Photochromic and Room-Temperature Phosphorescent D–A Hybrid Crystals Induced by Anion−π Interactions

Abstract

The donor–acceptor (D–A) hybrid crystals are an emerging class of crystalline hybrid complexes composed of semiconductive organic and inorganic components at the molecular level. These unique crystals not only possess intrinsic electron-transfer photochromic properties upon the high-energy irradiations but possibly exhibit unusual room-temperature phosphorescence (RTP) emissions when suitable charge-transfer states formed with the low-energy irradiations. Herein, we reported that an interesting class of D–A hybrid crystals indeed exhibited two such properties in which two D–A components, polyoxometalates (POMs) and naphthalene diimides (NDIs), are intercontacted through uncommon anion−π interactions. To go deep into their structure–property relationships, five D–A hybrid crystals with different POMs (PW12O40 3–, SiW12O40 4– or Mo6O19 2–) and protonated (or zinc-coordinated) pyrazolyl-substituted NDIs have been synthesized. Their light-induced color changes and RTP properties have been systematically investigated, which revealed that the matching electron energy levels of POMs and NDIs are the first factor to decide their RTP emissions while the heavy atoms in both POMs and coordination metal cations are mainly beneficial to their quantum yields. Notably, the RTP quantum yields for these interesting photochromic D–A hybrid crystals are up to 5.9%.

Photochromic and Room Temperature Phosphorescent Donor–Acceptor Hybrid Crystals Regulated by Core-Substituted Naphthalenediimides

“…Compared to the reported hybrid (core-unsubstituted analogues) (H 4 BDMPy-NDI)·(NMP) 4 ·(HPW 12 O 40 )) ( 3 ) (CCDC: 2058219) with segregated POM anions and protonated H 4 BDMPy-NDI ligands, there is no significant difference in the crystalline structure for the three complexes. All three hybrids are made up of PW 12 O 40 3– and NDI organic ligands to form alternating arrangement structures.…”

“…3,4 Moreover, photochromic properties, which are mainly dependent on the inorganic components and the molecular packing modes, have been extensively investigated. 5−9 Indeed, several groups, including ours, have reported an array of such D−A hybrid crystals with various inorganic components, like polyoxometalate anions, alkaline-earth metal oxide chains, 7 and metal halides, 9 as well as different packing patterns 8 (with or without coordinated metal cations).…”

“…12,13 For example, the hybrids composed of NDIs and PW 12 O 40 3− or SiW 12 O 40 4− can produce RTP due to the compatible energy levels between donors and acceptors. 8 On the other hand, the introduction of heavy atoms could promote efficient ISC and bring about RTP. 14,15 Compared with a hybrid including PMo 12 O 40 3− , the quantum yield (QY) of a hybrid containing SiW 12 O 40 4− is higher and produces up to a 7.2% yield owing to the heavyatom effect.…”

“…Donor–acceptor (D–A) hybrid crystals are an emerging kind of crystalline hybrid materials composed of semiconductive inorganic donors and organic acceptors and have drawn considerable attention because of their potential applications in optoelectronic devices. , Among them, the HOMO of both donors and acceptors can be excited to LUMO upon light irradiation and leads to the photoinduced electron transfer (PIET), which generates photochromism. , Moreover, photochromic properties, which are mainly dependent on the inorganic components and the molecular packing modes, have been extensively investigated. − Indeed, several groups, including ours, have reported an array of such D–A hybrid crystals with various inorganic components, like polyoxometalate anions, alkaline-earth metal oxide chains, and metal halides, as well as different packing patterns (with or without coordinated metal cations).…”

“…Except for the intrinsic photochromism caused by photoinduced electron transfers between donors and acceptors, these unique hybrid complexes might also produce interesting room temperature phosphorescence (RTP) by selection of suitable components. , There are two main methods that can effectively promote the emission of RTP. On the one hand, intermolecular charge transfer (ICT) states can be formed by the donor and acceptor of a hybrid with matching energy levels and bridge the Δ E ST , which further improve the intersystem crossing (ISC) process and thus activate phosphorescence at room temperature upon irradiation. , For example, the hybrids composed of NDIs and PW 12 O 40 3– or SiW 12 O 40 4– can produce RTP due to the compatible energy levels between donors and acceptors . On the other hand, the introduction of heavy atoms could promote efficient ISC and bring about RTP. , Compared with a hybrid including PMo 12 O 40 3– , the quantum yield (QY) of a hybrid containing SiW 12 O 40 4– is higher and produces up to a 7.2% yield owing to the heavy-atom effect .…”