Tuning the Photophysical Properties of Photostable Benzo[b]phospholeP-Oxide-Based Fluorophores

Abstract

We previously reported that constrained 2-phenylbenzo[b]phosphole P-oxides bearing a diphenylamino group show high photostability and thus are promising dyes for fluorescence imaging. Herein we investigated the impact of the bridging moieties on their photophysical properties. A series of benzo[b]phosphole P-oxides constrained with various carbon or silicon bridges were synthesized. All of these compounds showed significant solvatochromism in fluorescence due to the intramolecular charge-transfer character in the excited state. The dipole moments in the excited state for the carbon-bridged derivatives are slightly larger than the silicon-bridged counterparts. Nevertheless, the latter compounds showed orange-red fluorescence in polar solvents with ca. 30 nm red-shifted maxima compared to the carbon analogues. Most importantly, the assessment of their photobleaching resistance revealed that the photostability of this compound series highly relies on the steric bulkiness of the bridging moiety, and even the silicon-bridged derivative can show outstanding photostability, as far as the silicon-bridging moiety has sufficient bulkiness.

Negative fluorescence anisotropy of phosphole oxide-based dyes in nematic liquid crystals

“…The components of S TDM also suggest that CBF-S has lower anisotropy in its shape (low λ S and S LX~0 .23), which is the main reason for the low S TDM , similarly to the cases found on CP2 and CBM. Originally, the phenyl group attached to the phosphorus has been designed and required because of the synthetic reason, ie, availability of the starting materials and the stability toward the reaction conditions 39,47,48 . Here it is theoretically suggested that the structural nature, ie, >P(=O)Ph, also plays an important role in realising negative fluorescence anisotropy of phosphole oxide-based dyes in the present NLCs.…”

“…Five phosphole oxide-based fluorescent dyes (racemic mixtures)-(CP2), (CBM), (CBX), (CBF) and (CNX) (Fig. 2b)-were synthesised according to previously reported methods 39,[46][47][48] .…”

“…Here, with the aid of such theoretical analysis, we investigate steady-state fluorescence anisotropy of a series of phosphole oxidebased dyes 39,[46][47][48] in NLCs to clarify the relation between the experimentally observed negative anisotropy and the molecular structures. In addition, the theoretically derived general principle of the molecular design of dyes for controlling the fluorescence anisotropy and molecular alignment in NLCs, as well as conditions for realising strong negative anisotropy, is discussed.…”

Perylene Bisimide and Naphthyl‐Based Molecular Dyads: Hydrogen Bonds Driving Co‐planarization and Anomalous Temperature‐Response Fluorescence

“…However, most of the ICT related research was performed with variations among the donor, the acceptor, and the bridging units. To enhance the stimuli‐responsiveness and to broaden the functionality of ICT related fluorescent systems, proton transfer, cyclization, and other intramolecular interactions have been employed to regulate the degree of conjugation of the structure between the donor and the acceptor. One possibility for the design is to introduce an alkynyl group into the bridge connecting the donor and the acceptor as a part of the conjugated structure.…”

Phosphole <i>P</i>-Oxide-Containing π-Electron Materials: Synthesis and Applications in Fluorescence Imaging

“…30 However, a detailed rationalization of the high photostability should require further experimental investigations especially into the excited state dynamics, which is currently in progress in our laboratory. Interestingly, we have also demonstrated that a silicon bridged congener shows comparable photostability.…”