Optoelectronic and nonlinear optical properties of triarylamine helicenes: a DFT study

Abstract

This work involved the design of a new series of triarylaminehelicenes (TAH) with significant hole transport capacity and enhanced nonlinear optical response. The geometries, electronic properties and nonlinear response of TAH derivatives were studied using density functional theory at the B3PW91/6-311++G (2d, 2p) level. Charge transfer and nonlinear optical response were analyzed and correlated with modifications in geometry and energy levels. Calculations indicated that trivial changes in the torsional angle occur in TAH derivatives with electron-donating substituents as compared to those with electron-withdrawing substituents, resulting in lower reorganization energies for TAH derivatives 2-6. TAH derivatives with an -N(CH3)2 group have the greatest highest occupied molecular orbital (HOMO) level, and thus the least ionization potential, indicating significant hole transfer efficiency as compared to unsubstituted TAH. A decrease in the HOMO-LUMO gap occurs upon substitution with electron-releasing groups, whereas there is an increase in the case of -NO2, -COOH, and -CN TAH derivatives. Topological analysis of the HOMOs of the neutral molecules revealed that these orbitals are concentrated mainly in the helicene backbone, with an important contribution from fused phenyl rings, nitrogen atoms and carbonyl groups. However, the lowest unoccupied molecular orbitals (LUMO) are invariably constituted by fused phenyl rings without any contribution from the central nitrogen atom. Studying the effect of substitution on the nonlinear optical response of TAH derivatives, the calculated polarizability and hyperpolarizability at B3PW91/6-311++G (2d,2p) level of theory exhibited a prominent improvement as compared to unsubstituted TAH. Both electron-donating groups and electron-withdrawing groups result in a red shift in the electronic absorption bands of the substitution derivatives, in particular those with -N(CH3)2 and -NH2 groups.

Spectral and optoelectronic studies on 7,12,17-trioxa and 7,12,17-trithia [11] helicenes: a DFT view

“…We have observed that k h (reorganisation energy for hole transport) values are comparatively smaller as compared to the k e (reorganisation energy for electron transport) values demonstrating relevance of studied helical derivatives as p-type material for Organic Light Emitting devices. k h for TOH and TTH molecules are found lower than those reported for triarylamine helical systems [36]. Lin et al [60], have calculated the reorganization energies of Alq3 for hole and electron transport to be 0.242 and 0.276 eV, respectively.…”

“…The enhancement of b value for TTH as compared TOH also correlated with increased u ge and decreased excitation energy of former as compare to later, thus following the Oudar and Chemla two level model [66]. It is worth noting that TOH and TTH helical systems shows higher value of second order hyperpolarizability as compared to already used material for NLO devices [36,67]. In addition to it the effective pconjugation in TOH and TTH helical will cause ring current in these system, thus will display NLO activity even in absence of external field.…”

“…Recently tremendous focus is concentrated on the design of helicenes for tuning and exploring their much promising electronic properties on introducing hetero atoms in helical chain. Researcher have observed that low lying energy level of heterohelicenes particularly fused furans are known to show interesting utility in electronic devices as organic light-emitting diodes or organic fieldeffect transistors [32][33][34][35][36][37]. However the increase in internal strain on adding fused rings creates difficulties in synthesis of larger helicenes.…”

Computational Studies on Optoelectronic and Nonlinear Properties of Octaphyrin Derivatives

“…Conjugated organic systems are principally explored as hole transport materials for the organic light emitting devices (Fink et al, 1998; Jurchescu et al, 2004; Park et al, 2011; Tao et al, 2011; Kim et al, 2013; Wu et al, 2014; Islam and Pandith, 2014b; Fan et al, 2015). Because of troublesome processbility and instability in air, the exploration, design and synthesis of electron transport material has remained a significant challenge and hot stock within the field of organic electronics (Pandith and Islam, 2014; Zhao et al, 2014).…”

“…Because of troublesome processbility and instability in air, the exploration, design and synthesis of electron transport material has remained a significant challenge and hot stock within the field of organic electronics (Pandith and Islam, 2014; Zhao et al, 2014). Within the recent years, conjugated nitrogen containing organic derivatives have been found as promising n-type or p-type materials for the fabrication of OLED (Fink et al, 1998; Jurchescu et al, 2004; Park et al, 2011; Tao et al, 2011; Kim et al, 2013; Pandith and Islam, 2014; Wu et al, 2014; Zhao et al, 2014; Islam and Pandith, 2014b; Fan et al, 2015). The material acquires this property because of their excellent optoelectronic properties, good oxidation and thermal stabilities, large electron affinities and high electron mobilities.…”