Investigations on Polymeric and Monomeric Intramolecularly Hydrogen-Bridged UV Absorbers of the Benzotriazole and Triazine Class

Abstract

Various copolymers of MA-TIN 1, 2-[2-hydroxy-3-tert-butyl-5-(O-[2-hydroxy-3-(2-methylpropenoyloxy)propyl]-2-carbonyloxyethyl)phenyl]benzotriazole, and MA-TZ 1, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(2-hydroxy-3-[2-methylpropenoyloxy])propoxyphenyl]-1,3,5-triazine, with styrene, methyl methacrylate, and methacrylic acid have been synthesized by radical polymerization. Their absorption spectra in the long-wavelength UV region appear unchanged compared to those of the monomeric UV absorbers, indicating the stabilizer chromophore to remain unimpaired in the course of the polymerization. Both the monomeric and the polymeric stabilizers exhibit a strongly Stokes-shifted, temperature-dependent, low-quantum-yield fluorescence which arises from an intermediate species formed by intramolecular proton transfer. The intramolecular hydrogen bond which is essential for the photostability of this type of UV absorbers thus is still intact in the copolymers. Activation energies for the radiationless deactivation process can be evaluated from the temperature dependence of the proton-transferred fluorescence. These energies lie between 4 and 5 kJ/mol for most of the benzotriazole and triazine stabilizers investigated and show hardly any matrix dependence. Fluorescence-decay measurements with crystalline MA-TIN 1 at different temperatures reveal a close correspondence of the temperature dependence between decay times and relative quantum yields. The radiationless process thence is concluded to originate from the proton-transferred level S1‘. The decay time at room temperature is estimated at 70 ps, close to the value for crystalline TIN P. The proton-transferred fluorescence of MA-TIN 1, in contrast, exhibits a biexponential decay profile.

Sensing of Cyanide Using Highly Selective Thiazole-based Cu2+Chemosensor

“…This can be attributable to a π -π* transition; this is favored by the planar orientation enforced by the intramolecular hydrogen bonding. 11,15 However, upon addition of Cu 2+ to the solution of 1, a new absorption band at 381 nm becomes enhanced gradually, while the absorption band at 334 nm decreased synchronously, due to the disruption of hydrogen bonding between the phenolic hydrogen and thiazole nitrogen (Scheme 2). As shown in Figure 1 only (Figure 2).…”

A simple coumarin-based colorimetric and ratiometric chemosensor for acetate and a selective fluorescence turn-on probe for iodide

“…From UV-vis titration spectra (Fig. 1a) it can be seen that as the number of equivalents of AcO À ([Bu 4 N]AcO salt) increases, the absorbance of the peak centered at 411 nm is gradually decreased with concomitant appearance of a new red shifted peak around 573 nm resulting from the pÀp n transition [53,54], of the chromophore (2,4-dinitrophenylhydrazine). Furthermore, two well-defined isosbestic points were observed at 325 and 463 nm, which suggests the complex formation between the receptor R1 and AcO À during the course of the titration.…”

TDDFT assessment of excited state intramolecular proton transfer in a panel of chromophore 2-hydroxypyrene-1-carbaldehyde

“…It is worth mentioning that the ESIPT process was found to proceed exceptionally fast at a subpicosecond time scale because it involves a negligible activation barrier [16][17][18][19][20][21][22]. This ultrafast nature of ESIPT molecules attracts highest scientific interest whereby paving potential avenues for prospective applications, such as luminescent materials [23,24], fluorescent chemosensors [25], photostabilizers [26,27], molecular probes [28], metal ion sensors [29][30][31], and organic light emitting devices (OLEDs) [32,33].…”