- Thiol-Activatable Triplet-Triplet Annihilation Upconversion with Maleimide-Perylene as the Caged Triplet Acceptor/Emitter
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Efficient thiol-activated triplet-triplet annihilation (TTA) upconversion system was devised with maleimide-caged perylene (Py-M) as the thiol-activatable triplet acceptor/emitter and with diiodoBodipy as the triplet photosensitizer. The photophysical processes were studied with steady-state UV-vis absorption spectroscopy, fluorescence spectroscopy, electrochemical properties, and nanosecond transient absorption spectroscopy. The triplet acceptor/emitter Py-M shows week fluorescence (φF = 0.8%), and no upconversion (φUC = 0%) was observed. The quenching of fluorescence of Py-M is due to photoinduced electron-transfer (PET) process from perylene to maleimide-caging unit, which quenches the singlet excited state of perylene. The fluorescence of Py-M was enhanced by 200-fold (φF = 97%) upon addition of thiols such as 2-mercaptoethanol, and the φUC was increased to 5.9%. The unique feature of this thiol-activated TTA upconversion is that the activation is based on addition reaction of the thiols with the caged acceptor/emitter, and no side products were formed. The previously reported cleavage approach gives side products which are detrimental to the TTA upconversion. With nanosecond transient absorption spectroscopy, we found that the triplet excited state of Py-M was not quenched by any PET process, which is different from singlet excited state (fluorescence) of Py-M. The results are useful for study of the triplet excited states of organic chromophores and for activatable TTA upconversion.
- Mahmood, Zafar,Zhao, Jianzhang
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- Molecular implementation of sequential and reversible logic through photochromic energy transfer switching
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Photochromic spiropyrans modified with fluorophores were investigated as molecular platforms for the achievement of fluorescence switching through modulation of energy transfer. The dyads were designed in such a way that energy transfer is only observed for the open forms of the photochrome (merocyanine and protonated merocyanine), whereas the closed spiropyran is inactive as an energy acceptor. This was made possible through a deliberate choice of fluorophores (4-amino-1,8-naphthalimide, dansyl, and perylene) that produce zero spectral overlap with the spiro form and considerable overlap for the merocyanine forms. From the Foerster theory, energy transfer is predicted to be highly efficient and in some cases of 100 % efficiency. The combined switching by photonic (light of I>530 nm) and chemical (base) inputs enabled the creation of a sequential logic device, which is the basic element of a keypad lock. Furthermore, in combination with an anthracene-based acidochromic fluorescence switch, a reversible logic device was designed. This enables the unambiguous coding of different input combinations through multicolour fluorescence signalling. All devices can be conveniently reset to their initial states and repeatedly cycled. Copyright
- Remon, Patricia,Hammarson, Martin,Li, Shiming,Kahnt, Axel,Pischel, Uwe,Andreasson, Joakim
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p. 6492 - 6500
(2011/08/06)
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- Pyrenylmethyldeoxyadenosine: A 3′-cap for universal DNA hybridization probes
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A ligand that stabilizes a three-dimensional structure can be expected to have a positive effect on the specificity with which this structure is formed. Here we report on a ligand covalently linked to an oligonucleotide that increases duplex stability, but decreases base-pairing selectivity at the terminus. The ligand consists of a dangling 2′-deoxyadenosine residue with a pyrenylmethyl substituent at the N6-position, that is, a deoxynucleoside with a covalently linked polycyclic aromatic hydrocarbon (PAH). In the presence of the pyrene-bearing nucleosides the UV melting point (ΔTm) of duplexes increases by up to 29.1°C. The modified residue lowers the base-pairing fidelity at the terminal and penultimate position of duplexes with a depression in ΔΔTm observable in 20 out of 24 sequence contexts tested. The effect can be rationalized based on a modeled three-dimensional structure. The results are significant for the understanding of base-pairing fidelity in DNA duplexes as modulated by the presence of a polycyclic aromatic hydrocarbon. The fidelity-decreasing effect may be useful for universal hybridization probes that bind to a broader range of sequences than conventional oligonucleotides.
- Printz, Michael,Richert, Clemens
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experimental part
p. 3390 - 3402
(2010/01/19)
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