Photoisomerization of all-trans-1,6-Diphenyl-1,3,5-hexatriene. Temperature and Deuterium Isotope Effects

Saltiel, Jack; Krishnamoorthy, G.; Huang, Zhiyuan; Ko, Dong-Hoon; Wang, Shujun

doi:10.1021/jp021540g

Cited by 18 publications

(42 citation statements)

References 69 publications

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“…The same phenomenon was also observed for the solvent-dependent photoisomerization of the terminal double bond in all-trans-1,6-diphenyl-1,3,5-hexatriene. 35 The preexponential factor is also larger for 2H in acetonitrile/THF (9:1) than in methylcyclohexane (Table 4). Whether this phenomenon is common for all the aminostilbenes 1 and 2 requires more thorough investigations, which are in progress in our laboratory, and the results will be reported in due course.…”

Section: Discussionmentioning

confidence: 95%

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

et al. 2006

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The electronic absorption and fluorescence spectra, quantum yields for fluorescence (Phi(f)) and trans --> cis photoisomerization (Phi(tc)), and fluorescence lifetimes of trans-4-(N-arylamino)-4'-cyanostilbenes (2H, 2Me, 2OM, 2CN, and 2Xy with aryl = phenyl, 4-methylphenyl, 4-methoxyphenyl, 4-cyanophenyl, and 2,5-dimethylphenyl, respectively), trans-4-(N-methyl-N-phenylamino)-4'-cyanostilbene (2MP), trans-4-(N,N-diphenylamino)-4'-cyanostilbene (2PP), trans-4-(N-methyl-N-phenylamino)-4'-nitrostilbene (3MP), and three ring-bridged analogues 2OMB, 2MPB, and 3MPB are reported. Whereas fluorescence and torsion of the central double bond account for the excited decay of the majority of these donor-acceptor substituted stilbenes in both nonpolar and polar solvents (i.e., Phi(f) + 2Phi(tc) approximately 1), exceptions are observed for 2OM, 3MP, and 3MPB in solvents more polar than THF and for 2Me and 2MP in acetonitrile as a result of the formation of a weakly fluorescent and isomerization-free twisted intramolecular charge transfer (TICT) state (i.e., Phi(f) + 2Phi(tc) << 1). The TICT state for 2OM, 2Me, and 2MP results from the torsion of the stilbenyl-anilino C-N single bond, but the torsion of the styryl-anilino C-C bond is more likely to be responsible for the TICT state formation of 3MP and 3MPB. In conjunction with the behavior of aminostilbenes 1, a guideline based on the values of Phi(f) and Phi(tc) for judging the importance of a TICT state for trans-stilbenes is provided. Accordingly, the TICT state formation is unimportant for the excited decay of trans-4-(N,N-dimethylamino)-4'-cyanostilbene (DCS). In contrast, our results support the previously proposed TICT state for trans-4-(N,N-dimethylamino)-4'-nitrostilbene (DNS).

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Section: Discussionmentioning

confidence: 95%

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

et al. 2006

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“…Sources and purification procedures for all-trans-1,6-diphenyl-1,3,5-hexatriene (100.0%, HPLC), benzophenone, trans-stilbene, anthracene, and acetonitrile have been described (8,10). Acetonitrile was used as received or purified using a known procedure (15).…”

Section: Methodsmentioning

confidence: 99%

“…Changing the solvent from methylcyclohexane (MCH) to acetonitrile (AN) increases the rates of photoisomerization in the singlet excited state manifold, the increase being especially pronounced (20-fold) at the terminal double bonds (8,10), thereby decreasing the singlet excited state lifetime and the contribution of the competing decay channels of fluorescence (φ f = 0.65 and 0.27 at 20°C in MCH (11) and AN (10), respectively) and intersystem crossing (φ is = 0.029 and 0.010 at 20°C in MCH (12) and AN (13,14), respectively). Photoisomerization in the ttt → ctt direction in AN is almost entirely a singlet excited state process (98%) that is attenuated by a factor of 1.36 on deuteration of the olefinic hydrogens of the terminal double bond (10).…”

Section: Introductionmentioning

confidence: 99%

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Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Saltiel¹,

Krishnamoorthy²,

Huang³

et al. 2003

Can. J. Chem.

