Electronic spectra and first‐order hyperpolarizability of 4‐(dicyanomethylene)‐2,6‐bis‐ (2′‐thiophene‐vinyl)‐pyran derivatives

On the basis of the ZINDO program, we have designed a program to calculate the first‐order hyperpolarizability β_ijk and β_μ according to the sum‐over‐states (SOS) expression. The first‐order hyperpolarizability of 4‐(dicyanomethylene)‐2,6‐bis‐(2′‐thiophene‐vinyl)‐pyran derivatives were studied. The calculated results were that the 4‐(dicyanomethylene)‐2,6‐bis‐(2′‐thiophene‐vinyl)‐pyran derivatives exhibit good nonlinearity with their β₀ values, which are slightly less than that of the corresponding 2,6‐bis‐styryl‐4‐(dicyanomethylene)‐pyran derivatives. It does not agree with the auxiliary donor–acceptor effects theory. The 4‐(dicyanomethylene)‐2,6‐bis‐(2′‐thiophene‐vinyl)‐pyran derivatives, having two low‐lying electronic excited states that contribute to the molecular hyperpolarizability in an additive manner, are good candidates as chromophores due to their high nonlinearities and good thermal stability. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 65–72, 2001