Orbital Control of the Color and Excited State Properties of Formylated and Fluorinated Derivatives of Azulene

Three mono-fluorinated derivatives of the flavin core system 10-methyl-isoalloxazine (MIA) were synthesized. Aqueous solutions of these compounds were characterized by steady-state and time-resolved spectroscopy. The positions for the fluorination (6, 7 and 8) were motivated by the nodal structure of the frontier orbitals of MIA. In comparison with MIA, the fluorination results in bathochromic (6F- and 7F-MIA) and hypsochromic (8F-MIA) shifts of the adiabatic excitation energy of the lowest allowed transition. Shifts of up to ~500 cm were observed. These spectroscopic shifts go along with changes in fluorescence quantum yields and lifetimes. In addition, triplet yields are affected. For 7F-MIA, a 50% increase in the fluorescence quantum yield as well as a 50% decrease in triplet yield is observed rendering the compound interesting for fluorescence applications. The measured effects are discussed in terms of qualitative perturbation theory.

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“…The respective energy denominator is smaller. Such predominance of the +M effect has been evoked in other fluorinated aromatics .…”

Section: Discussionmentioning

confidence: 87%

Impact of Mono‐Fluorination on the Photophysics of the Flavin Chromophore

Reiffers

Ziegenbein

Engelhardt

et al. 2018

Photochem & Photobiology

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“…In fact, it is estimated that 40% of all medicines are natural extracts or semi-synthetic derivatives of naturally derived intermediates. [9][10][11][12][13][14][15][16][17] As a nontoxic natural product found in the oils of Guajacum officinale and Matricaria chamomilla, as well as in the vibrant-blue mushroom Lactarius indigo, guaiazulene has been approved by the FDA as a cosmetic color additive. 6-8 Additionally, the non-toxic nature and the accompanying eco-friendly feature of natural dyes could set the stage for chemists to develop "green" routes towards photonic and conductive materials.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] Similarly, the physical, electronic, and optical properties of some natural pigments could offer access to key building blocks for developing bio-derived chromophoric materials. [9][10][11][12][13][14][15][16] Chemically, guaiazulene is a nonalternant hydrocarbon that is notable for its low transition energy to the S 1 state and unusually large S 1 -S 2 gap, [17][18][19][20][21][22][23][24][25][26][27] where S 1 and S 2 refer to the first and second electronically excited states, respectively. 3,8 Among known natural pigments, 6-8 guaiazulene has received recent popularity for its interesting physical and electronic properties.…”

Section: Introductionmentioning

confidence: 99%

Chromophoric materials derived from a natural azulene: syntheses, halochromism and one-photon and two-photon microlithography

et al. 2015

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In addition to their use as colorants in diet and cosmetics, various natural dyes possess photophysical properties that could enable their use as modular building blocks for preparing ecofriendly and non-toxic chromophores. Among natural pigments, guaiazulene holds great potential due to its unique optical and electronic properties. Thus, in order to explore and understand the properties of guaiazulene-containing chromophores, a series of 4-styrylguaiazulenes 3a-l were prepared by condensation of the C-4 methyl group of naturally-occurring guaiazulene 1 with various aromatic carboxaldehydes 2a-l. Treating these analogs 3a-l with a strong acid protonates the electron-rich C-3 and reveals a reversible halochromic behavior where the optical energy gap responds predictably to electrondonor strength and degree of π-conjugation. Additionally, acid-doping is accompanied by efficient fluorescence switch-on, where 3e(H+) and 3g(H+) exhibited considerably higher fluorescence quantum yields than the neutral precursor. These properties facilitated the design of a new nonerasable 3D fluorescence readout (permanent or write-once read-many, WORM) system, which is comprised of a switch-on fluorescent guaiazulene-containing chromophore 3e and commercially available iodonium photo-acid generator (PAG) in thin polymethyl methacrylate (PMMA) films. Scheme 1. Syntheses of 4-styrylguaiazulenes 3a-l.Reagents and conditions: (a) benzaldehyde 2a, method F, 54%; (b) 4-bromobenzaldehyde 2b, method G, 48%; (c) 4-(hexyloxy)benzaldehyde 2c, method G, 43%; (d) 4-(phenylthio)benzaldehyde 2d, method E, 35%; (e) 7-bromo-9,9-dihexyl-9H-fluorene-2carbaldehyde 2e, method F, 34%; (f) pyrene-1-carbaldehyde 2f, method E, 70%; (g) i. (b); ii. 3b, Pd(PPh 3 ) 2 Cl 2 , CuI, K 2 CO 3 , THF, 32%; (h) furan-2-carbaldehyde 2g, method G, 67%; thiophene-2carbaldehyde 2h, method G, 66%; 1-hexyl-1H-pyrrole-2-carbaldehyde 2i, method E, 71%; 1-ethyl-1Hindole-3-carbaldehyde 2j, method F, 48%; 9-ethyl-9H-carbazole-3-carbaldehyde 2k, method E, 75%. Color represents the different series compared in this work: 3a-d, 3e-g, 3h-j, and 3j-l.

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“…Although the effect of resonantly electron withdrawing or donating groups on the HOMO, LUMO and LUMO +1 energies of azulene was reported, these theoretical calculations were initially limited to derivatives with mildly electronically perturbing (e.g. formyl or fluorine) substituents [11]. …”

Section: Introductionmentioning

confidence: 99%

Computer aided chemical design: using quantum chemical calculations to predict properties of a series of halochromic guaiazulene derivatives

et al. 2016

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With the scientific community becoming increasingly aware of the need for greener products and methodologies, the optimization of synthetic design is of greater importance. Building on experimental data collected from a synthesized guaiazulene derivative, a series of analogous structures were investigated with time-dependent density functional theory (TD-DFT) methods in an effort to identify a compound with desirable photophysical properties. This in silico analysis may eliminate the need to synthesize numerous materials that, when investigated, do not possess viable characteristics. The synthesis of several computationally investigated structures revealed discrepancies in the calculation results. Further refined computational study of the molecules yielded results closer to those observed experimentally and helps set the stage for computationally guided design of organic photonic materials. Three novel derivatives were synthesized from guaiazulene, a naturally occurring chromophore, exhibiting distinct halochromic behaviour, which may have potential in a switchable optoelectronic system or combined with a photoacid generator for data storage. The protonated forms were readily excitable via two-photon absorption.

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Orbital Control of the Color and Excited State Properties of Formylated and Fluorinated Derivatives of Azulene

Cited by 100 publications

References 21 publications

Impact of Mono‐Fluorination on the Photophysics of the Flavin Chromophore

Impact of Mono‐Fluorination on the Photophysics of the Flavin Chromophore

Chromophoric materials derived from a natural azulene: syntheses, halochromism and one-photon and two-photon microlithography

Computer aided chemical design: using quantum chemical calculations to predict properties of a series of halochromic guaiazulene derivatives

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