Room‐Temperature Phosphorescence in Pure Organic Materials: Halogen Bonding Switching Effects

Abstract

Organic room-temperature phosphorescence (ORTP), when combined with external stimuli-responsive capability, is very attractive for sensors and bio-imaging devices, but remains challenging. Herein, by doping two β-iminoenamine-BF derivatives (S-2CN and S-2I) into a 4-iodoaniline (I-Ph-NH ) crystalline matrix, the formation of S-2CN⋅⋅⋅I-Ph-NH and S-2I⋅⋅⋅I-Ph-NH halogen bonds leads to bright-red RTP emissions from these two host-guest doped crystals (hgDCs) with quantum efficiencies up to 13.43 % and 15.96 %, respectively. Upon treatment with HCl, the competition of I-Ph-NH ⋅HCl formation against S-2I⋅⋅⋅I-Ph-NH halogen bonding switches off the red RTP from S-2I/I-Ph-NH hgDCs, whereas the stable halogen-bonded S-2CN⋅⋅⋅I-Ph-NH ensures red RTP from S-2CN/I-Ph-NH hgDCs remains unchanged. A security protection luminescence pattern by using these different HCl-responsive RTP behaviors was designed.

Switching of Monomer Fluorescence, Charge‐Transfer Fluorescence, and Room‐Temperature Phosphorescence Induced by Aromatic Guest Inclusion in a Supramolecular Host

“…In the present case, the fluorescence efficiency was regenerated because of the suppression of ISC, which resulted in a high Φ PL of 27 % (Figure (a)). Inclusion and removal of 8 as a guest can therefore regulate the phosphorescence and fluorescence switching of the resulting materials, which is rare behavior . Moreover, the intensity of phosphorescence emission decreased upon grinding a crystal of C8 (Figure , Figure S32 in the Supporting Information) even though the PXRD pattern agreed well with the simulated pattern determined from SCXRD analyses.…”

Enhanced Room‐Temperature Phosphorescence through Intermolecular Halogen/Hydrogen Bonding

“…It can be seen that a fast k Ph together with a slow k Ph,nr will significantly promote the phosphorescence emission process. Unfortunately, the T 1 →S 0 radiative transition is generally a very slow process because of the spin‐forbidden nature for metal‐free organic materials, and only a few examples have shown that k Ph could be promoted through intermolecular halogen bonding and an external heavy‐atom effect …”

“…Upon treatment with hydrochloric acid as an external stimulus, the competitive formation of the I‐Ph‐NH 2 ⋅ HCl complex disrupts the S‐2I⋅⋅⋅NH 2 ‐Ph‐I halogen bonding, and therefore, switches off the red RTP from S‐2I/I‐Ph‐NH 2 hgDCs; in sharp contrast, red RTP from S‐2CN/I‐Ph‐NH 2 hgDCs remains unchanged. A secure luminescence pattern was designed by using different HCl‐responsive behaviors of S‐2CN/I‐Ph‐NH 2 and S‐2I/I‐Ph‐NH 2 hgDCs (Figure b and c) …”

Room‐Temperature Phosphorescence in Metal‐Free Organic Materials

“…Because in pure organic compounds (especially π‐conjugation ones), the SOC constants are very weak with common value less than 0.1 cm −1 , resulting in low intersystem crossing (ISC) rate to yield triplet states from S 1 state, which in general cannot compete with the radiative or nonradiative decay rates from S 1 to S 0 in the photoluminescence (PL) process . Very recently, efficient ISC processes have been achieved through several strategies, including introduction of aromatic carbonyl groups and halogen bonding, as well as forming charge transfer states, radical anion pairs, and so on, and thus generating an observable RTP in organic materials. Another crucial reason for inefficient RTP is the deactivation of T 1 states induced by molecular vibration and rotation relaxation.…”