Selective Expression of Organic P hosphorescence Units: When H-Benzo[f]indole Meets 7H-Benzo[c]carbazole

Abstract

Phosphorescence selective expression in the development of ultralong organic room-temperature phosphorescence (UORTP) materials to enrich the properties and functions of smart materials is a very interesting topic but has not been realized yet due to the lack of organic phosphorescence units. In this work, we, for the first time, investigate the selective expression phenomenon of two organic phosphorescence units in a single molecule. First, we report a new phosphorescence unit 7H-benzo[c]carbazole (BCz) with the advantage of simple synthesis. BCz derivatives (PNBCz-1 and PNBCz-2) feature photoactivated green ultralong phosphorescence in the PMMA film at room temperature, and cation radicals are involved in the unique ultralong phosphorescence behavior, which is similar to H-benzo[f]indole (Bd) derivatives. Different from Bd, pure powders of BCz derivatives show intense red-shifted ultralong phosphorescence at 77 K, probably due to the extended π conjugated structure of BCz. Then, BCz and Bd were incorporated into a single skeleton and two asymmetric molecules (PNBCzBd-1 and PNBCzBd-2) were obtained. Surprisingly, in the PMMA film, PNBCzBd-1 and PNBCzBd-2 both show photoactivated yellow ultralong phosphorescence at room temperature assigned to the intrinsic phosphorescence emission of Bd, and intrinsic green phosphorescence of BCz is almost screened by Bd. Density functional theory (DFT) calculations reveal that the incorporation of Bd leads to the shifting of the phosphorescence emission centers from BCz units to Bd units. Therefore, the intrinsic phosphorescence emission of Bd is selectively expressed in the case of PNBCzBd-1 and PNBCzBd-2. To our best knowledge, this is the first example that reports the selective expression behavior of organic phosphorescence units. We believe that this study may impact the future research of UORTP materials and lay the foundation for their future applications.

Photo-activated time-dependent color-changeable ultralong organic room temperature phosphorescence by co-doping strategy

“…On the basis of all the results above and previous reports, 27,29–31 we proposed a mechanism of the photo-activated time-dependent changeable ultralong phosphorescence (Fig. 5).…”

“…It is reasonable to infer that singlet oxygen is involved in the photo-activated ultralong room temperature phosphorescence. According to previous works, 27,[29][30][31] singlet oxygen can be generated in the PMMA film by UV irradiation and will be consumed by oxidizing PMMA. As residual oxygen in the PMMA film is consumed totally, triplet excitons of CN2BCzBr and CNCzBCzBr can accumulate, leading to the activation and enhancement of ultralong phosphorescence.…”

“…[21][22][23][24] Since the discovery of H-benzo[f]indole (Bd, a carbazole isomer) in carbazole-based phosphorescence systems, 25,26 guest-matrix doping has become a popular strategy to construct UORTP materials. 27,28 In 2021, my group for the first time successfully obtained lab-synthesized Bd 29 and deeply investigated the UORTP properties of Bd and its derivatives: (1) Bd derivatives show photo-activated yellow UORTP in the PMMA film; (2) Bd derivatives function as excellent guests and form guest-matrix doping phosphorescence systems with Cz derivatives and other powder matrixes; (3) charge separation and charge recombination are involved in the ultralong phosphorescence mechanism for the guest-matrix doping systems. Then, we found that 5H-benzo[b]carbazole (BCz-1), 30 whose derivatives show almost the same UOP characteristics as Bd derivatives, is a readily obtained alternative to Bd.…”

“…[32][33][34][35] Stimulus-responsive color-changeable luminescent organic materials have attracted considerable attention in the past few years, especially for color-changeable UORTP materials. [36][37][38][39] According to our previous work, 27,[29][30][31] different phosphorescence units feature different phosphorescence lifetimes and different phosphorescence colors. Furthermore, there exist more variables in guest-matrix doping phosphorescence systems compared with single-component systems, [40][41][42] which offers more methods to tune the phosphorescence properties.…”

Extending the molecular conjugation of phosphorescence units to accurately modulate ultralong organic room temperature phosphorescence

“…On the basis of similarities of Bd, BCz-1 and BCz-2, we defined them as ''phosphorescence units''. [22][23][24][25][26][27] In another word, once an organic unit functions similarly to Bd, BCz-1 and BCz-2 in terms of UORTP, it can be regarded as a phosphorescence unit. Generally, UORTP properties (spectral shift of phosphorescence, phosphorescence efficiency, and phosphorescence lifetime) should be closely related to the molecular structures of phosphorescence units or phosphorescence molecules (constructed with phosphorescence units, such as a D-A structure 28,29 ), stacking mode of aggregates, [30][31][32][33] interactions between phosphorescence units 34 and a matrix, [35][36][37][38] etc.…”