White-Light Emission and Tunable Luminescence Colors of Polyimide Copolymers Based on FRET and Room-Temperature Phosphorescence

Abstract

Thermally stable copolyimide (CoPI) films exhibiting high optical transparency and room-temperature phosphorescence (RTP) were prepared by copolymerizing fluorescent dianhydride and brominated phosphorescent dianhydride with an alicyclic diamine. The CoPI films underwent a 5 wt % degradation at a temperature higher than 349 °C and exhibited dual fluorescent and phosphorescent emissions owing to their efficient Förster resonance energy transfer from the fluorescent to phosphorescent dianhydride moieties in the main chains, followed by an intersystem crossing from the singlet to triplet state of the latter moiety atoms. The CoPIs displayed bright RTP under a vacuum with various colors produced when adjusting the copolymerization ratio. CoPI with 5 mol % phosphorescent moiety (CoPI-05) emitted white light with high optical transparency owing to the suppression of the PI chain aggregation that causes a yellowish coloration. The copolymerization of fluorescent and phosphorescent PI moieties can control the photoluminescent properties of PI films and is applicable to color-tunable solid-state emitters, ratiometric oxygen sensors, and solar-spectrum converters.

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

“…However, white light generated by combining plural fluorophores often faces problems such as re-absorption, phase separation, and temporal change in emission colors. Meanwhile, white light can also be obtained from a single phase or a single molecule, by introducing two or three light-emitting elements into a single molecule [4] and single polymer [5], or using organic-inorganic hybrid semiconductors [6], metal complexes [7], and room-temperature phosphorescent polymers [8]. 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.…”

“…The Förster resonance energy transfer (FRET) is a well-known energy transfer phenomenon [35], in which the excitation energy between two chromophores in close distance is directly transferred through non-radiative dipole-dipole coupling, and has been applied to white light-emitting materials [36]. We have also reported a white-light fluorescent PI copolymer based on FRET and room-temperature phosphorescence [8]. ESIPT is a process in which the excited state is relaxed by the structural relaxation (tautomerization) from the normal (N*) form to the tautomer (T*) form, through proton transfer in the excited state, resulting in a large energy gap between the absorption and emission, leading to a very large ν.…”

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

“…The present authors recently reported a novel white-light emitting PI film by copolymerizing a fluorescent and a phosphorescent PIs [5,12]. Moreover, we have also reported that, by introducing heavy halogens, iodine and bromine, into the dianhydride moiety of PIs, bright phosphorescence (Ph) can be observed at room temperature owing to the heavy atom effect [13,14].…”

Shedding light on predicting and controlling emission chromaticity in multicomponent photoluminescent systems

“…19 However, many multicomponent PL systems possess intra-or intermolecular energy transfer (ET) mechanisms such as Fluorescence Resonance Energy Transfer (FRET). 11,13,14,20,21 Accounting for ET processes makes applying colour-mixing theory a challenge since ET differs from system to system. However, what if ET processes were mitigated or suppressed?…”