Polyimide and Imide Compound Exhibiting Bright Red Fluorescence with Very Large Stokes Shifts via Excited-State Intramolecular Proton Transfer

Abstract

A novel polyimide (PI) emitting a prominent red fluorescence was prepared based on 3,6-dihydroxypyromellitic dianhydride (P2HDA) and 4,4′-diaminocyclohexylmethane (DCHM). In order to investigate the fluorescence properties of the PI, an imide model compound, N,N′-dicyclohexyl-3,6-dihydroxypyromellitimide (P2H-Ch), corresponding to one repeating unit of the PI, was also synthesized. The UV−vis absorption and fluorescence spectra of P2H-Ch in CHCl 3 and the solid PI film demonstrated intense red fluorescence at around 640 nm with a very large Stokes shift (ν) of 7655 and 8994 cm −1 , respectively, via the excited-state intramolecular proton transfer (ESIPT). Moreover, the corresponding monoanion and dianion species were formed in basic conditions with an organic base (DBU) and basic salt (NaOH), which were characterized by highly visible halochromism. The introduction of −OH groups into the pyromellitic moiety of imide compounds or PIs at their para positions led to the long-wavelength fluorescent emission as well as to the high pH sensitivity.

Polymer functionalization by luminescent supramolecular gels

“…Many materials exhibiting high Stokes shifts required for wavelength conversion have been reported. 30,37,38,59,[70][71][72] In this section, we discuss the application of a luminescent supramolecular gel as an organic fluorescent system. Supramolecular gels do not rely on the chemical structure of the doped dye for the Stokes shift.…”

A convenient method for the synthesis of 3,6-dihydroxy-benzene-1,2,4,5-tetracarboxylic acid tetraalkyl esters and a study of their fluorescence properties

“…Apart from the historical importance, 27 these molecules have recently been used to synthesize novel polyimides exhibiting red fluorescence with large Stokes shift values due to excited state intramolecular proton transfer phenomena. 28 Compared to earlier methods for the synthesis of these molecules, the current method is milder, higher yielding and less-toxic. Further studies regarding the chemical transformations, electrochemistry and detailed photophysical properties are under way in our laboratory.…”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…[6] When the interconversion of these forms merely involves movement of ap roton along the hydrogen bond, proton transfer can be av ery rapid process, denoted as excited-state intramolecular proton transfer (ESIPT). [312,313] Recently, the state-of-the-art development of the ESIPTc hromophores and their applications in biological imaging, chemosensors, and white-light emitting materials have been reviewed. [311] The most remarkable photophysical property of the ESIPTchromophores is the large Stokes shift, compared to normal fluorophores.…”

“…[312,[361][362][363] Inclusion of RAHB rings along the polymerb ackbone mayl ead to planarization, large Stokes shift, ESIPT,and increased fluorescence quantum efficiency,w hich can have ad irect impact on the application of those materials as sensors, films, or molecular switches. [312,[361][362][363] Inclusion of RAHB rings along the polymerb ackbone mayl ead to planarization, large Stokes shift, ESIPT,and increased fluorescence quantum efficiency,w hich can have ad irect impact on the application of those materials as sensors, films, or molecular switches.…”

“…For example, RAHB-assisted planarization of asymmetrically functionalized alternating phenylene-pyridinylene copolymers have been reported (Scheme 93). [312] When the polyimide (pale yellow at pH 7) is soakedi nN aOH aqueous solutions at pH 11 (deep red) and 14 (deep blue), intense absorption peaks correspondingt ot he monoanion and dianion forms are observed at 529 and 617 nm, respectively.I tw as confirmed that the RAHB introduction into the polyimidee nabled to generate and control the characteristic red fluorescence, its high sensitivity to basic conditions, and visible halochromism. The large Stokes shift in the valueso fl max and l emis also confirmed the possibility of ESIPT for both polymers that was facilitated by RAHB (Scheme 93).…”