Dissecting Tetra-N-phenylbenzidine: Biphenyl as the Origin of Room Temperature Phosphorescence

Abstract

Amorphous purely organic thin films are able to show efficient phosphorescence under ambient conditions at room temperature. This opens the perspective to a wide range of new applications, which have attracted lots of interest in the field of material science recently. Therefore, an increasing number of different molecules displaying room temperature phosphorescence (RTP) have already been reported. Whereas the efficiency, the lifetime, or the oxygen sensitivity is frequently discussed, the origin of RTP mainly remains vague. Often, material design rules tend to the development of increasingly complex structures. Here, the well-known tetra-N-phenylbenzidine (TPD), an archetypical material showing highly efficient fluorescence and RTP, is broken down to its fragments. As the complexity of the system decreases with the molecule’s size, spectroscopic investigation of this molecular family enables a deeper understanding of the appearance of RTP. With spectral and time-resolved measurements, RTP can be detected for all compounds containing a biphenyl core, with lifetimes up to 0.9 s under inert gas conditions. These findings form the basis of a deeper understanding of the appearance of RTP in organic molecules and therefore allow for a more focused investigation of new materials.

Aromatic Phosphonates: A Novel Group of Emitters Showing Blue Ultralong Room Temperature Phosphorescence

“…Further, we recently reported that the origin of phosphorescence for TPB is the biphenyl motif. [ 51 ] Based on this, our group pursued several approaches with different side groups and substituents to extend the phosphorescence lifetime even more, where the presented one turned out to be most efficient.…”

“…The investigation of the emission properties shows the biluminescent behavior of our targets, i.e., the simultaneous emission of fluorescence and phosphorescence. Since PMMA itself emits by excitation at 275 nm [ 51 ] (Figure 2a and Figure S12, Supporting Information), data evaluation for PMMA samples will only be performed with an excitation wavelength λ exc = 300 nm. The position of the fluorescence and phosphorescence peaks of the four targets are nearly unaffected by excitation wavelength and matrix ( Table 1 ).…”

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

“…For example, 22Cz may be considered as a bis(biphenyl) derivative, a ring‐fused 2,2’‐dialkoxybiphenyl, or simply a twisted p ‐quaterphenyl. The power of such an approach was well evidenced in a recent report by Fries et al, which revealed that the origins of room temperature phosphorescence (RTP) in tetra‐ N ‐phenylbenzidine were a consequence of its biphenyl core [30] …”

A metal-free 2D layered organic ammonium halide framework realizing full-color persistent room-temperature phosphorescence

“…BPAB displays blue single-molecule RTP peak at 475 nm with two shoulders, as reported previously. 27,31 While HLB-NTAB and HLB-NIAB exhibit green and yellow RTP at 509 nm and 586 nm (Fig. S9b and S9c), corresponding to their single-molecule phosphorescence, respectively.…”