A chromene compound having a skeleton represented by the following formula (1) and exhibiting double peak characteristic:
wherein Z is a group represented by anyone of the following formulas:
(R
1
is an electron donor group having a Hammett constant σ
p
of less than −0.20, with the proviso that when there are a plurality of R
1
's, R
1
's may be the same or different, and R
2
is a group having a Hammett constant σ
p
of −0.20 to 0, with the proviso that when there are a plurality of R
2
's, R
2
's may be the same or different)
and “a” is an integer of 1 to 3, with the proviso that when “a” is 2 or 3, Z's may be the same or different but
cannot be