Rational design of cyclopenta[b]naphthalenes for better optoelectronic applications and their photophysical properties using DFT/TD-DFT methods

Abstract

The cyclopenta[b]naphthalenes (CPNs) have been drawing lot of attention in OLED applications and in this work eleven new candidates have been evaluated for their performance and four experimentally reported systems have been chosen for validating computed results. CPN derivatives with different acceptor groups such as –CHO, –COOH, –CN, –NO₂ and the common donor group–N(CH₃)₂ have been chosen and their ground and excited state properties have been investigated. The geometric and electronic structures of the molecules in the ground state have been computed at B3LYP/6-311+G(d,p) level and absorption and emission spectra, both in the gas phase and in DCM, have been computed at TD-PBE1PBE/6-311+G(d,p) level and using polarizable continuum model (PCM). While CPN1 (1,7-susbstituted) and CPN2 (1,6-susbstituted) derivatives have λ_hole < λ_electron and hence can be used as hole transport material, CPN3 (1,5-susbstituted) have λ_hole > λ_electron and it makes them better electron transport materials. The hole and electron transport properties can be fine-tuned with substitution with different donors and acceptor groups in the CPN frame work. The photophysical characterization of the CPNs reveal that their absorption and emission have π → π* character and are contributed mainly by HOMO → LUMO transition. Also, the study reveals that these molecules have improved electron injection and transport balance and can be used as efficient ‘trifunctional materials’ (emitter, hole and electron transporters) in organic light-emitting diodes.