Photolysis of dimethoxynitrobenzyl-"caged" acids yields fluorescent products

Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

The exciton, an excited electron-hole pair bound by Coulomb attraction, plays a key role in photophysics of organic molecules and drives practically important phenomena such as photoinduced mechanical motions of a molecule, photochemical conversions, energy transfer, generation of free charge carriers, etc. Its behavior in extended π-conjugated molecules and disordered organic films is very different and very rich compared with exciton behavior in inorganic semiconductor crystals. Due to the high degree of variability of organic systems themselves, the exciton not only exerts changes on molecules that carry it but undergoes its own changes during all phases of its lifetime, that is, birth, conversion and transport, and decay. The goal of this review is to give a systematic and comprehensive view on exciton behavior in π-conjugated molecules and molecular assemblies at all phases of exciton evolution with emphasis on rates typical for this dynamic picture and various consequences of the above dynamics. To uncover the rich variety of exciton behavior, details of exciton formation, exciton transport, exciton energy conversion, direct and reverse intersystem crossing, and radiative and nonradiative decay are considered in different systems, where these processes lead to or are influenced by static and dynamic disorder, charge distribution symmetry breaking, photoinduced reactions, electron and proton transfer, structural rearrangements, exciton coupling with vibrations and intermediate particles, and exciton dissociation and annihilation as well.

Wavelength-Selective Uncaging of Two Different Photoresponsive Groups on One Effector Molecule for Light-Controlled Activation and Deactivation

Photocleavable protecting groups (PPGs) play a pivotal role in numerous studies. They enable controlled release of small effector molecules to induce biochemical function. The number of PPGs attached to a variety of effector molecules has grown rapidly in recent years satisfying the high demand for new applications. However, until now molecules carrying PPGs have been designed to activate function only in a single direction, namely the release of the effector molecule. Herein, we present the new approach Two-PPGs-One-Molecule (TPOM) that exploits the orthogonal photolysis of two photoprotecting groups to first release the effector molecule and then to modify it to suppress its induced effect. The moiety resembling the tyrosyl side chain of the translation inhibitor puromycin was synthetically modified to the photosensitive ortho-nitrophenylalanine that cyclizes upon near UV-irradiation to an inactive puromycin cinnoline derivative. Additionally, the modified puromycin analog was protected by the thio-coumarylmethyl group as the second PPG. This TPOM strategy allows an initial wavelength-selective activation followed by a second light-induced deactivation. Both photolysis processes were spectroscopically studied in the UV/vis- and IR-region. In combination with quantum-chemical calculations and time-resolved NMR spectroscopy, the photoproducts of both activation and deactivation steps upon illumination were characterized. We further probed the translation inhibition effect of the new synthesized puromycin analog upon light activation/deactivation in a cell-free GFP translation assay. TPOM as a new method for precise triggering activation/deactivation of effector molecules represents a valuable addition for the control of biological processes with light.