Room‐Temperature Phosphorescence from a Series of 3‐Pyridylcarbazole Derivatives

Abstract

Exploration of pure metal-free organic molecules that exhibit strong room-temperature phosphorescence (RTP) is an emerging research topic. In this regard, unveiling the designp rinciples for an efficient RTP molecule is an essential,b ut challenging, task. As mall moleculei sa ni deal platformt op recisely understand the fundamental role of each functional component because the parent molecule can be easily derivatized. Here, the RTP behaviors of as eries of 3-pyridylcarbazole derivatives are presented. Experimental studies in combinationw itht heoretical calculations reveal the crucial role of the no rbital on the centralp yridine ring in the dramatic enhancemento ft he intersystem crossing between the charge-transfer-excited singlet state and the lo-cally excited triplet states. Single-crystal X-ray crystallographic studies apparently indicate that both the pyridine ring and fluorine atom contribute to the enhancemento ft he RTP because of the restricted motion owing to weak CÀH···N and H···F hydrogen-bonding interactions. The singlec rystal of the fluorine-substituted derivatives hows an ultra-long phosphorescent lifetime( t P )o f1 .1 sa nd ap hosphorescence quantum yield (F P )o f1.2 %, whereast he bromine-substituted derivative exhibits t P of 0.15 sw ith a F P of 7.9 %. We believe that this work providesafundamentala nd universal guideline for the generation of pure organic molecules exhibiting strongR TP.[a] Prof.

Supramolecular architectures sustained by delocalised C–I⋯π(arene) interactions in molecular crystals and the propensity of their formation

“…145 This is the exceptional observation within this category. Thus, for 36, 105 71, 138 127, 190 130, 193 and 139, 202 respectively. 105,138,258,193,264 Each of these iodide-containing molecules also has a chloride congener, respectively.…”

“…Two independent molecules also comprise the asymmetric unit of in each of 23 92 and of 36. 105 In each of these crystals, only one of the independent molecules self-associates about a centre of inversion to form a dimeric aggregate; the second independent molecule is similarly orientated but, with parameters outside the search criteria, see ESI Table 2. Despite having the common feature of two independent molecules in the crystallographic asymmetric unit, a different situation pertains in the crystals of each of 10 30 99 and 42.…”

“…105,138,258,193,264 Each of these iodide-containing molecules also has a chloride congener, respectively. 104,138,259,260,193,250 While a delocalised C-Cl•••π(arene) interaction is apparent in the congener of 127, 190 the only other congener to exhibit a C-Cl•••π(arene) interaction is that of 36, 105 i.e. a side-on contact.…”

“…No C-F•••π(arene) interactions were noted in four of the known fluoride congeners. 105,145,193,250 There are two polymorphs known for the fluoride congener of 127, 190 namely two monoclinic (P2 1 /c) polymorphs. In the Z' = 4 form, 261 a two-molecule aggregate formed between two of the independent molecules is sustained by a close to delocalised C-F•••π(arene) interaction with many other, side-on delocalised C-F•••π(arene) interactions being apparent.…”

Efficient metal-free organic room temperature phosphors

“…To understand the effect of a heavy atom to obtain longer RTP, Sasabe, Kido and coworkers studied the RTP features of a series of 3-pyridylcarbazole derivatives with H, F, Cl, Br, and I as substituents on the pyridine ring. 85 The crystals of the fluorine-substituted derivative CzPyF ( Scheme 2 ) showed an ultralong τ p of 1.1 s and ϕ p of 1.2%. Theoretical and experimental data revealed the crucial role of n orbital on the central pyridine ring in enhancing the intersystem crossing between 1 CT* and the locally excited triplet ( 3 LE*) states.…”