Theoretical studies of the electronic structures and optical properties of stable blue-emitting polymer based on 4H-cyclopenta-[def]-phenanthrene

Abstract

Geometries, ionization potentials (IPs), electron affinities (EAs) and optical properties of two series of π-conjugated oligomers (2,6-(4,4-bis(2-ethylthexyl)-4H-cyclopenta-[def]-phenanthrene))nCPPn (2,6-(4,4-bis(2-ethylthexyl)-8,9-dihydro-4H-cyclopenta-[def]-phenanthrene))nHCPPn (n=1–4) were studied theoretically. The ground and the excited state geometries were optimized by B3LYP and CIS methods with 6-31G∗ basis sets, respectively. The absorption and the emission spectra were calculated by TD-B3LYP method. The lowest-lying absorption is assigned to π→π∗ transition, and the fluorescence can be described as originating from the 1[ππ∗] excited state. IPs, EAs, H–L gaps, absorption and emission properties of PCPP (n=∞) and PHCPP (n=∞) were obtained by extrapolation method. The fact that the lowest-lying absorption and the emission of PCPP are blue-shifted compared with those of PHCPP, can be interpreted by the smaller effective repeating units of PCPP. The extra absorption band at 289nm of PCPP is contributed by the π→π∗ transition involving the extra π-conjugation CC bond.