Rigid Molecular Architectures That Comprise a 1,3,5-Trisubstituted Benzene Core and Three Oligoaryleneethynylene Arms:  Light-Emitting Characteristics and π Conjugation between the Arms

Abstract

In view of increasing interest in light-emitting materials, we have investigated the light-emitting characteristics and occurrence of conjugation between arms of star-shaped rigid molecules that comprise a 1,3,5-triethynylbenzene core and methoxy group-substituted oligo(p-phenylethynylene) arms. Consequently, we achieved the ultimate goal (Phif approximately 1.0, log epsilon > 5) for organic molecules with respect to light-emitting ability by creating very intense violet-blue (8, Phif = 0.97, log epsilon = 5.11) and blue (9, Phif = 0.98, log epsilon = 5.29) bright light-emitters. Also, pi conjugation was found to occur between the arms of 9 despite the meta-substituted system. We found a linear relationship of kr (with positive slope) and kd (with negative slope) with the number of dimethoxyphenyleneethynylene units for MMPT (4, 6, 8) and DMPT (5, 7, 9) homologues and the contrasting solvent effect on lambdaem of 8 and 9. It is also interesting that lambdaabs, epsilon, lambdaem, and Phif of 9 are greater than those of the corresponding banana- and rod-shaped molecules.

Star‐shaped Organic Molecules That Comprise a 1,3,5‐Trisubstituted Benzene Core and Three Oligoaryleneethynylene Arms as Light‐emitting Materials

“…To be simple, we only give the transition orbitals of the molecules 6 and 7 (see Figure 5), and the other molecules also have similar distributions. The calculated absorption spectra (λ abs ) agree very well with the experimental results, 18 especially the ZINDO calculations.…”

“…Subsequently, on the basis of the excited geometries optimized by ab initio CIS, we calculated the emission spectra (λ em ) of the star-shaped molecules 1-5 by TDDFT and ZINDO methods in Table 4, which are also in good agreement with the experimental data. 18 Similar to the absorption spectra, both methods reflect that the emission wavelengths for the molecules 1-5 exhibit bathochromically red shifts to some extent as follows: 332.54 (1) ing with the trend of our calculated energy gaps, while the experimental data are at 353 (1)＜359 (2)＜384 (3)＜406 (4)＜409 nm (5). And small Stokes shifts were observed for the star-shaped molecules 1-5 from Table 5, which are presumably due to the star-shaped rigid molecular structures that hinder the geometrical relaxation.…”

“…However, with respect to the light-emitting characteristics for this type of molecules applied in OLEDs, only a few papers appear in the literature. 10,[15][16][17] Recently, Yamaguchi and coworkers 18 synthesized a series of the star-shaped rigid molecules that comprise a 1,3,5-triethynylbenzene core and methoxy group-substituted oligo(p-phenyleneethynylene) arms and evaluated their light-emitting characteristics. The optical and electronic properties for the organic star-shaped molecules can be modified or tuned by increasing the star-shaped molecular size and the number of the methoxy groups on the terminal benzene rings at each arm.…”

“…These structures of the star-shaped molecules correspond to the ones prepared and discussed by Yamaguchi and coworkers. 18 By consideration of the size of the molecules to be treated in this work, we used the DFT and HF, and the CIS methods for the calculation of optimized electronic ground state and lowest excited state geometries, respectively. On the base of these geometries, the electronic absorption and emission spectra were calculated by TDDFT and ZINDO methods.…”

“…These compounds can function as efficient emitter materials, especially for the molecules 6 and 7, which can separately create very intense violet-blue and blue bright light. 18 In this paper, we focus on studying optical and electronic properties of these star-shaped molecules and revealing the relationship between the properties and structures of these functional materials with the assistance of quantum-chemical calculations.…”