Polymer-Chain-Induced Tunable Luminescence Properties: Amphiphilic Poly(2-oxazoline)s Possessing a <i>N</i>,<i>N</i>-Dialkylpyrene-1-carboxamide Chromophore in the Side Chain

We report a polymer-chain-induced tunable luminescence system based on a newly synthesized fluorescent polymer, <i><i>N</i></i>,<i><i>N</i></i>-dialkylpyrene-1-carboxamide-modified poly­(2-methyl-2-oxazoline) (<b>POZO-py</b>) at various ratios of pyrene induction. Photoluminescence and thermal properties of the <b>POZO-py</b> were analyzed in detail. Differential scanning calorimetry (DSC) measurements revealed that the glass-transition temperature (<i>T</i>_g) of <b>POZO-py</b> was above room temperature, which implies that <b>POZO-py</b> is in the glassy state at room temperature. <b>POZO-py-(0.73) (</b>i.e., pyrene content of 0.73%, <i>M</i>_n = 2270, <i>T</i>_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 <i><i>N</i></i>,<i><i>N</i></i>-diethylpyrene-1-carboxamide (a model compound, <b>PA</b>), because the polymer chain prevented the molecular mobilities of the pyrene moieties. In particular, <b>POZO-py</b> showed strong emission (Φ_fl = 0.52) in glycerin, which is a highly viscous solvent. Highly modified <b>POZO-py-(2.9)</b> (i.e., with a pyrene content of 2.9%, <i>M</i>_n = 2450, <i>T</i>_g = 48 °C) and <b>POZO-py-(9.1)</b> (<i>M</i>_n = 2640, <i>T</i>_g = 57 °C) exhibited both monomer and excimer emissions. These excimers consisted of a <i>static excimer</i> and a <i>dynamic excimer</i>. These results were not obtained for the low-molecular <b>PA</b>. Thus, <b>POZO</b> can induce improved and tunable photoluminescence properties of <i><i>N</i></i>,<i><i>N</i></i>-dialkylpyrene-1-carboxamide. The synthesis and photoluminescence properties of <i><i>N</i></i>,<i><i>N</i></i>-dialkylpyrene-1-carboxamide-modified poly­(2-ethyl-2-oxazoline)-gel (<b>PEtOZO-py-gel</b>) were also determined

Additional Insights into Luminescence Process of Polycyclic Aromatic Hydrocarbons with Carbonyl Groups: Photophysical Properties of Secondary <i>N</i>-Alkyl and Tertiary <i>N</i>,<i>N</i>-Dialkyl Carboxamides of Naphthalene, Anthracene, and Pyrene

Here we report the substitution effects of <i>N</i>-alkyl and <i>N</i>,<i>N</i>-dialkyl carboxamide groups on the fluorescence properties of polycyclic aromatic hydrocarbon chromophores, so as to control their fluorescence properties. The fluorescence properties of compounds obtained using solvents with different polarities showed very little change, indicating that the modified compounds do not form charge transfer states. TD-DFT calculations and measurements performed at low temperature (78 K) and in viscous solvents revealed that the <i>N</i>-alkyl and <i>N</i>,<i>N</i>-dialkyl carboxamide groups tend to reduce the contributions from intersystem crossing and increase those from internal conversion. Considering that the fluorescence mechanism of low-fluorescence carbonyl compounds such as aldehyde and ketone is dominated by intersystem crossing and that of high-luminescence carbonyl compounds such as carboxylic acid and ester is dominated by a radiative process, it can be said that the photophysical process of <i>N</i>-alkyl and <i>N</i>,<i>N</i>-dialkyl carboxamides is novel. In addition, the calculation results for excited states indicated that such contributions can be controlled by selecting the appropriate polycyclic aromatic hydrocarbon or amide structure, in addition to solvent viscosity and temperature

A novel pyrene-based two-photon active fluorescent dye efficiently excited and emitting in the ‘tissue optical window (650–1100 nm)’

We synthesized a novel pyrene-based A–π–A dye that can be excited and fluoresce efficiently in the ‘tissue optical window’.</p