Fluorescence emissions of imide compounds and end-capped polyimides enhanced by intramolecular double hydrogen bonds

Abstract

The structure and optical properties of a newly synthesized imide compound (DHNHPI) that forms intramolecular double hydrogen bonds (intra-HBs) were investigated. This compound exhibits intense absorption at 372 nm (ε = 5091 cm(-1) M(-1)) and strong emission at 427 nm (Φ = 0.507) in CHCl3. Under basic conditions, the absorption and fluorescence peaks showed large bathochromic shifts by 70 nm and 95 nm, respectively, compared with the neutral condition due to conversion to anion form. Based on the single-crystal X-ray diffraction analysis, DHNHPI can exert intermolecular π-π interactions between adjacent molecules along the stacking direction, with resultant emission peaks exhibiting longer wavelengths (∼525 nm) in the solid state. Moreover, an end-capped polyimide having DHNHPI moieties at the termini exhibited a strong fluorescence peak at 427 nm by photo-excitation at 332 nm. The large Stokes shift of 6701 cm(-1) clearly indicates the occurrence of an effective Förster-resonance energy transfer from the main chains to the fluorescent end-groups. These facts demonstrate that the incorporation of two -OH groups, which form intra-HBs, endows imide compounds and polyimides with enhanced fluorescence properties as well as high sensitivity towards pH.

Conformational differentiation of α‐cyanohydroxycinnamic acid isomers: a Raman spectroscopic study

“…Data from fluorescence spectroscopy of CHCA3 and CHCA4 also argue for the formation of ring–ring π‐interaction in CHCA3 but not in CHCA4. A ring–ring π‐interaction leads to a stacking of the ring that often results in a red‐shifted emission . Steady state fluorescence spectra of CHCA3 showed emission at 466 nm, which is red‐shifted compared with that of CHCA4, which has an emission peak at 443 nm (Figure S2).…”

“…A ring-ring π-interaction leads to a stacking of the ring that often results in a red-shifted emission. [30][31][32] Steady state fluorescence spectra of CHCA3 showed emission at 466 nm, which is red-shifted compared with that of CHCA4, which has an emission peak at 443 nm ( Figure S2). This suggests that ring-ring π-stacking between CHCA3 molecules exists and is more extensive than that between CHCA4 molecues.…”

Fluorescence Sensor with A New ON1–OFF–ON2 Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene‐diurea Compound

“…The weakening of the acidity of the urea N-H moiety at 9 position of anthracene might be induced by the electron-donating ureaÁÁÁAcO À moiety located at 10 position. Furthermore, 3,6-dihydroxy-N-cyclohexylphthalimide (DHNHPI), which has two symmetrically placed intramolecular proton transfer sites, also shows a resonance effect to avoid the ESIPT mechanism in the excited state (38). This resonance effect may play an important role in the occurrence of the ESIPT reaction.…”

The theoretical study about the ESIPT mechanism for 2,4‐bis(benzooxazol‐2′‐yl)hydroquinone: Single or double?

“…They found that the HBs endowed imide compounds and polyimides with enhanced fluorescence properties as well as high sensitivity towards pH. [40] Cheng et al have designed and synthesized a series of Salen ligands, combined with two intramolecular HBs and different nonconjugated alkyl bridges ((CH 2 ) n , n = 2-9, 12; cyclohexyl). [41] It can be confirmed that these Salen ligands should be used in mechanofluorochromism (crystal defect-induced emission) and living cell imaging.…”

“…Kanosue and Ando have synthesized novel imide compound 3,6‐Dihydroxy‐N‐cyclohexylphthalimide (DHNHPI) containing two intramolecular HBs. They found that the HBs endowed imide compounds and polyimides with enhanced fluorescence properties as well as high sensitivity towards pH . Cheng et al have designed and synthesized a series of Salen ligands, combined with two intramolecular HBs and different nonconjugated alkyl bridges ((CH 2 ) n , n = 2‐9, 12; cyclohexyl) .…”