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Irradiation of all-trans-1,6-diphenyl-1,3,5-hexatriene (ttt-DPH) in degassed acetonitrile (AN) gives ctt-and tct-DPH, relatively inefficiently, mainly via isomerization in the singlet excited state. The triplet contribution to the photoisomerization is small due to a very low intersystem crossing yield (φ is = 0.01). Central bond isomerization is quenched in the presence of air by a factor of 1.4, consistent with the expected quenching of the lowest singlet and triplet excited states by oxygen. However, the presence of air enhances terminal bond photoisomerization by nearly twofold. Triplet-sensitized ttt-DPH photoisomerization favors tct-DPH formation and is quenched by oxygen. It follows that the interaction of singlet-excited ttt-DPH with O 2 suppresses isomerization to tct-DPH but opens a new isomerization pathway to ctt-DPH. The presence of dimethylfuran, a singlet O 2 trap, has no effect on the photoisomerization, eliminating the possible involvement of singlet O 2 in this new reaction. ttt-DPH radical cations are ruled out as intermediates because the presence of fumaronitrile, which leads to their formation, suppresses both central and terminal bond photoisomerizations. In contrast to acetonitrile, ctt-DPH formation is quenched by oxygen in methylcyclohexane, suggesting the requirement of a polar environment. Strikingly different deuterium isotope effects distinguish the direct and O 2 -induced photoisomerization pathways. A comparative study of ttt-DPH-d 0 with ttt-DPH-d 2 and ttt-DPH-d 4 , involving deuteration of one and both terminal double bonds, reveals an inverse kinetic isotope effect (k H ox /k D ox = 0.92) for the O 2 -induced reaction. An attractive mechanism for the new oxygen-induced photoisomerization involves charge transfer from the S 1 state of ttt-DPH to oxygen followed by collapse of the exciplex to either a zwitterionic or a biradicaloid species through bonding at one of the benzylic positions. Rotation about the new single bond in this intermediate followed by reversion to DPH and O 2 gives the observed result. 679Résumé : L'irradiation du 1,6-diphénylhexa-1,3,5-triène complètement trans (ttt-DPH), dans de l'acétonitrile dégazé (AN) conduit d'une façon relativement inefficace à la formation des ctt-et tct-DPH, principalement par le biais d'une isomérisation dans l'état excité singulet. La contribution triplet à la photoisomérisation est faible en raison du très faible rendement du passage intersystème (φ is = 0,01). L'isomérisation de la liaison centrale est piégée en présence d'air par un facteur de 1,4 qui est en accord le piégeage par l'oxygène des états excités singulet et triplet les plus bas. Toutefois, la présence d'air augmente la photoisomérisation de la liaison terminale par un facteur égal pratiquement à deux. La photoisomérisation du ttt-DPH sensibilisée au niveau triplet favorise la formation de tct-DPH et elle est piégée par l'oxygène. Il en découle que l'interaction de l'oxygène avec le ttt-DPH excité à l'état singulet supprime l'isomérisation en tct-DPH mais qu'elle co...

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“…Unlike the S 1 -state, the energy of the S 2 -state is influenced by the solvent, which leads to a solvent dependent S 1 -S 2 energy gap and because of the state mixing to a solvent dependent S 1 radiative rate [14]. Saltiel et al presented evidence showing that the fluorescence spectrum of DPH not only consists of the combined S 1 /S 2 -emission, but also of emission from the s-cis conformers of DPH [23][24][25][26][27]. Catalán confirmed the influence of s-cis conformers on the emission spectra also for other minicarotenes by calculations [28,29].…”

Section: Introductionmentioning

confidence: 99%

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S1-State Competes with Formation of O2 Contact Charge Transfer Complex

Hunger¹,

Kleinermanns²

2013

OJPC

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The fluorescence kinetics of 1,6-diphenyl-1,3,5-hexatriene (DPH) dissolved in cyclohexane was investigated as a function of temperature, concentration and 355 nm excitation pulse energy. At concentrations above 2.5 μM and excitation energies above 1 mJ a long-lived, very intense emission, which appears within less than 5 ns and lasts up to 70 ns, is observed. During the first 50 ns the decay does not follow an exponential but rather a linear behaviour. In oxygen saturated solutions the long-lived emission is suppressed and solely short-lived fluorescence with τ < 5 ns can be detected. A kinetic simulation was performed, based on a model whereupon the long-lived emission originates from the S 1 -state and competes with the formation of DPH-O 2 contact charge-transfer complexes and intersystem crossing which both quench the fluorescence. Our investigations show that even the small amount of oxygen dissolved in nitrogen saturated solutions has a distinct influence on the fluorescence kinetics of DPH.

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Photoisomerization of all-trans-1,6-Diphenyl-1,3,5-hexatriene. Temperature and Deuterium Isotope Effects

Cited by 18 publications

References 69 publications

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex

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Photoisomerization of all-trans-1,6-Diphenyl-1,3,5-hexatriene. Temperature and Deuterium Isotope Effects

Cited by 18 publications

References 69 publications

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

Photoinduced Single- versus Double-Bond Torsion in Donor−Acceptor−Substituted trans-Stilbenes

Stereoselective O2-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S&lt;sub&gt;1&lt;/sub&gt;-State Competes with Formation of O&lt;sub&gt;2&lt;/sub&gt; Contact Charge Transfer Complex

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Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex