We report a polymer-chain-induced tunable luminescence system based on a newly synthesized fluorescent polymer, N , N -dialkylpyrene-1-carboxamide-modified poly(2-methyl-2-oxazoline) (POZO-py) at ...various ratios of pyrene induction. Photoluminescence and thermal properties of the POZO-py were analyzed in detail. Differential scanning calorimetry (DSC) measurements revealed that the glass-transition temperature (T g) of POZO-py was above room temperature, which implies that POZO-py is in the glassy state at room temperature. POZO-py-(0.73) (i.e., pyrene content of 0.73%, M n = 2270, T g = 40 °C), having the lowest pyrene induction ratio, showed higher fluorescence quantum yields in several solvents, e.g., water, or in the thin film state than did N , N -diethylpyrene-1-carboxamide (a model compound, PA), because the polymer chain prevented the molecular mobilities of the pyrene moieties. In particular, POZO-py showed strong emission (Φfl = 0.52) in glycerin, which is a highly viscous solvent. Highly modified POZO-py-(2.9) (i.e., with a pyrene content of 2.9%, M n = 2450, T g = 48 °C) and POZO-py-(9.1) (M n = 2640, T g = 57 °C) exhibited both monomer and excimer emissions. These excimers consisted of a static excimer and a dynamic excimer. These results were not obtained for the low-molecular PA. Thus, POZO can induce improved and tunable photoluminescence properties of N , N -dialkylpyrene-1-carboxamide. The synthesis and photoluminescence properties of N , N -dialkylpyrene-1-carboxamide-modified poly(2-ethyl-2-oxazoline)-gel (PEtOZO-py-gel) were also determined.
Herein, we discuss a new pyrene-based push-pull dye (
PC
) and our investigation of its photophysical properties and applicability to biological studies. The newly synthesized dye exhibits highly ...polarity-sensitive fluorescence over a significantly wide range (
i.e.
, the green to far-red region), accompanied by high fluorescence quantum yields (
Φ
FL
> 0.70 in most organic solvents) and superior photostability to that of the commonly used Nile Red (
NR
) dye, which also fluoresces in the green to red region. When human prostate cancer cells stained with
PC
were imaged using a confocal laser scanning fluorescence microscope,
PC
was found to selectively stain the lipid droplets. Under the cell conditions where the formation of droplets was inhibited,
PC
could be distributed to both the remaining droplets and the intercellular membranes, which could be distinguished based on the fluorescence solvatochromic function of
PC
. Furthermore,
PC
efficiently stained normal human skin tissue blocks treated with a transparency-enhancing agent and enabled clear visualization of individual cells in each tissue architecture by means of two-photon fluorescence microscopy (2PM). Interestingly,
PC
provides bright 2PM images under tissue-penetrative 960 nm excitation, realizing much clearer and deeper tissue imaging than conventional pyrene dyes and
NR
. These results suggest that
PC
could replace several commonly used dyes in various biological applications, particularly the rapid and accurate diagnosis of tissue diseases, typified by biopsy.
Herein, we discuss a new pyrene-based push-pull dye (
PC
) and our investigation of its photophysical properties and applicability to biological studies.
Two-photon, excitation fluorescent microscopy featuring autofluorescence or immunofluorescence, combined with optical clearance using a transparency-enhancing technique, allows deep imaging of ...three-dimensional (3D) skin structures. However, it remains difficult to obtain high-quality images of individual cells or 3D structures. We combined a new dye with a transparency-enhancing technology and performed high-quality structural analysis of human epidermal structures, especially the acrosyringium. Human fingertip skin samples were collected, formalin-fixed, embedded in both frozen and paraffin blocks, sliced, stained with propidium iodide, optically cleared using a transparency-enhancing technique, and stained with a new fluorescent, solvatochromic pyrene probe. Microscopy revealed fine skin features and detailed epidermal structures including the stratum corneum (horny layer), keratinocytes, eccrine sweat glands, and peripheral nerves. Three-dimensional reconstruction of an entire acrosyringium was possible in one sample. This new fluorescence microscopy technique yields high-quality epidermal images and will aid in histopathological analyses of skin disorders.
A three-dimensional pyrene assembly on a tetraphenylethane skeleton enhanced the fluorescence quantum yield compared to the yield obtained when using monomeric species, without changing the shape of ...the emission spectrum. The unique spacing of the pyrene units may prevent intramolecular fluorescence quenching or non-radiative decay.
We report an enhancement of the fluorescence quantum yield by a three-dimensional dye assembly on a tetraphenylethane skeleton.
We report the synthesis of highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and the evaluation of their photophysical properties. The key step is the synthesis of the ...2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole via oxidative cyclization of 2-thienylcarbothioamide using PhI(OAc)2 as an oxidant.
