Energy transfer in the azobenzene-naphthalene light harvesting system

Dalia Abdallah, Jamie Whelan, Julian M. Dust, Shmaryahu Hoz, Erwin Buncel

Research output: Contribution to journalArticle

Abstract

We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2. These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET. Photophysical data, including initial rate constants for photoisomerization (trans to cis, t-1 →c-1, and cis to trans, c-1 →t-1), the relevant c-1 →t-1 quantum yields, and fluorescence quenching with free naphthalene, 3, as D were measured. Therefore, (1) irradiation of 3 at (270 nm) to give 3* generates fluorescence at 340 nm that is 65% quenched by the trans isomer of 2 (t-2) and 15% quenched by c-1. Comparable naphthalenic fluorescence of c-1 (LH model A) is quenched beyond detectability. (2) Rates of photoisomerization were determined spectrophotometrically for c-1 →t-1 starting from the c-1 photostationary state as compared with the c-2 →t-2 benchmark. (3) Progressing toward more complex LH systems, the initial rate constants, k, for c-4 →t-4 (LH model B), were measured as compared with the c-5 →t-5 benchmark. (4) A new criterion for ET (D → A) efficiency emerges that combines h (c → t) ratios and light absorption on irradiation (at 270 nm) ratios. On the basis of this new criterion, both 1 and 4 exhibit virtually quantitative ET efficiency. (5) Quenching data of 1 (almost complete) and 4 (95%) and ET are discussed by comparison with the relevant model azoarenes, 2 and 5, respectively, and in terms of geometrical considerations. Implications for the extension of the results, notably the new criterion for ET efficiency, in these LH models A and B to the polymer and block copolymer D-(CRR′)n - A and D - (CRR′)n - A - (CR″R‴)m - D targets are considered.

Original languageEnglish (US)
Pages (from-to)6640-6647
Number of pages8
JournalJournal of Physical Chemistry A
Volume113
Issue number24
DOIs
StatePublished - Jun 18 2009

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naphthalene
Energy transfer
energy transfer
Photoisomerization
Fluorescence
fluorescence
Quenching
Rate constants
quenching
Irradiation
Molecules
irradiation
Quantum yield
electromagnetic absorption
block copolymers
complex systems
methylene
Isomers
Light absorption
Block copolymers

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Energy transfer in the azobenzene-naphthalene light harvesting system. / Abdallah, Dalia; Whelan, Jamie; Dust, Julian M.; Hoz, Shmaryahu; Buncel, Erwin.

In: Journal of Physical Chemistry A, Vol. 113, No. 24, 18.06.2009, p. 6640-6647.

Research output: Contribution to journalArticle

Abdallah, Dalia ; Whelan, Jamie ; Dust, Julian M. ; Hoz, Shmaryahu ; Buncel, Erwin. / Energy transfer in the azobenzene-naphthalene light harvesting system. In: Journal of Physical Chemistry A. 2009 ; Vol. 113, No. 24. pp. 6640-6647.
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abstract = "We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2. These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET. Photophysical data, including initial rate constants for photoisomerization (trans to cis, t-1 →c-1, and cis to trans, c-1 →t-1), the relevant c-1 →t-1 quantum yields, and fluorescence quenching with free naphthalene, 3, as D were measured. Therefore, (1) irradiation of 3 at (270 nm) to give 3* generates fluorescence at 340 nm that is 65{\%} quenched by the trans isomer of 2 (t-2) and 15{\%} quenched by c-1. Comparable naphthalenic fluorescence of c-1 (LH model A) is quenched beyond detectability. (2) Rates of photoisomerization were determined spectrophotometrically for c-1 →t-1 starting from the c-1 photostationary state as compared with the c-2 →t-2 benchmark. (3) Progressing toward more complex LH systems, the initial rate constants, k, for c-4 →t-4 (LH model B), were measured as compared with the c-5 →t-5 benchmark. (4) A new criterion for ET (D → A) efficiency emerges that combines h (c → t) ratios and light absorption on irradiation (at 270 nm) ratios. On the basis of this new criterion, both 1 and 4 exhibit virtually quantitative ET efficiency. (5) Quenching data of 1 (almost complete) and 4 (95{\%}) and ET are discussed by comparison with the relevant model azoarenes, 2 and 5, respectively, and in terms of geometrical considerations. Implications for the extension of the results, notably the new criterion for ET efficiency, in these LH models A and B to the polymer and block copolymer D-(CRR′)n - A and D - (CRR′)n - A - (CR″R‴)m - D targets are considered.",
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AU - Buncel, Erwin

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N2 - We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2. These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET. Photophysical data, including initial rate constants for photoisomerization (trans to cis, t-1 →c-1, and cis to trans, c-1 →t-1), the relevant c-1 →t-1 quantum yields, and fluorescence quenching with free naphthalene, 3, as D were measured. Therefore, (1) irradiation of 3 at (270 nm) to give 3* generates fluorescence at 340 nm that is 65% quenched by the trans isomer of 2 (t-2) and 15% quenched by c-1. Comparable naphthalenic fluorescence of c-1 (LH model A) is quenched beyond detectability. (2) Rates of photoisomerization were determined spectrophotometrically for c-1 →t-1 starting from the c-1 photostationary state as compared with the c-2 →t-2 benchmark. (3) Progressing toward more complex LH systems, the initial rate constants, k, for c-4 →t-4 (LH model B), were measured as compared with the c-5 →t-5 benchmark. (4) A new criterion for ET (D → A) efficiency emerges that combines h (c → t) ratios and light absorption on irradiation (at 270 nm) ratios. On the basis of this new criterion, both 1 and 4 exhibit virtually quantitative ET efficiency. (5) Quenching data of 1 (almost complete) and 4 (95%) and ET are discussed by comparison with the relevant model azoarenes, 2 and 5, respectively, and in terms of geometrical considerations. Implications for the extension of the results, notably the new criterion for ET efficiency, in these LH models A and B to the polymer and block copolymer D-(CRR′)n - A and D - (CRR′)n - A - (CR″R‴)m - D targets are considered.

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