Developing Quinoidal Fluorophores with Unusually Strong Red/Near-Infrared Emission

Abstract

Despite the dominant position of aromatic fluorophores, we report herein the design and synthesis of quinoidal fluorophores based on rarely emissive quinoidal bithiophene. Quinoidal bitheno[3,4-b]thiophene, QBTT-C6, consisting of cruciform-fused (E)-1,2-bis(5-hexylthiophen-2-yl)ethene and quinoidal bithiophene, shows a fluorescence quantum yield of 8.5%, 25-fold higher than that of the parent quinoidal QBT chromophore, but its maximum emission is at similar wavelengths. QBTT-Ar's featuring intramolecular charge transfer can further shift the maximum emission into the near-infrared region. The intramolecular charge transfer is programmably enhanced by tuning the substituents on the aryl groups from the electron-withdrawing trifluoromethyl to the electron-donating methoxy groups. Unexpectedly, a positive relationship between intramolecular charge transfer and fluorescence quantum yield is observed; as a result, QBTT-FL gives an unprecedentedly high fluorescence quantum yield of up to 53.1% for quinoidal oligothiophenes. With detailed photophysical and theoretical investigations, we demonstrate that the nonradiative intersystem crossing (S1 → T2) is significantly restrained in QBTT-Ar's, which can be attributed to the faster reverse intersystem crossing (T2 → S1) characteristic of a small activation energy. This work reveals the possibility for developing red/near-infrared fluorophores from the less explored quinoidal molecules because of their intrinsically narrow bandgaps.

J-aggregation of a sulfur-substituted naphthalenediimide (NDI) with remarkably bright fluorescence

“…However, this possibly originates from the low LUMO energy level of cNDI-1 which was estimated to be -3.84 eV from cyclic voltammetry ( Fig S7). In J-aggregate, E LUMO is further reduced by 0.14 eV (estimated from UV/Vis spectra) due to excitonic coupling, and thus gets more closer to the triplet state which in one hand reduces the propensity for ISC and may also turns on the possibility of ultra-fast reorganization from triplet state to S 1 state 19 and thus results in enhanced emission. …”

Dithienoindophenines: p‐Type Semiconductors Designed by Quinoid Stabilization for Solar‐Cell Applications

“…Surprisingly, donor materials with purely quinoidal frameworks have rarely been reported to date, with low PCEs of ≤1.1 % . Generally, quinoidal oligothiophenes (QOT) with rigid and planar Kekulé structures show unique optoelectronic properties such as narrow optical bandgaps with large absorption coefficients, singlet‐fission property, near‐infrared fluorescence, and excellent charge‐transport properties, which are highly desirable for OPV applications. However, the most well‐known dicyanomethylene‐terminated QOTs such as quinoidal bithiophene (QBT) are typically n ‐type semiconductors because of their high electron affinities.…”

Combining Benzotriazole and Benzodithiophene Host Units in Host–Guest Polymers for Efficient and Stable Near‐Infrared Emission from Light‐Emitting Electrochemical Cells

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growing interest for applications in, for example, bioimaging, [1][2][3][4][5] telecommunication, [6][7][8][9][10][11][12] and as chemical sensors, [13][14][15][16][17] due to important advantages such as light weight, flexibility, areal emission, and low power consumption. [18][19][20][21][22] Accordingly, there is currently an intense development of NIR-emitting organic semiconductors, including lanthanide complexes, [23,24] organic small molecules (SMs), [25,26] conjugated polymers, [27][28][29][30] and transition-metal complexes, [11,31] which are implemented in NIR-emissive devices, primarily organic light-emitting diodes (OLEDs). However, a general drawback with efficient OLEDs is that they depend upon a sophisticated multilayer active-material structure and a low-work-function cathode.Compared with conventional OLEDs, the light-emitting electrochemical cell (LEC) exhibits several important advantages.

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