In this Letter, we synthesize highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and evaluate their photophysical properties. The key step is the synthesis of 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole (2) via oxidative cyclization of 2-thienylthioanilide using PhI(OAc)2 as the oxidant. The target dyes could be easily synthesized by the Suzuki–Miyaura cross-coupling reaction of 2 and an appropriate π-donor. The photophysical properties of the 2-thienylbenzothiazole chromophore were controlled by the π-donor moiety. It was found that 2 exhibited large Stokes shifts (5345cm−1) and a high quantum efficiency for fluorescence (ΦF=0.94 in CH2Cl2). Therefore, it can be expected to be a useful photofunctional material in liquid crystal laser dyes and nonlinear optical materials.
Herein, we report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) ( POZO-py ) and poly(2-ethyl-2-oxazoline) ( PEtOZO-py ), which contain D–π–A pyrene dye units in their side ...chains. These new fluorescent polymers display solvatochromism and bright fluorescence in a variety of solvents, ranging from toluene (475 nm) to methanol (515 nm) and water (535 nm). Furthermore, amphiphilic gels (amphigels) of POZO-py and PEtOZO-py were synthesized by cross-linking the amine sites of partially hydrolyzed POZO-py and PEtOZO-py . Amphigels were formed rapidly when bridging ethyleneimine moieties were used for POZO-py and PEtOZO-py . These amphigels swell in various solvents, resulting in a solvatochromic shifts of the fluorescence emission. We furthermore determined the relationship between the swelling process, the solvatochromic properties, and the polymer structure of the POZO-py and PEtOZO-py gels. The different swelling properties led to different amphigel structures in water and hence, to different maximum fluorescence wavelengths. For example, a POZO-py amphigel with 10% ethyleneimine bridging exhibited the same solvatochromic behavior as POZO-py in solution. These results are significant in order to evaluate the solvatochromic properties of pyrene chromophores in polymers and to investigate gel structures and functional group interactions in gels.
Recently, much attention has been focused on organic fluorescent dyes with a high absorption coefficient and high fluorescent quantum yield, with the aim of using them in fascinating applications, ...for example, in organic electroluminescence and molecular imaging and as sensors and probes. In 1951, Prof. Zen-ichi Yoshida (Kyoto University) published certain requirements, which are of great significance, for the design of highly fluorescent dyes (Yoshida’s fluorescence rules) in this journal (J. Synth. Org. Chem., Jpn., 9, 230 (1951)). Currently, several modern techniques are available for investigating photophysical processes; therefore, it is necessary to establish sophisticated processes and guidelines for dye design. This review would serve as a guide for the design of highly fluorescent dyes. First, the significance of linear π-extension of aromatic or carbon-carbon multibonds and π-extension of polycyclic aromatic compounds for the synthesis of highly luminescent dyes is emphasized. Second, a Jablonski diagram describing a photophysical process is presented. Two important processes—intersystem crossing and internal conversion—play notable roles in fluorescence enhancement. Third, florescent dyes based on intramolecular charge-transfer complexes are described. Furthermore, a case study on the structure-photoluminescence property relationship for pyrene carbonyl dyes (pyrene with aldehyde, ketone, carboxylic acid, ester, and dialkylamide groups) is presented. The photophysical properties of pyrene modified by carbonyl substituents are successfully revised and systematized by measuring the absolute fluorescence quantum yield in various solvents and by performing density functional theory (DFT) calculations. Moreover, it is demonstrated that the photoluminescence properties of such compounds can be predicted on the basis of TD-DFT calculations.
A novel aggregation-induced emission active dye consisting of a simple and highly solvatochromic D- pi -A type 1,1'-binaphthyl chromophore was synthesised. The new dye exhibited dual-mode ...fluorescence in response to different types of restriction of intramolecular rotation; aggregation induces green emission, and blue emission is observed in a glassy matrix.
Herein, we report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) (
POZO-py
) and poly(2-ethyl-2-oxazoline) (
PEtOZO-py
), which contain D-π-A pyrene dye units in their side ...chains. These new fluorescent polymers display solvatochromism and bright fluorescence in a variety of solvents, ranging from toluene (475 nm) to methanol (515 nm) and water (535 nm). Furthermore, amphiphilic gels (amphigels) of
POZO-py
and
PEtOZO-py
were synthesized by cross-linking the amine sites of partially hydrolyzed
POZO-py
and
PEtOZO-py
. Amphigels were formed rapidly when bridging ethyleneimine moieties were used for
POZO-py
and
PEtOZO-py
. These amphigels swell in various solvents, resulting in a solvatochromic shifts of the fluorescence emission. We furthermore determined the relationship between the swelling process, the solvatochromic properties, and the polymer structure of the
POZO-py
and
PEtOZO-py
gels. The different swelling properties led to different amphigel structures in water and hence, to different maximum fluorescence wavelengths. For example, a
POZO-py
amphigel with 10% ethyleneimine bridging exhibited the same solvatochromic behavior as
POZO-py
in solution. These results are significant in order to evaluate the solvatochromic properties of pyrene chromophores in polymers and to investigate gel structures and functional group interactions in gels.
We report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) (
POZO-py
) and poly(2-ethyl-2-oxazoline) (
PEtOZO-py
), which contain D-π-A pyrene dye units in their side chains.
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