Ambient Room Temperature Phosphorescence and Thermally Activated Delayed Fluorescence from a Core-Substituted Pyromellitic Diimide Derivative

Abstract

Triplet harvesting under ambient conditions plays a crucial role in improving the luminescence efficiency of purely organic molecular systems. This requires elegant molecular designs that can harvest triplets either via room temperature phosphorescence (RTP) or by thermally activated delayed fluorescence (TADF). In this context, here we report a donor core-substituted pyromellitic diimide (acceptor) derivative as an efficient charge-transfer molecular design from the arylene diimide family as a triplet emitter. Solution-processed thin films of carbazole-substituted CzPhPmDI display both RTP- and TADF-mediated twin emission with a long lifetime and high efficiency under ambient conditions. The present study not only sheds light on the fundamental photophysical process involved in the triplet harvesting of donor–acceptor organic systems, but also opens new avenues in exploring an arylene diimide class of molecules as potential organic light-emitting materials.

Spin–Orbit Natural Transition Orbitals and Spin-Forbidden Transitions

“…According to our survey of past research discussing spin-forbidden transitions in the context of NTOs, the latter were obtained either from 1TDMs between spin-free SR states belonging to different spin multiplicities, that is, without “integration” over spin degrees of freedom, or from SR spin-1TDMs. For recent publications, see, for example, refs , − , , , and . The NTOs thus obtained are clearly very useful for assigning a spin-forbidden transition.…”

“…Recent applications of the NTO method have been primarily in photochemistry and -physics and studies of excited states. A small selection of available studies is presented by refs − . Visualization of NTOs has been particularly useful for systems for which the descriptions of an electronic transition of interest involve a considerable number of pairs of occupied and unoccupied MOs with relatively low weights, which renders the assignment of the excitation difficult.…”

Achieving Thermally Activated Delayed Fluorescence from Benzophenone by Host–Guest Complexation

“…In contrast, for Bzp in MeCN, the strength of phosphorescence is decreased monotonically with increasing temper- ature (Figure 4c and Table S2); it follows a general trend as most of the RTP chromophores. 29,30 Bzp:MSN complexes show a much slower emission lifetime with increasing temperatures, suggesting efficient TADF activity and rule out the possibility of only the RTP process. One can expect that the rate of phosphorescence (k p ) in chromophores will not get larger at high temperature.…”

Progress and perspectives: fluorescent to long-lived emissive multifunctional probes for intracellular sensing and imaging

“…28). 24,26,27,[206][207][208][209] Though TADF and RTP processes share many common prerequisites such as stable triplet-states, small singlet-triplet energy gaps (DE ST ), and high spin-orbit coupling (SOC) interactions, the origin of long-lived emission in each case follows different photophysical pathways. 30,207,[209][210][211][212] In the subsequent sections, we outline the mechanistic perspectives, design strategies of small organic molecule-based TADF and RTP probes, and their use in time-resolved bioimaging.…”