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Theoretical Studies on the Electronic and Optical Properties of a New Class of Aromatic Oligomers and Polymers
Author(s) -
LI LeiJiao,
FENG JiKang,
REN AiMin,
TIAN WeiQuan
Publication year - 2008
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200890152
Subject(s) - chemistry , oled , singlet state , ab initio , excited state , density functional theory , zindo , homo/lumo , ground state , computational chemistry , molecule , atomic physics , organic chemistry , physics , layer (electronics)
The purpose of this work is to provide an in‐depth interpretation of the optical and electronic properties of a series of aromatic oligomers and polymers, including [ N ‐(4‐(5‐(3‐(1,3,4‐oxadiazol‐2,5‐ylene)phenyl)‐1,3,4‐oxadiazol‐2‐ylene)phenyl)‐ N ‐(1,4‐phenylene)amine] n (NPPP) n and [ N ‐(4‐(5‐(3‐(1,3,4‐oxadiazol‐2,5‐ylene)phenyl)‐1,3,4‐oxa‐diazol‐2‐ylene)phenyl)‐ N ‐(1,4‐phenylene)naphthalene‐1‐amine] n (NPPN) n ( n =1–4). These polymers and oligomers show great potential for application to organic light‐emitting diodes (OLEDs) as efficient blue emitters due to the tuning of the optical and electronic properties. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited state of NPPP 1 was optimized with ab initio configuration interaction singles (CIS). To assign the absorption and emission peaks observed in the experiment, the absorption and emission spectra of the ground and lowest singlet excited states were calculated with time‐dependent DFT (TD‐DFT) and Zerner's independent neglect of differential overlap (ZINDO). All DFT calculations were performed using the B3LYP functional and the 6‐31G basis set. The results show that the HOMO, LUMO, energy gaps, ionization potentials, and electron affinities for these polymers are affected by increasing the conjugated chain, which favors the hole and electron injection into OLED. The trend of the variation of Δ H‐L and the lowest excitation energies with 1/ n , and the electronic structure and optical properties of these polymers were extrapolated and analyzed. The absorption spectra exhibit red shifts to some extent [the absorption spectra: 359.47 (NPPP 1 )<370.84 (NPPP 2 )<373.84 (NPPP 3 )<375.33 nm (NPPP 4 ); 361.14 (NPPN 1 )<370.34 (NPPN 2 )<373.39 (NPPN 3 )<374.62 nm (NPPN 4 )]. Our calculated spectra agree well with the experimental findings where available, showing small but systematic deviations.