A fulgide photoswitch is presented as a novel actinometer for a broad range of wavelengths from the UV to the NIR region (340–700 nm). It is easily accessible and has a robust photochemistry and high fatigue resistance. Its photophysics and photochemistry are described in detail. Quantum yields of photoswitching were measured for a series of wavelengths and standardized against known standards (ferrioxalate actinometry, calibrated photodiode). We also present a method for the precise determination of photoswitching quantum yields by global analysis of the whole spectra and an alternative quick and easy method for rapid determination of photon fluxes.

In the development of photolabile protecting groups, it is of high interest to selectively modify photochemical properties with structural changes as simple as possible. In this work, knowledge of fluorophore optimization was adopted and used to design new coumarin‐ based photocages. Photolysis efficiency was selectively modulated by inactivating competitive decay channels, such as twisted intramolecular charge transfer (TICT) or hydrogen‐bonding, and the photolytic release of the neurotransmitter serotonin was demonstrated. Structural modifications inspired by the fluorophore ATTO 390 led to a significant increase in the uncaging cross section that can be further improved by the simple addition of a double bond. Ultrafast transient absorption spectroscopy gave insights into the underlying solvent‐dependent photophysical dynamics. The chromophores presented here are excellently suited as new photocages in the visible wavelength range due to their simple synthesis and their superior photochemical properties.

Recently, photochromic derivatives of nucleobases have drawn attention for regulating oligonucleotide hybridization with light for photopharmacological applications. The nucleobase moiety provides attractive interaction for hybridization, whereas the photochromic moiety can alter the interaction upon irradiation due to conformational changes. Herein we report the synthesis of 2-phenyldiazenyl-substituted 2'-deoxyadenosine (dA Azo) and 2'-deoxyguanosine (dG Azo) and investigate their influence in a DNA context by UV/Vis absorption, fluorescence and CD spectroscopies. For comparison, the literature-known azobenzene C-nucleoside DNAzo was used as a reference system. It could be shown that photochromic purines improve overall hybridization affinity compared to azobenzene C-nucleosides. In particular, 2'-deoxyadenosine analogue dA Azo increases melting temperatures by 7.5°C in the favored trans state with 86 % of the switching efficiency of the reference system.

Photoactivatable compounds for example photoswitches or photolabile protecting groups (PPGs, photocages) for spatiotemporal light control, play a crucial role in different areas of research. For each application, parameters such as the absorption spectrum, solubility in the respective media and/or photochemical quantum yields for several competing processes need to be optimized. The design of new photochemical tools therefore remains an important task. In this study, we exploited the concept of excited‐state‐aromaticity, first described by N. Colin Baird in 1971, to investigate a new class of photocages, based on cyclic, ground‐state‐antiaromatic systems. Several thio‐ and nitrogen‐functionalized compounds were synthesized, photochemically characterized and further optimized, supported by quantum chemical calculations. After choosing the optimal scaffold, which shows an excellent uncaging quantum yield of 28 %, we achieved a bathochromic shift of over 100 nm, resulting in a robust, well accessible, visible light absorbing, compact new photocage with a clean photoreaction and a high quantum product (ϵ⋅Φ) of 893 M−1 cm−1 at 405 nm.

The photochemistry of fluorenols has been of special interest for many years. This is because both the fluorenol and the fluorenyl cation are antiaromatic in the ground state due to...