Organic Charge‐Transfer Complexes for Near‐Infrared‐Triggered Photothermal Materials

Abstract

When light-absorbing materials are excited by visible or near-infrared (NIR) light, they will eventually come back to their original equilibrium state, and a part of the absorbed photon energy is released as heat through nonradiative transitions during this process. The heat is determined by absorption ability under excitation wavelength and photothermal conversion efficiency, which is strongly related to the radiative and nonradiative transition rates. A good photothermal material should have high photothermal conversion efficiency, suitable absorption spectrum, and high light absorption ability, and can be used for photoacoustic imaging, [1][2][3] cancer photothermal therapy, [4,5] seawater desalination, [6][7][8] lightdriven thermoelectric system, [9,10] and so on. Especially, the second infrared window (NIR-II, 1000-1700 nm) absorbed photothermal materials have received much attention in biological applications for weak light scattering, low tissue absorption, deep tissue penetration depth, and high maximum permission exposure (up to 1.0 W cm À2 under 1064 nm laser excitation). Up to now, varied photothermal materials can roughly be categorized into two parts: inorganic materials and organic counterparts. For the potential long-term toxicity of inorganic materials, organic counterparts possess low toxicity, easy structural modification, tunable properties, and abundant molecules, so organic photothermal materials have rapidly developed during the last two decades. Typical organic photothermal materials embrace porphyrin, [11] cyanine dyes, [12,13] diketopyrrolopyrrole, [5] polyaniline, [14] polypyrrole, [15] semiconducting polymers, charge-transfer complexes (CTCs), [16] and so on.Among them, the CTCs are composed of electron-donating (D) and electron-accepting (A) molecules, and formed once charge delocalization takes place between the D and A leading to an enhanced molecular polarization, [17] which can be described as [18] In 1973, a famous CTC (TTF-TCNQ) was first reported, which was made of tetrathiafulvalene and 7,7 0 ,8,8 0 -tetracyanoquinodimethane; the researchers found that the electrical conductivity of TTF-TCNQ was comparable with metals. [19] From then on, the electrical properties of CTCs have got much attraction,

Supramolecular Organic Ferroelectric Materials from Donor–Acceptor Systems

“…[34,35] Such CT complexes have been studied extensively for creating elegant supramolecular assemblies [34,35] and in search for new organic materials. [51][52][53] They were found to be suitable as organic FE materials since alternately stacked D-A co-crystals can exhibit ionic nature due to partial charge transfer from the D to the A moiety (Figure 2). As a consequence of such charge transfer process, the charge-neutral …DADADADA.…”

“…They generally exhibit weak association constant (<20 M −1 ), but in a few selected examples significantly higher values have been reported due to the stabilization by other noncovalent interactions such as H‐bonding [34,35] . Such CT complexes have been studied extensively for creating elegant supramolecular assemblies [34,35] and in search for new organic materials [51–53] . They were found to be suitable as organic FE materials since alternately stacked D‐A co‐crystals can exhibit ionic nature due to partial charge transfer from the D to the A moiety (Figure 2).…”

A narrow-bandgap photothermal material based on a donor–acceptor structure for the solar–thermal conversion application

“…[11][12][13] Organic materials have received signicant attention from researchers due to a high molar extinction coefficient, a designable structure and easy modication. Currently the common organic photothermal materials mainly involve organic polycyclic p-conjugated molecules, 14,15 organic cocrystal materials, 16,17 charge-transfer complexes, [18][19][20] and organic D-A type materials. [21][22][23] Among them, some also face the shortcomings of poor photostability, photobleaching, restricted absorption wavelength and limited absorption capacity, which lead to low photothermal conversion efficiency.…”

Polyurethane-Based Photo/Thermal Energy-Storage Capsules Made with Manganese Phtalocyanine as a Photothermal Agent

“…The second is metal and metal oxide nanoparticles such as silver, platinum, titanium dioxide, and alumina. Carbon-based nanomaterials such as graphene and carbon nanotubes are the third type. − Efficient photothermal materials are the ones which have strong absorption, high photothermal conversion efficiency, and good light stability. , Phthalocyanine is a kind of functional compound having a large conjugated system with 18 π electrons in plane. Phthalocyanine has strong absorption in the red light region and good photothermal stability, and it is a good photothermal conversion material. , The absorption band of phthalocyanine can be further red-shifted to the near-infrared region by structural modifications, which benefits its further application .…”