Noncovalent Polymerization‐Activated Ultrastrong Near‐Infrared Room‐Temperature Phosphorescence Energy Transfer Assembly in Aqueous Solution

Abstract

Noncovalent macrocycle‐confined supramolecular purely organic room‐temperature phosphorescence (RTP) is a current research hotspot. Herein, a high‐efficiency noncovalent polymerization‐activated near‐infrared (NIR)‐emissive RTP‐harvesting system in aqueous solution based on the stepwise confinement of cucurbit[7]uril (CB[7]) and β‐cyclodextrin‐grafted hyaluronic acid (HACD), is reported. Compared with the dodecyl‐chain‐bridged 6‐bromoisoquinoline derivative (G), the dumbbell‐shaped assembly G⊂CB[7] presents an appeared complexation‐induced RTP signal at 540 nm via the first confinement of CB[7]. Subsequently, benefitting from the stepwise confinement encapsulation of the β‐cyclodextrin cavity, the subsequent noncovalent polymerization of the binary G⊂CB[7] assembly enabled by HACD can contribute to the further‐enhanced RTP emission intensity approximately eight times in addition to an increased lifetime from 59.0 µs to 0.581 ms. Moreover, upon doping a small amount of two types of organic dyes, Nile blue or tetrakis(4‐sulfophenyl)porphyrin as an acceptor into the supramolecular confinement assembly G⊂CB[7] @ HACD, efficient RTP energy transfer occurs accompanied by a long‐lived NIR‐emitting performance (680 and 710 nm) with a high donor/acceptor ratio. Intriguingly, the prepared RTP‐harvesting system is successfully applied for targeted NIR imaging of living tumor cells by utilizing the targeting ability of hyaluronic acid, which provides a new strategy to create advanced water‐soluble NIR phosphorescent materials.

Enhancing NIR-II Phosphorescence through Phosphorescence Resonance Energy Transfer for Tumor-Hypoxia Imaging

“…These data indicated that efficient PRET between PD and FA was probably available. In addition, NIR-II emission spectrum of FA was also confirmed (Figure S3 in the Supporting Information), which was similar to our previous study . By referring to this previous study, FA had such a high NIR-II quantum yield (QY = 6.97%), which would support a good NIR-II QY of the PRET system in this study.…”

“…Fluorescence resonance energy transfer (FRET) was well-demonstrated to be an efficient strategy in red-shifted emission spectra, enhancing emission intensity and amplifying single oxygen generation. − In this system, the energy transfer was from the singlet state of donor to the singlet state of acceptor by an ideal spectral overlap of the donor and acceptor. Encouraged by this convenient strategy for amplifying the signals, phosphorescence resonance energy transfer (PRET) had been developed to acquire red-shifted phosphorescent emission by the energy transfer from excited triplet state of donors to singlet state of acceptor. , In this regard, we envisioned that high-efficiency PRET between excited triplet state of donor and singlet state of acceptor would achieve bright NIR-II phosphorescence by the spectral overlap of the phosphorescent donor and NIR-II fluorescent acceptor.…”

“…Encouraged by this convenient strategy for amplifying the signals, phosphorescence resonance energy transfer (PRET) had been developed to acquire red-shifted phosphorescent emission by the energy transfer from excited triplet state of donors to singlet state of acceptor. 31,32 In this regard, we envisioned that high-efficiency PRET between excited triplet state of donor and singlet state of acceptor would achieve bright NIR-II phosphorescence by the spectral overlap of the phosphorescent donor and NIR-II fluorescent acceptor.…”

Macrocyclic Supramolecular Assemblies Based on Hyaluronic Acid and Their Biological Applications

“…Macrocyclic supramolecular assemblies that are based on hyaluronic acid (HA) have drawn great attention in several fields, including drug delivery, − molecular recognition and bioimaging, , hydrogels, − and cellular and tissue engineering fields. , In the process of constructing HA-based macrocyclic supramolecular assemblies, macrocyclic compounds play a key role, and these compounds can encapsulate photosensitizers, drug molecules, and other size-matched molecules through host–guest interactions to form multifunctional supramolecular assemblies. − Taking advantage of the tumor cells’ targeting ability and good biocompatibility of HA, the coassembly of macrocyclic host–guest complexes with HA can not only target tumor cells but also enhance the biocompatibility and stability of the assemblies due to the multivalent interactions, thereby expanding their biological applications. − As a significant component of an extracellular matrix, HA is a water-soluble, biocompatible, and biodegradable linear polysaccharide that contains alternating repeating disaccharide units, β-1,4- d -glucuronic acid−β-1,3- N -acetyl- d -glucosamine, possessing multiple carboxyl, hydroxyl, and acetylamino groups. , HA can specifically bind some overexpressed receptors (e.g., cluster determinant 44 (CD44) and HA-mediated motor receptor (RHAMM) also known as CD168) on the surfaces of various cancer cells, realizing receptor-mediated endocytosis, which displays widespread applications in drug delivery systems. − Moreover, HA has important therapeutic roles in angiogenesis and macrophage polarization, which can be used in wound healing dressings and biomaterials approaches to treating infarction, brain injury, and so on. − Therefore, the coassembly of HA and macrocyclic host–guest complexes functions as an excellent drug carrier and has a role in supramolecular diagnosis and treatment research, targeted imaging, injectable hydrogels, and bioscaffolds.…”

Modulating Emission of Organic Emitters from Fluorescence to Red Afterglow through Boric Acid-Assisted Energy Transfer

“…Due to the difficulties in stabilizing and manipulating excitons at relatively low-lying triplet excited states, it is more challenging to produce red or deep-red afterglow materials, − while red/deep-red emissive afterglow materials are the essential core elements for achieving solid-state lighting and full-color display. Except molecular skeleton and structural microenvironment engineering, modulating the energy transfer from a long-lived energy donor to a fluorescent energy acceptor is also an alternative strategy to develop afterglow materials. − This strategy could circumvent the tedious molecular engineering required for manipulating the RTP or TADF process. − In addition, the emission wavelength of afterglow materials could also be conveniently shifted to the red color region, by the suitable choice of energy acceptors. To fabricate efficient afterglow materials through energy transfer, the distance between the donor and acceptor should be small enough (<10 nm for Förster resonance energy transfer, and 1 nm for Dexter energy transfer), and the energy levels of the donor and acceptor should also be well matched with each other. ,, For example, George’s group proposed the energy transfer strategy to produce afterglow materials, through utilization of energy transfer from a long-lived energy donor to singlet of fluorescent dye .…”