Abstract
N-cyclohexylphthalimide-substituted trifluoroacetylamino (CF3CONH-) group (3TfAPI), which forms an intramolecular hydrogen bond, was synthesized, and it exhibited a bright yellow fluorescence owing to the excited-state intramolecular proton transfer (ESIPT) in the solution and crystalline states. In addition, CF3CONH-substituted phthalic anhydride (3TfAPA) was synthesized, which was attached to the termini of a blue-fluorescent semi-aromatic polyimide (PI) chain. Owing to the efficient Förster resonance energy transfer (FRET) occurring from the main chain to the termini and the suppression of deprotonation (anion formation) at the 3TfAPA moiety by H2SO4 doping, the resulting PI films display bright white fluorescence. Moreover, the enhancement of the chain rigidity by substituting the diamine moiety results in an increase in the quantum yield of white fluorescence (Φ) by a factor of 1.7, due to the suppression of local molecular motion. This material design strategy is promising for preparing thermally stable white-light fluorescent PIs applicable to solar spectral convertors, displays, and ICT devices.
Highlights
White light-emitting organic molecules and polymers have received a great deal of attention because they can be used for facile production of light weight, low-cost, white organic light-emitting diodes (WOLEDs), which are expected to contribute to the miniaturization of various displays and ICT devices
We have reported a white-light fluorescent PI copolymer based on Förster resonance energy transfer (FRET) and room-temperature phosphorescence [8]
We resumed a detailed investigation of the structure and optical properties of 3TfAPI in the crystalline and solution states and we developed novel white light luminescent PI films by attaching a novel excited-state intramolecular proton transfer (ESIPT) anhydride having the same skeletal structure as 3TfAPI (3TfAPA, Scheme 1) as an end-capping agent for blue-fluorescent PIs (ODPA/DCHM or oxydiphthalic dianhydride (ODPA)/tDACH)
Summary
White light-emitting organic molecules and polymers have received a great deal of attention because they can be used for facile production of light weight, low-cost, white organic light-emitting diodes (WOLEDs), which are expected to contribute to the miniaturization of various displays and ICT devices. Solid white light-emitting organic materials based on a single luminophore typically possess high thermal and mechanical stability, as well as excellent productivity [1,2]. The fluorescence spectrum of solid-state luminophores is narrow, making it difficult to obtain a luminescence spectrum covering the entire visible region. White light generated by combining plural fluorophores often faces problems such as re-absorption, phase separation, and temporal change in emission colors. Achieving white light from a single-phase or molecule is beneficial because of their stability of luminescent color, ability to avoid phase separation, and simple manufacturing processes. It is a prerequisite to achieve white-light emission to exhibit a fluorescence spectrum that covers the entire visible region
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