Photoenolization via excited state double proton transfer induces “turn on” fluorescence in diformyl diaryl dipyrromethane
K.C.G. SreedeviAjesh P. ThomasK. H. AparnaRenuka PradhanM. L. P. ReddyUpakarasamy LourderajA. Srinivasan
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A light triggered enolization in diformyl diaryl dipyrromethane by excited state dual proton transfer (ESDPT) induces “turn on” fluorescence.Keywords:
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Diarylethenes 1a-4a, having a fluorescent 2,4,5-triphenylimidazole chromophore in the aryl group, were synthesized. Upon excitation of the triphenylimidazole chromophore with 366 nm, 1a-4a underwent photocyclization reactions, and the solutions containing 1a-4a changed color from colorless to red-purple or to blue. The colors disappeared by irradiation with visible (lambda > 480 nm) light. The fluorescence intensity of the solutions also reversibly changed with the photochromic reactions. The fluorescence quantum yields of 1a, 2a, 3a, and 4a were determined to be 4.6, 7.7, 9.1, and 8.4%, respectively. The fluorescence quantum yields decreased with the increase in photocyclization quantum yields.
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Abstract A new design strategy to control the efficiency of a photocleavage reaction based on changing the nature of the excited state is presented. A novel class of photoactive compounds has been synthesized by combining the classical o ‐nitrobenzyl scaffold with an environmentally sensitive dye, 4‐amino‐nitrobenzothiazole. Irradiation in a polar solvent led to an excited state that was inoperative for photochemistry whereas excitation in a nonpolar solvent led to an excited state that was photochemically active. While our design hypothesis tests true for the on/off control of a photochemical process, an alternative photochemical ring‐opening of the heterocycle appears to be the preferred process in contrast to the intended photocleavage process.
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A new series of fluorophores, 5-methoxy-2-(2-, 3- or 4-pyridyl)thiazoles (2-, 3- or 4-MPT, respectively), were synthesized and their photophysical properties investigated. 2- and 4-MPT are highly fluorescent in polar solvents. Combined with theoretical calculations, studies of the excited state lifetimes in different solvents reveal that their fluorescence mainly results from the internal charge transfer excited state. Acidobasic properties of their ground states and excited states were studied with steady and transient fluorescence spectroscopy. 2- and 4-MPT displayed a pH sensitive fluorescent behavior with a dual-emission in the range 2 to 6 in an aqueous system.
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<p>A strategy to control the efficiency of a photocleavage reaction based on changing the nature of the excited state is presented. A novel class of photoactive compounds has been synthesized by combining the classical o-nitrobenzyl scaffold with an environmentally sensitive dye, 4-amino-nitrobenzothiazole. Irradiation in a polar solvent lead to an excited state that is inoperative for photochemistry whereas excitation in a nonpolar solvent lead to an excited state that is photochemically active. A photochemical degradation appears to be the preferred process in contrast to the intended photocleavage process.</p>
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This paper presents a strategy for improving the all-visible-light switching response of turn-on mode fluorescent diarylethene derivatives. Introduction of neopentyl or isobutyl substituents at the reactive carbons (2- and 2'-positions) of an oxidized bis(benzothienyl)perfluorocyclopentene derivative, which undergoes both cyclization and cycloreversion reactions upon irradiation with visible light, was effective in increasing the cycloreversion quantum yield by one or two orders of magnitude in comparison with the yield of an ethyl-substituted derivative. Any significant influence on the cyclization and fluorescence quantum yields was not observed by the introduction of neopentyl or isobutyl substituents.
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Photochromic dithienylethene moieties were covalently attached to fluorescent 4,4-difluoro-8-(4'-iodophenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (iodo-BODIPY) via a phenylacetylene linker. UV light induced isomerization of the photochrome results in significant decrease in fluorescence intensity. This fluorescence can be recovered with visible light. Steady-state fluorescence measurements demonstrate that the emission of the dye can be modulated by external light. An intramolecular energy transfer mechanism accounts for the fluorescence quenching in the UV light produced isomers.
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The molecular structure and spectral properties of a novel acylhydrazone ligands 2-hydroxy-naphthaldehyde-5-chloro-salicyloylhydrazone (H3L) and its Sn metal complexes [(n-Bu2)Sn(HL)] in solution, crystal and thin films were investigated by using steady state and time resolved fluorescence spectrum. The experimental results show that for H3L, compared with it in solution, the fluorescence intensity is enhanced as it is crystal and thin films, the fluorescence peak is red-shift, and the excited state lifetime is longer. The transition energies of the unimolecule is 240.2 kJ x mol(-1). For (n-Bu2)Sn(HL), the fluorescence intensity is stronger as it is crystal than it is in solution and the fluorescence peak is red-shilft, the excited state lifetime is longer. The fluorescence is quenched as it is in thin films. The transition energies of the unimolecule is 230.4 kJ x mol(-1). The fluorescence intensity of (n-Bu2)Sn(HL) is four times higher than the H3L. The excited state lifetime of (n-Bu2) Sn(HL) is longer than H2L too. In theory, these phenomena could be explained by that with the increase of the conjugated system and the rigid construction, the fluorescence intensity is stronger and the excited state lifetime is longer.
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