Pure Organic Room Temperature Phosphorescence from Unique Micelle‐Assisted Assembly of Nanocrystals in Water

Abstract

Pure organic room temperature phosphorescence (RTP) is highly preferable because of its long lifetime and potential applications. However, these kinds of materials are still very scarce due to the weak spin-orbit coupling between singlet and triplet states and easily nonradiative decay of the excited states. Achieving room temperature phosphorescence under visible light excitation is particularly challenging in aqueous solution. Herein, a micelle-assisted assembling strategy has been developed to realize pure organic RTP in water by using donor-acceptor molecules. A visible-light responsive long-lived RTP in water with a lifetime more than 3 ms is obtained by the prepared nanocrystals. However, the same molecules show no RTP as rigid bulk crystals. Spectroscopic studies, single-crystal structure analysis, X-ray diffraction patterns, and density functional theory calculations reveal that the intermolecular interactions, heavy atom effect, and the molecular packing way play critical role to the long-lived RTP character for the assembled nanocrystals in water and thermally activated delayed fluorescence for crystals in solid.

Host–guest materials with room temperature phosphorescence: Tunable emission color and thermal printing patterns

“…As shown in Figure S9, in molecular dimer or trimer with DMAP:Tmb = 1:1 or 2:1, Tmb acted as the main emitter and showed the typical π‐π* transition from the HOMO of Tmb to the corresponding LUMO, which were well identical to the experimental results. As for the tetramer with DMAP:Tmb = 3:1, obvious intermolecular charge transfer could be observed, from the occupied orbital of Tmb to the vacant orbital of the neighboring DMAP, which has been frequently considered to be much beneficial for the ISC transition as well as the resultant RTP emission in previous reports 35–38 . Further on, the energy levels and the corresponding SOC constants between S 1 and T n were calculated.…”

“…34 Furthermore, a new shoulder peak at about 360 nm appeared in the UV-vis absorption spectrum of cocrystal in comparison with the individual DMAP and Tmb samples ( Figure S7), indicating the intermolecular charger transfer between DMAP and Tmb. 35,36 Accordingly, the intersystem crossing (ISC) could be largely promoted, thus leading to the efficient RTP emission of Tmb in the cocrystal state. 37,38 To make a deep insight into the RTP mechanism of DMAP-Tmb cocrystal, the time-dependent density functional theory calculations were carried out ( Figures S8-S10).…”

“…As for the tetramer with DMAP:Tmb = 3:1, obvious intermolecular charge transfer could be observed, from the occupied orbital of Tmb to the vacant orbital of the neighboring DMAP, which has been frequently considered to be much beneficial for the ISC transition as well as the resultant RTP emission in previous reports. [35][36][37][38] Further on, the energy levels and the corresponding SOC constants between S 1 and T n were calculated. In general, the energy level difference between S 1 and T n less than 0.3 eV is considered to be able to process ISC and the larger SOC values indicate more efficient ISC transition.…”

Ultralong Room-Temperature Phosphorescence of Silicon-Based Pure Organic Crystal for Oxygen Sensing

“…2,[8][9][10][11] Particularly, pure organic materials are highly desirable for oxygen detection due to their long-lived room temperature phosphorescence (RTP), low-cost, large Stokes shift and good processibility. [12][13][14][15] In general, achieving pure organic ultralong RTP should consider two design principles: 1) promotion of intersystem crossing (ISC) through incorporating halogen atoms, [16][17][18][19] heteroatoms [20][21][22] , or aromatic carbonyl groups [23][24][25] ; 2) suppression of rapid non-radiative transition of triplet excited state to ground state by crystallization 24,[26][27][28][29][30] , host-guest interaction 31,32 , polymer-matrix assistance 33,34 etc. Crystal engineering is the most widely employed method to achieve pure organic room temperature phosphorescence, owing to the tightly packing of molecules to suppress non-radiative decays from molecular motions by a number of halogen bonds, hydrogen bonds and intermolecular π─π interactions in crystals.…”

Engender Persistent Organic Room-Temperature Phosphorescence by Trace Ingredient Incorporation

“…In the last century, researchers believed that it was difficult to use pure organic materials to emit phosphorescence at room temperature due to the difficulty of intersystem crossing (ISC) between singlet and triplet, and fast non-radiative transition (5). Recently, pure organic RTP with long lifetime and high efficiency have been realized by several methods, such as crystal or co-crystal packing (6)(7)(8)(9), polymer and host-guest supramolecular system (10)(11)(12)(13), and bimolecular charge separation state (14). However, it is still an urgent need for more convenient strategies to construct RTP as 2 well as a reliable mechanism for afterglow luminescence.…”