescence of the BTZ moiety is quenched, due to photoinduced energy transfer (PEnT) from1BTZ*to the BODIPY moiety, followed by quenching of the BODIPY emission due to sequential PEnT from the1BODIPY* moiety to ZnP, resulting in the appearance of the ZnP emission, indicating the occurrence of a two‐step singlet–singlet energy transfer. Further, a supramolecular tetrad, BTZ‐BODIPY‐ZnP:ImC60, was formed by axially coordinating the triad with imidazole‐appended fulleropyrrolidine (ImC60), and parallel steady‐state measurements displayed the diminished emission of ZnP, which clearly indicated the occurrence of photoinduced electron transfer (PET) from1ZnP* to ImC60. Finally, femtosecond transient absorption spectral studies provided evidence for the sequential occurrence of PEnT and PET events, namely,1BTZ*‐BODIPY‐ZnP:ImC60→BTZ‐1BODIPY*‐ZnP:ImC60→BTZ‐BODIPY‐1ZnP*:ImC60→BTZ‐BODIPY‐ZnP.+:ImC60.−in the supramolecular tetrad. The evaluated rate of energy transfer,kEnT, was found to be 3–5×1010 s−1, which was slightly faster than that observed in the case of BODIPY‐ZnP and BTZ‐BODIPY‐ZnP, lacking the coordinated ImC60. The rate constants for charge separation and recombination,kCSandkCR, respectively, calculated by monitoring the rise and decay of C60.−were found to be 5.5×1010and 4.4×108 s−1, respectively, for the BODIPY‐ZnP:ImC60triad, and 3.1×1010and 4.9×108 s−1, respectively, for the BTZ‐BODIPY‐ZnP:ImC60tetrad. Initial excitation of the tetrad, promoting two‐step energy transfer and a final electron‐transfer event, has been successfully demonstrated in the present study.

     
    more » « less