A structural remedy toward bright dipolar fluorophores in aqueous media.

The donor-acceptor (D-A) type dipolar fluorophores, an important class of luminescent dyes with two-photon absorption behaviour, generally emit strongly in organic solvents but poorly in aqueous media. To understand and enhance the poor emission behaviour of dipolar dyes in aqueous media, we undertake a rational approach that includes a systematic structure variation of the donor, amino substituent of acedan, an important two-photon dye. We identify several factors that influence the emission behaviour of the dipolar dyes in aqueous media through computational and photophysical studies on new acedan derivatives. As a result, we can make acedan dyes emit bright fluorescence under one- and two-photon excitation in aqueous media by suppressing the liable factors for poor emission: 1,3-allylic strain, rotational freedom, and hydrogen bonding with water. We also validate that these findings can be generally extended to other dipolar fluorophores, as demonstrated for naphthalimide, coumarin and (4-nitro-2,1,3-benzoxadiazol-7-yl)amine (NBD) dyes. The new acedan and naphthalimide dyes thus allow us to obtain much brighter two-photon fluorescent images in cells and tissues than in their conventional forms. As an application of these findings, a thiol probe is synthesized based on a new naphthalimide dye, which shows greatly enhanced fluorescence from the widely used N,N-dimethyl analogue. The results disclosed here provide essential guidelines for the development of efficient dipolar dyes and fluorescence probes for studying biological systems, particularly by two-photon microscopy.

Reaction-based two-photon probes for in vitro analysis and cellular imaging of monoamine oxidase activity.

Reaction-based fluorescent probes for monoamine oxidases A and B are developed based on a new two-photon absorbing compound and its precursor. The probes show turn-on fluorescence response to the enzymes owing to the two-photon absorbing compound produced by the enzymatic activity, as monitored by one- as well as two-photon microscopy for the first time.

C3-symmetric cage-like receptors: chiral discrimination of α-chiral amines in a confined space.

Cage-like receptors that have internal binding sites and a C(3)-symmetric chiral bias have been synthesized, and their chiral discrimination behavior toward α-chiral amines as their ammonium salts has been compared with that of their open structures.

Chiral discrimination of alpha-amino acids with a C(2)-symmetric homoditopic receptor.

Chiral discrimination of alpha-amino acids has been realized by a C(2)-symmetric homoditopic receptor, which is based on a binaphthyl chiral skeleton with 2,2'diisopropoxy substituents and a common binding side arm, (o-carboxamido)-trifluoroacetophenone moiety, in the 3,3'-positions, which recognizes alpha-amino acids as their amino carboxylate forms through formation of stabilized adducts.