Lanthanide-based gels, using citric acid as an assembler ligand, provide pure white light emission and monitor changes in pH as well as temperature over a wide range through a mixed ligand design strategy.

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Organic materials exhibiting mechano-fluorochromic behavior in their gel state are extremely rare in the literature. Similarly, examples of mechano-fluorochromic organic materials with crystal-to-crystal phase transitions have not been reported until date. Herein, we achieved these two remarkable properties in phenothiazine derivatives S1 and S2[(E)-N′-((10-ethyl-10H-phenothiazin-3-yl)­methylene)-3,4,5-tris­(hexadecyloxy)­benzohydrazide and (E)-N′-((10-ethyl-10H-phenothiazin-3-yl)­methylene)­isonicotinohydrazide)], where S1 formed mechano-luminescent xerogel and S2 exhibited the rare feature of crystal-to-crystal phase transition with mechano-luminescence behavior. Study of the photophysical properties of S1 and S2 indicated the suppression of twisted intramolecular charge transfer (TICT) upon self-assembly, leading to blue-shifted emission from S1 and S2. While both S1 and S2 exhibited the propensity to aggregate and disclosed the aggregation induced emission (AIE) behavior in a binary solvent (THF/H2O) mixture, only S1 resulted in a robust gel, which was further utilized for developing a superhydrophobic surface with a contact angle of 157.56°. Upon mechanical grinding, both pristine sample and xerogel of S1 showed an emission color change from light green (505 nm) to yellowish green (530 nm), whereas S2 exhibited an emission color change from cyan blue (480 nm) to green (535 nm). Furthermore, both fluorophores exhibited red-shifted emission under application of increased pressure. Mechanistic studies indicated that grinding resulted in crystal to amorphous phase transition in S1, whereas grinding in S2 demonstrated the rare feature of crystal-to-crystal phase transition. The mechano-fluorochromic (MFC) natures of S1 and S2 were supported by single point energy calculations using density functional theory (DFT).

Semiconductor quantum dot (QD)–graphene composites are promising materials for photovoltaics and photocatalysis because of efficient charge extraction and transport property of graphene. Analysis of their ultrafast carrier-transfer dynamics has been limited to only QD–graphene sheets, such as CdTe–graphene sheets and CdS–graphene sheets. Herein, we investigate the carrier-transfer dynamics of CdTe QDs (CdTe QDs) in the presence and absence of graphene QDs (GQDs) by using femtosecond transient absorption spectroscopy. Although the surfaces of both the QDs are in negatively charged state, as evident from the zeta potential measurements, we observed a strong excited-state interaction between two similarly charged QDs, leading to an efficient quenching of the excitonic emission of the CdTe QDs in the presence of GQDs. A detailed analysis of the rise time and 1S bleach recovery provides the evidence of electron transfer from CdTe QDs to GQDs with the hole-trapping process by surface defects. On the basis of the mechanistic study, an overall charge-transfer scheme that accounts for the faster bleach recovery of CdTe QDs in the presence of GQDs is proposed. Moreover, we have evidenced the consequences of charge transfer through the measurements of improved four-probe photoconductivity (from 1.39 (±0.12) × 10–4 S m–1 to 1.47 (±0.24) × 10–3 S m–1) and decreased charge-transfer resistance [from 6944 (±0.3) to 5761 (±0.3) Ω] exhibited by CdTe QDs in the presence of GQDs. These findings described in the present study are hoped to open up design strategies for developing light-harvesting inorganic–organic hybrid QD assemblies with better efficiency.

Luminescent polymer based metallogels have gained considerable interest due to their wide range of applications in the fields of tissue engineering, drug delivery, sensing, and optical systems. One of the...