Perylene dyes have transcended their role as simple colorants and have been reinvigorated as functional dyes. Based on the substitution at the peri position by six-membered carboxylic imides, the perylene family is principally embellished with perylene diimides (PDIs) and perylene monoimides (PMIs). Perylene dyes are widely acclaimed and adorned on account of their phenomenal thermal, chemical, and photostability juxtaposed with their high absorption coefficient and near-unity fluorescence quantum yield. Although symmetric PDIs have always been in the limelight, its asymmetrical counterpart PMI is already rubbing shoulders, thanks to the consistent efforts of several scientific minds. Recently, there has been an upsurge in engendering PMI-based versatile organic architectures decked with intriguing photophysical properties and pertinent applications. In this review, the synthesis and photophysical features of various PMI-based derivatives along with their relevant applications in the arena of organic photovoltaics, photocatalysis, self-assembly, fluorescence sensing, and bioimaging are accrued and expounded, hoping to enlighten the less delved but engrossing realm of PMIs.

require the simultaneous emission from either three primary colored (red, green, and blue) or two complementary colored (such as blue and orange) emitters to span the visible spectrum (see Scheme 1). [4] Multi-component approach relies on energy transfer between complementary emissive chromophores to attain WL emission [4d,5] while in single-component approach, WL emission occurs from a single molecule. Single-component white light (SCWL) emitters have surpassed their multicomponent analogs from the viewpoint of superior stability, color reproducibility, less phase separation, negligible color aging issue, and easy device fabrication. [6] Kasha's rule clearly states that fluorophores always tend to attain the lowest vibrational states resulting in monochromatic emission. [7] So, realization of WL emission from a single molecular system is difficult and is therefore of great significance. SCWL emission obtained via covalent grafting of emissive units in a single-molecular backbone is often not efficient due to intramolecular FRET (Förster Resonance Energy Transfer) or TBET (Through Bond Energy Transfer). [8] Hence, several systems rely on mechanisms such as intramolecular energy transfer (IET), [4e] intramolecular electron transfer, [4g] excited-state intramolecular proton transfer (ESIPT), [4h,9] intramolecular charge transfer (ICT), [10] host-guest interaction, [11] and self-assembly, [4f,12] to attain SCWL emission (Scheme 1). Organic radical anions are open-shell molecular entities carrying a negative charge. They have found widespread applications in catalysis, magnetic materials, near-infrared photothermal effect, and optoelectronic materials. [13] For the development of efficient radical-based functional materials, stability is imperative. [14] To generate persistent ambient-stable radical anion, electron-deficient perylenediimide derivatives (PDI) are an obvious choice as they are inherently electron-deficient and offer ample opportunity to conjugate electron-withdrawing groups at different regions of the π-scaffold. In recent years, several reports related to chemical, electrochemical, and photochemical generation of stable PDI-based radical anion have surfaced. [13e,15] Stability of radicals can be modulated by resorting to either a covalent [15d,16] or non-covalent approach. [13d,17] Adoption of supramolecular strategies can tune the stability of radicals in a dynamic fashion. However, to the best of our knowledge, the potential of White light-emitting materials have attracted considerable attention in lighting devices and display media. This article reports the first-ever demonstration of a radical-based self-assembly for white light emission. Singlecomponent white light (SCWL) emitters are more advantageous than multicomponent ones due to better stability, color-reproducibility, and negligible color aging problem. The present study demonstrates SCWL emission arising out of the dynamic self-assembly of a photo-reduced perylene diimide derivative (PF-BPDI). Photo-reduction of PF-BPDI leads...

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Dissipative self-assembly is ubiquitous in nature and underlie many complex structures and functions in natural systems, primarily enabled by the consumption of chemical fuels. However, dissipative self-assembly fueled by light have also been parallelly developed. Photoswitchable molecules have been widely investigated as prototypical molecular systems for light driven dissipative self-assembly. Elucidation of optically fueled dissipative self-assembly by a photo-responsive yet non-photoswitchable molecule however remains elusive. This contribution thus demonstrates the first ever report of an optically fueled dissipative self-assembly arising from a redox active perylene diimide scaffold (DIPFPDI). Photo-reduction of neutral DIPFPDI in a poor solvent DMF affords its radical anion and batches of optical re-fueling leads to an increased concentration of radical anion, inducing the construction of an H-type aggregate. Nevertheless, when the influx of visible light is adjourned, the radical anions are converted to their neutral precursors and thus the self-assembled state is no longer sustained. Signature of H-type aggregation is deduced from steady-state UV-Vis, fluorescence as well as time-resolved fluorescence spectroscopy. Theoretical insights reveal that dimerization is more feasible in the charged states because of greater delocalization of the excess charge in the charged states.

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