Theoretical Study of Nonlinear Optical Properties of "Parallel...

Chromophores containing two parallel nonconjugated D-pi-A units are effective chromophores with high hyperpolarizability and good optical transparency. It provides a method for the design and synthesis of effective chromophores. The semiempirical method ZINDO was employed to study the relationship between enhancement of the static first hyperpolarizabilities (beta(0)) per D-pi-A unit and the number of parallel nonconjugated D-pi-A units in a chromophore. The results show that the chromophores containing two parallel nonconjugated D-pi-A units would exhibit higher beta(0) values than two times the beta(0) value of the corresponding reference chromophore containing a D-pi-A unit. The chromophore containing three parallel nonconjugated D-pi-A units exhibits the highest enhancement of beta(0) per D-pi-A unit, which is 10.1 times the beta(0) value of the corresponding reference chromophore. However, the beta(0) value of the chromophore containing four parallel nonconjugated D-pi-A units is very small, and the enhancement of beta(0) value per D-pi-A unit decreases sharply, from 10.1 to 0.3, with increasing the number of parallel D-pi-A units in a chromophore from 3 to 4. It could give a useful suggestion for designing chromophores containing parallel nonconjugated D-pi-A units.