Molecular Conformation and Aggregation Regulation of Bay-substituted Perylene Bismides: ortho-Methyl Steric Hindrance†

doi:10.7503/cjcu20170387

Abstract

Abstract:

The introduction of optoelectronically inactive long chain alkyl substituents commonly used to improve the solubility and film processing can inhibit intermolecular charge transfer in organic semiconductors. Therefore, to decrease the inactive alkyl substituents is important for next generation semiconductors. Herein, we designed and synthesized two perylene bisimide derivatives (PBI1 and PBI2) and investigated the effect of ortho-methylphenyoxyl substituent in bay area on molecular conformation and packing modes in the solid-state. The single crystal analysis confirmed that introduction of CH₃ could significantly affect the molecular conformation of PBI, leading to cross-style four phenoxyl groups. The steric hindrance of CH₃ inhibited the intermolecular π-π stacking, increased the solubility and enhanced the film-forming characters. The results show that CH₃ at the key positions of π-conjugated skeleton could effectively regulate the molecular aggregation. The strategy provides an excellent method to enhance the film processing and decrease the optoelectronic inactive alkyl substituents, therefore an important step forward for the design of new optoelectronic materials.

Key words: Perylene bisimide, Steric hindrance, Aggregation, Molecular conformation, ortho-Methyl substituent

CLC Number:

O621
O649.5

TrendMD:

ZHANG Wenqiang, ZHOU Jiadong, MA Weitao, ZHU Na, XIE Zengqi, LIU Linlin, MA Yuguang. Molecular Conformation and Aggregation Regulation of Bay-substituted Perylene Bismides: ortho-Methyl Steric Hindrance^†[J]. Chem. J. Chinese Universities, 2017, 38(10): 1757.

Figures/Tables 9

Fig.1 Molecular structures of PBI1(A) and PBI2(B)

Fig.2 Crystal structure of PBI1 from front view(A) and side view(B), side view along N—N direction(C), packing styles between two adjacent PBI molecules from side view(D) and top view(E) Hydrogen atom omitted in (A, B); butyl-substituents omitted for simplicity in (C); phenoxyl substituents omitted here for simplicity(E).

Scheme 1 Packing styles of PBI1 and PBI2 with different molecular conformations

Fig.3 TGA thermograms of PBI1 and PBI2 measured under nitrogen flow (20 mL/min) at a heating rate of 10 ℃/min(A) and DSC curves of PBI1(B) and PBI2(C), respectively measured under nitrogen flow at a heating rate of 10 ℃/min and a cooling rate of 5 ℃/min

Fig.4 UV-Vis absorption(A) and PL spectra(B) of PBI1 and PBI2 in solution and film state, in 1.5×10-5 mol/L chloroform and temperature-dependent UV-Vis absorption spectra of PBI1(C) and PBI2(D) in 10-4 mol/L methylcyclohexane

Fig.5 Cyclic voltammogram (CV) curves of PBI1 and PBI2 in dichloromethane, 0.1 mol/L n-Bu4NPF6 as electrolyteInset: CV curves of Fc/Fc+, 298 K, scan rate: 50 mV/s.

Table 1 Summary of optical properties and energy levels of PBI1 and PBI2

Sample	λ_abs /nm		λ_em/nm		E_HOMO/eV		E_LUMO/eV
Sample	Solution	Film	Solution	Film	Cyclic voltammetry method	B3LYP/ 6-31G(d,p)	Cyclic voltammetry method	B3LYP/ 6-31G(d,p)
PBI1	572	601	608	666	-5.57	-5.27	-3.78	-2.96
PBI2	572	446	603	622	-5.62	-5.29	-3.81	-2.97

Fig.6 AFM images of PBI1(A) and PBI2(B) films and SEM images of PBI1(C) and PBI2(D) films

Fig.7 XRD patterns of PBI1(a) and PBI2(b) films on quartz plate spin-coated from 5 mg/mL chloroform at rotating speed of 1500 r/min

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