π‐Extended Push‐Pull‐Type Bicyclic Fluorophores Based on Quinoline and Naphthyridine Frameworks with an Iminophosphorane Fragment

Abstract

Emissive quinoline and naphthyridine derivatives, bearing an iminophosphorane (IPP) fragment as an electrondonating group and two trifluoromethyl groups as electronwithdrawing groups, were prepared as electron push-pulltype bicyclic fluorophores: quinoline-IPP (1) and naphthyridine-IPP (2). Compared to those of the precursor bicyclic amines without the IPP moiety, the fluorescence quantum yields (Φ f ) of 1 and 2 were considerably higher, not only in low polarity solvents but also polar solvents. Moreover, the molar absorption coefficients (ɛ) were enhanced; thus, 1 and 2 are fluorophores with relatively high brightness (Φ f × ɛ). Using density functional theory calculations, the t indices were calculated, and these reveal that locally excited character is dominant in both molecules. Because of the sterically bulky IPP fragments, 1 and 2 emitted with moderate Φ f values, even in the solid state. Further, by exploiting the low crystallinity of 1 and 2, emissive amorphous thin films were prepared.

High-Z′ Crystal Structure of Tricyclic Imidazonaphthyridine Derivatives and the Thermal Profiles of Their Polymorphs

“…Because of the H-type and J-type arrangements based on the π–π stacking of INA–AN-α and -β1 , the former and latter exhibited blue-shifted and red-shifted emissions, respectively . The smallest dihedral angle, θ 3 (Figure c), might account for the production of the emissive and nonemissive crystals because it enabled the effective function of an electron donor through the An ring. − Moreover, the C atoms of the phenyl ring in INA–AN-α were in close contact (3.32 Å) by π–π stacking (Figure S5), yielding a fixed phenyl ring. Thus, the rigid phenyl ring may cause the suppression of nonradiative decay based on heat to afford the emissive crystal of INA–AN-α .…”

Acid responsiveness of emissive morpholinyl aminoquinolines and their use for cell fluorescence imaging

“…2,4-Bis(trifluoromethyl)quinolin-7-amine (TFMAQ) and N-phenyl-2,4-bis(trifluoromethyl)quinolin-7amine (TFMAQ-Ph) were prepared using the reported procedures. 6,7 Thin-layer chromatography (TLC) was performed using 60 F 254 silica gel plates (Merck). Silica gel column chromatography was performed using Silica Gel 60 N (Kanto Chem., Ltd) as the stationary phase.…”

“…1 and S2 †), as expected for push-pull-type fluorophores. [6][7][8] Key photophysical parameters of the compounds (10 μM solutions) are summarised in Table 2. As shown in the absorption spectra of the secondary amine analogues (1, 4, 5, and TFMAQ-Me in Schemes 1 and 2), the absorption peaks of compound 1 (i.e.…”

“…[1][2][3][4][5] Thus, many researchers have reported fluorescent probes that are specifically designed to work in these acidic environments. For example, we reported push-pull-type emissive aminoquinoline (2,4-bis(trifluoromethyl)quinolin-7-amine, TFMAQ) [6][7][8] and aminonaphthyridine (Nap) [9][10][11][12] derivatives having bi-or tricyclic frameworks that respond to acidic or basic environments by exhibiting changes in their absorption and fluorescence spectra. As an example of an acid-responsive probe (Scheme 1), the tricyclic dihydroimidazonaphthyridine derivative DHIm 10 shows enhanced fluorescence intensity in the acidic tumour microenvironment because the aromaticity of the system is enhanced by the protonation of the nitrogen atom in the dihydroimidazole ring; this enables its use as a 'turn-on' type fluo-rescent probe.…”

Thieno[3,2-b]phosphole-based AIEgens: facile preparation and dual modulation of solid-state luminescence

“…Such characteristics are consistent with those commonly observed in AIE-based materials 71 and are in agreement with our previously published work. 63 To achieve red-emitting fluorophores, we previously designed and reported a push-pull system with strong amine donor groups (D) [72][73][74] and utilized the phosphole oxide scaffold as the acceptor moiety (A). The derivatives 3e and 3g, which are substituted with diphenylamine, exhibit intense red luminescence with emission wavelengths of 649 and 634 nm, respectively.…”