1.  Field of the Invention
The present invention relates to a novel pyran derivative, and more specifically, it relates to a novel pyran derivative which has sensitivity to light in a visible light range, particularly in a wavelength range longer than green light and which can function as a photosensitizer for a photopolymerizable or photocrosslinkable photosensitive resin composition. 
Furthermore, the present invention relates to a photopolymerizable and/or photocrosslinkable photosensitive resin composition which can be sensitized by the above-mentioned pyran derivative, and a hologram medium in which this composition is used. 
2.  Related Background Art
In recent years, with the development of dye lasers, various novel compounds have been synthesized as laser dyes.  Above all, 4H-pyrans can emit light very efficiently in a wide range of 600 to 700 nm by laser excitation, and therefore they have been developed as dyes for a long-wavelength light zone dye laser (U.S. Pat.  No.  3,852,683).  Thus, it is expected that these dyes are applied to an EL display utilizing their characteristics by which light is absorbed and fluorescence is emitted (U.S. Pat.  No.  4,769,292). 
With regard to the application of these dyes to photosensitive materials for electrophotography, various investigations have been made, but they have not been applied as sensitizers by which an electron or energy is transferred to another compound. 
Heretofore, among the 4H-pyrans, a compound represented by the formula (7) has been commercially available: ##STR1##
The above-mentioned compound has an absorption maximum at 481 nm in a dimethyl sulfoxide solution [Optics Comm.,  29, p. 331 (1979)], and it has sensitivity to light having a wavelength of 488 nm from an Ar laser but its sensitivity to light having a wavelength of 514.5 nm is poor.  In addition, this compound scarcely exhibits the sensitivity to light having a wavelength of 632.8 nm from an He--Ne laser inconveniently.  That is, in order to use the 4H-pyrans as the sensitizers for the light having long wavelengths, its absorption maximum is required to be shifted to a longer wavelength side, and it can be considered that a contrivance such as the alteration of substituents is necessary.