The effect of acceptor strength on excited state charge‐transfer (CT) and charge separation (CS) in central phenothiazine (PTZ) derived symmetric 1 (PTZ-(TCBD-TPA)2) and asymmetric, 2 (PTZ-(TCBD/DCNQ-TPA)2) push-pull conjugates, in which triphenylamine (TPA) act as end capping and 1,1,4,4–tetracyanobuta–1,3–diene (TCBD) and cyclohexa–2,5–diene–1,4–ylidene–expanded TCBD (DCNQ) act as electron acceptor units is reported. Due to strong push-pull effects, intramolecular charge transfer (ICT) was observed in the ground state extending the absorption into the near-IR region. Electrochemical, spectroelectrochemical and computational studies coupled with energy level calculations predicted both 1 and 2 to be efficient candidates for ultrafast charge transfer. Subsequent femtosecond transient absorption studies along with global target analysis, performed in both polar and nonpolar solvents, confirmed such processes in which the CS was efficient in asymmetric 2 having both TCBD and DCNQ acceptors in polar benzonitrile while in toluene, only charge transfer was witnessed. This work highlights significance of number and strength of electron acceptor entities and the role of solvent polarity in multi-modular push-push systems to achieve ultrafast CS.
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Far‐Red Excitation Induced Electron Transfer in Bis Donor‐AzaBODIPY Push‐Pull Systems; Role of Nitrogenous Donors in Promoting Charge Separation
A far‐red absorbing sensitizer, BF2‐chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push‐pull systems linked with different nitrogenous electron donors, viz.,
- NSF-PAR ID:
- 10444113
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 29
- Issue:
- 53
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Push–pull systems comprising of triphenylamine–tetracyanobutadiene (TPA‐TCBD), a high‐energy charge‐transfer species, are linked to a near‐IR sensitizer, azaBODIPY, for promoting excited‐state CS. These systems revealed panchromatic absorption owing to intramolecular CT and near‐IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs‐TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA‐TCBD entities in
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Abstract Push–pull systems comprising of triphenylamine–tetracyanobutadiene (TPA‐TCBD), a high‐energy charge‐transfer species, are linked to a near‐IR sensitizer, azaBODIPY, for promoting excited‐state CS. These systems revealed panchromatic absorption owing to intramolecular CT and near‐IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs‐TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA‐TCBD entities in
3 seem to prolong lifetime of the CS state. We have been successful in demonstrating efficient CS upon both high‐energy CT and low‐energy near‐IR excitations, signifying importance of these push–pull systems for optoelectronic applications operating in the wide optical window. -
Novel push-pull systems comprised of triphenylamine-tetracyanobutadiene, a high-energy CT species is linked to a near-IR sensitizer, azaBODIPY, for promoting excited state CS. These new systems revealed panchromatic absorption due to combined effect of intramolecular CT, and near-IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs-TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA-TCBD entities in 3 seem to prolong lifetime of the CS state. Importantly, we have been successful in demonstrating efficient CS upon both high-energy CT and low-energy near-IR excitations, signifying importance of these push-pull systems for optoelectronic applications operating in the wide optical window.more » « less
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