Influence of π–π Hyperconjugation Effect on Thermal, Morphological, and Photoelectronic Properties of Non-Conjugated Pyrene Derivatives

Abstract

In this paper, four pyrene–fluoroene derivatives with conjugated and nonconjugated pyrene substitution were designed and synthesized. In PFP1 and PFP2, there are nonconjugated pyrene substitution on C9 and conjugated pyrene on C2 and/or C7 of the fluorene moiety, and in the control molecules BP1 and BP2, there is only the conjugated pyrene in the C2 and/or C7 of the fluorene core. There is a special π–π hyperconjugation effect between nonconjugated pyrene and the pyrene–fluorene conjugation in the system (PFP1 and PFP2), which means the electron cloud of such two isolated conjugation systems (nonconjugated pyrene group and pyrene–fluorene group) could be delocalized and transferred to each other. Because of delocalization of electron cloud, the molecule size of PFP1 and PFP2 might have been decreased and led to decreased phase transition temperature compared with that of BP1 and BP2. Also due to the electron transfer between the molecules, the intermolecular force between PFP1 and PFP2 has been improved, which is the reason that they are more amorphous than BP1 and BP2. The easy electron transfer also makes the PFP1 and PFP2 show improved hole injection and device performance compared with that of BP1 and BP2.

Theoretical Exploration of Carrier Dynamics in Amorphous Pyrene–Fluorene Derivative Organic Semiconductors

“…However, the used methods for investigating the amorphous OSCs are the methods for single crystal, ,,− which should not be suitable since the packing pattern and transfer pathways in the amorphous and single crystal are greatly different. The four materials (BP1, BP2, PFP1, and PFP2) have been synthesized, and their primary optoelectronic properties have been investigated in our previous work . All of the research materials in this report have been explored through the real amorphous methods.…”

“…The molecular monomer structure shown in Figure 1 was first optimized using molecular mechanics and the COMPASS force field. 22 Cubic amorphous cells (10) were prepared for each molecule. Each cell is filled with enough optimized monomer molecules to reach about 1600 atoms per cell.…”

“…The four materials (BP1, BP2, PFP1, and PFP2) have been synthesized, and their primary optoelectronic properties have been investigated in our previous work. 10 All of the research materials in this report have been explored through the real amorphous methods. So the intrinsic bipolar transfer characteristics achieved in this report could be considered to be the subsequent work in our group and could be real characteristics of amorphous OSCs.…”

“…To systematically compare, oxadiazole group has also been incorporated as the electron-withdrawing group (OP1 and OP2), which should be the n-type and electron transfer according to the general concept. Among these compounds, BP1, BP2, PFP1, and PFP2 have been synthesized in our previous work, 10 OP1 and OP2 with oxadiazole substitution are just theoretically designed up to now.…”

“…Besides the charge-transfer investigation on the common commercial OSCs, the newly synthesized materials should be focused on since their amount is greatly larger than the commercial materials. During then, after years of research on pyrene–fluorene derivatives, − our group discovered the π–π hyperconjugation effect, , which means the electron cloud of two isolated conjugation systems (nonconjugated pyrene group and pyrene–fluorene group) could be delocalized and transferred to each other. Then, the further exploration of the inner charge transfer in such materials is necessary for their further application.…”