Enhancement in Nonlinear Optical Response of Oligothiophenes by Induction of Polarons

In this study, the electronic and nonlinear optical propertiesof neutral ((nTh) and polaronic states (nTh*) of oligothiophenes are studied. Electronic properties are evaluatedthrough HOMO-LUMO gap, ionization potential (IP), and electronicaffinity (EA). The results of global reactivity descriptors also indicatethe stability of nTh*. The linear and nonlinear opticalproperties are evaluated through the polarizability and static anddynamic hyperpolarizabilities. The polaronic states of these polymersshow high hyperpolarizability (beta(o) ) up to 2.7 x 10(4) au as compared to neutral counterparts.This remarkable increase is mainly due to low transition energiesarising from the induction of polaron. The NLO response of polaron-basedoligothiophenes are much better than their neutral counterparts. Furthermore,the frequency dependent calculations for polaronic state of oligothiophenes(nTh*) are also performed at commonly used laserfrequencies of 532 and 1064 nm. The results of frequency dependentcalculations reveal that the values of dynamic hyperpolarizabilityare more pronounced than static hyperpolarizability. Time-dependentcalculations show enough transparency of polaronic state of nTh* in the UV region, which reveals that the materialsshow good NLO response and could be used in the field of optoelectronics.

Automated summary

This study investigates the electronic and nonlinear optical properties of neutral and polaronic states of oligothiophenes. The stability of the polaronic states is indicated by the results of global reactivity descriptors. The polaronic states exhibit much higher hyperpolarizability and better nonlinear optical response compared to the neutral states.