Abstract
In order to identify optimal conditions for singlet fission, we are examining the photophysics of 1,3-diphenylisobenzofuran (1) dimers covalently coupled in various ways. In the two dimers studied presently, the coupling is weak. The subunits are linked via the para position of one of the phenyl substituents, in one case (2) through a CH2 linker and in the other (3) directly, but with methyl substituents in ortho positions forcing a nearly perpendicular twist between the two joint phenyl rings. The measurements are accompanied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Although in neat solid state, 1 undergoes singlet fission with a rate constant higher than 1011 s-1; in nonpolar solutions of 2 and 3, the triplet formation rate constant is less than 106 s-1 and fluorescence is the only significant event following electronic excitation. In polar solvents, fluorescence is weaker because the initial excited singlet state S1 equilibrates by sub-nanosecond charge transfer with a nonemissive dipolar species in which a radical cation of 1 is attached to a radical anion of 1. Most of this charge transfer species decays to S0, and some is converted into triplet T1 with a rate constant near 108 s-1. Experimental uncertainties prevent an accurate determination of the number of T1 excitations that result when a single S1 excitation changes into triplet excitation. It would be one if the charge-transfer species undergoes ordinary intersystem crossing and two if it undergoes the second step of two-step singlet fission. The triplet yield maximizes below room temperature to a value of roughly 9% for 3 and 4% for 2. Above ∼360 K, some of the S1 molecules of 3 are converted into an isomeric charge-transfer species with a shorter lifetime, possibly with a twisted intramolecular charge transfer (TICT) structure. This is not observed in 2.
| Original language | English |
|---|---|
| Pages (from-to) | 4680-4695 |
| Number of pages | 16 |
| Journal | Journal of Physical Chemistry B |
| Volume | 117 |
| Issue number | 16 |
| DOIs | |
| Publication status | Published - Apr 25 2013 |
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ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Materials Chemistry
- Surfaces, Coatings and Films
Cite this
Toward designed singlet fission : Solution photophysics of two indirectly coupled covalent dimers of 1,3-diphenylisobenzofuran. / Johnson, Justin C.; Akdag, Akin; Zamadar, Matibur; Chen, Xudong; Schwerin, Andrew F.; Paci, Irina; Smith, Millicent B.; Havlas, Zdeněk; Miller, John R.; Ratner, Mark A; Nozik, Arthur J.; Michl, Josef.
In: Journal of Physical Chemistry B, Vol. 117, No. 16, 25.04.2013, p. 4680-4695.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Toward designed singlet fission
T2 - Solution photophysics of two indirectly coupled covalent dimers of 1,3-diphenylisobenzofuran
AU - Johnson, Justin C.
AU - Akdag, Akin
AU - Zamadar, Matibur
AU - Chen, Xudong
AU - Schwerin, Andrew F.
AU - Paci, Irina
AU - Smith, Millicent B.
AU - Havlas, Zdeněk
AU - Miller, John R.
AU - Ratner, Mark A
AU - Nozik, Arthur J.
AU - Michl, Josef
PY - 2013/4/25
Y1 - 2013/4/25
N2 - In order to identify optimal conditions for singlet fission, we are examining the photophysics of 1,3-diphenylisobenzofuran (1) dimers covalently coupled in various ways. In the two dimers studied presently, the coupling is weak. The subunits are linked via the para position of one of the phenyl substituents, in one case (2) through a CH2 linker and in the other (3) directly, but with methyl substituents in ortho positions forcing a nearly perpendicular twist between the two joint phenyl rings. The measurements are accompanied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Although in neat solid state, 1 undergoes singlet fission with a rate constant higher than 1011 s-1; in nonpolar solutions of 2 and 3, the triplet formation rate constant is less than 106 s-1 and fluorescence is the only significant event following electronic excitation. In polar solvents, fluorescence is weaker because the initial excited singlet state S1 equilibrates by sub-nanosecond charge transfer with a nonemissive dipolar species in which a radical cation of 1 is attached to a radical anion of 1. Most of this charge transfer species decays to S0, and some is converted into triplet T1 with a rate constant near 108 s-1. Experimental uncertainties prevent an accurate determination of the number of T1 excitations that result when a single S1 excitation changes into triplet excitation. It would be one if the charge-transfer species undergoes ordinary intersystem crossing and two if it undergoes the second step of two-step singlet fission. The triplet yield maximizes below room temperature to a value of roughly 9% for 3 and 4% for 2. Above ∼360 K, some of the S1 molecules of 3 are converted into an isomeric charge-transfer species with a shorter lifetime, possibly with a twisted intramolecular charge transfer (TICT) structure. This is not observed in 2.
AB - In order to identify optimal conditions for singlet fission, we are examining the photophysics of 1,3-diphenylisobenzofuran (1) dimers covalently coupled in various ways. In the two dimers studied presently, the coupling is weak. The subunits are linked via the para position of one of the phenyl substituents, in one case (2) through a CH2 linker and in the other (3) directly, but with methyl substituents in ortho positions forcing a nearly perpendicular twist between the two joint phenyl rings. The measurements are accompanied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Although in neat solid state, 1 undergoes singlet fission with a rate constant higher than 1011 s-1; in nonpolar solutions of 2 and 3, the triplet formation rate constant is less than 106 s-1 and fluorescence is the only significant event following electronic excitation. In polar solvents, fluorescence is weaker because the initial excited singlet state S1 equilibrates by sub-nanosecond charge transfer with a nonemissive dipolar species in which a radical cation of 1 is attached to a radical anion of 1. Most of this charge transfer species decays to S0, and some is converted into triplet T1 with a rate constant near 108 s-1. Experimental uncertainties prevent an accurate determination of the number of T1 excitations that result when a single S1 excitation changes into triplet excitation. It would be one if the charge-transfer species undergoes ordinary intersystem crossing and two if it undergoes the second step of two-step singlet fission. The triplet yield maximizes below room temperature to a value of roughly 9% for 3 and 4% for 2. Above ∼360 K, some of the S1 molecules of 3 are converted into an isomeric charge-transfer species with a shorter lifetime, possibly with a twisted intramolecular charge transfer (TICT) structure. This is not observed in 2.
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UR - http://www.scopus.com/inward/citedby.url?scp=84876758520&partnerID=8YFLogxK
U2 - 10.1021/jp310979q
DO - 10.1021/jp310979q
M3 - Article
C2 - 23383860
AN - SCOPUS:84876758520
VL - 117
SP - 4680
EP - 4695
JO - Journal of Physical Chemistry B Materials
JF - Journal of Physical Chemistry B Materials
SN - 1520-6106
IS - 16
ER -