Photoluminescence Properties of Novel Fluorescent Polyimide Based on Excited State Intramolecular Proton Transfer at The End Groups

Abstract

Excited state intramolecular proton transfer (ESIPT) is one of the distinctive photophysical processes of fluorescent compounds and polymers, which induces enhanced fluorescence with a very large Stokes shift. In this work, 6FDA/DCHM/3HPA polyimides (PIs) having bulky-CF 3 groups were synthesized, in which 3HPA is an end-group which exhibits ESIPT with enhanced green emission when irradiated by UV light at 365 nm. Introduction of bulky side chains can improve fluorescent properties via suppression of aggregation induced quenching as well as intermolecular interactions. All the 6FDA-based PI films were colorless and transparent in the visible region, and the PIs having 3HPA end-groups exhibited obvious green emission at 530 nm, when excited at 340 nm. Compared with the corresponding ODPA-based PIs which have no bulky side groups, the 6FDA-based PIs demonstrated significantly higher quantum yields in the solid state (Φ = 0.14−0.25), which is attributable to the looser aggregation structures owing to the bulky and less polarizable-CF3 group and the absence of energy transfer to/from the non-fluorescent main chain units. Accordingly, the experimental results proved that the introduction of bulky-CF 3 groups using 6FDA moiety is a promising way to create highly fluorescent end-capped PIs.

Synthesis and Characterization of White-Light Luminescent End-Capped Polyimides Based on FRET and Excited State Intramolecular Proton Transfer

“…However, since it has been reported that PI films with acid dianhydrides, such as PMDA and BPDA, emit fluorescence in the visible region, the improvement of the fluorescence property of PI is desired [16][17][18][19]. To suppress the CT and LE(n−π*) transitions and enhance the LE(π−π*) transitions between the S 0 and S 1 states, we have developed a series of highly fluorescent PIs with high Φ values by combining dianhydrides with high electron-accepting ability, whose HOMO-LUMO transitions are LE(π−π*), and alicyclic diamines with low electrondonating ability [15,[20][21][22][23][24][25][26][27][28][29]. With other methods, highly fluorescent fully aromatic PIs have been developed by introducing aggregation-induced emission (AIE)-active bulky moieties, such as modified triarylamine [30,31] or tetraphenylethylene structures [32], in their main or side chains.…”

“…Hence, white emission, which requires long-wavelength fluorescence with a very large ν, is challenging to achieve. To overcome this problem, the uses of excited-state intramolecular proton transfer (ESIPT) and intersystem crossing (ISC) followed by phosphorescence emission are advantageous [21,28,33]. In addition, molecules having a donor-acceptor structure exhibit large Stokes-shifted fluorescence owing to the effective spatial separation of HOMO and LUMO [34].…”

Photophysical analysis of dual fluorescence and phosphorescence emissions observed for semi-aliphatic polyimides at lower temperatures

“…They exhibit large Stokes-shifted orange and green FL through an excited state intramolecular proton transfer (ESIPT). 13–19…”

“…They exhibit large Stokes-shifted orange and green FL through an excited state intramolecular proton transfer (ESIPT). [13][14][15][16][17][18][19] Recently, metal-free room-temperature phosphorescence (RTP) has attracted significant attention owing to the very large Stokes shifts and ultra-long luminescence lifetime. 20,21 In general, phosphorescence is rarely observed at RT in air because it is easily deactivated by local molecular motions and quenching by atmospheric oxygen during the long lifetime of the excited triplet (T 1 ) state.…”

Photoluminescence Properties of Copolyimides Containing Naphthalene Core and Analysis of Excitation Energy Transfer between the Dianhydride Moieties

“…Therefore, PIs have been applied in numerous fields, including automotive, microelectronic, photonic, electronic, and aerospace industries. Owing to their characteristic photoluminescence (PL) properties and excellent performance, PI films have been extensively studied as novel thermally stable photoluminescent materials [3][4][5][6][7][8][9][10][11].…”