Polar alignment of dye molecules in sectors of host lattices revealed by phase sensitive second harmonic generation and scanning pyroelectric microscopy

Phase sensitive second harmonic generation (PS-SHG) was applied to investigate the effect of polar surface recognition of dye molecules (amaranth and sunset yellow, as well as dimethylaminostyryl-pyridine) in symmetry related sectors of host lattices such as KH2PO4 and phthalic acid, respectively. PS-SHG revealed bi-polar states in all cases, meaning that sectors growing in opposite directions feature opposite absolute polarities. Scanning pyroelectric microscopy demonstrated that the dipole moments of amaranth in KH2PO4 are pointing towards the growing crystal face. The present work reveals symmetry breaking through anomalous mixed crystal growth to produce physical properties associated with polar axes.