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

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))n CPPn (2,6-(4,4-bis(2-ethylthexyl)-8,9-dihydro-4H-cyclopenta-[def]-phenanthrene))n HCPPn (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 289 nm of PCPP is contributed by the π → π∗ transition involving the extra π-conjugation CC bond.