A photosensitizer dye is provided and it is a ruthenium-based complex represented by formula :wherein X1 is one of formulae to and X2 is hydrogen or the same as X1. When the memory cell is not accessed, data stored in the memory cell is copied to the capacitor and then power supply to the inverter is stopped. Another example is to relate queries based on the identification that the queries are associated with a single search session.