Molecules and solids in planetary nebulae and proto-planetary nebulae

Recent millimeter-wave and infrared spectroscopic observations have identified a large number of organic molecules through their rotational and vibrational transitions. In particular, the detections of the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic materials at the late stages of stellar evolution. High resolution imaging observations in the submillimeter (e.g., SMA) and in the mid-infrared (e.g., Gemini) have made possible the mapping of the distribution of these compounds, allowing us to infer the history of circumstellar chemistry. In this paper, we present some of the recent spectroscopic and imaging observations of the circumstellar envelopes of evolved stars and discuss a scenario of chemical evolution including the possible role of photochemistry in the late stages of stellar evolution.