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Conformationally dynamic ?-conjugation: probing structure-property relationships of fluorescent tris(N-salicylideneaniline)s.

ABSTRACT: We recently reported the design and synthesis of a series of conformationally dynamic chromophores that are built on the C(3)-symmetric tris(N-salicylideneaniline) platform. This system utilizes cooperative structural folding-unfolding motions for fluorescence switching, which is driven by the assembly and disassembly of hydrogen bonds between the rigid core and rotatable peripheral part of the molecule. Here, we report detailed time-resolved spectroscopic studies to investigate the structure-property relationships of a series of functionalized tris(N-salicylideneaniline)s. Time-resolved fluorescence decay spectroscopy was applied to determine the main relaxation mechanisms of these ?-extended fluorophores, and to address the effects of hydrogen bonding, steric constraints, and extension of the ?-conjugation on their relaxation dynamics. Our results agree well with the conformational switching model that was previously suggested from steady-state experiments. Notably, extension of the ?-conjugation from peripheral aryl groups resulted in the stabilization of the excited states, as evidenced by longer lifetimes and lower nonradiative decay constants. As a consequence, an increase in the fluorescence quantum yields was observed, which could be explained by the suppression of the torsional motions about the C-N bonds from an overall increase in the quinoid character of the excited states. A combination of time-resolved and steady-state techniques also revealed intermolecular interactions through ?-? stacking at higher concentrations, which provide additional de-excitation pathways that become more pronounced in solid samples.

SUBMITTER: Vieweger M

PROVIDER: S-EPMC3224823 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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Conformationally dynamic π-conjugation: probing structure-property relationships of fluorescent tris(N-salicylideneaniline)s.

Vieweger Mario M Jiang Xuan X Lim Young-Kwan YK Jo Junyong J Lee Dongwhan D Dragnea Bogdan B

The journal of physical chemistry. A 20111027 46

We recently reported the design and synthesis of a series of conformationally dynamic chromophores that are built on the C(3)-symmetric tris(N-salicylideneaniline) platform. This system utilizes cooperative structural folding-unfolding motions for fluorescence switching, which is driven by the assembly and disassembly of hydrogen bonds between the rigid core and rotatable peripheral part of the molecule. Here, we report detailed time-resolved spectroscopic studies to investigate the structure-pr ...[more]

PMID: 22004068

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Project description:Through the study of structure-property relationships using a combination of experimental and computational analyses, a number of phenoxazine derivatives have been developed as visible light absorbing, organic photoredox catalysts (PCs) with excited state reduction potentials rivaling those of highly reducing transition metal PCs. Time-dependent density functional theory (TD-DFT) computational modeling of the photoexcitation of N-aryl and core modified phenoxazines guided the design of PCs with absorption profiles in the visible regime. In accordance with our previous work with N, N-diaryl dihydrophenazines, characterization of noncore modified N-aryl phenoxazines in the excited state demonstrated that the nature of the N-aryl substituent dictates the ability of the PC to access a charge transfer excited state. However, our current analysis of core modified phenoxazines revealed that these molecules can access a different type of CT excited state which we posit involves a core substituent as the electron acceptor. Modification of the core of phenoxazine derivatives with electron-donating and electron-withdrawing substituents was used to alter triplet energies, excited state reduction potentials, and oxidation potentials of the phenoxazine derivatives. The catalytic activity of these molecules was explored using organocatalyzed atom transfer radical polymerization (O-ATRP) for the synthesis of poly(methyl methacrylate) (PMMA) using white light irradiation. All of the derivatives were determined to be suitable PCs for O-ATRP as indicated by a linear growth of polymer molecular weight as a function of monomer conversion and the ability to synthesize PMMA with moderate to low dispersity (dispersity less than or equal to 1.5) and initiator efficiencies typically greater than 70% at high conversions. However, only PCs that exhibit strong absorption of visible light and strong triplet excited state reduction potentials maintain control over the polymerization during the entire course of the reaction. The structure-property relationships established here will enable the application of these organic PCs for O-ATRP and other photoredox-catalyzed small molecule and polymer syntheses.

Dataset Information

Conformationally dynamic ?-conjugation: probing structure-property relationships of fluorescent tris(N-salicylideneaniline)s.

Publications

Conformationally dynamic π-conjugation: probing structure-property relationships of fluorescent tris(N-salicylideneaniline)s.

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