Highly Luminescent 2D‐Type Slab Crystals Based on a Molecular Charge‐Transfer Complex as Promising Organic Light‐Emitting Transistor Materials

Abstract

A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (Φ ≈ 60%) is realized by non-negligible oscillator strength of the S transition, and rigidified 2D-type structure. Moreover, this luminescent 2D-type CT crystal exhibits balanced ambipolar transport (µ and µ of ≈10 cm V s ). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active-layered organic light-emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed-stacked CT cocrystals in OLET applications.

Elucidating the Excited State of Mechanoluminescence in Organic Luminogens with Room‐Temperature Phosphorescence

“…Communications from solution to aggregation states suggest formation of intermolecular CT states for CzS-CH 3 and CzS-C 2 H 5 aggregates (Supporting Information, Figure S17). [11] Intermolecular CT states could result in an enhanced ISC process. Moreover,t he increased dipole moments from 2.43 and 2.40 debye in isolated CzS-CH 3 and CzS-C 2 H 5 ,t o3 .74 and 3.45 debye in the corresponding dimers,s uggests formation of intermolecular CT states in the molecular dimers.T hus, the formed CT states enable good communication between the excited singlet and triplet states,which produces efficient phosphorescence in crystals upon UV irradiation.…”

“…These characteristics could contribute greatly to the relatively high PL efficiencies of these materials. [11] With this packing mode,a ne fficient intermolecular electronic coupling effect should exist, thus having asignificant influence on light emissions,including PL and ML. [11] With this packing mode,a ne fficient intermolecular electronic coupling effect should exist, thus having asignificant influence on light emissions,including PL and ML.…”

“…[12] Isolated molecules of CzS-CH 3 and CzS-C 2 H 5 presented p-p*t ransitions because of the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and LUMO + 1 electron clouds spread across the phenothiazine moiety (Supporting Information, Figure S16). [11] Intermolecular CT states could result in an enhanced ISC process. Moreover,t he oscillator strength (f)o fC zS-C 2 H 3 (0.0011) was much larger than that of CzS-CH 3 (0.0002), which is deemed to be amajor contributor to the higher PL efficiencyo fC zS-C 2 H 3 (8.1 %) compared to that of CzS-CH 3 (3.0 %).…”

“…[10] In particular, molecular dimers were formed with multiple C À H···p and C À H···N bonds. [11] With this packing mode,a ne fficient intermolecular electronic coupling effect should exist, thus having asignificant influence on light emissions,including PL and ML. ForCzS-CH 3 ,six C À H···p interactions (ranging from 2.90 to 3.90 )a nd three C À H···N interactions (3.07 to 3.90 )w ere present in the molecular dimers.I nterestingly, these dimers were connected by relatively weak hydrogen bonds,including one CÀH···p (2.56 )and two CÀH···N (3.55 to 3.77 )bonds.The same phenomena were observed in the CzS-C 2 H 5 crystal:t wo molecules interact with each other through six C À H···p (ranging from 3.00 to 3.90 )a nd two C À H···N bonds (3.34 and 3.36 )toform adimer.Each set of CzS-C 2 H 5 dimers are linked with three C À H···p (ranging from 2.68 to 3.93 )a nd one CÀH···N bonds (3.76 ), or one CÀH···p (3.10 )a nd two CÀH···N bonds (3.24 and 3.42 ).…”

The Emergence of Organic Single‐Crystal Electronics

“…[108] Although the charge transport of organic semiconductors can be both p-type and n-type,the real measurements of most organic semiconductors are either hole transport or electron transport, and one motivation behind organic cocrystals is to realize intrinsic ambipolar transport. Compared with al arge number of organic donors,t he reported organic acceptors used for the formation of organic cocrystals are limited to af ew examples,s uch as TCNQ, [108,109] F 2 TCNQ, [110] 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ), [110c, 111] TCNQ derivatives, [112] C 60 , [113] naphthalenetetracarboxydiimides (NDIs), [114] (2Z,2'Z)-3,3'-(1,4phenylene)bis(2-(3,5-bis(trifluoromethyl)phenyl)acrylonitrile) (CN-TFPA), [115] and others. [116] In 2004, ambipolar transport, with both hole and electron mobilities on the order of 10 À3 cm 2 V À1 s À1 ,w as observed in as ingle crystal of bis(ethylenedithio)tetrathiafulvalene-F 2 TCNQ (BEDT-TTF-F 2 TCNQ) at low temperature.…”