Structural, Optical, and Theoretical Studies of a Thermochromic Organic Crystal with Reversibly Variable Second Harmonic Generation

N-(3,5-Ditert-butylsalicylidene)-2-aminopyridine (1) exhibits bulk second harmonic generation (SHG) activity (2 vs urea). X-ray diffraction measurements show a non-centrosymmetric structure (P32). Experimental data of polarization-dependent SHG match the theoretical calculations on the basis of the crystallographic data. 1 is also thermochromic in the crystalline state, and SHG at 120 K is 4 times as high as at room temperature. Comparison is made with the isostructural isomer, N-(3,5-ditert-butylsalicylidene)-4-aminopyridine (2), which exhibits reversible photoinduced SHG variations.