Fluorogenic probes for bioimaging have become essential tools for life science and medicine, and the key to their development is a precise understanding of the mechanisms available for fluorescence off/on control, such as photoinduced electron transfer (PeT) and Forster resonance energy transfer (FRET). Here we establish a new molecular design strategy to rationally develop activatable fluorescent probes, which exhibit a fluorescence off/on change in response to target biomolecules, by controlling the twisted intramolecular charge transfer (TICT) process. This approach was developed on the basis of a thorough investigation of the fluorescence quenching mechanism of N-phenyl rhodamine dyes (commercially available as the QSY series) by means of timedependent density functional theory (TD-DFT) calculations and photophysical evaluation of their derivatives. To illustrate and validate this TICT-based design strategy, we employed it to develop practical fluorogenic probes for HaloTag and SNAP-tag. We further show that the TICT-controlled fluorescence off/on mechanism is generalizable by synthesizing a Si−rhodamine-based fluorogenic probe for HaloTag, thus providing a palette of chemical dyes that spans the visible and near-infrared range.

We have confirmed that a self-assembled monolayer (SAM) film of octadecanethiol (ODT), CH3(CH2)17SH, can be formed on a cleaved GaAs (110) surface, by using an atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). Circular depressions were observed on the surface after film formation. The area of the circular depressions increased with immersion time, indicating that the solution oxidized the interface between ODT molecules and the GaAs surface, resulting in removal of ODT molecules. The oxidation was considerably faster in pure ethanol solution than that in ODT solution, demonstrating that the SAM film protects the GaAs surface from oxidation. High-resolution lateral force microscope (LFM) images revealed a periodic structure that had two types of lines: periodic lines 0.57 nm apart and lines rotated 55° with respect to them. A structural model of the SAM successfully explained both the features in high-resolution LFM images and the depression depth observed in AFM images.

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Photoperiodic response and vase life of 28 cultivars of ornamental sunflower (Helianthus annuus) were evaluated. Plants were grown in a glasshouse under 16-hour long-day (LD) or 11.5-hour shortday (SD) conditions. Most cultivars (82%) reached visible flower bud stage earlier under SD than LD. All cultivars flowered under both SD and LD conditions, but in 26 cultivars (92.9%) flowering was significantly delayed under LD, demonstrating them to be quantitative SD plants. The delay was variable among the cultivars. A 14-day or greater hastening of flowering was found under SD in 18 cultivars. Photoperiod had no effect on flowering of `Lemon Eclair' and `Moonshadow'; these cultivars are day-neutral (DN) plants. For some cultivars the LD photoperiod increased plant height and the number of nodes and leaves. Vase life varied from 6.8 to 11.2 days depending on the cultivar, but no photoperiodic effect was found.