Effect of Substituents at Imide Positions on the Laser Performance of 1,7-Bay-Substituted Perylenediimide Dyes

Abstract

Perylenediimide (PDI) compounds with no substituents in their core are widely used as the active units of thin-film organic lasers. Recently, baysubstituted PDIs (b-PDIs) bearing two sterically hindering diphenylphenoxy groups at the 1,7-bay positions have received great attention because they show red-shifted emission with respect to bay-unsubstituted PDIs, while maintaining high photoluminescence (PL) quantum yields and low amplified spontaneous emission (ASE) thresholds even at high doping rates. However, their ASE photostability is relatively low compared to that of state-of-the-art PDIs. Thus, the design of b-PDIs with improved ASE photostability remains a challenge. Here, the synthesis of two b-PDIs with phenyl-type substituents at the imide positions is reported. Complete characterization of their optical properties, including absorption, PL, ASE, and transient spectroscopy, supported also by quantum chemical calculations, is performed with the dyes diluted in either a liquid solvent or a polystyrene film. Film experiments were accomplished at very low doping rates, to resemble the isolated molecule behavior, and also in a range of increasing doping rates, to investigate concentration quenching effects. The reported b-PDIs show improved ASE photostability (3fold) with respect to b-PDIs with aliphatic-type substituents at the imide positions, whilst they show more propensity toward aggregation.

The Effect of Imide Substituents on the Excited State Properties of Perylene Diimide Derivatives

“…Also, the PIA lifetimes of -2EH and -DIA were 4.3 and 4.6 ns, respectively (Table 3), in reasonable agreement with emission lifetimes in zeonex. These values are also similar to PDI derivatives reported with monomer structure [10,14,25]. At 1.0 x 10 -3 M of DiBrPDIs, both PDIs' GSB-SE first overlap peaks shifted to a few nm longer wavelengths because of highly absorption of white light continuum of probe by DiBrPDIs [14] while the SE peaks did not change.…”

“…One of them is direct chemical modification [14,20,21], while dispersal in an optical host material with low doping rates of emitter can also avoid ACQ [10,22]. As high concentrations are often required in applications though, the more commonly used method to reduce the aggregation of PDIs is by connecting steric groups from imide or bay positions [14,20,[23][24][25]. Although structures attached from the imide group do not participate in π conjugation system of PDI, electron donating groups (containing amine or carbazole) can interact with the PDI core in photoinduced electron transfer processes and quench PDIs' PL by directly, affecting their photophysical properties [26,27].…”

Donor–acceptor naphthalimides and peryleneimides for all-solution-processed thin film lasers

“…Significantly better values were obtained with the PI -based films, with ASE half-lives up to 2.2 × 10 4 pump pulses (∼37 min). Importantly, these ASE half-life values are comparable or better than those of state-of-the-art materials emitting at similar wavelengths 6,34,35,41 (see comparative table with different materials in Table S10 in the ESI†). For example, perylenediimide derivatives PDI-O ( λ ASE = 578 nm) 34 and b -PDI-Tp ( λ ASE = 618 nm) 41 present ASE half-lives of 3.8 × 10 4 and 1.6 × 10 4 pump pulses respectively, while other materials such as COPV5 ( λ ASE = 571 nm) 35 or nanographene FZ2 ( λ ASE = 591 nm) 6 have ASE half-lives of 2.2 × 10 4 and 7.5 × 10 3 pump pulses.…”

“…2c), among which, COPV4 has similar λ ASE (548 nm) than NI1 ( λ ASE ∼ 546 nm); COPV2 and COPV2-Tip 37 (dark blue symbols, Fig. 2c), the latter with λ ASE ∼ 474 nm, close to that of NI2 ( λ ASE ∼ 476 nm); and b -PDI-A 41 (dark green symbols, Fig. 2c) whose emission ( λ ASE ∼ 624 nm) is between those of PI1 ( λ ASE ∼ 638 nm) and PI2-3 ( λ ASE ∼ 600 nm).…”

“…34 More recently, certain bay-substituted PDIs (called b -PDIs) with emissions up to around 620 nm and with sufficient efficiency in terms of threshold have been reported. 40,41 In relation to the COPV n (with n = 1 to 6) family, 35 the compound emitting at a longer wavelength is COPV6 ( λ ASE ∼ 583 nn).…”