Computational Study on the Charge Transport and Optical Spectra of Anthracene Derivatives in Aggregates

Abstract

A recent experiment [Angew. Chem. Int. Ed. 2017, 56, 722-727] found that a (1 : 9) blend film of two anthracene derivatives, 2fluorenyl-2-anthracene (FlAnt) and 2-anthryl-2-anthracence (2 A), exhibit both efficient white light emission and high hole mobility, thus promising for organic light-emitting transistors (OLETs). Employing quantum chemistry at the polarizable continuum model (PCM) and the quantum mechanics/molecular mechanics (QM/MM) levels, we investigated the excitedstate structures, optical spectra, band structure and the carrier mobility for FlAnt and 2 A from solution to aggregate phases. We suggest using the ratio of intermolecular excitonic coupling J and intramolecular excited state relaxation energy E to judge the bathochromic shift in optical emission in aggregates. For FlAnt, 1 = J/E is calculated to be less than 0.17, a critical value we identified earlier, and the spectra in solution and aggregate phases present quite similar features (blue emission). However, 1 is~0.5 for 2 A systems, and the calculated emission in the aggregate phase exhibits a remarkable bathochromic shift. In addition, the 0-0 emission is strongly suppressed in the herringbone stacking. These observations justify the experimental findings that (i) 2 A is blue emissive in solution but yellowgreen in the aggregate phase, whereas FlAnt is always blue, and (ii) the blend of them show white emission. By using the "quantum nuclear tunneling" model we proposed earlier, we found the hole mobility for FlAnt and 2 A are 0.5 and 4.2 cm 2 V À 1 s À 1 , respectively, indicating both are good hole transport materials.

Intermolecular Charge-Transfer-Induced Strong Optical Emission from Herringbone H-Aggregates

“…9,10 Nevertheless, superior OLET candidates require both strong photoluminescence and high charge mobility, which are normally considered as two contradictory properties and difficult to be simultaneously satisfied within one organic compound. 3,7,11,12 Such contradiction arises from the fact that large transfer integrals, which are essential to high charge mobility, may introduce lower-lying intermolecular chargetransfer (CT) state that quenches optical emission. Furthermore, the reported promising organic transistors to date are typically tight-packing H-aggregates rather than J-aggregates 13 of which the emission process is prohibited within the traditional Kasha's exciton model (Figure 1).…”

“…Over the last two decades, promising advantages of organic light-emitting transistors (OLETs) have been significantly explored, which promote the performance of organic light-emitting and display devices. − Compared with organic light-emitting diodes (OLEDs), OLETs combine the switching abilities of a transistor that simplifies the circuitry required for display applications. Owing to its capability of providing high current density and low optical loss at the electrodes, OLET also has great potential in realizing electrically pumped organic lasers. , Nevertheless, superior OLET candidates require both strong photoluminescence and high charge mobility, which are normally considered as two contradictory properties and difficult to be simultaneously satisfied within one organic compound. ,,, Such contradiction arises from the fact that large transfer integrals, which are essential to high charge mobility, may introduce lower-lying intermolecular charge-transfer (CT) state that quenches optical emission. Furthermore, the reported promising organic transistors to date are typically tight-packing H-aggregates rather than J-aggregates of which the emission process is prohibited within the traditional Kasha’s exciton model (Figure ).…”

Intermolecular Charge-Transfer-Induced Strong Optical Emission from Herringbone H-Aggregates

“…From the attachment-detachment densities, three diabatic states, |F * E⟩ , |FE * ⟩ , and |F − E + ⟩ , are successfully constructed for each compound. The calculated exciton couplings, which corresponds to the value of the matrix element 12 , are all positive, indicating that these face-to-edge dimers should be identified as H-aggregates in conventional Kasha picture. The transfer integrals and exciton couplings of the investigated systems are also calculated via FMO method (Table S5), and the resulting values are in good agreement with those given by the localized diabatization method, which rationalizes the diabatization process.…”

“…[9][10] Nevertheless, superior OLET candidates require both strong photoluminescence and high charge mobility, which are normally considered as two contradictory properties and thus difficult to be simultaneously satisfied within one organic compound. 3,7,[11][12] Such contradiction arises from the fact that large transfer integrals, which are essential to high charge mobility, may introduce lowerlying intermolecular charge-transfer (CT) state to quench optical emission. Furthermore, the reported promising organic transistors to date are typically tight-packing H-aggregates rather than J-aggregates, 13 of which the emission process is prohibited within the traditional Kasha's exciton model (Figure 1).…”

Intermolecular Charge-Transfer-Induced Strong Optical Emission from Herringbone H-Aggregates

“…[9][10] Nevertheless, superior OLET candidates require both strong photoluminescence and high charge mobility, which are normally considered as two contradictory properties and thus difficult to be simultaneously satisfied within one organic compound. 3,7,[11][12] Such contradiction arises from the fact that large transfer integrals, which are essential to high charge mobility, may introduce lowerlying intermolecular charge-transfer (CT) state to quench optical emission. Furthermore, the reported promising organic transistors to date are typically tight-packing H-aggregates rather than J-aggregates, 13 of which the emission process is prohibited within the traditional Kasha's exciton model (Figure 1).…”