Understanding the stability of zeolitic imidazolate framework-8 (ZIF-8) under physiological conditions is critical in biotechnology and biomedicine for biosensing, biocatalysis, and drug delivery.

The design of efficient radical photoinitiating systems requires a systematic and detailed evaluation of their photochemical characteristics. Correlating absorbance and the corresponding electronic transitions of a photoinitiator is critical for understanding its photoinduced reaction pathways. In the current contribution, we provide an in-depth investigation into the photochemistry and photophysics of two oxime ester derivatives (O-benzoyl-α-oxooxime, OXE01, and O-acetyloxime, OXE02), known for their excellent performance in pigmented formulations. In particular, we shed light on their wavelength-dependent photopolymerization properties. We utilized a combination of UV–vis spectroscopy, density functional theory (DFT) calculations, photochemically induced dynamic nuclear polarization spectroscopy (photo-CIDNP), and pulsed-laser polymerization with a wavelength-tunable laser with subsequent size exclusion chromatography coupled to high-resolution electrospray ionization mass spectrometry (PLP-SEC-ESI-MS) for obtaining detailed insights. Both photoinitiators have high molar extinction coefficients (ε) of greater than 1.75 × 104 L mol–1 cm–1 at close to 330 nm, with the n−π* and π–π* transitions, relevant for cleavage of the N–O bond, at approximately 335 nm according to DFT calculations. We have probed the wavelength-dependent initiation behavior of both OXE01 and OXE02 in the presence of methyl methacrylate (MMA) via PLP with a wavelength-tunable laser between 285 and 435 nm at constant photon counts. Surprisingly, the highest conversions of MMA were found at a wavelength of 405 nm, even though the molar extinction coefficients of the photoinitiators are low (ε405 of 45 and 2 L mol–1 cm–1 for OXE01 and OXE02, respectively) compared with shorter wavelengths. Accordingly, the absorption spectrum of a photoinitiator is not a straightforward guide for selecting the most efficient excitation wavelength.

In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R] (R=mesityl (1 a), phenyl (1 b)), a previously unknown class of highly efficient Ge-based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one-pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The efficiency of 1 a,b as photoinitiators is demonstrated in photobleaching (UV/Vis), time-resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo-DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long-wavelength visible-light photoinitiators for free-radical polymerization.

Diazocines are bridged azobenzenes with superior photophysical properties. In contrast to azobenzenes the Z configuration is thermodynamically stable and the E isomer is metastable. We present a new class of nitrogen bridged diazocines with bathochromically shifted switching wavelengths and remarkably high quantum yields (−NH–CH2− bridged diazocine: ΦZ→E = 0.57, ΦE→Z = 0.8). Z to E isomerization is induced by irradiation with blue light, whereas switching back to the Z isomer is accomplished with light in the near-infrared window (up to 740 nm), which is important for medical applications like photopharmacology (deep tissue penetration). Furthermore, substitution at the bridging nitrogen should provide access to widely applicable tricyclic, photoswitchable pharmacophores. The −NAc–CH2− bridged derivative is soluble in water, and all photophysical properties (conversion rates, quantum yields, and thermal half-lives) are largely retained. Hence, this diazocine is an ideal photoswitch for applications in biochemical systems and in photopharmacology.

For the series of para-substituted triphenylamines, optimized geometries, HOMO and LUMO energy levels, ionization potentials Ip, reorganization energies for hole transport λ(+), and frontier orbital contours have been calculated by means of ab initio computations. Relationships between them and the Hammett parameter are presented. According to calculations, electron releasing substituents increase the HOMO and LUMO energies of TPA, while electron withdrawing ones decrease it. This behavior is reflected in subsequent decreasing and increasing of ionization potentials of substituted TPAs. Calculations show that there exists also a strong substituent effect on the reorganization energy λ(+), which is a dominating factor of hole mobility. It is concluded that proper tuning of the HOMO and LUMO levels (and, as a result, ionization potential, Ip) and reorganization energy λ(+) (consequently, hole mobility) of the triphenylamine can be done by alteration of the TPA electronic structure by an appropriate substitution. It is demonstrated that the proper adjustment of the HOMO levels of HTM facilitates the reduction of an energy barrier at the interface of ITO/HTL and HTL/EL and ensure the high hole injection and hole transport rate. On the other hand, appropriate adjustment of the LUMO level prevents an electron leak from the EL into the HTM layer. Results of these calculations can be useful in the process of designing new HTM materials of desired properties (high efficiency, stability, and durability).